Stress derivation from earthquake focal mechanisms

Abstract

One of the most evident effects of stress release in the crust are tectonic earthquakes. Due to the large amount of existing earthquake focal mechanisms from regional studies and the steadily increasing number of CMT solutions made routinely public by e.g. the Global CMT Project (formerly by the Harvard seismology group) or the NEIC/USGS, single earthquake focal mechanisms (FMS) make up the majority of data records in the WSM database. Focal mechanism data provide information on the relative magnitudes of the principal stresses, so that a tectonic regime can be assigned. The determination of principal stress orientations and relative magnitudes from these mechanisms must be done with appreciable caution. Three types of data records from focal mechanisms are distinguished in the WSM database: Single (FMS), formal inversions (FMF), and average/composite (FMA) focal mechanisms. The main difference between these in terms of stress indication is their reliability to indicate regional tectonic stress. 1