Implementation and Validation of EXSIM (A Stochastic Finite-Fault Ground-Motion Simulation Algorithm) on the SCEC Broadband Platform

Abstract

Online Material: Input files for running EXSIM. This article describes the validation exercise associated with preparing EXSIM, a stochastic extended finite‐fault algorithm for ground‐motion simulation, for use as a time‐history simulation module on the Southern California Earthquake Center (SCEC) Broadband Platform (BBP), version 14.3. This involved importing the algorithm to the SCEC computational platform and standardization and calibration of the input parameters. Herein, we (1) provide a brief overview of the EXSIM method of simulating time histories, (2) summarize its input parameters and their assigned values for generic applications in eastern and western North America (ENA and WNA, respectively), and (3) show comparisons of response spectra from EXSIM simulations with those of selected earthquake suites and ground‐motion prediction equations (GMPEs). EXSIM is an open‐source stochastic finite‐source simulation algorithm, written in FORTRAN, that generates time series of ground motion for earthquakes (Motazedian and Atkinson, 2005; Boore, 2009; Assatourians and Atkinson, 2012). A fault plane, having a specified size according to its seismic moment, is divided into an array of subsources, each of which is treated as a point source. Time series from the subsources are modeled using the point‐source stochastic model developed by Boore (1983, 2003) and popularized by the Stochastic‐Method SIMulation (SMSIM) computer code (Boore, 2003, 2005). The ground motion from each subsource is treated as random Gaussian noise of a specified duration, having an underlying spectrum as given by the Brune (1970, 1971) point‐source model for shear radiation. The Brune model specifies the Fourier spectrum at the source by seismic moment and stress parameter and is attenuated in the frequency domain according to an empirical attenuation model. The duration of motion for each subsource comes from the source duration plus the path duration. The time series from the subsources are summed in the time domain, with appropriate …