Jaromir Jansky, Vladimír Plicka , Oldřich Novotný

The West-Bohemia/Vogtland region is well known for the occurrence of intraplate earthquake swarms. Those are monitored by the seismic network WEBNET. The relative locations, often used for estimation of the swarm time development, depend on the quality of the initial absolute location. In routine practice, hypocenters in the area are mostly located using the upper crustal 1-D velocity-depth model WEBN, composed of homogeneous layers, and the HYPO-like location algorithms. Using the P- and S-wave phase arrivals of the 156 events, selected from the 2008 earthquake swarm and recorded by 22 network stations, we demonstrate how the absolute hypocentre positions are influenced by variation of individual location parameters. These parameters include: the S-wave travel-time weight, the location starting depth, the Vp/Vs velocity ratio, the station elevation travel-time correction, and the (slight) crustal model velocity-depth variation. We locate the swarm under these variable conditions, discuss the results and derive the stations travel-time model correction to improve the location accuracy.