ABSTRACT

Instead of single planes, faults are volumes of rocks containing centimeters-thick fault cores surrounded by hundreds-meter-thick fractured rocks, called fault damage zones. As discovered worldwide, fault damage zones around major faults accommodate a significant portion of plate motion through seismic and aseismic deformation. However, the poorly understood link between fault damage zones and earthquake source processes remains a fundamental issue that hinders the advancement of earthquake physics research and seismic hazard mitigation. Using a combination of new fault zone imaging methods and fully dynamic earthquake cycle models, the project aims to understand how fault damage zones impact the generation of earthquakes that occur within seconds and how the structure of fault damage zones involves over hundreds of years under the influence of earthquakes and interseismic slip. The project will also promote and enrich the learning experiences of a wide range of students and increase the diversity of students majoring in geophysics. The research lies on the interface of seismic data analysis, earthquake modeling, and fault zone geology, providing a unique opportunity to synergize various research facets and promote communication between different research communities.

The current understanding of earthquake source physics is limited by the lack of constraints on the spatial distribution of fault damage zones and their effects on seismicity and interseismic deformation. Previous fault zone studies have relied on near-fault seismic arrays to obtain a cross-sectional view at the array location. The project will image the along-strike variation of fault damage zones and characterize site effects using broadband seismic networks to investigate whether fault damage zones strongly affect seismicity patterns. The project will also improve the understanding of stress drop variation by considering the effects of fault zone waves on earthquake source spectra. Moreover, previous simulations of earthquakes in fault zones have modeled either single earthquakes using arbitrary stress conditions or earthquake cycles without dynamic waves. The project will model earthquakes and interseismic deformation by considering damage rheology and dynamic effects of the fault zone wavefield. The seismic observations and earthquake cycle simulations together will unveil how fault damage zones influence earthquake source processes and how earthquakes and interseismic deformation contribute to the formation of fault damage zones. Additionally, the project will involve graduate students to design and lead hands-on geophysical activities related to the research for Earth Camp, a UM outreach program that provides week-long experiences to educate underrepresented high school students. It will promote the communication between non-science majors and graduate students by introducing poster fairs in a first-year undergraduate seminar course, and strengthen the research skills of students by developing research projects in upper-level undergraduate and graduate courses.

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.

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