Homogeneous Moment-Magnitude Calibration in Switzerland
- Citation data:
Bulletin of the Seismological Society of America, ISSN: 0037-1106, Vol: 95, Issue: 1, Page: 58-74
- Publication Year:
- Earth and Planetary Sciences
An earthquake catalog containing a uniform size estimate is important for long-term seismic hazard assessment in regions of low-to-moderate seismicity. During the update of the Earthquake Catalog of Switzerland (ECOS), we performed regression analyses to convert all earthquake size information in ECOS to physically meaningful moment magnitude M. For 34 events in and near Switzerland, we determined seismic moment (thus M) by regional waveform inversion. Independent Mestimates for the same events do not exist; however, Mfrom European-Mediterranean events, obtained in the same way, agree with Mfrom Harvard CMT solutions. All other size estimates, M, M, m, M, and intensities, are calibrated relative to these 34 events. Teleseismic Mand mfrom international data centers are directly regressed against M. Most observations in ECOS consist of local magnitudes (M, M) and intensities. For local magnitudes, we first calibrated the Swiss Seismological Service's M. Then we calibrated magnitudes from observatories in neighboring countries (France, Germany, Italy) using only events in the border region (e.g., France-Switzerland). Modern instrumental records exist only since the mid-1970s. We calibrated the macroseismic dataset, which represents by far the largest period in the catalog, by determining surface wave magnitude Mfor stronger twentieth century Swiss earthquakes from analog seismograms. These M, which were converted to M, connect intensities and M. After calibration, all 20,300 events in ECOS have a unified M, including a class-type uncertainty estimate based on the original magnitude scale. ECOS covers the period 250-2001, from 44° N to 51° N and 4° E to 13° E. The largest event in ECOS is the 1356 M6.9 Basle earthquake.