Simulation of Ground Motion in the Zagros Region of Iran Using the Specific Barrier Model and the Stochastic Method

Abstract

Abstract Physically based ground‐motion prediction equations for soil and rock sites in the Zagros region have been developed based on the specific barrier model (SBM) used within the context of the stochastic model. Instead of direct time‐domain simulation, random vibration theory was used to estimate measures of peak motion in terms of the pseudospectral velocity of anelastic harmonic oscillator with 5% viscous damping. To avoid the uncertainties, calibration of the source model uses a database of carefully selected strong motion data without ambiguity about the site condition. Therefore, only rock sites are selected for determining source parameters. Also, to avoid any inconsistencies caused by magnitude conversion formulas, we restricted the dataset only to events with available moment magnitudes. Regression analysis is performed using the random effects model that considers both interevent and intraevent variabilities to effectively deal with the problem of an unequal number of records from different earthquakes. No sign of self‐similarity breakdown is observed between the source radius and its seismic moment. The local and global stress drops derived for the Zagros region (39 and 116 bars, respectively) are more consistent with the values obtained by other authors for an interplate regime than the values for an intraplate region. However, from the viewpoint of source heterogeneity (as the ratio of the stress drops is an indicator of the complexity of the source and heterogeneity of slip on the fault) the Zagros events, which have a stress‐drop ratio of about three are more homogeneous than other interplate events. Stochastic simulations are then implemented to predict peak ground motion and response spectra parameters for rock and soil site conditions. Online Material: Catalog tables of earthquakes and attenuation tables.