Collaborative Research: Investigating fault slip associated with very large earthquakes

The 2011 Tohoku-oki earthquake was the largest ever recorded with modern instrumentation in Japan. Slip on the shallow portion of the fault was significant and led to an unusually large tsunami. This project will analyze unique samples of the fault zone recovered after the earthquake from hundreds of meters below the seafloor. The scientific focus is on investigating how slip on the fault is distributed and evolves over time. The results will be important for understanding the conditions that lead to large earthquakes and tsunamis. The project will provide research opportunities and training for undergraduate and graduate students. This study will analyze samples from three separate cores recovered from the plate boundary fault zone. The sites are only 30 m apart but the thickness of the fault zone varies from 1 m to 15 m. Trace element geochemistry will fingerprint and match the lithologies within the fault zones to the sedimentary units on the incoming plate. Analysis of organic biomarker thermal maturity will map where localized temperature rise has occurred, thereby determining which fault strands within each fault zone have experienced earthquake slip, how much slip has occurred, and how much frictional energy has been expended. Finally, potassium/argon dating will determine if all of the faults have failed recently (i.e. in the Tohoku earthquake) or if some strands have not failed for a long period of time and can be presumed to be inactive. The work will address three scientific questions: 1) How does structural complexity affect spatial distribution of earthquake slip within a plate boundary fault? 2) How does structural complexity evolve over time? 3) Does structural complexity act as an energy sink and thus potentially inhibit rupture propagation? This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.