RAPID Response to Tohoku Earthquake: Participation in Marine Geophysical Surveys of the Quake Rupture Zone

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We propose to participate in one or two marine geophysical surveys covering the rupture zone of the March 2011 great earthquake off Tohoku, Honshu, Japan during summer, 2011. In response to this great earthquake, the Institute For Research on Earth Evolution (IFREE) of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has undertaken a program of marine geophysical surveys to try to detect seafloor and subsurface structures associated with the quake?s rupture. One cruise will include multibeam bathymetric mapping during OBS recovery and redeployment in June-July. A more extensive MCS survey is planned for August. Coupled with the extensive on-land seismograph and GPS network, the offshore data set presents an unprecedented opportunity to study deformation associated with rupture during a great earthquake. Moore and his students have been invited to participate in the offshore to help with data acquisition and on-board data processing and to participate in the structural interpretation and synthesis of the offshore data sets. The main advantage of participating in the cruises is that we will also be able to participate in the data analysis phase. We will be able to combine the new data sets with seismic reflection and bathymetric data collected previously by IFREE. The seismic reflection data to be collected in the earthquake rupture zone will be used as a site survey for a proposal to IODP for Rapid Response Drilling off Tohoku. The seismic data will be essential for defining drilling targets. We note that the older seismic lines in this area, while excellent for interpreting the regional tectonics, do not image any potential drill sites, so high-quality images will be required in advance of any drilling. The main reason why this work needs to be funded quickly is because the Japanese will be carrying out the work as already scheduled, whether or not we are able to participate. If we have to go through the ?standard? proposal process, with the next proposal deadline being in August, the work will have already been completed by the time funding decisions could be made. We would thus lose out on this opportunity for U.S. scientists to have early access to this large data set at relatively low cost.Broader impactsOne product of this project will be a seismic reflection and multibeam bathymetry data set that will help characterize the Earth?s best documented great earthquake. Although this data set will exist within Japan, it will not be released to non-Japanese researchers for many months (or years). Our participation will ensure that US scientists will be able to help interpret the data. The seismic reflection data will be used as a site survey to determine whether or not a rapid-response drilling program will have suitable drill targets. This project will also provide valuable sea-going experience for two graduate students.