10:30 〜 10:45
[S07-8-01] Ground motion pattern generated by the undercrustal seismic source of the Vrancea region, Romania
The seismogenic source of strong earthquakes (Mw > 7) from the bend of the Southeastern Carpathians is located in the undercrustal lithosphere, in a complex tectonic setting.
A modest number of strong motion records – all analogue – is presently available for Vrancea events with moment magnitude above 6, due to the low occurrence rate of these seisms, as well as to the poor seismic instrumentation in the region, before 1980. The strongest digitally recorded intermediate-depth earthquake is the Mw 6.0 event of October 27, 2004.
Detailed macroseismic maps are available for the strongest Vrancea seisms which occurred at the end of the XXth century (4 earthquakes with moment magnitude 7.4, 7.1, 6.9, and 6.4, respectively). They all display a peculiar shape of the isoseismals, with a pronounced asymmetry. The few existing instrumental records support these features.
During the past decades the Romanian seismic network has continuously been developed and upgraded; at present, it covers the entire country, and comprises 118 permanent digital stations equipped with 3-component accelerometers.
Taking advantage of the significant amount of recently collected high-quality data, we examine the space distributions of the ground motion parameters (PGA, PGV) yielded by several tens of moderate-sized undercrustal earthquakes, with Mw between 4.0 and 5.6. Their hypocenters cover well the seismogenic zone. The focal mechanisms indicate – with few exceptions – reverse faulting, nevertheless, the orientation of the nodal planes show a notable diversity.
The individual ground motion distributions display noticeable differences, but also important common characteristics – largest parameter values in the Extra-Carpathian area, rapid decrease of ground shaking towards the Intra-Carpathian region. The study evidences that the local and regional geological conditions control the ground motion pattern to a larger degree than the source parameters (magnitude, mechanism, hypocenter location).
A modest number of strong motion records – all analogue – is presently available for Vrancea events with moment magnitude above 6, due to the low occurrence rate of these seisms, as well as to the poor seismic instrumentation in the region, before 1980. The strongest digitally recorded intermediate-depth earthquake is the Mw 6.0 event of October 27, 2004.
Detailed macroseismic maps are available for the strongest Vrancea seisms which occurred at the end of the XXth century (4 earthquakes with moment magnitude 7.4, 7.1, 6.9, and 6.4, respectively). They all display a peculiar shape of the isoseismals, with a pronounced asymmetry. The few existing instrumental records support these features.
During the past decades the Romanian seismic network has continuously been developed and upgraded; at present, it covers the entire country, and comprises 118 permanent digital stations equipped with 3-component accelerometers.
Taking advantage of the significant amount of recently collected high-quality data, we examine the space distributions of the ground motion parameters (PGA, PGV) yielded by several tens of moderate-sized undercrustal earthquakes, with Mw between 4.0 and 5.6. Their hypocenters cover well the seismogenic zone. The focal mechanisms indicate – with few exceptions – reverse faulting, nevertheless, the orientation of the nodal planes show a notable diversity.
The individual ground motion distributions display noticeable differences, but also important common characteristics – largest parameter values in the Extra-Carpathian area, rapid decrease of ground shaking towards the Intra-Carpathian region. The study evidences that the local and regional geological conditions control the ground motion pattern to a larger degree than the source parameters (magnitude, mechanism, hypocenter location).