A detailed analysis of the Strazhitza (Bulgaria) seismic sequences of 1986: location, focal mechanism and regional stress tensor

Oncescu, Mihnea Corneliu; Trifu, Cezar‐Ioan; Hristova, Tania; Simeonova, Stela; Solakov, Dimcho

doi:10.1016/0040-1951(90)90063-e

Cited by 7 publications

(1 citation statement)

References 3 publications

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“…Inversion of fault slip data [Bergerat, 1988] suggests two stages in the tectonic evolution of the Pannonian Basin, related to E-W extension: (1) an initial transtensional process in middle to late Miocene time, when E-W extension occurred together with N-S compression, and conjugate NW-SE and NE-SW strike-slip faults and pull-apart basins developed [see also Horvath and Royden, 1981]; and (2) a pure extensional rifting process in Pliocene time, where normal faulting dominated [Bergerat, 1988] In the region of the Eastern Carpathians only very few data are available, and those indicate a considerable complexity in both stress regime and orientation [Fuchs et al, 1979;Oncescu, 1984Oncescu, , 1987Oncescu, , 1989]. For example, in Bulgaria, south of the Carpathians, normal fault and thrust fault earthquakes of comparable magnitudes occur at the same site with similar Shmax orientation of NW-SE [Oncescu et al, 1990].…”

Section: Carpathians and Pannonian Basinmentioning

confidence: 99%

Regional patterns of tectonic stress in Europe

Müller¹,

Zoback²,

Fuchs³

et al. 1992

J. Geophys. Res.

407

219

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Nearly 1500 stress orientation determinations are now available for Europe. The data come from earthquake focal mechanisms, overcoring measurements, well bore breakouts, hydraulic fracturing measurements, and young fault slip studies and sample the stress field from the surface to seismogenic depths. Three distinct regional patterns of maximum compressive horizontal stress (SHmax) orientation can be defined from these data: a consistent NW to NNW SHmax stress orientation in western Europe; a WNW‐ESE SHmax orientation in Scandinavia, similar to western Europe but with a larger variability of SHmax orientations; and a consistent E‐W SHmax orientation and N‐S extension in the Aegean Sea and western Anatolia. The different stress fields can be attributed to plate‐driving forces acting on the boundaries of the Eurasian plate, locally modified by lithospheric properties in different regions. On average, the orientation of maximum stress in western Europe is subparallel to the direction of relative plate motion between Africa and Europe and is rotated 17° clockwise from the direction of absolute plate motion. The uniformly oriented stress field in western Europe coincides with thin to medium lithospheric thickness (approximately 50–90 km) and high heat flow values (>80 m W/m2). In western Europe a predominance of strike‐slip focal mechanisms implies that the intermediate principal stress is vertical. The more irregular horizontal stress orientations in Scandinavia coincide with thick continental lithosphere (110–170 km) and low heat flow (<50 m W/m2). The cold thick lithosphere in this region may result in lower mean stresses associated with far‐field tectonic forces and allow the stress field to be more easily perturbed by local effects such as déglaciation flexure and topography. The stress field of the Aegean Sea and western Anatolia is consistent with N‐S extension in a back arc setting behind the Hellenic trench subduction zone. The stress field is influenced in places by regional geologic structures, e.g., in the Western Alps, where SHmax directions show a slight tendency toward a radial stress pattern. Not all major geologic structures, however, appear to affect the SHmax orientation, e.g., in the vicinity of the Rhine rift system horizontal stress orientations are continuous.

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