Spatiotemporal characterization of interswarm period seismicity in the focal area Nový Kostel (West Bohemia/Vogtland) by a short-term microseismic study

The West Bohemia/Vogtland region is one of the seismically most interesting areas in Europe because of its swarm-like occurrence of seismicity. The installation of the local West Bohemian seismological network (WEBNET) has made the recording of small magnitude seismicity (detection threshold ML≈−0.5) possible. We investigated if microseismicity exists below the detection threshold of WEBNET. A microseismic field campaign was carried out in the focal area Nový Kostel. The measurement was performed with three small arrays lasting for 6 d in a seismically quiet, interswarm period. We were able to detect and locate 13 microearthquakes in the magnitude range −1.5 ≤ ML ≤−0.1 and achieved a detection threshold about one magnitude lower than the local network. A relative location suggests that the recorded seismicity is rather related to a specific fault segment than randomly distributed. The determined fault zone is aligned NW—SW and confirms the viability of mapping active faults with short-term measurements. The results demonstrate that a linear extrapolation of the b-value, determined by the network bulletin, down to ML = −0.5 fits well with the amount of our recorded events.