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iSAS/IODP Proposal Cover Sheet
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Title:
Proponent(s):
Keywords:
(5 or less)
NanTroSEIZE Reference Sites:
Sampling and Measuring Inputs to the Seismogenic Zone
Michael Underwood, Juichiro Ashi, Wonn Soh, Julia Morgan, Saneatsu Saito,
Liz Screaton, Demian Saffer, Masataka Kinoshita, Gregory Moore, Harold Tobin,
Pierre Henry, Ken Ikehara, Miriam Kastner, Yukinobu Okamura, Arthur Spivack,
Kohtaro Ujiie
Subduction inputs; physical and chemical hydrology;
lithostratigraphy; structural geology; heat flow and diagenesis
Area:
Nankai Trough,
Shikoku Basin
Contact Information:
Contact Person:
Department:
Organization:
Address
Tel.:
E-mail:
Michael Underwood
Department of Geological Sciences
University of Missouri
101 Geology Building
573-882-4685
UnderwoodM@missouri.edu
Fax: 573-882-5458
Permission to post abstract on iSAS Web site:
X
Yes
No
Abstract: (400 words or less)
A foremost goal of IODP is to drill into the seismogenic zone of a plate-boundary fault that is capable
of generating M8 earthquakes. The Nankai Trough of southwest Japan is a prime candidate to pursue that
objective with the aid of riser drilling technology. The proposal for NanTroSEIZE (Nankai Trough
Seismogenic Zone Experiment), in its entirety, identifies seven phases or milestones. The complete
program plan will test four fundamental hypotheses: (1) Systematic and progressive changes in material
properties and state control the onset of seismogenic behavior and locking of subduction thrusts. (2)
Subduction zone megathrusts are weak faults; that is, they slip under conditions of low resolved shear
stress. (3) Within the seismogenic zone, relative plate motion is accommodated primarily by coseismic
frictional slip in a concentrated zone. (4) Physical properties, chemistry, and state of the fault zone change
with time throughout the earthquake cycle (interseismic and coseismic). A long-term borehole
observatory will be installed to test the forth hypothesis. The first three hypotheses will be tested
thorough comparisons among structural fabrics, variables of state (stress, pore pressure, temperature) and
in situ parameters (mineral and fluid composition, meso- and micro-scale structural fabric, strain rate, and
microseismicity). We will, in essence, trade time for space by tracking the physical and chemical
character down dip, from the shallow aseismic portion of the fault to the seismogenic zone.
An international planning process for NanTroSEIZE resulted in the choice of the Kii Peninsula region
as the first-priority for a Nankai drilling transect. The only glaring disadvantage of the Kii transect, at
present, is the sparse amount of data concerning subduction inputs. Data from previous DSDP and ODP
drilling legs cannot be imported to the Kii region because the stratigraphic, thermal, and diagenetic
parameters of the subduction zone change so much along strike. Accordingly, oceanic reference sites
must be drilled within the subducting Shikoku Basin to define initial conditions just prior to subduction.
Two Shikoku Basin sites will show how basement relief influences the geometry of sedimentary facies,
permeability, and fluid flow. We propose one additional site at the toe of the accretionary prism to
characterize early-phase deformation and to verify how strata are partitioned above and below the frontal
decollement. The prism-toe site, moreover, will add a third dimension to the characterization of facies
architecture, hydrogeology, thermal structure, and diagenetic reaction progress.
Scientific Objectives: (250 words or less)
The first phase of the NanTroSEIZE will sample and measure subduction inputs along the Kii Peninsula
transect of Nankai Trough. We propose two oceanic reference sites seaward of the trench: one above a
basement high; the other above an adjacent basement flat. This pair of reference sites in Shikoku Basin
will capture the end-member conditions of sand-rich versus sand-poor facies in the lower part of the
section. The best way to document the stratigraphic range of hydrologic, compositional, and mechanical
input variables is to integrate the following drilling components: (1) continuous coring, with penetration
100-200 m into igneous basement; (2) a complete suite of LWD logs; (3) documentation of sediment
composition and diagenesis; (4) hydrologic tests of in situ permeability (packer, pump, etc.); (5) highresolution borehole measurements of temperature and pore pressure; (6) chemical analysis of pore fluids,
including fluids extracted from igneous basement; and (7) installation of conventional borehole seals
(CORK) and osmotic samplers. The goal of tracking physical and chemical changes in fluid-sediment
interaction -- along a P-T path from basin to prism toe -- will be achieved via hydrologic tests,
geochemical analyses, and measurements of thermal and physical properties. Characterization of structural
architecture, at all scales, requires core-log-seismic integration. Drilling completely through the
decollement into basement will be a challenge because total sediment thickness at the prism toe is nearly
2000 m. Such a site is essential, however, to verify the location and nature of structural partitioning by the
fault, as well as to map early phases of fault-related deformation.
Proposed Sites: (Only High Priority Sites are listed here.)
Site Name
Position
NT1a-01A
Lat: 32° 44.8878’ N
Long: 136° 55.0236’ E
NT1a-02A
NT1a-03A
Water
Depth
(m)
Penetration (m)
Brief Site-specific Objectives
Sed
Bsm
Total
3540
460 m
200 m
660 m
Complete characterization of
Shikoku Basin strata above
basement high; CORK
Lat: 32° 47.4996’ N
Long: 137° 55.0236’ E
4210
730 m
200 m
930 m
Complete characterization of
Shikoku Basin strata above
basement flat
Lat: 33° 1.23258’ N
Long: 136° 47.9485’ E
4125
1740 m
10 m
1750 m
Characterization of deformation
and structural partitioning by
decollement at toe of Nankai
accretionary prism
NanTroSEIZE Reference Sites:
Sampling and Measuring Inputs to the Seismogenic Zone
Phase 1a of NanTroSEIZE Complex Drilling Project
Lead Proponents
Michael Underwood
University of Missouri, USA
underwood@missouri.edu
Juichiro Ashi
University of Tokyo, Japan
ashi@ori.u-toyko.ac.jp
Wonn Soh
IFREE, Japan
soh@jamstec.go.jp
Julia Morgan
Rice University, Houston, USA
morganj@rice.edu
Saneatsu Saito
JAMSTEC, Japan
saito@jamstec.go.jp
Liz Screaton
University of Florida, USA
screaton@ufl.edu
Demian Saffer
University of Wyoming, USA
dsaffer@uwyo.edu
Masataka Kinoshita
JAMSTEC, Japan
masa@jamstec.go.jp
Greg Moore
University of Hawaii,
Honolulu, USA
New Mexico Tech, USA
gmoore@hawaii.edu
Ken Ikehara
Ecole Normale Superieure,
Paris, France
AIST, Japan
henry@mailhost.geologie.en
s.fr
k-ikehara@aist.go.jp
Miriam Kastner
UCSD/Scripps, USA
kastner@ucsd.edu
Yukinobu Okamura
AIST, Japan
okamura-y@aist.go.jp
Arthur Spivack
University of Rhode Island,
USA
IFREE, Japan
spivack@gso.uri.edu
Co-Proponents
Harold Tobin
Pierre Henry
Kohtaro Ujiie
tobin@nmt.edu
ujiiek@jamstec.go.jp
I. INTRODUCTION
The Seismogenic Zone Experiment
Subduction-related earthquakes account for ~90% of Earth’s seismic moment release.
During the past decade, scientists have enhanced their understanding of earthquake rupture
propagation using a combination of field instruments, laboratory experiments, and theory.
One of the remaining enigmas, however, is the spatial shift in fault-zone behavior from stable
sliding to stick-slip. This shift seems to occur over a fairly consistent range of P-T
conditions, but our inability to pinpoint parameters that control the locking of faults impairs
efforts to mitigate earthquake and tsunami hazards. In particular, we lack vital data regarding
ambient conditions and in situ mechanical properties, especially at depths where earthquakes
are generated. A foremost goal of the international research community, therefore, is to drill
into the seismogenic zone of an active plate-boundary fault, sample the deformed rocks, and
monitor active processes in situ. Several such projects have been proposed, but subduction
zone megathrusts (as opposed to strike-slip faults) offer unmistakable advantages as targets
of investigation. Their dip angles are typically less than 30°; as such, they are amenable to
both high-quality seismic imaging and borehole intersections of the fault plane at
progressively greater depths. The strategy of SEIZE (Seismogenic Zone Experiment) differs
fundamentally from that of SAFOD (San Andreas Fault Observatory at Depth) because we
will document the evolution of fault-rock properties, by trading time for space along the
dipping plate boundary. We plan to initiate sampling of the “seismic conveyor belt” at
shallow depths outboard of the trench (with non-riser drilling) and finish with riser drilling 56 km below the seafloor, where interplate earthquakes actually occur.
The proposal for NanTroSEIZE (Nankai Trough Seismogenic Zone Experiment) is a
culmination of several years of international planning by a substantial number of scientists.
Recent workshops included experts in seismology, geodesy, and rock mechanics who had no
previous experience with scientific ocean drilling as well as scientists with extensive DSDP
and ODP experience. Our scientific goals form a centerpiece of the IODP Initial Science
Plan, which states (pg. 68): “As one of its inaugural activities, IODP will drill through a
seismogenic fault zone to characterize the composition, deformation microstructures and
physical properties of the rocks at in situ conditions.” The rationale for applying riserdrilling technology toward that end has been articulated in ODP/IOPD planning documents
(CONCORD, COMPLEX, Seismogenic Zone DPG), as well as the NSF science plan for
SEIZE (MARGINS, 1999). The accompanying “umbrella proposal” for NanTroSEIZE
elaborates on scientific hypotheses (summarized below), describes the entire program plan,
and explains how generic non-riser and riser drilling will be integrated. This proposal is
limited to one component: the so-called “oceanic reference sites.” Those targets must be
drilled, cored, and logged using a non-riser platform to characterize the sedimentary,
hydrologic, geochemical, and thermal inputs to the Nankai subduction zone.
Scientific Hypotheses of SEIZE
Hypothesis #1: Systematic and progressive changes in material properties and state
control the onset of seismogenic behavior and locking of subduction thrusts. One corollary
to this hypothesis states that the up-dip limit of seismicity coincides with the down-dip
completion of the smectite-to-illite reaction, at a temperature of approximately 125-150°C
(Hyndman et al., 1995; Oleskevich et al., 1999). We doubt, however, that the physicalchemical evolution of the fault system is quite so simple (e.g., Moore and Saffer, 2001). In
fact, the nature of the slip surface at seismogenic depths remains a mystery in detail. We
believe that three possibilities need to be considered when evaluating down-dip increases in
shear strength: (a) changes in frictional properties -- caused by alteration of rock
composition (e.g., clay-mineral and/or silica reactions, precipitation of crystalline cements,
pressure solution) and/or shear localization and fabric development (Marone, 1998); (b)
increases in effective stress -- driven by declining fluid overpressure and coupled (perhaps)
with exhaustion of mineral dehydration reactions (Byerlee, 1990); (c) modification to a well
organized rock fabric which can define weak planes of slip (i.e., phyllitic cleavage or
foliation) -- driven by incipient metamorphic reactions, cementation, and/or phyllosilicate
growth.
We emphasize here that the three categories listed above are not mutually exclusive.
The challenge is to recognize and quantify the relative contribution of each. By penetrating
the fault and emplacing borehole instruments near the up-dip limit of earthquakes, scientists
finally will be able to constrain many of the fault’s variables of state (stress, pore pressure,
temperature). We will also document such in situ parameters as mineral and fluid
composition, meso- and micro-scale structural architecture, strain rate, and microseismicity.
By combining long-term downhole measurements with analyses of cores and logs, we will
show which of the in situ parameters, if any, can be linked by proxy to geologic features that
capture earlier stages of rock evolution -- both within and adjacent to the fault zone. Toward
that end, we intend to map the sequential history of overprinting deformation and
cementation, date fault rock constituents and authigenic phases, analyze fluid inclusions and
veins to obtain P-T and chemical history, and characterize fault fabric at all scales. An
equally important goal will be to document how the state variables and in situ parameters
change as a function of lateral heterogeneity and/or down-dip evolution. In other words: How
do physical and chemical properties of wall rocks and shear zones evolve down the “seismic
conveyor belt” from the seafloor to the seismogenic zone?
Hypothesis #2: Subduction zone megathrusts are weak faults; that is, they slip under
conditions of low resolved shear stress. Evidence is mounting from multiple tectonic
settings (e.g., San Andreas transform) to suggest that plate-boundary faults are weak -relative to surrounding rock, and in an absolute sense (Hickman, 1991). A theoretical case
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was made decades ago for weak low-angle thrusts (Hubbert and Rubey, 1959). Potential
causes of this phenomenon include: (a) intrinsic weakness of fault gouge (e.g., high content
of clay, especially expandable clays of the smectite group); (b) elevation of pore fluid
pressure within the fault (resulting in low effective stress); and (c) dynamic weakness
generated during rapid slip events. As with Hypothesis #1, these three options are not
mutually exclusive. Samples from the Nankai seismogenic zone, plus in situ measurement of
state variables, will help us quantify the respective contribution of each. The plan to assess
both fault-zone evolution and activity raises intriguing questions: Are coseismic slip and fluid
expulsion coupled? Are bound fluids in shear zones chemically distinct from those in
adjacent wall rocks? Do such fluids provide proxies for source and/or flow path? Does
resolved shear stress change gradually or abruptly down dip?
Hypothesis #3: Within the seismogenic zone, relative plate motion is accommodated
primarily by coseismic frictional slip in a concentrated zone. Two implications of this
hypothesis are: (a) the seismogenic zone of the plate-boundary fault is locked, and (b) little
strain is accommodated elsewhere (i.e., within the upper plate). One way to test these ideas
is by drilling through faults that splay off the décollement, to constrain their contribution to
interplate motion. Slip on the splay faults is important in a practical sense because it is
capable of generating tsunamis. Monitoring both the splay faults and the décollement will
allow comparisons of strain rate and temperature. Coring and logging will expose heretofore
hidden elements of their geologic scale and geometry. How thick is the entire damage zone,
as opposed to the fault core? Do fault-zone dimensions change in the down-dip direction in
concert with material properties? How do features created by a single event or generation of
deformation compare with the rock’s cumulative history? What is the typical lifetime of such
structures? What role do authigenic vein minerals play in fault zone healing/sealing? What
is the rate of fracture sealing? How does the total amount of energy release vary between
seismic versus aseismic slip events? To answer such questions completely, we need to
compare shallow reference sites (prism toe and splay faults) with deep riser holes.
Hypothesis #4: Physical properties, chemistry, and state of the fault zone change with
time throughout the earthquake cycle (interseismic and coseismic). If temporal changes in
fault properties (fluid pressure, stress, temperature, fluid chemistry, seismic velocity,
permeability, etc.) modulate the earthquake cycle, then we might be able to capture the
governing changes during a lifetime of long-term monitoring. This prospect hinges on the
earthquake recurrence cycle for each fault segment of interest, but initiation of the
experiment now will provide a legacy opportunity for decades of future research.
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II. INTEGRATED DRILLING STRATEGY
Why Choose Nankai Trough?
The Nankai Trough of southwest Japan (Fig. 1) is among the more comprehensively
studied subduction zones in the world. It has a remarkable 1300-year historical record of
great earthquakes (Mw ~8.0) (Kumagai, 1996), and segmentation of seismicity along strike
has been remarkably consistent, with recurrence intervals of ~120 years. Recent events
include the 1944 Tonankai (Mw=8.2) and 1946 Nankaido earthquakes (Ando, 1975). The
Tokai segment (Fig. 1) has not ruptured since 1854 and is probably long overdue. Onland
geodetic data show that the subducting and overriding plates are strongly coupled in
southwest Japan, essentially moving together (Miyazaki and Heki, 2001). Similarly,
microseismicity is relatively low near the updip limits of the 1946 earthquake (Obana et al.,
2001), consistent with interseismic strain accumulation on the megathrust. Such conditions
are ideal for long-term monitoring.
Figure 1. Map showing location
of Nankai margin and Ashizuri,
Muroto, Kii, and Tokai transect
areas. Boxes depict areas of
coseismic slip during 1944 and
1946 earthquakes. Areas marked
in black on the bathymetric
background represent locations
where water depth is less than 2.5
km and the plate interface is less
than 6.0 km below seafloor.
Nankai differs from the other SEIZE focus area (Central America) in many ways: Costa
Rica is characterized by smaller and more frequent earthquakes, low heat flow, low rates of
sediment accumulation, and subduction-erosion rather than accretion (Protti et al., 1994).
Nankai is comparable, in some respects, to other sediment-rich accretionary margins with
histories of great earthquakes (e.g., Cascadia, Eastern Aleutian Trench), but it offers several
important advantages. Unlike Cascadia and the Aleutians, for example, the Nankai
megathrust is shallow enough to intersect within the water-depth and drill-string
specifications of the riser vessel Chikyu. Young subduction lithosphere was formed by backarc spreading in the Shikoku Basin (Okino et al., 1994), which creates a relatively high
geothermal gradient near the deformation front (Wang et al., 1995; Kinoshita and Yamano,
1995). Consequently, key diagenetic/metamorphic reactions (i.e., those suspected of
changing fault-zone properties) probably advance to completion within the depth range for
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riser drilling. Decades of DSDP/ODP drilling, geophysical surveys, and submersible studies
have created an impressive inventory of background information; additional data are being
added to the collection each year, particularly by such Japanese institutes as JAMSTEC and
ORI. High-quality seismic images, including 3-D seismic, provide clearly defined targets for
deep drilling. Cretaceous and Tertiary rock analogues are exposed onshore in the Shimanto
Belt (Taira et al., 1988). Such outcrops preview the anticipated rock-vein fabrics and P-T
proxies at seismogenic depths (Underwood, 1993; Sakaguchi, 1996.). Active out-of-sequence
faults splay from the décollement, cutting through the accretionary prism to the seafloor
(Park et al., 2002b). Offsets along such faults (Fig. 2) probably generate co-seismic
tsunamis, and fossil analogues are integral elements of the Shimanto Belt (Ohmori et al.,
1997). Collectively, the Nankai margin provides an ideal confluence of earthquake history,
target imagery, pre-existing data, onshore analogues, and engineering feasibility.
Figure 2. Depth migrated MCS profile and interpretation of Line 5 (from Park et al., 2002b)
across the central Nankai Trough, located off the east coast of Kii Peninsula. See Fig. 1 for
location of trackline. Possible riser and non-riser sites are superimposed on the interpreted
profile.
Kii Peninsula transect
During the preliminary stage of planning, the Nankai Trough Seismogenic Zone
Working Group identified three regions (Muroto, Kii, Tokai) as candidates for an IODP
transect (Fig. 1). The first constraint on site selection is imposed by the operational capability
of the Chikyu -- currently 2.5 km water depth (riser length limit) and 10 km total drill string
length. Drilling time increases exponentially as a function of total depth drilled, so it will be
5
important to minimize the sub-bottom depth needed to reach the subduction interface
(Hyndman, 1999). Black filled areas in Fig. 1 represent locations where the water depth is
≤2.5 km and the downgoing plate can be intersected ≤6 km below seafloor (bsf).
After careful deliberation of both scientific and logistical criteria, a consensus opinion
emerged during the Boulder NanTroSEIZE workshop (July, 2002) to set the Kii Peninsula
transect (Fig. 1) as the top priority for the Complex Drilling Plan. Crustal structure is well
imaged at potential riser and non-riser sites by a wealth of new seismic reflection/refraction
data collected by JAMSTEC (Fig. 2). A splay fault is evident on four existing MCS profiles
(Park et al., 2002b), and an associated seafloor scarp can be recognized in swath-bathymetry
data. Tsunami waveform inversion (Tanioka and Satake, 2001a) indicates that the Kumano
forearc basin, including the outer ridge, was entirely within the coseismic slip area during the
1944 earthquake. The plate interface can be reached at ~6 km bsf in ~2 km water depth.
Thermal gradients, as calculated from the depth of bottom-simulating reflectors, predict
temperatures near the top of the oceanic basement of ~180-200°C (Park, unpublished data).
This projection of near-surface temperature to depth, though model-dependent, exceeds the
150°C threshold hypothesized for the onset of stick-slip behavior (Hyndman et al., 1995). A
shallow riser site seaward of Kumano Basin would penetrate a splay fault at ~4-5 km bsf,
where the likely temperature is ~150 °C. Thus, two thrust faults under different P-T-stress
conditions are accessible within the hypothesized seismogenic window. Clearly, the
structural, geophysical, and thermal conditions along the Kii transect are ideal for a
successful drilling program into the Nankai seismogenic zone. At present, however, there is
a distinct lack of information about materials entering the subduction system in this location,
which ultimately govern plate boundary deformation. This proposal puts forward a
comprehensive program to characterize sedimentary, hydrologic, geochemical, and thermal
inputs to the Nankai subduction zone along the Kii transect, and document early stages of
deformation in this setting.
Phased Objectives
The NanTroSEIZE Complex Drilling Project (CDP) proposal, also submitted to IODP, is
the “umbrella proposal” describing in more detail how our scientific goals will be addressed
by drilling, in situ measurements, laboratory analyses, and modeling. We envision several
overlapping phases or milestones during the next six or seven years, including the following:
Ongoing - Geophysical Site Characterization: Although the Nankai system has been studied
intensively already, we are still planning additional geophysical surveys -- especially 3-D
seismic within the Kii transect area, wide-angle surveys to define the velocity structure, and
high resolution heat flow surveys. Acquisition of new geophysical data will continue
throughout the NanTroSEIZE program. Phase 1A - Non-Riser Oceanic Reference Sites:
Several non-riser reference sites must be drilled early in the IODP program to document
6
inputs from the incoming Shikoku Basin sedimentary section and igneous basement, plus
structural partitioning by the décollement near the prism toe. This is the specific focus of this
proposal. Phase 1B - Non-Riser Upslope Prism Sites, including Pilot Hole(s) at the
Candidate Site(s): We further propose one non-riser splay fault site to a depth of 1-2 km,
plus a site at the seaward edge of the Kumano forearc basin, to characterize the structural
evolution, uplift history, and diagenesis of the upper part of the accretionary prism. Sampling
across the shallow portion of the splay fault will document its history of displacement and
might capture fluids migrating from deep-seated sources. One or more pilot holes must also
be drilled in non-riser mode to characterize the engineering elements of prospective targets
for riser drilling and to design the casing program (Hyndman, 1999). We anticipate using the
Chikyu for this purpose. Phase 2 – Riser Penetration of Splay Fault: The first riser drilling
objective will be to sample, log, and install downhole observatories across a splay fault to
~3.5 km below seafloor. This phase will access the splay fault system where it is implicated
in co-seismic rupture and tsunamigenesis, and investigate fault properties at never-beforesampled P-T conditions. It will also provide the operations group with critical physical and
mechanical properties data and valuable experience to design the deeper drilling phase. Phase
3 – Riser Penetration of Décollement: Drilling operations will culminate at the seismogenic
plate interface using LWD/MWD technology and as much coring as possible. Sampling at
~5.5 - 6 km below seafloor will constitute an unprecedented scientific achievement. Phase 3
drilling will be followed by installation of a Deep Borehole Observatory: for long-term
monitoring and active in situ testing.
III. GENERIC REASONS FOR DRILLING FOR OCEANIC REFERENCE SITES
Why Are Additional Oceanic References Sites Necessary?
As outlined in previous sections, the complete NanTroSEIZE plan includes goals that
depend heavily on riser drilling and monitoring of in situ conditions at unprecedented depths.
Another exciting opportunity, however, is to track the evolution of the fault zone and wall
rocks from lower P-T (stable sliding) to higher P-T (stick-slip) conditions. To accomplish
this, the plan includes oceanic reference sites to document the following:
• Down-dip changes in fault zone composition and structural architecture
• Three-dimensional patterns of permeability and fluid pressure
• Temperature structure and down-dip progression of mineral reactions
• Changes in frictional properties as driven by compaction and diagenesis
• Spatial and temporal evolution of fluid chemistry, including basement sources
An obstacle to planning is the three-dimensional heterogeneity of Shikoku Basin stratigraphy
and basement architecture (Le Pichon et al., 1987a, 1987b,1996; Mazzotti et al., 2001; Moore
et al., 2001; Park et al., 2002a). With the Kii transect emerging as top priority, there is a
glaring need to more fully characterize its lithologic, thermal, and hydrogeologic inputs.
7
Inputs from Shikoku Basin
As constrained by existing DSDP and ODP boreholes, the Nankai décollement propagates
through the lower facies of the Shikoku Basin (Fig. 3). This stratigraphic interval, rather than
the overlying trench wedge, is the essential one to characterize for tracking physical and
chemical changes toward seismogenic depths. However, the situation on a regional scale is
complicated. Previous drilling of the Muroto and Ashizuri transects documents how the
basin's depositional history has been strongly influenced by seafloor relief created during the
Figure 3. Stratigraphic columns for two reference sites of ODP Leg 190, Sites 1173 (Muroto
transect) and 1177 (Ashizuri). See Figure 4 for locations. Décollement horizon projects
through mudstone unit at 1173 and above turbidite sand at 1177. Plotted to the right are
profiles of porewater chloride concentration and %smectite in the clay sized fraction at ODP
Sites 1173 and 1177. Depths are recalculated relative to the top of Shikoku Basin facies.
construction of the underlying igneous basement. The Muroto transect (Fig. 4) occupies a
unique position near the axis of a fossil (middle Miocene) back-arc spreading center; younger
seamounts of the Kinan chain are superimposed on the fabric of the ridge. Evidently,
elevation of the seafloor inhibited transport and deposition of sand by turbidity currents, so
Miocene-Pliocene sediments deposited above the ridge consist almost entirely of hemipelagic
mudstone (Fig. 3). The seismic-reflection response within this facies is nearly transparent
(Fig. 5). The Ashizuri transect, in contrast, is located southwest of the basement high, where
coeval strata of the lower Shikoku Basin consist largely of unconsolidated sand-rich
siliciclastic turbidites. Those buried turbidites produce strong continuous reflectors (Fig. 5),
and have been cored at DSDP Site 297 and ODP Site 1177 (Fig. 3). With its proximity to the
decaying volcanic heat sources of the spreading ridge and seamounts, heat flow is also higher
2
along the Muroto transect (180 mW/m at Sites 1173 and 1174), as compared to the Ashizuri
8
Figure 4. Bathymetric
map showing Muroto and
Ashizuri transect areas,
and position of Kinan
Seamount chain. Numbers
indicate DSDP and ODP
drill sites.
2
transect (~70-80 mW/m at DSDP Sites 582 and 583). Clay mineral diagenesis,
consequently, advances more rapidly along the Muroto transect. At Site 1173, there is clear
evidence for volcanic-ash to smectite alteration giving way to smectite-to-illite diagenesis
seaward of the trench, and progressive depletion of smectite can be tracked through Site 1174
to Site 808 (Fig. 6). In addition, the I/S mixed-layer phase becomes increasingly illitic as
burial increases below the trench wedge and prism toe. In other words, the Muroto reference
section is “pre-cooked.” The effects of in situ smectite dehydration are apparent in profiles
Figure 5. Along strike comparison of
seismic reflection character at Nankai
deformation front; thrust faults and
prism deformation front are indicated in
red. Profiles organized from northeast
(A - Tokai) to southwest (F - Ashizuri).
Strong, continuous reflectors define
dipping lower Shikoku Basin, except
along Muroto transect (E - NT62-8).
9
of porewater chloride (Fig. 3), although it is important to note that the chemical mass has not
been balanced for in situ versus advected components. At Site 1177, conversely, smectite
increases to 60-70% of the clay-sized fraction within the lower Shikoku Basin (due to
volcanic ash alteration), but there is no evidence for smectite-to-illite diagenesis (Fig. 6). In
addition, the profiles of porewater chemistry are substantially different at Site 1177 (Fig. 3);
presumably, this is due to erratic focusing of water along highly permeable sands that are not
in hydro-geochemical communication. There are also signs of fluid diffusion between a
basement reservoir and the lower Shikoku Basin strata.
Figure 6. Stratigraphy, relative claymineral abundance (% smectite), and
progression of smectite-to-illite
diaganesis (% illite in I/S mixed-layer
clay) at ODP Site 808 (Underwood
and Pickering, 1993). Shown to the
right are comparisons of relative claymineral abundance (% smectite) for
upper and lower Shikoku Basin at
ODP Sites 1173, 1174, and 1177
(Underwood, unpublished). Depths
are normalized to the top of Shikoku
Basin facies. Increase in % smectite is
due to alteration of volcanic ash.
Progressive depletion of smectite at
1173 and 1174 is due to replacement
by illitic I/S mixed-layer clay.
Basement temperatures (°C) estimates
are based on extrapolation of linear
gradients from the upper few 100 m.
As we progress through the NanTroSEIZE program plan, several questions will have to
be answered regarding inputs to the Kii subduction segment, as described below. Currently,
we have no borehole data from that region, and the amount of near-surface heat flow data is
minimal. Data from Muroto cannot be imported into this location, due to continuing volcanic
activity after the opening of the Shikoku Basin. Without appropriate reference sites,
predictive models and hypotheses for initial conditions and down-dip evolution of the plate
boundary within the Kii transect remain conjectural.
How does basement structure affect the stratigraphic architecture of the northeast
Shikoku Basin? Some answers to this question are known already, as outlined above.
However, as one moves across the Kii transect area (i.e., the northeast flank of the fossil
back-arc ridge) toward the Tokai transect (Le Pichon et al., 1987a; Mazzotti et al., 2001), the
bathymetry of Shikoku Basin becomes increasingly complicated due to remnant fragments of
the Zenisu Ridge (Fig. 7). In general, the total thickness of sediment in Shikoku Basin
10
Figure 7. Bathymetry of Kii
transect area from multi-beam
swath mapping. Bathymetric
highs within the Shikoku
Basin demark the Zenisu
Ridge. Locations of proposed
drilling sites and tracklines
Line 5, KR9806-01, KR980602, and KR0211-S0 are
shown.
increases toward the north, although the composition and source(s) of the sediment remain
unknown. Seismic thickness decreases above larger basement highs, and a more transparent
acoustic character indicates they lack the sand packets that characterize most other parts of
the lower Shikoku Basin (Fig. 8). Basement-controlled heterogeneity carries with it
implications for permeability and fluid flow -- both outboard and inboard of the deformation
front. Thus, we propose two non-riser reference sites within the Kii transect: one above a
basement depression and one above a nearby basement high. This pairing of sites will
characterize end-member conditions: sand-rich to sand-poor lower Shikoku Basin.
Figure 8. Seismic reflection profile across northeast Shikoku Basin shows complicated
structure and morphology of the oceanic basement and basin stratigraphy in this area. Time
migration of profile KR0211-S0; track line is shown in Figures 7 and 13. Proposed site
NT1a-01A is located above a basement high.
11
How does the physical hydrology of the Shikoku Basin and the Kii accretionary prism
respond to variations in primary lithostratigraphic architecture and basement structure?
Although substantial physical properties data exist for the Shikoku Basin strata along the
Muroto and Ashizuri transects, they are of little use to the Kii transect because of the firstorder differences in lithostratigraphy. To fully characterize the distribution of porosity and
permeability, we are mapping the turbidite sand bodies to the northeast of the Shikoku
spreading ridge with seismic data (Ike et al., 2002). We need to characterize their hydrologic
properties directly via cores, logs, and packer tests. The turbidite sand bodies of Shikoku
Basin almost certainly provide high-permeability conduits for fluid flow right up to the time
in which the pore space is filled by chemical cement. Active flow through sand layers at Site
1177 is evident from the irregular porewater chloride profile (Fig. 3). Up-dip termination of
sand bodies against the central basement high (or pinch-out against smaller fragments of
Zenisu Ridge) probably creates compartments of excess pore pressure even before the
Shikoku Basin strata are buried beneath the trench wedge. This will occur if overpressures
are translated laterally from sediments that are buried rapidly beneath the trench wedge
and/or accretionary prism (e.g., Bredehoeft, et al., 1988). Drilling two reference holes (one
above basement low, the other above basement high) will help us evaluate this possibility
quantitatively. Another important stratigraphic interval is the upper boundary of the
turbidites. In the Ashizuri region, the décollement appears to pass through a relatively
impermeable mudstone unit just above the top of the turbidites (Fig. 3). Perhaps that zone is
a favored zone of weakness because fluids migrate out of the turbidite section, are unable to
drain through the overlying aquitard, and create an overpressured horizon at the boundary.
Tectonic acceleration of burial beneath the prism toe should amplify compaction
disequilibrium and fluid overpressure, even in the absence of in situ dehydration reactions
and/or fluid flow from deeper sources.
How do fluids from the igneous basement affect subduction processes? The physical and
chemical character of fluids in the igneous crust of Shikoku Basin remains completely
unconstrained by direct sampling. It is important to note that riser drilling, unlike previous
drilling at the prism toe, will penetrate to a position where the décollement ramps downsection, close to the basalt-sediment interface (Fig. 2). Thus, we must consider how
basement fluids evolve chemically and physically in the down-dip direction. Another goal is
to determine if or how “exotic” fluids migrate up-dip from the basement. If fluid flow is
focused along the décollement and/or splay faults, we need to determine its physical effect on
fault-zone strength and whether or not pulses of flow modulate the earthquake cycle. To
characterize the basaltic host rock’s physical properties and fluid chemistry prior to
subduction, we require at least one of the reference holes to extend 100-200 m into basement.
12
How have system-wide patterns of sediment dispersal affected composition within the
trench wedge and Shikoku Basin, particularly on the northeast side of the fossil spreading
ridge? Seismic data are being used to map facies units within the Shikoku Basin (and, for
that matter, the Nankai trench wedge), but we need cores to determine sediment composition
for three basic reasons. First, sandstone diagenesis and porosity reduction depend heavily on
the initial texture and mineral composition of the sand. Currently, we do not know whether
Pliocene-Miocene turbidites on the northeast side of Shikoku Basin shared a common source
with coeval sand bodies on the southwest side. Leg 190 showed that core recovery within
sand-rich units is poor at shallow depths (i.e., above the onset of sandstone cementation).
This lesson applies to the upslope prism sites and riser holes, as well. Armed with core,
porewater, and thermal data from oceanic reference sites, it will be possible to forecast the
onset of cement precipitation (e.g., quartz, calcite, zeolite), framework grain dissolution, and
formation of pseudo-matrix by compaction and/or tectonic deformation of ductile rock
fragments and phyllosilicates. Second, we know almost nothing about clay mineralogy and
volcanic-ash stratigraphy on the northeast side of Shikoku Basin. The clay budget is integral
to several important hydration and dehydration reactions, and clays (e.g., % smectite)
strongly affect the coefficient of internal friction (Fig. 9). One prediction to ponder is
Figure 9. Lab results (ring shear and direct shear tests) for standard mineral mixtures and
naturally occurring sediments from DSDP Site 297, Ashizuri Transect (from Brown et al., in
review). Diagram A shows coefficient of friction as a function of weight-% smectite; B
shows coefficient of internal friction as a function of weight-% total clay. Mildly altered
vitric ash (designated by the “A plots off the expected trend. Reference curves from Lupini et
al. (1981) and Logan and Rauenzahn (1987) have been added for comparison. Diagram C
shows coefficient of friction for different mixtures of smectite + quartz, plus “pure” chlorite
and “pure” illite, under conditions of increasing effective normal stress.
enrichment of both detrital and authigenic smectite toward the northeast in response
increasing amounts of volcanogenic input from the Izu-Bonin island arc. If true, then the
lower Shikoku Basin offshore Kii should be inherently weaker than it is offshore Muroto. A
third justification for compositional analysis is core-log-seismic integration. IODP coring
policy is still in development, but riser-drilling will probably sample more by core cuttings
13
than by continuous coring. Interpretations of lithostratigraphy within the riser holes,
therefore, will hinge on our ability to relate LWD data to actual lithologies; that cannot be
accomplished without continuous coring at the non-riser reference sites.
How do thermal structure and primary sediment/rock composition modulate diagenesis
and fluid-rock interactions? From clay mineralogy, we already know that reaction progress
is more advanced along the Muroto transect than it is along Ashizuri (Fig. 6). Lithosphere age
within the Kii transect area is approximately 20 Ma (Okino et al., 1999), and should have
lower heat flow than young crust along the Muroto transect. Heat flow generally decreases
with age and distance from the Kinan seamounts (Fig. 10), but we must verify this regional
pattern in local detail with high-quality borehole measurements. Because of the likelihood of
active fluid flow, data from surface probes and BSR approximations may not be
representative. The Kii transect’s thermal structure is one of the more important input
variables to document because of its affect on sediment diagenesis and fluid chemistry. Fluid
Figure 10. Heat flow data
from Shikoku Basin and
Nankai accretionary prism,
showing difference in thermal
inputs along strike.
chemistry and physical properties change down-section and down-dip in response to a host of
temperature-dependent hydration reactions (e.g., volcanic ash to zeolite + smectite) and
dehydration reactions (e.g., opal to quartz, smectite to illite), together with the precipitation
of crystalline cements (e.g., carbonates, zeolites, silica). In the case of smectite, there are
three temperature-dependent dehydration steps (Colten-Bradley, 1986). As strata pass
through the threshold for each step, interlayer water may be liberated in distinct pulses,
leading to compartments of fluid overpressure within poorly drained intervals. Accurate
modeling of this phenomenon in 3-D requires reliable temperature data. The growth of
phyllosilicates (e.g., illite to phengite or muscovite) in zones of incipient metamorphism also
depends largely on temperature (Merriman and Peacor, 1999). Authigenic phases in the
igneous basement, inherited from early ridge-flank hydrothermal processes, are also
14
susceptible to diagenetic reactions at higher temperatures. For example, saponite (a member
of the smectite group) is common in MOR basalt. Finally, our integrated program includes
plans to obtain additional heat flow data from the subduction front to calculate temperature
increases toward seismogenic depths. Linear geothermal gradients projected from a nearsurface BSR are probably not reliable. Improved thermal models are vital for planning
purposes because final decisions regarding deep riser holes will be constrained by the
temperature thresholds of the proposed instruments and electronic arrays.
Partitioning of Inputs at Toe of Accretionary Prism
Two questions pertain to the shallow up-dip portion of the décollement within the Kii
transect area. As with input parameters, we cannot borrow data directly from Muroto or
Ashizuri because the subduction system changes so dramatically along strike (e.g., Fig. 1).
Only by drilling through the prism toe can we verify the location and physical character of
the décollement.
Through which stratigraphic interval does the décollement propagate near the Kii
deformation front? The answer is important because faulting at the prism toe partitions the
approaching stratigraphy into domains of frontal offscraping and transfer beneath the plate
boundary to seismogenic depths. The NSF-MARGINS science plan for SEIZE includes
components of numerical simulations and laboratory experiments that are, and will be,
designed to simulate down-dip changes in physical properties, shear strength, fluid chemistry,
physical hydrology, and the like. Down-dip predictive models will be of dubious value
without proper characterization of, and correct discrimination between, the types of sediment
that are actually accreted at the prism toe (versus those subducted/underplated to deeper
positions). Seismic reflection data across the Kii transect clearly show the position of the
frontal fault near the prism toe (Fig. 11), but show little evidence for seaward propagation of
the décollement within the deeper Shikoku Basin strata. One interpretation of the seismic
profile is that the décollement steps up to seafloor, thereby thrusting older accretionary prism
strata (upper Shikoku Basin facies?) over the late Quaternary trench-wedge facies.
Submersible observations of the prism toe also suggest that semi-lithified sediments of
unknown age have been uplifted and exposed along a fault scarp (Ashi et al., 2002). Farther
inboard, the fault ramps down into the lower Shikoku Basin facies (Park et al., 2002b).
Figure 11. Interpretation of
seismic reflection Line 5 at toe of
accretionary prism, Kii transect
area. Position of décollement is
shown in red, and may intersect
the seafloor near the prism toe.
Location of proposed drilling site
NT1a-03A is shown.
15
Alternatively, the décollement is incompletely developed beneath the Nankai Trough, but in
the future will propagate seaward along the same horizon within the Shikoku Basin units.
Regardless, the structural geometry displayed in this location (Fig. 11) is very unusual, given
the thick trench wedge that is being accreted, and implies that the fault-tip behavior near Kii
is fundamentally different than it is at Muroto or Ashizuri. Drilling will help to constrain the
factors that control this behavior (see below).
Which factor(s) control the initial position of the fault tip at the prism toe, as well as the
location of ramps and flats, and mechanical behavior throughout? One generic possibility to
consider (e.g., Deng and Underwood, 2001) is a reduction in shear strength along a specific
stratigraphic interval with low intrinsic strength, caused perhaps by unusually high contents
of clay-sized particles and/or smectite-rich clay (Fig. 9). This scenario seems doubtful for
Kii if the fault tip truly steps up to the seafloor, and thrusts upper Shikoku Basin strata over
the sandy trench wedge (Fig. 11). Furthermore, there is no such anomaly in % smectite or %
clay along the décollement horizon at Muroto or Ashizuri (Fig. 6). Another generic
possibility is a reduction of effective stress due to excess pore pressure. Causes of excess
pore pressure could be as diverse as rapid up-dip migration of pore fluids from deep-seated
sources, in situ mineral dehydration within poorly drained mudstone, or compaction
disequilibrium caused by rapid loading of an impermeable mudstone beneath the landwardthickening trench wedge. Pinch-outs of highly permeable sand against mudstone aquitards, if
combined with compaction disequilibrium and pressure-driven fluid flow, could lead to a
complicated array of stratigraphically controlled compartments of excess pore pressure in the
critical interval where the décollement ramps down into the lower Shikoku Basin facies.
Strata near the basalt-sediment interface contain abundant volcaniclastic debris and smectite,
at least within the Muroto and Ashizuri transects (Fig. 6). Alteration of ash typically forms
bentonite (>75% smectite), and lab tests prove that such deposits sustain abnormally low
coefficients of internal friction (Fig. 9). Those rocks, therefore, could provide zones of
preferential weakness where the décollement ramps down to the seismogenic zone (Fig. 2).
IV. SPECIFIC DRILLING AND SAMPLING OBJECTIVES
At a minimum, three oceanic reference sites must be drilled within the Kii transect area
(Fig. 7) to test the influence of turbidite stratigraphy, basement topography, and thermal
structure on fluid flow, and to verify structural partitioning at the deformation front. We
propose two sites in the Shikoku Basin seaward of the trench wedge, one above “normal”
basement, the other above a basement high. This configuration will test end-member
hypotheses of basement-influenced flow patterns. A third site at the prism toe will penetrate
the frontal décollement, to determine the partitioning of material across the décollement, and
initial physical properties changes at the deformation front. Total sediment thickness at the
prism toe is ~2000 m, so only one such hole to basement seems practical.
16
In the category of lithostratigraphy, we will integrate basin-wide mapping of seismic
stratigraphy with conventional core descriptions, logging, and compositional analyses (e.g.,
grain size, bulk mineralogy, sand petrology, clay mineralogy) to establish spatial and
temporal patterns of sediment dispersal. Much of this can be accomplished using standard
shipboard protocols, including multi-sensor data. For effective core-log-seismic integration,
and to characterize sand-rich intervals with lower potential for core recovery, we need a full
suite of LWD logs (density, porosity, natural gamma, resistivity). A vigorous program of
shorebased analyses (X-ray diffraction, ICP-MS bulk chemistry, thin-section petrography,
SEM-EDS, TEM-EDS, etc.) should also include such components as volcanic glass
geochemistry, apatite fission-track geochronology, and radiometric dating of detrital
phyllosilicates and K-feldspar. It will be important to document the fine details of detrital
phyllosilicates (crystallinity index, mica polytype, bo value) for comparison with incipient
metamorphic phases expected in the deep riser hole. Such data will help test whether or not
mineral changes during the transformation of mudstone to slaty or schistose rock fabric can
be linked to the onset of stick-slip behavior.
Fluids affect virtually all other categories of subduction inputs, the prism taper angle,
and décollement behavior (Moore and Vrolijk, 1990; Morgan and Karig, 1995; Moore et al.,
2001; Saffer and Bekins, 1999, 2002). As parts of NanTroSEIZE, we must consider: (a) the
spatial and temporal distribution of pore pressure, temperature, and fluid chemistry, within
and adjacent to active faults, and within the igneous basement; (b) fluid sources, pathways,
and flow rates within domains controlled by both deformation and stratigraphy/compaction;
(c) the roles of fluid flow and pore pressure in fault strength and behavior; and (d) and the
hydrologic response to regional strain. Perhaps the seismogenic zone is connected
hydrologically to the seafloor via fault conduits; perhaps fluid escape is channeled along
splay faults and the décollement. To determine how pore pressure and fluid composition
vary in both time and 3-D space, we propose to drill an array of boreholes instead of a narrow
two-dimensional transect. Direct measurements will constrain a new generation of numerical
models (e.g., Saffer and Bekins, 1998).
Figure 12 shows hypothetical flow patterns within sediment and basement under
different sets of assumptions. Permeability and fluid flow within the oceanic basalt will be
affected by many variables (Fisher, 1998), and the sediment hydraulic impedance controls the
degree to which the basement aquifer and ocean remain coupled (Snelgrove and Forster,
1996; Giambalvo et al., 2000). If, for example, the basement is permeable and connected to
the sediments, then flow lines should converge on the basement high as porewater is driven
into the Shikoku Basin by loading beneath the prism toe. Conversely, if fluids are unable to
flow from the turbidites into basement, then flow lines will diverge around the basement
high. We can discriminate between these patterns by comparing thermal and geochemical
signatures close to and far from the basement high. Similarly, if flow in the igneous
17
Figure 12. Schematic diagrams of hypothetical flow patterns in sediment and igneous
basement under different combinations of assumed conditions.
basement is driven primarily by density differences, then cooler water beneath a thinner
sediment cover should flow away from the crest of the basement high. A site near the
basement high should yield thermal and geochemical evidence of infiltrating seawater,
whereas a site distal to the basement structure would not. To test these predictions, we will
follow the standard ODP protocol for pore-water sampling and shipboard chemical analysis,
including fluids extracted from fine-grained turbidite layers. Shorebased labs will
concentrate on the analysis of trace/minor elements in the pore fluids, together with isotopes
that are particularly diagnostic of sources and fluid-rock reactions (e.g., helium, chlorine,
strontium) (e.g., Kastner et al., 1993; Spivak et al., 2002).
The plan for drilling in Shikoku Basin also includes LWD logging and a suite of
hydrologic tests to quantify porosity, resistivity, and permeability. We expect compaction
and diagenesis to be modest (relative to the Muroto transect), so it should be effective to
measure pore pressure within the Shikoku Basin turbidites (and mudstone) with a DVTP-type
probe. This will be important for testing whether discontinuous sands translate pore pressure
laterally. Horizontal and vertical permeability of the unconsolidated sediment will be
measured using a combination of whole-round samples (both sand-rich and mud-rich, tested
at in situ effective stresses), and single-well packer tests (Fisher and Zwart, 1997). Our goal
is to quantify properties of a full range of well-characterized lithologies, then scale upward to
LWD and seismic data.
We propose long-term monitoring of fluid chemistry, temperature, and pore pressure
within the Shikoku Basin turbidites and the upper part of igneous basement. This objective
can be achieved by installing a pair of sealed boreholes and osmotic fluid samplers at a basin
site that penetrates ~100 m into basalt. The first installation will target part of the turbidite
section; a bridge plug will be required to isolate the bottom of the open hole from underlying
basement. Long-term monitoring in the upper oceanic crust will require a cased hole. When
combined with down-hole probe measurements, this combination of CORKs will provide
critical constraints on the thermal, chemical, and hydrologic state of the incoming plate. We
also expect the first CORK to capture a pressure response (and possibly a thermal signature)
18
during drilling of the second. By pumping fluids out of the basement at the second CORKed
hole, we should significantly improve the chemical sampling program because the borehole
volume will be cleared of drilling-induced contaminants. Comparison of pressure records at
the two CORK holes will provide information on the hydraulic connection between the
igneous crust and the sediment. By casing the entire sediment column in a second hole, and
leaving basement open, the second CORK will serve as an effective pore-pressure indicator
during strain. This approach takes advantage of the lower compressibility of basalt, as
compared to consolidated sediment. Monitoring of the tidal response should calibrate the
strain response, so that any perturbation recorded in pore pressure can be related to strain.
Capturing the physical effects of fluid flow at the prism toe may be possible, as well, but that
would require an A-CORK to isolate intervals between packers. Design of an A-CORK array
should be deferred until the coring/logging results can be thoroughly digested (as with ODP
Legs 190 and 196). This two-step plan will ensure thoughtful placement of packer intervals,
bridge plugs, casing, screening, and instrument arrays in what could prove to be a
complicated sequence of faulted strata.
In the category of physical properties, we will document depth-dependent and faciessensitive variations in bulk density, porosity, void ratio, electrical conductivity, and thermal
conductivity, using standard shipboard measurements. LWD logs will be used to deconvolve
the physical properties in situ. This phase will be followed by a more time-intensive program
of shorebased engineering tests (e.g., consolidation, direct shear, ring shear, and
permeability) under conditions of increasing normal effective stress. Those tests of wholeround core samples will help to define in situ burial conditions, establish whether states of
over- and under-consolidation exist on a widespread basis, and pin-point lithology-dependent
coefficients of internal friction (Lupini et al., 1981; Logan and Rauenzahn, 1987; Brown et
al., in review). They will also provide lithology-specific solutions to the relation between
effective stress and void ratio, which will permit modeling of in situ pore pressure (Moore
and Tobin, 1996). Only by testing analogous natural lithologies can such lab experiments
correctly simulate the effective stress conditions expected down dip, thereby permitting
comparisons between frictional strength at aseismic and seismogenic depths -- before, that is,
the riser phase of NanTroSEIZE begins.
Documentation of heat flow and diagenesis needs to be carefully coordinated with
parallel efforts in lithostratigraphy, fluids, and physical properties. Temperature data will be
important for discriminating among models of fluid flow (Fig. 12). Infiltration of seawater
into a basement high, for example, should produce a clear thermal signature. Most of the
products of diagenesis will have to be documented via shorebased chemical analyses of
specific authigenic phases, X-ray diffraction, TEM, and SEM-EDS. As stated previously,
heat flow modeling will influence logistical decisions for positioning the deep riser hole.
Thus, we propose high-resolution borehole temperature measurements at all of the reference
19
sites using a DVTP-type tool at a depth spacing of ~50 m. In addition, thermistor strings will
be installed in the sealed boreholes.
The structural geology component of NanTroSEIZE will track the décollement's
evolution from prism toe to seismogenic zone. This effort starts with detailed core
description and measurement of structural elements (e.g., bedding, fractures, deformation
bands, scaly fabric, fold hinges, veins) using cores from the reference sites. Absolute
orientations will be restored using natural remanent magnetism (NRM) declination. Such
data will define the initial thickness of the fault zone, determine if there are narrow zones of
concentrated slip near the propagating tip, whether such zones are lithology-dependent, and if
links exist between deformation fabrics and physical properties (e.g., porosity). These goals
also require a full suite of LWD logs, especially from the prism-toe where deformation
geometries will be complicated and core recovery less certain. Borehole images from the
microresistivity-at-bit tool will be particularly useful for mapping structural features in their
true orientations, and for assessing in situ stress. To build a database at all scales, a
shorebased program will include such methods as thin-section petrography, SEM and CTscan, X-ray goniometry, magnetic fabric, and chemical analyses of fracture-filled veins and
fluid inclusions.
V. PROSPECTIVE DRILLING TARGETS
We emphasize here that specific details regarding site characterization will probably
change after acquisition and processing of new seismic reflection data. Figure 13 shows the
trackline chart for JAMSTEC Cruise KR02-11, which collected data from the Kii transect
area during August-September 2002 (i.e., just prior to the iSAS proposal deadline). Our first
iteration of target characterization is based on interpretations of seismic data collected in
1998 and 2001.
Figure 13. Trackline chart for
JAMSTEC Cruise KR02-11, which
collected seismic reflection data
during August-September, 2002
20
NT1a-01A: Shikoku Basin, above basement high (Seismic Line KR9806-02). This site
will be drilled near the crest of a bathymetric mound that is associated with a basement high
(Fig. 14). The site is located on trackline KR9806-02 at a water depth of approximately 3540
m. Depth to basement is approximately 460 m. Acoustic character is largely transparent,
which indicates that the strata are composed of hemipelagic mud and mudstone, with few
sand packets. Coring at this site should penetrate 100-200 m below the sediment-basalt
interface. This site is the top priority for tests of basement hydrogeology.
NT1a-02A: Shikoku Basin, above basement low (Seismic Line KR9806-01). This site
will be drilled in a region of relatively flat basement topography (Fig. 14). The site is located
on trackline KR9806-01 at a water depth of approximately 4210 m. Depth to basement is
approximately 730 m. Acoustic character within the lower part of the Shikoku Basin is
dominated by sharp, continuous reflectors, similar to what has been observed along the
Ashizuri transect. Based on this seismic response, we expect numerous packets of sandy
turbidites to be interbedded with hemipelagic mudstone.
Figure 14. Seismic reflection profiles showing location of proposed site NT1a-01A and
NT1a-02A. Tracklines are shown in Figure 7. Shikoku Basin site above basement high is on
seismic profile KR9806-02. Shikoku Basin site above basement low is on seismic profile
KR9806-01.
NT1a-03A: Prism toe (Seismic Line 5). This site will be drilled through the toe of the
accretionary prism near the base of slope (Fig. 15). The site is located on trackline Line 5 at
a water depth of approximately 4125 m. Depth to basement is approximately 1740 m. The
21
inferred position of the décollement is approximately 250 mbsf; strata above the fault appear
to be semi-consolidated, but we expect to encounter abundant unconsolidated sand (trench
wedge facies) beneath the fault. Thus, drill-in casing could be required to maintain borehole
stability from ~ 240 to 540 mbsf. A second discontinuity in reflector geometry at ~ 530 mbsf
could be caused by seaward propagation of the fault tip into the Shikoku Basin facies. The
lower Shikoku Basin facies appears to be ~ 740 m in thickness at this location. Although
penetration to basement is desirable, a more important goal is to sample as much of the lower
Shikoku Basin as possible. That unit is what must be tracked down-dip to the seismogenic
zone.
Figure 15. Seismic reflection profile showing location of proposed site NT1a-03A at the toe
of the accretionary prism, Kii Peninsula transect. Trackline is shown in Figure 7. Depth
conversion of profile Line 5 at drill site indicates that depth to basement is approximately
1750 m.
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and implications for transport of fluid and heat: Jour. Geophys. Res., 105: 913-928.
Hickman, S., 1991, Stress in the lithosphere and the strength of active faults: Rev. Geophys., 29: 759775.
Hubbert, W.W., and Rubey, M.K., 1959, Mechanics of fluid-filled porous solids and its application to
overthrust faulting: Geol Soc. Am. Bull., 70: 115-166.
Hyndman, R., 1999, Seismogenic Zone Deep Drilling and Measurement: Report of Detailed Planning
Group: http://joides.rsmas.miami.edu/files/seizerept.pdf.
Hyndman, R., Wang, K, Yamano, M., 1995, Thermal constraints on the seismogenic portion of the
southwestern Japan subduction thrust: J. Geophys. Res., 100: 15,373-15,392
Ike, T., Park, J-O., Moore, G., and Kaneda, Y., 2002, Variations in basement topography and
sediment thickness on the Philippine Sea plate subducting along the Nankai Trough: Eos, Trans,
Am. Geophys. Un..
Kastner, M., Elderfield, H., Jenkins, H., Gieskes, J.M., and Gamo, T., 1993. Geochemical and
isotopic evidence for fluid flow in the western Nankai subduction zone, Japan. Proc. ODP, Sci.
Results, 131: College Station, TX (Ocean Drilling Program), 397-413.
Kinoshita, M., and Yamano, M., 1995, Heat flow distribution in the Nankai Trough region, In:
Geology and Geophysics of the Philippine Sea, Terra Scientific Publishing Company: 77-86.
Kumagai, H., 1996, Time sequence and the recurrence models for large eathquakes along the Nankai
Trough revisited: Geophys. Res. Lett., 23: 1139-1142.
Le Pichon, X., and 16 others et al., 1987a, The eastern and western ends of Nankai Trough: results of
Box 5 and Box 7 Kaiko survey: Earth Planet. Sci. Lett., 83: 199-213.
Le Pichon, X., and 16 others, 1987b, Nankai Trough and the fossil Shikoku Ridge: results of Box 6
Kaiko survey: Earth Planet. Sci. Lett., 83: 186-198.
Le Pichon, X., Lallemant, S.J., Tokuyama, H., Thoue, F., Henry, P., 1996, Structure and evolution of
the backstop in the Eastern Nankai Trough area (Japan): implications for the soon to come Tokai
earthquake: Island Arc, 5: 440-454.
23
Logan, J.M., and Rauenzahn, K.A., 1987, Frictional dependence of gouge mixtures of quartz and
montmorillonite on velocity, composition and fabric: Tectonophys., 144: 87-108.
Lupini, J.F., Skinner, J.F., and Vaughan, A.E., 1981, The drained residual strength of cohesive soils:
Géotechnique, 31: 181-213.
MARGINS,
1999,
The
Seismogenic
Zone
Experiment
(SEIZE)
Science
plan:
http://www.ldeo.columbia.edu/margins/SEIZE_sci_plan.html.
Marone, C., 1998, Laboratory-derived friction laws and their application to seismic faulting: Ann.
Rev. Earth Planet. Sci., 26: 643-696.
Mazzotti, S., Lallemant, S. J., Henry, P., LePichon, X., Tokuyama, H., Takahashi, N., 2001,
Lithospheric scale tectonics of the Eastern Nankai subduction: intraplate shortening and
undethrusting of a large basement ridge: Marine Geol., in press.
Merriman, R.J., and Peacor, D.R., 1999, Very low-grade metapelites: mineralogy, microofabrics and
measuring reaction progress, in Frey, M., and Robinson, D. (eds.), Low-Grade Metamorphism:
Blackwell Science, Oxford, 10-60.
Miyazaki, S., and Heki, K., 2001, Crustal velocity field of southwest Japan: Subduction and arc-arc
collision: J. Geophys. Res., 106: 4305-4326.
Moore, G.F., Taira, A., Klaus, A., and others, 2001, New insights into deformation and fluid flow
processes in the Nankai Trough accretionary prism: Results of Ocean Drilling Program Leg 190:
Geophysics, Geochemistry, Geosystems, 2:10-25.
Moore, J.C., and Vrolijk, P.J., 1992, Fluids in accretionary prisms: Rev. Geophys., 30: 113-135.
Moore, J.C., and Tobin, H., 1996, Estimated fluid pressures of the Barbados accretionary prism and
adjacent sediments: Proc. ODP, Sci. Results, 156: College Station, TX, 229-238.
Moore, J.C., and Saffer, D.M., 2001, Updip limit of the seismogenic zone beneath the prism of
southwest Japan: An effect of diagenetic to low-grade metamorphic processes and increasing
effective stress: Geology, 29: 183-186.
Morgan, J.K., and Karig, D.E., 1995, Décollement processes at the Nankai accretionary margin:
Propagation, deformation, and dewatering: J. Geophys. Res., 100: 15221-15231.
Obana, K., Kodaira, S., Mochizuki, K. and Shinohara, M., 2001, Micro-seismicity around the seaward
updip limit of the 1946 Nankai earthquake dislocation area: Geophys. Res. Lett., 28: 2333-2336.
Okino, K., Shimakaw, Y., and S. Nagaoka, S., 1994, Evolution of the Shikoku Basin: J. Geomag.
Geoelec., 46:463-479.
Okino, K., Shimakawa, Y. and Nagaoka, S., 1994. Evolution of the Shikoku Basin: J. Geomag.
Geoelectr, 46: 463-479.
Oleskevich, D.A., Hyndman, R.D., and Wang, K., 1999, The updip and downdip limits to great
subduction earthquakes: Thermal and structural models of Cascadia, south Alaska, SW Japan, and
Chile: J. Geophys. Res., 104: 14,965-14,991.
Ohmori, K., Taira, A., Tokuyama, H., Sakaguchi, A., Okamura, M., and Aihara, A., 1997,
Paleothermal structure of the Shimanto accretionary prism, Shikoku, Japan: Role of an out-of-
24
sequence thrust: Geology, 25: 327-330.
Park, J-O., and 7 others, 2002a, A deep strong reflector in the Nankai accretionary wedge from
multichannel seismic data: Implications for underplating and interseismic shear stress release: J.
Geophys. Res., 107: 10.1029/2001JB000262.
Park, J-O., Tsuru, T., Kodaira, S., Cummins, P.R., and Kaneda, Y., 2002b, Splay fault branching
along the Nankai subduction zone: Science, 297: 1157-1160.
Protti M., Guendel, F., McNally, K., 1995, Correlation between the age of the subducting Cocos Plate
and the geometry of the Wadati-Benioff zone under Nicaragua and Costa Rica, in GSA Special
Paper 295, 309-326.
Saffer, D.M., and Bekins, B.A., 1998, Episodic fluid flow in the Nankai accretionary complex:
Timescale, geochemistry, flow rates, and fluid budget: J. Geophys. Res., 103: 30,351-30,370.
Saffer, D. M., and Bekins, B.A., 1999, Fluid budgets at convergent plate margins: Implications for the
extent and duration of fault-zone dilation: Geology, 27: 1095-1098.
Saffer, D.M., and Bekins, B.A., 2002, Hydrologic controls on the morphology and mechanics of
accretionary wedges: Geology, 30: 271-274.
Sakaguchi, A., 1996, High geothermal gradient with ridge subduction beneath Cretaceous Shimanto
accretionary prism, southwest Japan: Geology, 24: 795-798.
Snelgrove, S.H., and Forster, C.B., 1996, Impact of seafloor sediment permeability and thickness on
off-axis hydrothermal circulation: Juan de Fuca Ridge eastern flank: J. Geophys. Res., 101: 29152925.
Spivack, A.J., Kastner, M., and Ransom, B., 2002, Elemental and isotopic chloride geochemistry and
fluid flow in the Nankai Trough: Geophys. Res. Lett., 29: 10.1029/2001GL014122.
Taira, A., Katto, J., Tashiro, M., Okamura, M. and Kodama, K., 1988, The Shimanto Belt in Shikoku,
Japan: Evolution of a Cretaceous to Miocene accretionary prism: Mod. Geol., 12: 5-46.
Tanioka, Y., and Satake, K., 2001a, Detailed coseismic slip distribution of the 1944 Tonankai
earthquake estimated from tsunami waveforms. Geophys. Res. Lett., 28: 1075-1078.
Tanioka, Y., and Satake, K., 2001b, Coseismic slip distribution of 1946 Nankai earthquake and
aseismic slips caused by the earthquake: Earth, Planets, Space, 53: 235-241.
Underwood, M.B. (ed.), 1993, Thermal evolution of the Shimanto Belt of southwest Japan: GSA Spec.
Paper 273: 1-172.
Underwood, M.B., and Pickering, K., 1996, Clay-mineral provenance, sediment dispersal patterns,
and mudrock diagenesis in the Nankai accretionary prism, southwest Japan, Clays Clay Min.,
44:339-356.
Wang, K., Hyndman, R.D., and Yamano, M., 1995, Thermal regime of the southwest Japan
subduction zone: effects of age history of the subducting plate: Tectonophys., 248: 53-69.
25
iSAS/IODP Site Summary Forms:
Form 1 - General Site Information
Please fill out information in all gray boxes
Revised
New
Revised 7 March 2002
Section A: Proposal Information
Title of Proposal:
NanTroSEIZE Reference Sites:
Sampling and Measuring Inputs to the Seismogenic Zone
Date Form September 30, 2002
Submitted:
Reference site to penetrate the entire sedimentary section and into oceanic crust;
document basement hydrogeology at a bathymetric mound associated with a
Site Specific
Objectives with basement high of the Shikoku Basin. This site is the top priority for tests of
Priority basement hydrogeology.
(Must include general
objectives in proposal)
List Previous
Drilling in Area:
No scientific drilling in the immediate vicinity. DSDP 87, ODP 131, 190 and 196
were conducted about 200 km southwest of this proposal sites.
Section B: General Site Information
If site is a reoccupation
Site Name:
(e.g. SWPAC-01A)
NT1a-01A
of an old DSDP/ODP
Site, Please include
Area or Location:
Nankai Trough off Kii
former Site #
Latitude: Deg: 32 N
Min: 44.8878
Jurisdiction:
Longitude: Deg: 136 E
Min: 55.0236
Distance to Land:
Coordinates
System:
WGS 84,
Priority of Site: Primary: X
Other (
Alt:
Japan
130 km to Cape Shiono-Misaki
)
Water Depth:
3540 m
Section C: Operational Information
Sediments
Proposed
Penetration:
(m)
Basement
460 m
200 m
What is the total sed. thickness? 460
m
Total Penetration: 660
General Lithologies:
Coring Plan:
(Specify or check)
Silt with sandy turbidites and ash layers
Hemipelagic mudstone
m
Basalt
2-APC/XCB at Hole A, RCB to TD at Hole B, LWD to TD at Hole C
1-2-3-APC
VPC*
XCB
MDCB*
PCS
RCB
Re-entry
HRGB
* Systems Currently Under Development
Wireline Logging
Plan:
Standard Tools
Special Tools
LWD
Neutron-Porosity
Borehole Televiewer
Formation Fluid Sampling
Density-Neutron
Litho-Density
Nuclear Magnetic
Borehole Temperature
Resistivity-Gamma Ray
Resonance
& Pressure
Gamma Ray
Geochemical
Borehole Seismic
Acoustic
Resistivity
Side-Wall Core
Others (
Others (
Sampling
Acoustic
Formation Image
Max.Borehole
Temp. :
Expected value (For Riser Drilling)
Mud Logging:
(Riser Holes Only)
Cuttings Sampling Intervals
)
)
°C
from
m
to
m,
m intervals
from
m
to
m,
m intervals
Basic Sampling Intervals: 5m
Estimated days:
Future Plan:
Drilling/Coring: 7 days
Logging: 4 days
Total On-Site: 11 days
Longterm Borehole Observation Plan/Re-entry Plan
Re-entry and set A-CORK (Leg 196-type) in Hole C after LWD
Hazards/
Weather:
Please check following List of Potential Hazards
Shallow Gas
Hydrocarbon
Complicated Seabed Condition Hydrothermal Activity
Soft Seabed
Landslide and Turbidity Current
Currents
Shallow Water Flow
Methane Hydrate
Abnormal Pressure
Fractured Zone
Diapir and Mud Volcano
Man-made Objects
Fault
High Temperature
H2S
High Dip Angle
Ice Conditions
CO2
What is your Weather
window? (Preferable
period with the reasons)
April-July
Form 2 - Site Survey Detail
iSAS/IODP Site Summary Forms:
Please fill out information in all gray boxes
Proposal #:
New
Site #: NT1a-01A
Data Type
SSP
Requirements
Exists
In DB
High resolution
seismic reflection
No
4
5a
Deep Penetration
seismic reflection
Yes
Seismic Velocity†
Yes
Seismic Grid
Refraction
Yes
No
:Location of Site on line (SP or Time only)
Primary Line(s):
Refraction
Yes
Location of Site on line (SP or Time only)
KR9806-2 SP2710
Crossing Lines(s):
(surface)
5b
Details of available data and data that are still to be collected
Crossing Lines(s):
2
3
Date Form Submitted: Sept. 30, 2002
Primary Line(s)
1
Revised
KR0211-S0
Stacking velocity and migration velocity from MCS lines. OBS data
Two ship COP (maximum offset 20 km) will be obtained by JAMSTEC at
the end of September, 2002.
OBS data by Nakanishi et al. (1997)
(near bottom)
6
3.5 kHz
No
7
Swath
bathymetry
Side-looking
sonar (surface)
Side-looking
sonar (bottom)
Photography
or Video
Heat Flow
Yes
8a
8b
9
10
Location of Site on line (Time)
Multi-narrow-beam data by JAMSTEC R/V Yokosuka
No
No
No
Yes
11a
Magnetics
Yes
Heat flow data are available 5 km northwest of this site. New heat flow
measurements are planned at this site in late 2002. A two week heat flow
survey is scheduled for the next fiscal year
Compiled map published from AIST, Japan
11b
Gravity
Yes
Compiled map published from AIST, Japan
12
13
14a
14b
15
Sediment cores
Rock sampling
Water current data
Ice Conditions
OBS
microseismicity
Navigation
Other
No
No
16
17
SSP Classification of Site:
SSP Comments:
Available on JODC web page (http://www.jodc.go.jp)
Analyzing now
Yes
SSP Watchdog:
Date of Last Review:
X=required; X*=may be required for specific sites; Y=recommended; Y*=may be recommended for specific sites;
R=required for re-entry sites; T=required for high temperature environments; † Accurate velocity information is required for
holes deeper than 400m.
Form 3 - Detailed Logging Plan
iSAS/IODP Site Summary Forms:
New
Proposal #:
Water Depth (m): 3540
Site #: NT1a-01A
Sed. Penetration (m): 460
Do you need to use the conical side-entry sub (CSES) at this site? Yes
Are high temperatures expected at this site?
Yes
Are there any other special requirements for logging at this site?
Yes
If “Yes” Please describe requirements:
What do you estimate the total logging time for this site to be:
Revised
Date Form Submitted: Sept. 30, 2002
Basement Penetration (m): 200
No
No
No
4 days
Relevance
(1=high, 3=Low)
Measurement Type
Neutron-Porosity
Scientific Objective
Estimation of water content in sedimentary sequences and basement.
1
Litho-Density
Estimation of water content, bulk density, and mineral composition in
1
sedimentary sequences and basement.
Natural Gamma Ray
Estimation clay contents and mineral composition in sedimentary
1
sequences and basement.
Resistivity-Induction
Estimation of water content and electro-magnetic properties in
1
sedimentary sequences and basement.
Acoustic
Determination of in situ velocity and estimation of physical properties.
1
Comparison with seismic velocity and create synthetic seismograms.
FMS
Imaging of sedimentary structures and fractures. Core-log correlation of
1
structural features.
BHTV
Resistivity-Laterolog
Magnetic/Susceptibility
Density-Neutron (LWD)
Estimation of water contents, bulk density, and lithology in unstable
1
borehole environments.
Resitivity-Gamma
Ray
Estimation of water contents, electro-magnetic properties, and lithology in
(LWD)
unstable borehole environments.
Other: Special tools (CORK,
CORK for basement hydrogeology
1
1
PACKER, VSP, PCS, FWS,
WSP
For help in determining logging times, please contact the ODP-LDEO Wireline Logging Services group
at:
borehole@ldeo.columbia.edu
http://www.ldeo.columbia.edu/BRG/brg_home.html
Phone/Fax: (914) 365-8674 / (914) 365-3182
Note: Sites with greater than 400 m of
penetration or significant basement
penetration require deployment of
standard toolstrings.
iSAS/IODP Site Summary Forms:
Form 4 – Pollution & Safety Hazard Summary
Please fill out information in all gray boxes
New
Proposal #:
1
3
4
5
6
7
8
Based on Previous DSDP/ODP
drilling, list all hydrocarbon
occurrences of greater than
background levels. Give nature
of show, age and depth of rock:
From Available information,
list all commercial drilling in
this area that produced or
yielded significant hydrocarbon
shows. Give depths and ages of
hydrocarbon-bearing deposits.
Are there any indications of gas
hydrates at this location?
Are there reasons to expect
hydrocarbon accumulations at
this site? Please give details.
What “special” precautions will
be taken during drilling?
What abandonment procedures
do you plan to follow:
Please list other natural or
manmade hazards which may
effect ship’s operations:
APC to refusal, then XCB to refusal. RCB to 660 m
None
None
No
No
Standard monitoring of C
layers.
Summary: What do you
consider the major risks in
drilling at this site?
1
to Cn ; shallow casing to stabilize shallow sandy turbidite
None
Strong Kuroshio current, typhoon (June to Oct.)
(e.g. ice, currents, cables)
9
Date Form Submitted: Sept. 30, 2002
Summary of Operations at site:
(Example: Triple-APC to refusal, XCB
10 m into basement, log as shown on
page 3.)
2
Site #: NT1a-01A
Revised
Current
Form 5 – Lithologic Summary
iSAS/IODP Site Summary Forms:
Proposal #:
Subbottom
depth (m)
460
Site #: NT1a-01A
Key reflectors,
Unconformities,
faults, etc
New
Date Form Submitted:
Assumed
velocity
(km/sec)
Lithology
Paleoenvironment
Holocene
to lower
Miocene
1.6-1.9
hemipelagite
backarc basin
floor
20 Ma
2.0
volcanic
sediment and
basement basalt
Age
Revised
unconformity
backarc basin
Avg. rate
of sed.
accum.
(m/My)
Comments
iSAS/IODP Site Summary Forms:
Form 1 - General Site Information
Please fill out information in all gray boxes
Revised
New
Revised 7 March 2002
Section A: Proposal Information
Title of Proposal:
NanTroSEIZE Reference Sites:
Sampling and Measuring Inputs to the Seismogenic Zone
Date Form September 30, 2002
Submitted:
Reference site to penetrate the entire sedimentary section and into oceanic crust;
complete characterization of Shikoku Basin strata above basement flat; document
Site Specific
Objectives with basement hydrogeology at a region of flat basement topography of the Shikoku
Priority Basin. Priority 1.
(Must include general
objectives in proposal)
List Previous
Drilling in Area:
No scientific drilling in the immediate vicinity. DSDP 87, ODP 131, 190 and 196
were conducted about 200 km southwest of this proposal sites.
Section B: General Site Information
If site is a reoccupation
Site Name:
(e.g. SWPAC-01A)
NT1a-02A
of an old DSDP/ODP
Site, Please include
Area or Location:
Nankai Trough off Kii
former Site #
Latitude: Deg: 32 N
Min: 47.4996
Longitude: Deg: 137 E
Min: 9.2784
Coordinates
System:
WGS 84,
Priority of Site: Primary: X
Other (
Alt:
Jurisdiction:
Distance to Land:
Japan
145 km to Cape Shiono-Misaki
)
Water Depth:
4210 m
Section C: Operational Information
Sediments
Proposed
Penetration:
(m)
Basement
730 m
200 m
What is the total sed. thickness? 730
m
Total Penetration: 930
General Lithologies:
Coring Plan:
(Specify or check)
Silt with sandy turbidites and ash layers
Hemipelagic mudstone
m
Basalt
2-APC/XCB at Hole A, RCB to TD at Hole B, LWD to TD at Hole C
1-2-3-APC
VPC*
XCB
MDCB*
PCS
RCB
Re-entry
HRGB
* Systems Currently Under Development
Wireline Logging
Plan:
Standard Tools
Special Tools
LWD
Neutron-Porosity
Borehole Televiewer
Formation Fluid Sampling
Density-Neutron
Litho-Density
Nuclear Magnetic
Borehole Temperature
Resistivity-Gamma Ray
Resonance
& Pressure
Gamma Ray
Geochemical
Borehole Seismic
Acoustic
Resistivity
Side-Wall Core
Others (
Others (
Sampling
Acoustic
Formation Image
Max.Borehole
Temp. :
Expected value (For Riser Drilling)
Mud Logging:
(Riser Holes Only)
Cuttings Sampling Intervals
)
)
°C
from
m
to
m,
m intervals
from
m
to
m,
m intervals
Basic Sampling Intervals: 5m
Estimated days:
Future Plan:
Drilling/Coring: 14 days
Logging: 6 days
Total On-Site: 20 days
Longterm Borehole Observation Plan/Re-entry Plan
Re-entry and set A-CORK (Leg 196-type) in Hole C after LWD
Hazards/
Weather:
Please check following List of Potential Hazards
Shallow Gas
Hydrocarbon
Complicated Seabed Condition Hydrothermal Activity
Soft Seabed
Landslide and Turbidity Current
Currents
Shallow Water Flow
Methane Hydrate
Abnormal Pressure
Fractured Zone
Diapir and Mud Volcano
Man-made Objects
Fault
High Temperature
H2S
High Dip Angle
Ice Conditions
CO2
What is your Weather
window? (Preferable
period with the reasons)
April-July
Form 2 - Site Survey Detail
9.27849.2784
iSAS/IODP Site Summary Forms:
Please fill out information in all gray boxes
Proposal #:
New
Site #: NT1a-02A
SSP
Requirements
Data Type
Exists
In DB
High resolution
seismic reflection
No
4
5a
Deep Penetration
seismic reflection
Yes
Primary Line(s):
Seismic Velocity
†
Seismic Grid
Refraction
Refraction
:Location of Site on line (SP or Time only)
Location of Site on line (SP or Time only)
KR9806-1 SP 1740
Crossing Lines(s):
Yes
Yes
No
(surface)
5b
Details of available data and data that are still to be collected
Crossing Lines(s):
2
3
Date Form Submitted: Sept. 30, 2002
Primary Line(s)
1
Revised
Yes
KR0211-S0 nearby
Stacking velocity and migration velocity from MCS lines. OBS data
Two ship COP (maximum offset 20 km) will be obtained by JAMSTEC at
the end of September, 2002.
OBS data by Nakanishi et al. (1997)
(near bottom)
6
3.5 kHz
No
7
Swath
bathymetry
Side-looking
sonar (surface)
Side-looking
sonar (bottom)
Photography
or Video
Heat Flow
Yes
8a
8b
9
10
Location of Site on line (Time)
Multi-narrow-beam data by JAMSTEC R/V Yokosuka
No
No
No
11a
Magnetics
Yes
Additional dense heat flow measurements are planned for a total of four
weeks at the end of this year (2002) and for the next fiscal year.
Compiled map published from AIST, Japan
11b
Gravity
Yes
Compiled map published from AIST, Japan
12
13
14a
14b
15
No
No
16
Sediment cores
Rock sampling
Water current data
Ice Conditions
OBS
microseismicity
Navigation
17
Other
SSP Classification of Site:
SSP Comments:
Yes
Available on JODC web page (http://www.jodc.go.jp)
Analyzing now
Yes
SSP Watchdog:
Date of Last Review:
X=required; X*=may be required for specific sites; Y=recommended; Y*=may be recommended for specific sites;
R=required for re-entry sites; T=required for high temperature environments; † Accurate velocity information is required for
holes deeper than 400m.
Form 3 - Detailed Logging Plan
iSAS/IODP Site Summary Forms:
New
Proposal #:
Water Depth (m): 4210
Site #: NT1a-02A
Sed. Penetration (m): 730
Do you need to use the conical side-entry sub (CSES) at this site? Yes
Are high temperatures expected at this site?
Yes
Are there any other special requirements for logging at this site?
Yes
If “Yes” Please describe requirements:
What do you estimate the total logging time for this site to be:
Revised
Date Form Submitted: Sept. 30, 2002
Basement Penetration (m): 200
No
No
No
6 days
Relevance
(1=high, 3=Low)
Measurement Type
Neutron-Porosity
Scientific Objective
Estimation of water content in sedimentary sequences and basement.
1
Litho-Density
Estimation of water content, bulk density, and mineral composition in
1
sedimentary sequences and basement.
Natural Gamma Ray
Estimation clay contents and mineral composition in sedimentary
1
sequences and basement.
Resistivity-Induction
Estimation of water content and electro-magnetic properties in
1
sedimentary sequences and basement.
Acoustic
Determination of in situ velocity and estimation of physical properties.
1
Comparison with seismic velocity and create synthetic seismograms.
FMS
Imaging of sedimentary structures and fractures. Core-log correlation of
1
structural features.
BHTV
Resistivity-Laterolog
Magnetic/Susceptibility
Density-Neutron (LWD)
Estimation of water contents, bulk density, and lithology in unstable
1
borehole environments.
Resitivity-Gamma
Ray
Estimation of water contents, electro-magnetic properties, and lithology in
(LWD)
unstable borehole environments.
Other: Special tools (CORK,
CORK to monitor fluid flow
1
PACKER, VSP, PCS, FWS,
WSP
For help in determining logging times, please contact the ODP-LDEO Wireline Logging Services group
at:
borehole@ldeo.columbia.edu
http://www.ldeo.columbia.edu/BRG/brg_home.html
Phone/Fax: (914) 365-8674 / (914) 365-3182
Note: Sites with greater than 400 m of
penetration or significant basement
penetration require deployment of
standard toolstrings.
iSAS/IODP Site Summary Forms:
Form 4 – Pollution & Safety Hazard Summary
Please fill out information in all gray boxes
New
Proposal #:
1
3
4
5
6
7
8
Based on Previous DSDP/ODP
drilling, list all hydrocarbon
occurrences of greater than
background levels. Give nature
of show, age and depth of rock:
From Available information,
list all commercial drilling in
this area that produced or
yielded significant hydrocarbon
shows. Give depths and ages of
hydrocarbon-bearing deposits.
Are there any indications of gas
hydrates at this location?
Are there reasons to expect
hydrocarbon accumulations at
this site? Please give details.
What “special” precautions will
be taken during drilling?
What abandonment procedures
do you plan to follow:
Please list other natural or
manmade hazards which may
effect ship’s operations:
APC to refusal, then XCB to refusal. RCB to 930 m
None
None
No
No
Standard monitoring of C
layers.
Summary: What do you
consider the major risks in
drilling at this site?
1
to Cn ; shallow casing to stabilize shallow sandy turbidite
None
Strong Kuroshio current, typhoon (June to Oct.)
(e.g. ice, currents, cables)
9
Date Form Submitted: Sept. 30, 2002
Summary of Operations at site:
(Example: Triple-APC to refusal, XCB
10 m into basement, log as shown on
page 3.)
2
Site #: NT1a-02A
Revised
Current
Form 5 – Lithologic Summary
iSAS/IODP Site Summary Forms:
Proposal #:
Subbottom
depth (m)
730
Site #: NT1a-02A
Key reflectors,
Unconformities,
faults, etc
New
Date Form Submitted: Sept. 30, 2002
Assumed
velocity
(km/sec)
Lithology
Paleoenvironment
Holocene
to lower
Miocene
1.6-1.9
hemipelagite
backarc basin
floor
20 Ma
2.0
volcanic
sediment and
basement basalt
Age
Revised
unconformity
backarc basin
Avg. rate
of sed.
accum.
(m/My)
Comments
iSAS/IODP Site Summary Forms:
Form 1 - General Site Information
Please fill out information in all gray boxes
Revised
New
Revised 7 March 2002
Section A: Proposal Information
Title of Proposal:
NanTroSEIZE Reference Sites:
Sampling and Measuring Inputs to the Seismogenic Zone
Date Form September 30, 2002
Submitted:
Penetrate the toe of the accretionary prism. A major objective is to know the
incoming sedimentary sequence. Although penetration to basement is desirable, a
Site Specific
Objectives with more important goal is to sample as much of the lower Shikoku Basin as possible.
Priority That unit is what must be tracked down-dip to the seismogenic zone.
(Must include general
objectives in proposal)
List Previous
Drilling in Area:
No scientific drilling in the immediate vicinity. DSDP 87, ODP 131, 190 and 196
were conducted about 200 km southwest of this proposal sites.
Section B: General Site Information
If site is a reoccupation
Site Name:
(e.g. SWPAC-01A)
NT1a-03A
of an old DSDP/ODP
Site, Please include
Area or Location:
Nankai Trough off Kii
former Site #
Latitude: Deg: 33 N
Longitude: Deg: 136 E
Coordinates
System:
WGS 84,
Priority of Site: Primary: X
Min: 1.23258
Min: 47.94852
Other (
Alt:
Jurisdiction:
Distance to Land:
Japan
100 km to cape Shiono-Misaki
)
Water Depth:
4125 m
Section C: Operational Information
Sediments
Proposed
Penetration:
(m)
Basement
1740 m
10 m
What is the total sed. thickness? 1740
m
Total Penetration: 1750
General Lithologies:
Coring Plan:
(Specify or check)
Silt with sandy turbidites and ash layers
Hemipelagic mudstone
m
Basalt
2-APC/XCB at Hole A, RCB to TD at Hole B, LWD to TD at Hole C
1-2-3-APC
VPC*
XCB
MDCB*
PCS
RCB
Re-entry
HRGB
* Systems Currently Under Development
Wireline Logging
Plan:
Standard Tools
Special Tools
LWD
Neutron-Porosity
Borehole Televiewer
Formation Fluid Sampling
Density-Neutron
Litho-Density
Nuclear Magnetic
Borehole Temperature
Resistivity-Gamma Ray
Resonance
& Pressure
Gamma Ray
Geochemical
Borehole Seismic
Acoustic
Resistivity
Side-Wall Core
Others (
Others (
Sampling
Acoustic
Formation Image
Max.Borehole
Temp. :
Expected value (For Riser Drilling)
Mud Logging:
(Riser Holes Only)
Cuttings Sampling Intervals
)
)
°C
from
m
to
m,
m intervals
from
m
to
m,
m intervals
Basic Sampling Intervals: 5m
Estimated days:
Future Plan:
Drilling/Coring: 20 days
Logging: 7 days
Total On-Site: 27 days
Longterm Borehole Observation Plan/Re-entry Plan
Re-entry and set A-CORK (Leg 196-type) in Hole C after LWD
Hazards/
Weather:
Please check following List of Potential Hazards
Shallow Gas
Hydrocarbon
Complicated Seabed Condition Hydrothermal Activity
Soft Seabed
Landslide and Turbidity Current
Currents
Shallow Water Flow
Methane Hydrate
Abnormal Pressure
Fractured Zone
Diapir and Mud Volcano
Man-made Objects
Fault
High Temperature
H2S
High Dip Angle
Ice Conditions
CO2
What is your Weather
window? (Preferable
period with the reasons)
April-July
Form 2 - Site Survey Detail
iSAS/IODP Site Summary Forms:
Please fill out information in all gray boxes
Proposal #:
New
Site #: NT01a-03A
Data Type
SSP
Requirements
Exists
In DB
High resolution
seismic reflection
No
4
5a
Deep Penetration
seismic reflection
Yes
Seismic Velocity†
Yes
Seismic Grid
Refraction
Yes
No
Primary Line(s):
Refraction
:Location of Site on line (SP or Time only)
Location of Site on line (SP or Time only)
KR0108-4 SP16550
Crossing Lines(s):
(surface)
5b
Details of available data and data that are still to be collected
Crossing Lines(s):
2
3
Date Form Submitted: Sept. 30, 2002
Primary Line(s)
1
Revised
Yes
Stacking velocity and migration velocity from MCS lines. OBS data
Two ship COP (maximum offset 20 km) will be obtained by JAMSTEC at
the end of September, 2002.
OBS data by Nakanishi et al. (1997)
(near bottom)
6
3.5 kHz
No
7
Swath
bathymetry
Side-looking
sonar (surface)
Side-looking
sonar (bottom)
Photography
or Video
Heat Flow
Yes
8a
8b
9
10
Location of Site on line (Time)
Multi-narrow-beam data by JAMSTEC R/V Yokosuka
No
No
No
11a
Magnetics
Yes
Additional dense heat flow measurements are planned for a total of four
weeks at the end of this year (2002) and for the next fiscal year.
Compiled map published from AIST, Japan
11b
Gravity
Yes
Compiled map published from AIST, Japan
12
13
14a
14b
15
Sediment cores
Rock sampling
Water current data
Ice Conditions
OBS
microseismicity
Navigation
Other
No
No
16
17
SSP Classification of Site:
SSP Comments:
Yes
Available on JODC web page (http://www.jodc.go.jp)
Analyzing now
Yes
SSP Watchdog:
Date of Last Review:
X=required; X*=may be required for specific sites; Y=recommended; Y*=may be recommended for specific sites;
R=required for re-entry sites; T=required for high temperature environments; † Accurate velocity information is required for
holes deeper than 400m.
Form 3 - Detailed Logging Plan
iSAS/IODP Site Summary Forms:
New
Proposal #:
Water Depth (m): 4125
Site #: NT01a-03A
Sed. Penetration (m): 1740
Do you need to use the conical side-entry sub (CSES) at this site? Yes
Are high temperatures expected at this site?
Yes
Are there any other special requirements for logging at this site?
Yes
If “Yes” Please describe requirements:
What do you estimate the total logging time for this site to be:
Revised
Date Form Submitted: Sept. 30, 2002
Basement Penetration (m): 10
No
No
No
7 days
Relevance
(1=high, 3=Low)
Measurement Type
Neutron-Porosity
Scientific Objective
Estimation of water content in sedimentary sequences and basement.
1
Litho-Density
Estimation of water content, bulk density, and mineral composition in
1
sedimentary sequences and basement.
Natural Gamma Ray
Estimation clay contents and mineral composition in sedimentary
1
sequences and basement.
Resistivity-Induction
Estimation of water content and electro-magnetic properties in
1
sedimentary sequences and basement.
Acoustic
Determination of in situ velocity and estimation of physical properties.
1
Comparison with seismic velocity and create synthetic seismograms.
FMS
Imaging of sedimentary structures and fractures. Core-log correlation of
1
structural features.
BHTV
Resistivity-Laterolog
Magnetic/Susceptibility
Density-Neutron (LWD)
Estimation of water contents, bulk density, and lithology in unstable
1
borehole environments.
Resitivity-Gamma
Ray
(LWD)
Estimation of water contents, electro-magnetic properties, and lithology in
1
unstable borehole environments.
Other: Special tools (CORK,
PACKER, VSP, PCS, FWS,
WSP
For help in determining logging times, please contact the ODP-LDEO Wireline Logging Services group
at:
borehole@ldeo.columbia.edu
http://www.ldeo.columbia.edu/BRG/brg_home.html
Phone/Fax: (914) 365-8674 / (914) 365-3182
Note: Sites with greater than 400 m of
penetration or significant basement
penetration require deployment of
standard toolstrings.
iSAS/IODP Site Summary Forms:
Form 4 – Pollution & Safety Hazard Summary
Please fill out information in all gray boxes
New
Proposal #:
1
3
4
5
Based on Previous DSDP/ODP
drilling, list all hydrocarbon
occurrences of greater than
background levels. Give nature
of show, age and depth of rock:
From Available information,
list all commercial drilling in
this area that produced or
yielded significant hydrocarbon
shows. Give depths and ages of
hydrocarbon-bearing deposits.
Are there any indications of gas
hydrates at this location?
APC to refusal, then XCB to refusal. RCB to 1750 m
None
None
No
Are there reasons to expect
hydrocarbon accumulations at
this site? Please give details.
No
6
What “special” precautions will
be taken during drilling?
Standard monitoring of C
layers.
7
What abandonment procedures
do you plan to follow:
None
8
Please list other natural or
manmade hazards which may
effect ship’s operations:
Summary: What do you
consider the major risks in
drilling at this site?
1
to Cn ; shallow casing to stabilize shallow sandy turbidite
Strong Kuroshio current, typhoon (June to Oct.)
(e.g. ice, currents, cables)
9
Date Form Submitted: Sept. 30, 2002
Summary of Operations at site:
(Example: Triple-APC to refusal, XCB
10 m into basement, log as shown on
page 3.)
2
Site #: NT1a-03A
Revised
Current
Form 5 – Lithologic Summary
iSAS/IODP Site Summary Forms:
Proposal #:
Subbottom
depth (m)
230
790
1000
1740
Site #: NT01a-03A
Key reflectors,
Unconformities,
faults, etc
Age
New
Date Form Submitted: Sept. 30, 2002
Assumed
velocity
(km/sec)
Lithology
Paleoenvironment
1.5
hemipelagite
Upper Shikoku
Basin
1.6-1.8
trench tubidite
Trench fill
1.9
hemipelagite
Upper Shikoku
Basin
2.4
hemipelagite
Lower Shikoku
Basin
2.9
volcanic
sediment and
basement basalt
backarc basin
fault
reflector
reflector
unconformity
Revised
20 Ma
Avg. rate
of sed.
accum.
(m/My)
Comments