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[S13-1-03] Moment tensor inversion based on the principal component analysis: Method and application to the 2014 earthquake sequence in West Bohemia, Czech Republic
We develop and test a new hybrid approach of the amplitude and waveform moment tensor inversions, which utilizes the principal component analysis of seismograms. The proposed inversion is less sensitive to noise in data being thus more accurate and more robust than the amplitude inversion. It also suppresses other unmodelled phenomena like a directivity of the source, errors caused by local site effects at individual stations and by time shifts in arrivals of observed and synthetic signals due to an inaccurate velocity model. The inversion is simple and computationally less demanding than the full waveform inversion and thus applicable to large datasets. The approach is numerically tested on synthetic data with a various level of noise. The applicability of the inversion is demonstrated on inverting more than 800 microearthquakes that occurred during the 2014 activity in West Bohemia, Czech Republic. The analysis revealed clustering of the moment tensors into several distinct types. Three types of MT are left-lateral strike slips associated with the most active fault in the focal zone. Another cluster is characterized by the right-lateral strike slips associated with the fault conjugate to the main fault. Finally, we identified a cluster with pure reverse focal mechanisms which are anomalous and not expected to occur in the region. These mechanisms were not detected in the previous seismic activity and they have an unfavourable orientation with respect to regional tectonic stress. This might indicate a presence of local stress heterogeneities caused, for example, by an interaction of faults or fault segments in the focal zone.