Abstract

In the most seismically active region of Hungary, an earthquake of ML 4.5 occurred near the town of Oroszlány on 29 January 2011. The mainshock was followed by more than 200 aftershocks. This event is the first earthquake in the country above ML 4 that was recorded on a significant number of three‐component digital seismic stations. According to the inversion of arrival times, the hypocenter of the mainshock was at a depth of about 5 km near Oroszlány with horizontal errors of about 1.5 km. The aftershocks were confined to a small region next to the mainshock. For the main event, we obtained an average moment magnitude of Mw 4.2, P‐ and S‐wave source radii of rP=970 and rS=972  m, and static stress drops of ΔσP=6.67×105 and ΔσS=17.60×105  Pa from the analysis of P‐ and S‐wave displacement spectra, respectively. The retrieved spectral source parameters for the investigated events agree well with the results of earlier research. We have also shown that our local waveform‐inversion method applied in this study is suitable to estimate the earthquake source mechanism for low‐magnitude events using local waveforms exclusively. The moment tensor computed for the mainshock from local waveform data shows a strike‐slip mechanism with a north–south‐striking and an east–west‐striking nodal plane, agreeing well with regional moment tensor solutions of other agencies. The source mechanisms of four aftershocks with ML≥2 were also successfully estimated. Three of them had strike‐slip mechanism very similar to that of the mainshock, whereas the fourth one was a thrust faulting event with some strike‐slip component. The subhorizontal P axis struck about northeast–southwest for both the mainshock and all the analyzed aftershocks, coinciding with the general trend of the compressional stress field in the epicentral region.

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