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Structural characteristics of epicentral areas in Central Europe: study case Cheb Basin (Czech Republic)
Institution:1. Gutenbergstr. 60, 14467 Potsdam, Germany;2. Gerokstr 58, 70184 Stuttgart, Germany;3. GeoForschungsZentrum, Telegrafenberg, 14473 Potsdam, Germany;1. Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 4006076, Maharashtra, India;2. Department of Mechanical and Industrial Engineering, Louisiana State University, Baton Rouge, LA 70803, USA;1. Department of Geological Sciences, Faculty of Science, Masaryk University, Kotlá?ská 2, 611 37 Brno, Czech Republic;2. Institute of Rock Structure and Mechanics, Czech Academy of Sciences, V Hole?ovi?kách 41, 182 09, Prague, Czech Republic;3. Cave and Karst Research Group, Department of Geology and Paleontology, Natural History Museum, Burgring 7, 1010, Vienna, Austria;1. University of Nevada Las Vegas School of Medicine, Department of Pediatrics, Las Vegas, NV, USA;2. Children’s Lung Specialists, Las Vegas, NV, USA;1. Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, Prague, 12843, Czech Republic;2. Institute of Geology, v. v. i., Academy of Sciences of the Czech Republic, Rozvojová 269, Prague, 16500, Czech Republic;3. AGICO Inc., Je?ná 29, Brno, 62100, Czech Republic
Abstract:The earthquake distribution pattern of Central Europe differs systematically from the neighbouring areas of NW and southern Europe regarding the fault plane kinematics. Within a belt between the French Massif Central and the northern part of the Bohemian Massif (1000 km) sinistral faulting along N-S zones dominates on the contrary to the Alps and their foreland with common bookshelf shears. One of the prominent N-S structures is the Regensburg-Leipzig-Rostock Zone (A) with several epicentral areas, where the main seismic center occurs in the northern Cheb Basin (NW Bohemia). The study demonstrates new structural results for the swarm-quake region in NW-Bohemia, especially for the Nový Kostel area in the Cheb Basin. There the N-S-trending newly found Po?atky-Plesná zone (PPZ) is identical with the main earthquake line. The PPZ is connected with a mofette line between Hartu?ov and Bublák with evidence for CO2 degassing from the subcrustal mantle. The morphologically more prominent Mariánské Lázně fault (MLF) intersects the PPZ obliquely under an acuate angle. In the past the MLF was supposed to be the tectonic structure connected with the epicentral area of Nový Kostel. But evidence from the relocated hypocentres along the PPZ (at 7–12 kms depth) indicate that the MLF is seismically non-active. Asymmetric drainage patterns of the Cheb Basin are caused by fault related movement along Palaeozoic basement faults which initiate a deformation of the cover (Upper Pliocene to Holocene basin filling). The PPZ forms an escarpment in Pliocene and Pleistocene soft rock and is supposingly acting as an earthquake zone since late Pleistocene time. The uppermost Pleistocene of 0.12–0.01 Ma deposited only in front of the fault scarp dates the fault activity. The crossing faults envelope crustal wedges under different local stress conditions. Their intersection line forms a zone beginning at the surface near Nový Kostel, dipping south with increasing depth, probably down to about 12 km. The intersection zone represents a crustal anomaly. There fault movements can be blocked up and peculiar stress condition influence the behaviour of the adjacent crust. An ENE-WNW striking dextral wrench fault was detected which is to expect as kinematic counterpart to the ca. N-S striking sinistral shear zones. Nearly E-W striking fracture segments were formerly only known as remote sensing lineaments or as joint density zones. The ENE shear zone is characterized by a set of compressional m-scale folds and dm-scale faults scattered within a 20 m wide wrench zone. It is built up of different sets of cleavage-like clay plate pattern of microscopical scale. The associated shear planes fit into a Riedel shear system. One characteristic feature are tiny channels of micrometer scale. They have originated after shear plane bending and are the sites of CO2 mantle degassing.
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