Crustal stress partitioning in the complex seismic active areas of Romania
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Crustal stress partitioning in the complex seismic active areas of Romania A. Bala1 · M. Radulian1,2 · D. Toma‑Danila1 Received: 25 March 2020 / Accepted: 28 May 2020 © Akadémiai Kiadó 2020
Abstract Analyzing the partitioning of stress and deformation in active orogenic settings is of fundamental importance for understanding the mechanisms driving the geodynamic evolution and seismicity, particularly in complex orogenic settings. In this respect, a quantitative understanding is obtained by coupling the large-scale geodynamic evolution with partitioning of local deformation and stress patterns derived from analyzing the seismicity character, focal plane solutions and kinematics of genetically related active structures. The goal of the present paper is to investigate the stress field characteristics in relation with the specific geotectonics and seismogenic zones of Romania. The principal stress components are computed by inverting the fault plane solutions provided by a completed and updated catalogue for the crustal earthquakes recorded since 1929 up to 2012. Our investigation is justified to the extent that the basic hypothesis of properly representing the seismic area partitioning by individual clusters of events is relevant at the scale of each earthquake-prone area and from statistical point of view (minimum 20–30 events). The catalogue covers mostly the area in front of the Carpathians Arc: Moesian Platform, Barlad Depression, North Dobrogean Orogen, Southern Carpathians belt (Făgăraş-Câmpulung, Central Southern Carpathian and Danubian seismogenic zones) and western part of Romania (Banat region). The seismicity is sporadic and the available fault plane solutions are less representative for the entire area in the inner side of the Carpathians and for the Dobrogea region, located between Danube river and Black Sea. Therefore, for these last two regions the resulted stress field properties are considered as preliminary. The formal stress inversion applied on groups of focal mechanisms proved to be a better estimation of the tectonic stress orientation that can be achieved in the study region in comparison with single focal mechanism, as shown in the World Stress Map Project 2016. Keywords Romania · Earthquake mechanism catalog · Seismic zones · Stress tensor · Stress inversion
* M. Radulian [email protected] 1
National Institute for Earth Physics, Magurele, Romania
2
Academy of Romanian Scientists, Bucharest, Romania
13
Vol.:(0123456789)
Acta Geodaetica et Geophysica
1 Introduction The main feature of the seismic activity in Romania is the concentration of strong earthquakes at the Carpathians Arc bend, at intermediate depths (60–180 km) in the Vrancea region (Fig. 1). Here, the Vrancea high-seismic-velocity body in the mantle is permanently releasing seismic energy in an extreme narrow volume (40 × 70 km in section and from 60 to 180 km depth). In average, three earthquakes with magnitude above 7 were reported each century for a time span of six centuries. Some prevalent hypotheses about the orig
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