The ISC Bulletin as a comprehensive source of earthquake source mechanisms

Abstract

In this article we summarize the availability of earthquake source mechanisms in the Bulletin of the International Seismological Centre (ISC). The bulletin in its current status contains ∼ 81000 seismic events with only one associated mechanism solution and ∼ 25000 events with at least two associated source mechanisms. The main sources of earthquake mechanisms in the ISC Bulletin are reported solutions provided by data contributors and ISC-computed focal mechanisms based on first motion polarities. Given the importance of using pre-determined fault plane solutions in different types of studies, here we briefly discuss the methodologies adopted by major data providers to the ISC and investigate the intra-event variability of the source mechanisms. We conclude that the overall agreement among different earthquake mechanisms for the same event as reported by different sources can show a similarity coefficient as high as 80 %, based on the rotation angles of their bestfitting double couple solutions, for the majority of the cases. The earthquake source mechanisms discussed in this work are freely available within the ISC Bulletin websearch at http://doi.org/10.31905/D808B830.