The 2011 West Bohemia (Central Europe) earthquake swarm compared with the previous swarms of 2000 and 2008

Abstract

This paper presents the basic characteristics of the 2011 West Bohemia/Vogtland earthquake swarm and compares it with the swarms in 2000 and 2008. All these swarms occurred in the Nový Kostel focal zone. Up to 25,000 ML≤3.7 events with depths between 6 and 10 km were detected in the 2011 swarm. Utilizing WEBNET data, we analysed the cumulative seismic moment, magnitude-frequency and interevent time distributions, space-time distribution of foci and typical focal mechanisms. For this purpose, we improved the formula for estimating the local magnitude ML used by WEBNET. The 2011 swarm exhibited much higher rapidity than the swarms of 2000 and 2008. The magnitude-frequency distributions of all the three swarms are similar, having the b-value close to 1.0. However, the events of higher magnitudes, roughly ML∼3.0+, depart markedly from the general trend of the weaker events. The probability density functions of the interevent times of all the swarms comply with power law ∝T−1.4, which points to Omori law-like mainshock-aftershock activity. All swarms exhibit a pronounced focal migration; however, no regularity was found. The spatial distribution of the 2011 foci indicates two active fault segments which differ from the segment triggered in the swarms of 2000 and 2008. Furthermore, we analysed the spatial distribution of the mini-swarm of 2013 and found that it complements the swarm of 2011. The prevailing focal mechanisms in the 2011 swarm are of both oblique-normal and oblique-thrust types and correspond closely to the geometry of the activated fault segments. Our analyses indicate that the Nový Kostel area is more complex than was believed to be.