Challenges and Solutions in Reassessing Parameters of Seismic Catalog over the last 50 Years: Example of the SI-Hex Collaborative Project

Abstract:

The increased number of stations with high quality sensors and the international exchange of waveform improve the location and magnitude for recent events. Various international organizations (ISC, EMSC, etc.) have produced “standard” exchange procedures to merge parametric data from different observatories. Nevertheless, this does not exist for events back to the year 60th despite they are of first importance for seismic hazard assessment.

Several initiatives are regularly done to produce upgraded catalogs covering such period but they are most of the time “only merging” available parametric data and using, for magnitude homogenization, regressions between various datasets.

The SI-Hex project provides a catalogue of seismicity for metropolitan France related to the years 1962-2009 by taking into account the contributions of the various seismological networks. In contrast with all the previous French catalogs of seismicity, this collaborative project makes use of the original data coming from all regional and national seismic networks operating in metropolitan France, together with parametric data coming from the surrounding European networks.

Hypocenter locations are based on preferential solutions extracted from a multi-origin database. For each event from 1962 to 2009, one origin is computed using a single 1D velocity model covering metropolitan France and by merging arrival times coming from French and European stations. In order to improve the accuracy in hypocenter location, solutions calculated by regional observatory with regional velocity models, are taken as preferential solution when available.

We provide for the first time a Moment magnitude M_w. It was computed from coda-wave for most of the M_w>3.4 events, and from converted local magnitudes M_L for the smaller events.

Special attention was paid to the discrimination between natural and artificial seismic events. Results are available at www.franceseisme.fr/sismicite.html.