Elucidating the Mechanics of Tsunami Generating Earthquake Rupture with Long Period Seismology

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Submarine earthquakes are capable of generating uncharacteristically large tsunamis, and drastically increase the hazard facing most of the world's population, which currently lives along the coastlines. Current techniques used to study submarine earthquakes are expensive and cannot be applied to most earthquakes of interest. The lack of observations has hindered the understanding of whether an earthquake will displace the seafloor and increase the likelihood of generating a significant tsunami. The theory developed in this project will provide a new fundamental tool for the study of submarine earthquakes with significant scientific and societal implications. A new framework will be developed that overcomes previous theoretical limitations and allows us to develop an easily utilized, inexpensive tool which will allow for the detection of slip on the seafloor from distant recordings of ground motion alone. This tool will then be used to examine giant earthquakes in the last 15 years that produced devastating tsunamis, as well as recent moderate-size earthquakes from around the world. By studying a large number of earthquakes with the newly developed tool, a better understanding will be obtained of why some earthquakes displace the seafloor while others do not. This project could provide an improvement for tsunami hazard assessment. The project supports the training of a postdoctoral investigator.The first component of this project will establish the theoretical and observational framework required to distinguish events for which slip reached and did not reach the surface. This theory will provide a simple seismological diagnostic tool, and has the added benefit of complementing numerical models, seafloor instrumentation, drilling, or marine surveys. The second component of this project will provide the necessary observations required to determine the physical mechanisms controlling submarine surface rupture by applying the diagnostic to long-period seismic data from a large number of events recorded by the Global Seismographic Network. The new framework will be validated using the large amount of shallow slip that was measured to have occurred during the 2011 Tohoku-Oki Earthquake. To what extent this type of shallow slip is observed in giant megathrust earthquakes, such as the 2010 and 2015 Chile and the 2004 and 2010 Sumatra tsunami earthquakes, as well as recent moderate-size earthquakes will be determined. Using the outcome of the survey of large and moderate-size earthquakes, an attempt will be made to determine the properties of fault zones (e.g., presence of accretionary wedge, subducted sediment thickness, fault dip-angle, etc.) that govern the rupture of the shallowest part of plate boundary.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.