Investigating Vrancea intermediate depth seismic activity in Romania using automatic waveform processing methods

Seismic activity in Romania is dominated by the intermediate-depth earthquakes generated inside the seismogenic body of the Vrancea seismic zone extending to the depth of 180 km. This earthquakes represent the main source of seismic hazard for Romania and neighbouring countries, with the most recent largest events of M 7.7 and 7.4 in 1940 and 1977 that caused significant and widespread destruction. Space distribution of the intermediate-depth earthquakes from Vrancea is constrained to a compact volume (60-180 km in depth and 20x50 km areal extent) falling into the category of, so called, “seismic nests”, which have peculiar and not well understood seismogenic mechanisms.

We present first results obtained by applying the automated waveform analysis schemes to the detection, location and characterization of seismicity from the Vrancea zone to the continuous data recorded at seismic stations of the Romanian seismic network. We evaluate the performance of the methods like network-based full-waveform coherency earthquake detection and location and the template-based waveform similarity analysis for building a detailed view of seismic activity in space and time and to provide a fully automated workflow for continuous seismic data analysis. We use case-specific, for Vrancea seismic region, synthetic example to test the detection and location scheme setup and resolution. The real dataset of continuous seismic data focuses on the two month time period around the recent, moderate (M 5.6) December 27, 2016 earthquake.

The preliminary results of the automated detection and location analysis indicate reduced foreshock and aftershock activity for this event. According to the Romanian earthquake catalog, this appears to be a common pattern for moderate (M ~5.0-6.0) magnitude events. We also discuss the results of the template-based waveform similarity analysis for the detected and located events, as well as how the combination of the two methods can contribute to the enhanced seismic monitoring and hazard assessment.