The August-December 2000 earthquake swarm in NW Bohemia: the first results based on automatic processing of seismograms

Main features of the August-December 2000 earthquake swarm which occurred in the major focal area of the North-West Bohemia/Vogtland swarm region are presented. Seismograms from four stations of WEBNET were automatically processed to get arrival times, first motion amplitudes and hypocentre coordinates of a representative set of events. Altogether 7017 microearthquakes in the magnitude range of M-L=0-3.3 were identified. It is shown the decay of activity of individual swarm phases followed the modified Omori law, which points to a partial similarity with aftershock sequences of tectonic earthquakes. The space-time distribution of a subset of 2913 events with low location residuals shows a strong space clustering of the earthquake hypocentres and their pronounced migration between individual swarm phases. Most of the activity took place along an elliptical, nearly vertically dipping, 6 kin long N-S oriented fault plane in depths ranging from 10.5 to 6.5 kin. The P and T axes were estimated by FOCMEC for the 782 strong events and three groups of earthquakes with similar faulting type were distinguished. In contrast to the normal and strike-slip faulting events that created the prevailing portion of the swarm and were distributed uniformly within the focal area, the reverse events were clustered in time and space. (C) 2002 Elsevier Science Ltd. All rights reserved.