Using a dynamic earthquake simulator to explore whether low velocity structure or conditionally stable fault friction contributes more to tsunami earthquake generation

Qingjun Meng, & Benchun Duan

Published September 11, 2022, SCEC Contribution #12336, 2022 SCEC Annual Meeting Poster #152

Tsunami earthquakes are a type of shallow subduction zone events that rupture slowly (<1.5 km/s) with exceptionally long duration and radiate energy with depleted high frequency content, causing abnormally large tsunami waves than their Ms magnitudes imply. Heterogeneous fault frictional properties at shallow depth have been thought to dominate tsunami earthquake generation. Some recent studies propose that heterogeneous upper-plate material properties determine rupture behavior of megathrust earthquakes, including shallow tsunami earthquakes. In this study, we use a recently developed dynamic earthquake simulator to systematically compare the influence from fault friction properties and upper plate material properties on tsunami earthquake characteristics. For heterogeneous fault friction, we consider fault models with isolated asperities (strongly velocity-weakening) embedded in a conditionally stable zone (weakly velocity-weakening). For heterogeneous upper-plate properties, we utilize a generic depth profile of seismic velocity and rigidity constrained from seismic surveys. We design a set of models to explore their individual and combined effects on tsunami earthquake generation and characteristics. We find that the conditionally stable zone in heterogeneous friction models could significantly slow down earthquake rupture speed to < 1.5 km/s over a wide depth range, as long as suitable weakly velocity-weakening properties exist. It further contributes to long normalized durations and high-frequency depletion in tsunami earthquakes. In contrast, the heterogeneous upper-plate property can only manage to reduce rupture speed to be ~1.5-2.0 km/s over a narrow depth range (1-3km), which is inconsistent with observed tsunami earthquake centroid depth range (up to 10 km). Nevertheless, for a model with both heterogeneous fault friction and upper-plate low-velocity layers, the upper-plate low-velocity layers could promote cascading rupture of multiple isolated asperities, contributing to large tsunami earthquake generation. In addition, a low effective normal stress (due to fluid over pressurization) may exist near shallow subduction zone and reduce the fault frictional strength. Such property could further contribute to the characteristics of tsunami earthquakes, including long normalized duration and low stress drop.

Key Words
tsunami earthquakes, fault friction, upper-plate material, effective normal stress, rupture speed, normalized duration

Citation
Meng, Q., & Duan, B. (2022, 09). Using a dynamic earthquake simulator to explore whether low velocity structure or conditionally stable fault friction contributes more to tsunami earthquake generation. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)