Seismicity and seismotectonics of West Saxony, Germany — new insights from recent seismicity observed with the Saxonian seismic network

A new network of permanently recording seismic stations in West Saxony has considerably improved detection threshold, location accuracy and depth determination in this seismically active region. Between 2001 and 2007 more than 900 events have been located. Seismicity mainly occurred along a band stretching north-south between Leipzig and Vogtland/NW Bohemia area with local magnitudes ranging between −0.8 and 2.8. Seismicity clearly delineates the Leipzig-Regensburg (L-R) fault zone striking N-S, and the Gera-Jachymov (G-J) fault zone striking roughly NNW-SSE. The hypocentral depths can be divided into two depth ranges, one at depths below 10 km, and a second at less than 10 km depth that only extends S-N from the Vogtland until the crossing between L-R and G-J fault zones. A small earthquake sequence that occurred near Werdau/Zwickau in August 2006 at almost the same epicenters as an earlier sequence 1997/98 seems to confirm this finding: a relative localization of 15 events with the double-difference technique clearly reveals two distinct subclusters at about 6 and 12–14 km depth. With the improved station coverage 33 new fault plane solutions from events along the L-R fault zone north of the swarmquake area could be determined from P-polarities and P/S ratios. They do not differ significantly from solutions in the Vogtland/NW-Bohemia area and are mostly compatible with a N-S oriented fault plane. Strike slip mechanisms with or without a dip slip component dominate.