Relationships Between Dynamic Strains and Ground Motions from Numerical Simulations of Elastic Wave Propagation

Session: Numerical Modeling of Rupture Dynamics, Earthquake Ground Motion and Seismic Noise [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Borehole strainmeters record seismic signals over a broad frequency range and can be used to estimate ground motions as a complement to broadband seismometers [Farghal et al., 2019]. In the far field, strains from planar seismic waves are proportional to velocity, but to improve our understanding of near-source relationships, a more realistic relationship between dynamic strains and ground motions is needed. We performed a suite of numerical wave propagation simulations that focuses on the relationship between dynamic strains and ground motions. We use SW4, an elastic wave propagation code, to simulate seismic waves propagating from simple point sources through a number of different velocity structures. We present results from simulations with four families of velocity models: (1) isotropic homogeneous media; (2) simple 1D layered velocity models; (3) random velocity structures with small-scale stochastic heterogeneities; and, (4) realistic velocity structures from California community velocity models. Our simulations show that the plane-wave assumption is approximately true for farfield motions in homogeneous media but can become complicated by a heterogeneous seismic velocity structure. In the nearfield, the relation is more complicated regardless of velocity structure. We determine what relationships exist between dynamic strains and ground motions and investigate how they are possibly related to the velocity structure. We also report on the variability and uncertainty in these relations associated with sharp spatial gradients in the velocity structure. The resulting relations should improve our understanding of how to interpret dynamic strain records in the context of ground motions studies.

Presenting Author: Evan T. Hirakawa

Authors