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Using Physics-Based Models to Explore Physical Controls on Tsunami Earthquake Generation

Session: Subduction Processes Along Latin America Subduction Zones I

Type: Oral

Date: 4/19/2021

Presentation Time: 10:45 AM Pacific

Description: 

“Tsunami earthquakes” generate tsunamis disproportionately large for their surface-wave magnitudes Ms (Kanamori, 1972). These earthquakes occur at the shallow portion of subduction zones, with characteristics of large discrepancy between Ms and Mw, long source duration, and depletion in high-frequency radiation. The 1992 Nicaragua earthquake along Latin America is the first tsunami earthquake recorded by modern seismic networks. Historical tsunami earthquakes also occurred along the Japan, Alaska, New Zealand, and Java subduction zones. Observational studies on these earthquakes have led to a conceptual model of tsunami earthquake generation, i.e., tsunami earthquakes are associated with ruptures on locally locked unstable patches within largely conditionally stable zones on shallow subduction interfaces. To test how well this conceptual model works for and to explore physical controls on tsunami earthquake generation, we use a recently developed dynamic earthquake simulator (Luo et al., 2020) to model slip behaviors of locked patches embedded within a conditionally stable subduction zone. The dynamic earthquake simulator is based on a finite element method to simulate both quasi-static (interseismic, nucleation, and postseismic) and dynamic (coseismic) processes of earthquake cycles on shallow-dipping thrust faults. We find that the normal stress level on locked patches and the rate-state friction parameter value of a-b of the conditionally stable zone are two major factors that control the tsunami earthquake generation. Normal stress variations on locked patches can be caused by subducted topographic reliefs with various heights. We also find that locked patches show different rupture behaviors depending on their normal stress levels, and can have complex interactions among them, including ruptures of multiple patches in one event, compound ruptures of multiple patches with time delays from hours to days, and ruptures of signal patch.

Presenting Author: Qingjun Meng

Student Presenter: Yes

Authors