IODP Proposal Cover Sheet

835 -FullJapan Trench Tsunamigenesis

Title

Tracking Tsunamigenic Slips Across and Along the Japan Trench (JTRACK): Investigating a new paradigm
in tsunamigenic megathrust slip with very deep water drilling using the D/V Chikyu

Proponents

S. Kodaira, J. Sample, M. Strasser, K. Ujiie, J. Kirkpatrick, P. Fulton, J. Mori, *. JTRACK working group(30 others),

Keywords

Tsunami, Earthquake, Subduction, Paleoseismology, Fault

Area

Japan TrenchContact Information
Contact Person:
Department:
Organization:
Address:Tel.:
E-mail:Shuichi KodairaIFREE
JAMSTEC
Showa machi 3173 15 Kanazawa
Yokohamaku2360001

Fax:

81457785438

81457785438

kodaira@jamstec.go.jp

Abstract
Understanding the huge slip and associated devastating tsunami of the 2011 Tohoku-oki earthquake is a high priority
challenge for IODP with important societal impacts. JTRACK investigates spatial and temporal aspects of physical,hydrological, and chemical properties of the fault zone to elucidate key factors that can control large (and small) slip on themegathrust. These results may be used to explain the 2011 earthquake, past tsunamigenic events along the Japan Trench,and possibly other great subduction earthquakes world-wide.
Planned drilling includes a variety of investigations targeting the fault zone and associated structures. Geologic studies will
focus on structure and physical properties, especially frictional characteristics for components of the input pelagic sediments,
such as the abundant smectite. Hydrological and chemical effects in and around the fault zone are largely unknown, but likely
contribute to earthquake processes. We plan analyses of interstitial water to evaluate the role of fluids during faulting, alongwith investigations of the local permeability structure. The evolving stress state following the earthquake will be studied withborehole breakouts and temperature/pressure monitoring in a borehole observatory. JTRACK has the unique opportunity tostudy fault healing after a large earthquake.
In addition to investigations of the 2011 earthquake, we plan paleoseismic studies of past earthquakes. Using shallow coresfrom this region, we have identified sediment remobilizations associated with three historical earthquakes over the last 1200years. We plan further development of techniques and more data collection to identify sediment proxies for past earthquakes.
These studies may enable reconstruction of earthquake histories over tens to hundreds of thousands of years. This may be
the only method for obtaining sufficient data to statistically evaluate (varying) recurrence intervals of great earthquakes.
The strategy for this proposal consists of two 3-hole transects across the Japan Trench in the region of the shallow plateboundary fault that ruptured in 2011. One transect for an area of large slip (~50 m) and the other for small (~5-10 m) slip.
Each transect has an ‘inner trench slope’ site mainly targeting the plate boundary fault zone, an ‘input’ site seaward of thetrench, and a ‘paleoseismology’ site to obtain long sediment records of past events.
The borehole sites have largely independent science objects and there are few logistical constraints on the order or timing ofdrilling. This may be advantageous for scheduling since operations can be done during several expeditions of short duration.

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835 -

Full

Scientific Objectives
1.Define spatially-varying physical and chemical properties and conditions of the sediments and fluids of the near-trench
megathrust that contribute to huge fault displacements and very large tsunamis.
We will investigate the detailed geologic structures and rock properties of the fault zone, especially frictional and strengthcharacteristics. Permeability and chemical studies will be used to infer the local hydrological structure and its effect on theearthquake rupture. Combining these observations and using comparisons of similar measurements for areas of high and low
slip during the 2011 earthquake, we will try to infer key factors that control the amount of displacement during large
earthquakes.
In addition, time dependent observations will be carried out to study fault healing after a large earthquake. How do the local
hydrological and stress conditions change during the few years following the large fault displacement during the earthquake ?
2.Develop and begin implementation of new methods to determine recurrence of great tsunamigenic earthquakes in thesediment record.
There is a high potential for using turbidites and other sedimentary features to reconstruct a long history of tsunamigenic
earthquakes. We plan development of analysis techniques along with detailed sediment core sampling. Long records that
include many earthquake occurrences are needed to establish the recurrence pattern of events similar to the 2011 Tohoku-okiearthquake.

Non-standard measurements technology needed to achieve the proposed scientific objectives.

Proposed Sites
Water
Depth(m)Penetration (m)Site Name

Position(Lat, Lon)

JTCT-02A

37.9267, 144.0688

6945

4500JTNT-02A

38.5272, 144.1992

7115

520

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SedBsmTotal

Brief Site-specific Objectives

450 Obtain sample and logging data of areference section on the incoming
plate seaward of the large slip area ofthe 2011 Tohoku earthquake as abaseline for comparison withsediments in the prism, plate-boundary
décollement and underthrust section.
Investigate the role of fluids in thereference input section with
geochemical and physical propertydata from continuous cores. Measure
the stress state in the incoming
sediment section from borehole andsediment property measurements.
520 Obtain sample and logging data of areference section on the incoming
plate seaward of the small slip area ofthe 2011 Tohoku earthquake as abaseline for comparison withsediments in the prism, plate-boundary
décollement and underthrust section.

-----

JTNT-03A

38.5760, 144.1227

7550

1800

JTCT-03A

38.0225, 144.0368

7180

1300JTCT-01A

37.9389, 143.9135

6930

950

0JTNT-01A

38.5520, 144.0355

74009800Page 3 of 3
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by if340_pdf(user 0.9157)- Investigate the role of fluids in thereference input section with
geochemical and physical property
data from continuous cores. Measure
the stress state in the incoming
sediment section from borehole andsediment property measurements.
180 D/V Chikyu HPSC coring, as proposed
in proposal 866Pre (Japan Trench
Paleoseismology) to recover acontinuous upper Pleistocene-to-Holocene stratigraphic successions
comprising sedimentary extreme event
deposits, which will be analyzed forproxy-evidence of large earthquakes.
To be established history of extreme
events will contribute to investigate
long-term recurrence pattern of greatearthquakes at Japan Trench
subduction zone.
130 D/V Chikyu HPSC coring, as proposed
in proposal 866Pre (Japan Trench
Paleoseismology) to recover acontinuous upper Pleistocene-to-Holocene stratigraphic successions
comprising sedimentary extreme event
deposits, which will be analyzed forproxy-evidence of large earthquakes.
To be established history of extreme
events will contribute to investigate
long-term recurrence pattern of greatearthquakes at Japan Trench
subduction zone.
950 Continuously core the frontal prism,
fault zone and subducted plate tooceanic basement in large slip area ofthe 2011 Tohoku earthquake to obtainrepresentative fault and surroundingrock samples and logging data forstructural analyses and laboratory
experiments. Install a long-term fault
zone observatory to monitor porepressure and temperature near theprevious JFAST temporary
temperature observatory. Investigate
the role of fluids in slip with
geochemical and physical property
data from continuous cores. Measurethe prism stress state from boreholeand sediment property measurements
and long-term observatory monitoring.
980 Continuously core the frontal prism,fault zone and subducted plate tooceanic basement in the small sliparea of the 2011 Tohoku earthquake
to obtain representative fault andsurrounding rock samples and logging
data for structural analyses andlaboratory experiments. Investigate therole of fluids in slip with geochemicaland physical property data fromcontinuous cores. Measure the prism
stress state from borehole andsediment property measurements.