ALBERT

Description: 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 (sub W) . For 34 events in and near Switzerland, we determined seismic moment (thus M (sub W) ) by regional waveform inversion. Independent M (sub W) estimates for the same events do not exist; however, M (sub W) from European-Mediterranean events, obtained in the same way, agree with M (sub W) from Harvard CMT solutions. All other size estimates, M (sub L) , M (sub D) , m (sub b) , M (sub S) , and intensities, are calibrated relative to these 34 events. Teleseismic M (sub S) and m (sub b) from international data centers are directly regressed against M (sub W) . Most observations in ECOS consist of local magnitudes (M (sub L) , M (sub D) ) and intensities. For local magnitudes, we first calibrated the Swiss Seismological Service's M (sub L) . 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 M (sub S) for stronger twentieth century Swiss earthquakes from analog seismograms. These M (sub S) , which were converted to M (sub W) , connect intensities and M (sub W) . After calibration, all 20,300 events in ECOS have a unified M (sub W) , including a class-type uncertainty estimate based on the original magnitude scale. ECOS covers the period 250-2001, from 44 degrees N to 51 degrees N and 4 degrees E to 13 degrees E. The largest event in ECOS is the 1356 M (sub W) 6.9 Basle earthquake.

Description: We estimate moment magnitudes M (sub w) for earthquakes in Switzerland recorded between 1998 and 2009 using three different spectral methods. The M (sub w) estimation in Switzerland is extended to lower magnitudes (local magnitude M (sub L) 0.1), and scaling relations between M (sub L) and M (sub w) are investigated. Above M (sub L) 4, the obtained M (sub w) estimates are consistent with the previously obtained scaling relation of M (sub w) =M (sub L) -0.3 at the Swiss Seismological Service (SED). Below M (sub L) 4, all three methods indicate that a 1:1-type relationship is inappropriate. Therefore, we propose a new piecewise empirical scaling relation for earthquakes in Switzerland. The scaling is linear below M (sub L) 2 and above M (sub L) 4. To obtain a smooth transition between the two linear scales we fit a quadratic relation in between (2〈 or =M (sub L) 〈 or =4). This scaling relation is also consistent with M (sub w) estimates from moment-tensor (MT) solutions based on broadband waveform fitting of local earthquakes with M (sub L) 〉3.0. We have tested all three methods carefully to ensure that the observed break in scale at around M 3 cannot be attributed to bias in the M (sub w) determination. However, we cannot determine with certainty from the dataset at hand whether the break in scaling is due to bias in the routine determination of M (sub L) or to physical properties of the source.