Source mechanisms of local and near-regional earthquakes

Hungary (the central part of the Pannonian basin) can be characterized by moderate seismicity with local earthquake magnitudes of mostly less than 3.5. The seismicity pattern shows that earthquakes are restricted to the upper part of the crust and the epicenters are distributed all around the country. Therefore, identification of active fault planes is generally a difficult issue in this region.

In areas of low-to-moderate seismicity, the small-magnitude local earthquakes provide the only key to determine fault parameters and small-scale tectonic structure. The focal mechanisms of small events can be used to infer the structure and kinematics of faults at depth and to constrain the crustal stress field in which the earthquakes occur. It is therefore important to determine mechanisms for small events as accurately as possible.

I have developed a probabilistic waveform inversion method to determine simultaneously earthquake-source mechanism, hypocentral location and source time function from the inversion of short-period waveform data of local events (Wéber 2006). Provided that a structural model of the region under study is available, synthetic seismograms generated by various types of source are constructed and compared with observed records in a suitable inversion scheme. The main advantage of such a procedure, in comparison with the classical body-wave polarity studies, is that complete seismograms are used in the analysis. This allows the retrieval not only of the fault-plane solution and hypocentral location, but also of the source time history (Wéber 2009). Since its first publication, the waveform inversion method has been improved in many respects and successfully applied for estimating the full moment tensor of both local and near-regional events in the Pannonian basin (Wéber and Süle 2014; Wéber 2016a; Wéber 2016b).

In the following sub-pages I firstly summarize the waveform inversion method, then an earthquake moment tensor catalog is published listing the focal parameters of those Hungarian events that have already been investigated by this inversion technique.