Detailed Analysis of Tectonic Stress in West Bohemia Swarm Area, Czech Republic

Session: Earthquake Source Parameters: Theory, Observations and Interpretations [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The West Bohemia region is characterized by a persistent seismic activity characterized by a frequent occurrence of earthquake swarms. Active tectonics in the area is related to Tertiary and Quaternary volcanism manifested by CO2 emanations and mineral springs. The earthquake swarms in West Bohemia are monitored by the seismic network WEBNET, which consist of 22 local stations with a sampling frequency of 250 Hz. We computed moment tensors of several thousands of events from the time period of 2008-2018: 3000 events of the 2008 swarm (maximum ML=3.8), 2000 events of the 2011 swarm (maximum ML=3.0), 800 of the seismic activity in 2014 (maximum ML=4.2), 650 of the 2017 swarm (maximum ML=3.5) and 1200 of the 2018 swarm (maximum ML=3.8). The moment tensors was inverted using the principal component analysis. The method is based on the assumption that a point source generates P waves with waveforms identical at all receivers irrespective of azimuths and take-off angles of the corresponding rays.

The retrieved moment tensors were used for the stress inversion using the public-open STRESSINVERSE code. The fault area was divided into a 2D grid along the fault with spacing of 0.5 km. In segments with a large number of moment tensors, we used spacing of 0.3 km. Stress parameters were computed in each fault segment separately. In the stress inversion, we employed very accurate moment tensors with RMS higher than 0.35. A minimum number of events in one segment was limited to 50. We discuss variations of the principal stress axes and of the stress ratio along the fault, in particularly, we focus on their dependence on depth. The reliability of all stress parameters was tested using several data subsets. The variations of the local stress in the focal zone indicate strong interactions of individual fault segments.

Presenting Author: Petra Adamova

Authors