Stress Tensor Inversion Using Seismological Data

Abstract

In order to understand crustal dynamics, including the occurrence of earthquakes and the development of mountain ranges, it is important to estimate the stress state in the Earth’s crust from observed data. This paper reviews stress tensor inversion techniques using seismological data. The techniques were originally applied to a dataset of slip orientations taken from focal mechanisms. Subsequently, other techniques, which use P wave first-motion polarities or centroid moment tensor（CMT）solutions, were developed. This paper clarifies the principles and basic hypotheses, on which each technique is built. In the techniques using focal mechanisms and P wave first-motion data, the Wallace-Bott hypothesis that a fault slips in the direction of maximum resolved shear stress plays the principal role; basically, we search for a stress state that satisfies observed data on the basis of the Wallace-Bott hypothesis. On the other hand, the stress inversion technique using CMT data is not based on the Wallace-Bott hypothesis; instead, it is assumed that stress released by earthquakes is proportional to the stress tensor in the region surrounding the hypocenter. The characteristics and advantages of these techniques are also compared from physical and pragmatic viewpoints. It would be valuable to further improve these techniques, as well as to compare their performance using synthetic and actual data to clarify the differences and advantages of their characteristics in more detail.