Abstract
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 ∼81 000 seismic events with only one associated mechanism solution and ∼25 000 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 best-fitting 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.
Highlights
The International Seismological Centre (ISC, http://www. isc.ac.uk/, last access: April 2019) currently collects station readings, hypocentre solutions, and other earthquake bulletin data from approximately 150 agencies around the world
In this paper we present an additional aspect of the ISC Bulletin, namely its source mechanism content and the opportunity for ISC users to complement the source mechanism information with all other data included in the ISC Bulletin
Centroidbased mechanism solutions should be used together with centroid locations, since (i) both the centroid mechanism and centroid location are parts of the same output and (ii) substantial differences may exist among centroid locations and standard hypocentre locations fitting the observed phase arrival times of body waves
Summary
The International Seismological Centre (ISC, http://www. isc.ac.uk/, last access: April 2019) currently collects station readings, hypocentre solutions, and other earthquake bulletin data from approximately 150 agencies around the world. Isc.ac.uk/, last access: April 2019) currently collects station readings, hypocentre solutions, and other earthquake bulletin data from approximately 150 agencies around the world. The ISC Bulletin contains over 7.6 million seismic events (mostly earthquakes, as well as chemical and nuclear explosions, mine blasts, and mining-induced events, and other types of seismic events), and approximately 256 million associated seismic station readings of arrival times, amplitudes, periods, and first motion polarities (International Seismological Centre, 2018, database last accessed in March 2019). If all conditions are met (details at http://www.isc.ac.uk/iscbulletin/review/, last access: April 2019), the ISC recomputes location and magnitude (currently only MS and mb) by combining all the available phase arrival times and amplitude measurements, respectively. The ISC aims to increase the number of collected bulletins from national data centres or other sources (Willemann and Storchak, 2001) and improve its procedures in earthquake location and magnitude determinations We aim to emphasize the availability of source mechanisms in the ISC Bulletin and discuss the different features of those solutions, aiming at helping ISC data users to decide how best to use the database according to the needs of their research
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