Modeling Dynamic Earthquake Ruptures Towards Identifying Seismological Observables of Co-Seismic Off-Fault Damage

Session: Numerical Modeling of Rupture Dynamics, Earthquake Ground Motion and Seismic Noise
Type: Oral
Date: 4/29/2020
Time: 11:30 AM
Room: 230 + 235
Description: 

Geological and geodetic observations of earthquakes suggest that the effect of co-seismic off-fault damage is non-negligible in rupture dynamics and in material properties. Modeling of earthquake damage suggests that stress concentrations during dynamic earthquake ruptures form a damage zone around fault cores, which changes the nearby elastic properties. This is observed by field observations of fracture density and by seismic tomography through low-velocity zones near the fault. Further improvements of spatial and temporal resolutions in seismological observations are necessary to resolve the time scale of such processes. This study aims to evaluate the relationship between off-fault damage mechanisms, rupture dynamics and the far-field radiation in order to identify the seismic signature of co-seismic off-fault damage.

To compute the earthquake source with co-seismic off-fault damage, we use the combined finite-discrete element method (FDEM), which allows for dynamic activation of off-fault damage during earthquake ruptures. Then, we couple its synthetic near-field radiation to SPECFEM2D in order to compute far-field radiation. Thus, our physics-based numerical model can resolve complexities over wide range of length scale associated with earthquake sources and wave propagation.

The comparison between the cases with and without allowing for co-seismic off-fault damage shows differences in synthetic intermediate- and far-field radiation. 1) High-frequency components in ground motion are enhanced all around the fault. 2) The rupture arresting phase, which clearly appears at the stations located orthogonal to the fault for the case without off-fault damage, is damped due to the smoothed rupture arrest by co-seismic damage around fault edges. 3) Radiated energy is enhanced in the direction parallel to the fault due to the substantial damage around fault edges. Future work will seek these signatures in the observations of recent large earthquakes such as 2016 Kumamoto and 2019 Ridgecrest earthquakes.

Presenting Author: Kurama Okubo

Authors