Far-field seismic spectral response resulting from complex rupture behaviors

Abstract:

Many earthquake physical properties, such as seismic moment, rupture extent and stress drop, can be estimated from far-field seismic wave spectra. Corner frequency and the high-frequency fall-off rate of the spectra are often measured in order to make an assessment of dynamic stress drop and other source parameters such as radiated energy. Based on specific theoretic models, some quantitative relations have been established between far-field spectra and source properties. The most widely accepted model is described in Madariaga (1976), who performed a finite-difference simulation of a circular crack model. An important relation is fc=kb/a, where fc is azimuthally averaged corner frequency, b is S-wave speed, a is circular radius and k is an empirical constant with different values for P and S wave spectra. Many other models have been proposed, including the recent dynamically realistic rupture simulations of Kaneko and Shearer (2014), all of which have yielded a variety of different values for . However, models to date have been for relatively simple ruptures and the effect of rupture complexity, including heterogeneous stress and slip, on stress drop and scaled energy estimates has not been fully explored. Here, we consider complicated ruptures, which include fault roughness and complex pre-stress distributions, and compute the spectra that would be recorded by realistic distributions of surface stations. We then process the synthetic data using methods commonly applied to real data and attempt to quantify which fault properties can be reliably estimated from the observations and the most likely sources of errors in the analysis.