Ground Motion Radiation Patterns from a Deterministic Earthquake Sequence Simulator

Session: Numerical Modeling of Rupture Dynamics, Earthquake Ground Motion and Seismic Noise
Type: Oral
Date: 4/29/2020
Time: 03:15 PM
Room: 230 + 235
Description: 

We are investigating the efficacy of a multi-cycle deterministic earthquake simulator as an extended earthquake rupture forecast (ERF) for use in generating synthetic ground motions for probabilistic seismic hazard analyses (PSHA). While use of deterministic ground motion simulations in PSHA calculations is not new (e.g. CyberShake; Graves et al., 2011; Jordan et al., 2018), prior studies relied on kinematic rupture generators to extend empirical ERFs. Fully-dynamic models, which simulate rupture nucleation and propagation of static and dynamic stresses, are computationally intractable for the large simulation domains and many seismic cycles required to perform PSHA. Instead, we use the Rate-State Earthquake Simulator (RSQSim; Dieterich & Richards-Dinger, 2010), to efficiently simulate millions of years of M>6 earthquake sequences on the California fault system. RSQSim produces full slip-time histories for each rupture, which, unlike kinematic models, emerge from frictional properties, fault geometry and stress transfer; all intrinsic variability is deterministic. We use these slip-time histories directly as input to wave propagation codes from the Southern California Earthquake Center (SCEC) BroadBand Platform for one-dimensional models of the Earth and from the SCEC CyberShake for three-dimensional models to obtain simulated deterministic ground motions.

We compare the median radiation patterns (T=[3,10] s) from ensembles of ground motion simulations of RSQSim ruptures with empirical predictions of rupture directivity and with simulations using the Graves and Pitarka (2016) kinematic rupture generator. Previous RSQSim simulations, which employ a fixed sliding speed approximation, produce low (1-1.5 km/s) rupture propagation velocities and lack sufficient fault-parallel directivity. We show results from a new variable slip speed version of RSQSim that produces more realistic propagation velocities (~3 km/s) and better matches empirical directivity models. Radiation patterns from this model are similar to those generated with the kinematic rupture generator.

Presenting Author: Kevin Milner

Authors