Coupling Long-Term Tectonic Loading with Short Term Earthquake Slip and Ground Motion

Sabber Ahamed, Eric G. Daub, & Eunseo Choi

Submitted April 13, 2018, SCEC Contribution #8048

We use a tectonic model to determine the initial stress conditions for a dynamic rupture simulation. The tectonic model resolves the long-term evolution of a normal fault system in terms of strain and stress accumulation or change in fault geometry over a geologic period. This work supplements the tectonic model with a rupture simulation that solves wave propagation and determines short-term earthquake slip evolution. We first create a long-term large-offset normal fault model and take a time-snapshot of the model at a 0.5 My. We then import the stress state, material properties, surface topography, and fault geometry from the tectonic model and use these as inputs to two dynamic rupture simulations. In the first simulation, rupture initiates near the free surface as the ratio of shear to normal stress is maximum at shallow depths. In the second simulation, we add 10 MPa cohesion at the surface that linearly decreases to 3 MPa at 5 km depth to prevent near surface rupture. Our results show that an increasing stress pattern with depth is responsible for creating a high rupture velocity and slip around 5 km depth that continues down-dip until it finds a barrier at 8 km depth. Peak ground velocity (PGV) is high (1.8 to 2 m/s) around the fault zone on the hanging wall while low (<0.25 m/s) on the footwall. Our approach shows how models can capture both the short-term earthquake slip and the long-term strain accumulation and can reduce uncertainty in the initial conditions for rupture simulations.

Key Words
Geophysics, Machine learning. earthquake rupture simulation, tectonic deformation, geodynamics

Ahamed, S., Daub, E. G., & Choi, E. (2018). Coupling Long-Term Tectonic Loading with Short Term Earthquake Slip and Ground Motion. Journal of Geophysical Research: Solid Earth, (submitted).