Automatic regional moment tensor inversion in the European-Mediterranean region

Abstract

SUMMARY We produce fast and automatic moment tensor solutions for all moderate to strong earthquakes in the European-Mediterranean region. The procedure automatically screens near real-time earthquake alerts provided by a large number of agencies. Each event with magnitude M ≥ 4.7 triggers an automatic request for near real-time data at several national and international data centres. Moment tensor inversion is performed using complete regional long-period (50‐100 s) waveforms. Initially the data are inverted for a fixed depth to remove traces with a low signal-tonoise ratio. The remaining data are then inverted for several trial depths to find the best-fitting depth. Solutions are produced within 90 min of an earthquake. We analyse the results for the period 2000 April to 2002 April to evaluate the performance of the procedure. For quality assessment, we compared the results with the independent Swiss regional moment tensor catalogue (SRMT), and divided the 87 moment tensor solutions into three groups: 38 A-quality solutions with well-resolved M w, depth and focal mechanism; 21 B-quality solutions with wellresolved M w; and 28 unreliable C-quality solutions. The non-homogeneous station and event distributions, varying noise level, and inaccurate earthquake locations affected solution quality. For larger events (M w ≥ 5.5) we consistently obtained A-quality solutions. For M w = 4.5‐5.5 we obtained A- and B-quality solutions. Solutions that pass empirical rules mimicking the a posteriori quality for our data set are automatically disseminated.