Some pitfalls and trade-offs in source parameter determination using body wave modeling and inversion

Abstract

This paper investigates the problem of non-uniqueness in body wave modeling for source quantification. In particular, it examines how variations in source structure, source time function, and focal depth interact to alter synthetic body waves, and shows that solutions with different model parameters are capable of producing synthetic waveforms which all fit the observed data equally well. The problem of non-uniqueness is illustrated by comparing source mechanisms and the resulting synthetic waveforms from several East African earthquakes. The shapes of synthetic waveforms are controlled by the focal depth, source crustal structure and source time function, as well as the strike, dip and rake of the earthquake. Results show that if any one of the model parameters is invalid, the resulting solution is highly suspect. This point is particularly important to consider when interpreting published results of body wave modeling studies. Several of the examples show how S-waves, surface reflected phases, and gravity surveys can be used to help constrain various model parameters.