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HORIZONTAL STRESS FIELD IN THE EARTH CRUST OF ROMANIA USING MULTIPLE FOCAL MECHANISM SOLUTIONS

Andrei Bălă

Abstract

A catalogue of fault plane solutions for earthquakes recorded in Romania between 1929 and 2012 is analyzed in order to outline statistical features of the fault plane solutions in correlation with the earthquake-prone areas in Romania. The catalogue contains both groups: crustal earthquakes (h < 50 km) and intermediate-depth earthquakes (h > 50 km), but only the crustal earthquakes are analyzed here. The catalogue covers mostly the area in front of the Carpathians Arc: Moesian Platform, Barlad Depression, North Dobrogean Orogen and Fagaras ? Campulung, Central Southern Carpathian seismogenic zones. The Intra-Carpathians area has a sparse seismicity and the available fault plane solutions are not enough to derive regional horizontal crustal stress based on multiple mechanism solutions. In our present investigations we have employed the formal stress inversions of a group of focal mechanisms (FMF), which is a better estimation of the tectonic stress orientation that can be achieved in a region with a homogeneous regional stress field, in comparison with single focal mechanism, as shown in World Stress Map Project . The formal stress inversion of multiple focal mechanisms (FMF) improves the quality of stress derivation, but it is linked to two main assumptions: (1) the chosen FMS lies in a region with a uniform stress field that is invariant in space and time; (2) the direction of earthquake slip follows the direction of the maximum shear stress, as in Wallace-Bott hypothesis . The 2D horizontal stress is determined in the crustal zones using local grids with cells containing at least 15- 20 fault plane solutions and is graphically represented, using STRESSINVERSE computer programs with public access .

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DOI resolver: doi.org/10.5593/sgem2019/1.1/s05.104

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