| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | May 9, 2017 |
| Latest Amendment Date: | May 9, 2017 |
| Award Number: | 1658580 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Deborah K. Smith
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | May 15, 2017 |
| End Date: | April 30, 2021 (Estimated) |
| Total Intended Award Amount: | $299,724.00 |
| Total Awarded Amount to Date: | $299,724.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
2425 CAMPUS RD SINCLAIR RM 1 HONOLULU HI US 96822-2247 (808)956-7800 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1680 East-West Rd. Honolulu HI US 96822-2234 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
PREEVENTS - Prediction of and, Marine Geology and Geophysics |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
This project is designed to help understand the frontal region of the Nankai subduction zone off of Japan, an area that has a documented history of many great earthquakes and tsunami in the past 2000 years. As such, it is currently believed to be endangered by earthquake and tsunami hazards. The Nankai subduction zone is similar in many ways to both the Cascadia and Aleutian subduction zones, but Nankai has a much more extensive data base than either of these U.S. examples. This study will provide information that will help to understand how variations in sediment thickness and type of sediment along subduction zones influence the occurrence of destructive earthquakes and which earthquakes might generate tsunami. The work also will help to understand the regional extent and potential timing of destructive earthquakes not only in Japan, but also along other subduction zones worldwide. This study is in collaboration with the Japan Agency for Marine Earth Science and Technology (JAMSTEC). The project supports the training of a U.S. graduate student.
This project is a collaborative effort between the University of Hawaii and the Japan Agency for Marine Earth Science and Technology (JAMSTEC). New JAMSTEC high-resolution seismic reflection data across the central and western Nankai Trough accretionary prism will be processed and interpreted. The Nankai Trough accretionary prism is arguably the best-studied sediment-dominated margin in the world, and thus serves as the type example. As such, the Nankai region has been the focus of numerous studies, including the new effort by JAMSTEC to collect high-resolution seismic reflection lines across the deformation front along the entire system. This study will integrate new interpretations with existing data from two 3D seismic and drilling transects along with all available JAMSTEC geophysical data along and between the transects, especially multichannel seismic reflection, Ocean Bottom Seismograph, multibeam bathymetry and Very Low Frequency seismicity data. The goal is to understand the inter-relations between regional variations of sediment thickness, oceanic crust topography, and deformational structures at the toe of the prism. The work will test the hypothesis that subducting topography, even relatively small irregularities such as small seamounts, causes thickness variations in the subducting hemipelagic and overlying trench turbidite sedimentary sections. This leads to variations in thickness and width within the proto-thrust zone (PTZ) and to discontinuities in ridges within the imbricate thrust zone (ITZ). Subduction of larger seamounts and fracture zones, with greater variations in sediment thickness, cause regional structural variations in the PTZ and ITZ. The project is also designed to determine whether or not these regional variations are correlated with variations in deeper features such as slow slip earthquakes.
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
This project supported the University of Hawaii Earth Sciences research group to collaborate with colleagues from the Japan Agency for Marine Earth Science and Technology (JAMSTEC) to study the Nankai Trough subduction zone, a tectonic plate boundary off the south coast of Japan. At the Nankai Trough, two tectonic plates converge on each other, leading to extensive geological faulting and deformations. Of particular interest is the occurrence of both earthquakes and slow slip events (slow earthquakes) between the two plates. The team used seismic reflection data collected by JAMSTEC to image geological layers and boundaries in the deep-water area of the Shikoku Basin. The goal was to reveal the location, geometry, and physical characteristics of the sediments, rocks, faults, and fluids that lie in the plate boundary zone. Specific goals included: (1) imaging of the subduction plate interface in the zone where repeated slow slip events have been documented over the past decade, in order to detect the structure and physical properties of the slipping fault(s); (2) imaging of the incoming plate structure and sedimentary cover, the accretionary complex overlying the plate boundary, and the lower plate beneath, and (3) understanding the evolution of the sedimentary sequence that is subducted along with the lower plate and how its deformation affects the physical properties of the plate boundary.
We have determined that the sub-seafloor region seaward of the subduction complex (incoming plate) has a rugged basement, including 1-2-km high seamounts, that is covered by laterally variable sedimentary strata. The strata include marine pelagic deposits as well as layers reworked submarine currents (contourites). We are able to predict that this part of the plate will be carried underneath the continental margin and will cause heterogeneous deformation because of the complicated nature of the basement and overlying sediment. In addition, a “proto-thrust zone” that varies from approximately 0.5 to 8 km in width occurs seaward of the frontal thrust and consists of dozens to more than hundred steeply-dipping, small offset thrust faults. This zone of deformation is where the future frontal thrusts will develop.
We also engaged in national-scale media events with our Japanese colleagues to spread awareness of the potential for large, damaging earthquakes in the Nankai Trough. Finally, this project was integral to the training of a female graduate student in geophysics, building the U.S. workforce in this area vital to the energy industry.
Last Modified: 08/11/2021
Modified by: Gregory F Moore
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