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<p>The study area is located in the western branch of the Southern Carpathians in Romania, between the Olt River and the Danube. The data on seismicity recorded before 1999–2000 indicate a sporadic seismic activity, mostly of small magnitude. A few events of magnitude above 5 (maximum magnitude Mw 5.7) have been reported through historical data, which are inherently imprecise. Recently, several significant crustal sequences occurred in the region in 2011–2012 (eastern part of Târgu Jiu city), 2011 and 2013 (Haţeg basin), 2014–2015 (Caransebeş–Mehadia basin), 2020 (Orşova basin). The most spectacular sequence was recorded at the contact between Southern Carpathians and Getic depression, in the northern part of Târgu Jiu city, starting in February with two shocks of magnitude above 5, and continuing for more than one year with more than 4000 aftershocks. The new recorded data are particularly valuable for interpreting the present-day seismotectonics and for redefining the regional seismic hazard. The motivation of the present study naturally came out from the need to elucidate what makes the regional tectonics able to suddenly activate an unexpected level of seismicity for an area previously characterized by apparently sporadic and insignificant seismic activity. In order to characterize the stress field, we collected all the earthquake focal mechanisms available from source catalogues that we considered to be of acceptable quality. For inversion, we defined 8 individualized clusters of earthquakes associated either to active tectonic faults, or to intramontane extensional basins, for which we assumed that the individual focal mechanisms follow the trends of a homogeneous stress field. The results show a clear model of mostly extensional stress field responsible for generating the earthquake swarms during the last decades. The configuration of the horizontal stress directions reveals a complex tectonic setting following a main NE-SW trending associated with the transcurrent movement along the active faults in the Danubian region (e.g., Cerna–Jiu fault, Timok fault) and significant rotations toward a NW-SE alignment in the intramontane basins and in the Getic depression. It reveals an overall extensional stress field predominance in the Southern Carpathians.</p>

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Seismotectonic features of the Southern Carpathians, Romania, resulted from focal mechanism inversion

  • 期刊论文

  • 发表日期：

    2026年1月12日

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  • A. Bălă,
  • M. Radulian,
  • M. Popa,
  • C. Gheablău

摘要

The study area is located in the western branch of the Southern Carpathians in Romania, between the Olt River and the Danube. The data on seismicity recorded before 1999–2000 indicate a sporadic seismic activity, mostly of small magnitude. A few events of magnitude above 5 (maximum magnitude Mw 5.7) have been reported through historical data, which are inherently imprecise. Recently, several significant crustal sequences occurred in the region in 2011–2012 (eastern part of Târgu Jiu city), 2011 and 2013 (Haţeg basin), 2014–2015 (Caransebeş–Mehadia basin), 2020 (Orşova basin). The most spectacular sequence was recorded at the contact between Southern Carpathians and Getic depression, in the northern part of Târgu Jiu city, starting in February with two shocks of magnitude above 5, and continuing for more than one year with more than 4000 aftershocks. The new recorded data are particularly valuable for interpreting the present-day seismotectonics and for redefining the regional seismic hazard. The motivation of the present study naturally came out from the need to elucidate what makes the regional tectonics able to suddenly activate an unexpected level of seismicity for an area previously characterized by apparently sporadic and insignificant seismic activity. In order to characterize the stress field, we collected all the earthquake focal mechanisms available from source catalogues that we considered to be of acceptable quality. For inversion, we defined 8 individualized clusters of earthquakes associated either to active tectonic faults, or to intramontane extensional basins, for which we assumed that the individual focal mechanisms follow the trends of a homogeneous stress field. The results show a clear model of mostly extensional stress field responsible for generating the earthquake swarms during the last decades. The configuration of the horizontal stress directions reveals a complex tectonic setting following a main NE-SW trending associated with the transcurrent movement along the active faults in the Danubian region (e.g., Cerna–Jiu fault, Timok fault) and significant rotations toward a NW-SE alignment in the intramontane basins and in the Getic depression. It reveals an overall extensional stress field predominance in the Southern Carpathians.