| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | May 17, 2013 |
| Latest Amendment Date: | May 17, 2013 |
| Award Number: | 1260555 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Candace Major
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | May 1, 2013 |
| End Date: | April 30, 2016 (Estimated) |
| Total Intended Award Amount: | $176,062.00 |
| Total Awarded Amount to Date: | $176,062.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
615 W 131ST ST NEW YORK NY US 10027-7922 (212)854-6851 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
61 Route 9W Palisades NY US 10964-1707 |
| 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): | OCEAN DRILLING PROGRAM |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
This proposal seeks to understand how shallow slip occurred during the Tohoku earthquake by determining the frictional strength of the fault before the rupture initiated and during slip. Using samples collected from the fault during IODP exp 341 (JFast), the PI?s will undertake:
1) Organic thermal maturity measurements to identify the rupture plane and quantify the frictional temperature anomaly induced by coseismic slip.
2) Microstructure observations to identify and characterize the fault that hosted the earthquake, including the identification of textures that indicate frictional weakening.
3) Friction measurements to constrain the steady-state frictional stress of the faults.
These results are crucial for understanding tsunami genesis in shallow subduction zones and will provide critical information for tsunami prediction and hazard mitigation. Importantly, only direct observation and measurement of the fault physical properties can determine these parameters.
The Tohoku quake was a surprise, previous work had indicated that such a quake was unlikely in region, especially one in which large amounts of slip occurred in ?weak? shallow accretionary prism sediment. Understanding this quake requires understanding frictional characteristics of rocks in fault zone. There are three plausible scenarios:
First, the fault could have undergone dramatic frictional weakening during rapid slip resulting in very low stress coseismically. Alternatively, stress prior to the earthquake was low and changes on the fault were small coseismically, with slip driven by stress transferred from the deeper part of the fault Finally, slip could have propagated through a velocity-strengthening region of the fault with little fault weakening on average.
Broader impacts: Information relating to how a major (and unexpected) tsunami-generating quake was hosted in shallow sediments. A better understanding of tsunamigenic earthquakes has great societal importance.
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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.
Overview
The earthquake that struck the Pacific coast of Japan in 2011 was one of the largest ever recorded. The earthquake was the result of the Pacific oceanic plate moving west beneath the continental plate of Japan. It caused the seafloor to shift by around 50 m, which in turn displaced the ocean, causing the devastating tsunami that resulted in enormous damage and loss of life. Our project aimed to investigate why the seafloor was able to move so much. We analyzed rocks from the fault between the two plates that were brought to the surface in drill core. We applied a new technique to constrain the frictional heating on the fault caused by the rocks rubbing past each other. This technique measures the change in the composition of organic molecules caused by the heat generated during an earthquake. We also examined the different rock types and fractures around the fault and used the distribution of these features to unravel the long-term history of the plate motions. The rocks within the fault are sedimentary rocks that formed on the seafloor as long ago as the Cretaceous.
Our results show that there is extensive damage to the rocks where the plates have collided. The characteristics of fractures surrounding the fault and properties of the rocks within the fault indicate that the movement during the earthquake was so large because the fault is ‘lubricated’ by the presence of very weak, almost slippery sediments. Similar sediments are present elsewhere along the coast of Japan, and may also be found in other parts of the Pacific Ocean. These weak sediments cannot arrest the fault motion once an earthquake has started, so the chance of a tsunami is higher where they are found.
Our results also identified fossil seismic heating signatures on multiple sub-faults that together make up the fault between the Pacific and Japanese tectonic plates. These heating signatures and other constraints indicate that multiple seismic events have ruptured through the plate boundary region that hosted the 2011 earthquake. While the magnitude of these events cannot be know from our data, these results suggest that there may have been additional tsunami-generating earthquake along this fault in the past.
Intellectual Merit
All of the work from this project helps to constrain the causes of extraordinary slip during the 2011 Tohoku earthquake. This is a major outstanding question in earthquake seismology, plate tectonics, fault mechanics, and civil and environmental engineering. The results will be transferrable to other subduction margins, and should facilitate improved appreciation and evaluation of the hazards from tsunamigenic earthquakes.
Broader Impacts
The contributions of this project to understanding the seismic hazards of convergent margins will improve societal decisions and governmental policies regarding the infrastructure engineering and risk in these regions.
This project also contributed to the research training and intellectual development of an undergraduate, two graduate students and supported the research and professional development of three early-career researchers.
Last Modified: 08/07/2016
Modified by: Heather M Savage
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