Inversion for local stress field inhomogeneities


In this thesis, the 1997 Vogtland/NW-Bohemia swarm has been selected for the analysis of inhomogeneities in the stress field because two predominant nearly perpendicular flat zones of seismicity are visible in the hypocentre distribution implying inhomogeneities in the stress field. This is unusual compared to other swarms originating from this area. An existing dataset of waveform data, P- and S-phase picks, and master event locations has been analysed regarding similarity of waveforms, location refinement, and estimation of relative moment tensors. The latter are used together with a regional dataset of 50 single focal mechanisms and 125 focal mechanisms from the 2000 hydraulic fracturing experiment at the KTB for an estimate of the regional homogeneous and the locally inhomogeneous stress field. An automated processing procedure consisting of coherence analysis,precise relocation, relative moment tensor inversion, and stress trajectory determination has been set up. The coherence analysis has been successfully applied using a new method that uses three component seismograms. 457 events are separated into 13 multiplets of similar waveforms of at least size 8. Another result are precise relative arrival time measurements which are fed into the precise relocation program "hypoDD". Two nearly perpendicular structures are found in the hypocentre distribution. 352 moment tensors are estimated using a relative moment tensor inversion. Three different algorithms to distinguish between fault plane and auxiliary plane are successfully applied to them...
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