CAREER: Using seismic sources to probe megathrust fault conditions

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

Subduction zones, where an oceanic tectonic plate slides beneath a continental plate, host devastating earthquakes and tsunamis that put some of the world’s most densely populated coastal regions at risk. The Cascadia Subduction Zone, which extends from northern California to southwest British Columbia, produces magnitude 9 'megathrust' earthquakes every few hundred years (on an irregular schedule), and the last was over three hundred years ago. Supported by this CAREER award, Fan and his group will use over two decades of earthquake data from large arrays of seismometers to characterize properties of the Cascadia Subduction Zone fault, as well as subduction faults in Japan and Alaska. They will investigate how fault zone properties in all three locations correspond to earthquake slip behaviors, which is necessary to forecast future megathrust earthquake ruptures and their potential impacts. The research findings will be incorporated into a multi-pronged education and outreach plan combining undergraduate instruction, undergraduate and graduate student research and mentoring, and a continuous outreach project involving California high school science teachers. Megathrust slip events and faulting environments co-evolve during seismic cycles. Understanding the source processes of various slip events at subduction zones can illuminate heterogeneous stress and strength conditions along the subduction interface. Imaging fine-scale material properties can also offer insights into physical mechanisms that may regulate the development of various types of slip events. This award will investigate these two aspects simultaneously by systematically detecting, locating, and modeling very low frequency earthquakes at megathrust seismogenic patch edges, resolving finite-source attributes of small to moderate magnitude earthquakes, and imaging fault zone properties with high-frequency body wave phases. Collectively, the results will be used to track spatiotemporal evolutions of the fault zone environments and unravel the interaction and triggering processes among different slip events. The award will comparatively study three subduction zones, including the Japan, Cascadia, and Alaska subduction zones, using both onshore and offshore seismic records. The expected findings on small-scale properties might be universal to all megathrust faults, while findings on stress and strength heterogeneities could inform future hazards at Cascadia and Alaska based on the knowledge from the Japan subduction zone. The education initiative will put into place foundational and sustainable bridging activities that will establish pathways for students into seismology and geophysics degrees and careers. 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.