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ZusammenfassungDie auf ihre Erdbebent~itigkeit hin untersuchte Traverse ist 1800 krn lang und erstreckt sich yon der Doggerbank (54 ~ N) bis zum nSrdlichen Apennin (44 ~ N). In einem Tiefenschnitt entlang der Traverse wird die r~iumliche Verteilung der Erdbebenherde betrachtet. In der Zahl der Herde und ihrer Anordnung zeigen sich Unterschiede zwischen den verschiedenen Teilgebieten der Traverse (Niederrheinische Bucht, Oberrhein-Graben, Schwabische Alb, Alpen, Apennin). Beziiglich der Herdtiefe ist ein gemeinsarnes Merkrnal fast aller Gebiete, dab sich die Erdbebenherde auf die oberen 20--25 krn der Erdkruste beschr~inken. Die st~irkste seismische Aktivit~it ist im Tiefenbereich yon 2,--12 km festzustellen. Dieses Ergebnis ist ftir das Verhalten der einzelnen Krustenabschnitte bei rezenter Bruchtektonik yon Bedeutung. Lediglich irn Bereich der Doggerbank scheinen die Herde an der Basis der Erdkruste oder irn obersten Erdmantel zu liegen, was auf besondere seisrnotektonische Verh~iltnisse in diesern Gebiet hindeutet. Demgegeniiber zeigt die Herdtiefenverteilung irn Alpengebiet trotz abweichender Krustenstruktur keine Besonderheiten gegeniiber dem n6rdlichen und siidlichen Vorland. Vergleicht man den aus seisrnographischen Messungen abgeleiteten rezenten Spannungszustand von Erdbebengebiet zu Erdbebengebiet, so ergibt sich fiir die Alpen und das n6rdlich anschlieBende Gebiet bis zur Nordsee ein sehr einheitliches Bild fiir die Orientierung der horizontalen Hauptspannungen (gr6Bte Hauptspannung NW--SE, kleinste Hauptspannung SW--NE). Irn Apennin ist die Spannungsverteilung gerade umgekehrt. AbstractThe seismic activity has been studied along a profile reaching from the North Sea to the northern part of the Apennine mountains covering 1800 km in length. A cross section of the Earth's crust along the profile forms the basis for this study. There are differences in number and spatial distribution of the foci between the different structure units of the studied region as the Lower Rhine Basin, the Upper Rhinegraben, the Swabian Jura, the Alps and the Apennines. It is a common feature of all epicentral regions that nearly all earthquake loci are situated inside the upper crust. This result is important regarding the behavior of different parts of the Earth's crust under the conditions of recent fracture tectonics. It seems that only in the North Sea region the foci reach depths near the "Moho" indicating the special seisrnotectonic situation of this area. On the other hand there could not be found any remarkable differences in the distribution of focal depths between the Alps and their northern and southern forelands although the crustal structure is quite different. Comparing the recent stress distribution as deduced from seismograph records for the different focal regions there results a very uniform picture for the orientation of the principal stress directions. *) Anschriften der Verfasser: Dr. L. AHORNEa, Abteilung fiir Erdbebengeologie des Geologischen Instituts der Universit~it K61n, 506 Bensberg, Vinzenz-Pallott...
A comprehensive study of the seismic hazard related to the four NNP sites in NW switzerland was performed within the project PEGAsOs. to account for the epistemic uncertainties involved in the process of the characterization of seismic source zones in the frame of probabilistic seismic hazard assessments, four different expert teams have developed and defended their models in the frame of an intensive elicitation process.Here, the results of one out of four expert groups are presented. the model of this team is based first of all on considerations regarding the large scale tectonics in the context of the Alpine collision, and neotectonic constraints for defining seismic source zones. this leads to a large scale subdivision based on the structural 'architectural' considerations with little input from the present seismicity. Each of the eight large zones was characterized by the style of present-day faulting, fault orientation, and hypocentral depth distribution. A further subdivision of the larger zones is performed based on information provided by the seismicity patterns. 58 small source zones have been defined in this way, each of them characterized by the available tectonic constrains, as well as the pros and cons of different existing geologic views connected to them. Of special concern in this respect were the discussion regarding thin skinned vs. thick skinned tectonics, the tectonic origin of the 1356 basel earthquake, the role of the Permo-carboniferous graben structures, and finally the seismogenic orientation of faults with respect to the recent crustal stress field. the uncertainties connected to the delimitations of the small source zones have been handled in form of their regrouping, formalized by the logic tree technique.the maximum magnitudes were estimated as discretized probability distribution functions. After declustering the used EcOs earthquake catalogue and an analysis of data completeness as a function of time the parameters of the frequency-magnitude relations were derived within their uncertainties. Introductionthe sites of the four nuclear power plants (NPP) in NW switzerland have been subject to a comprehensive analysis of seismic hazard evaluated in the frame of the PEGAsOs project (Abrahamson et al. 2004; coppersmith et al., this volume). the definition of seismic source zones (ssZ) and the derivation of the parameters characterizing the seismic activity in each ssZ are integral parts of any probabilistic seismic hazard assessment. Here we present the results of one of the four expert groups (EG1b) responsible for the delineation of ssZ and determining the seismic activity parameters in the source zones.the study area was set up as the envelope of the radii of 300 km around all sites studied. this guarantees that the study area encompasses all seismic sources which have a seismic influence on the target sites. It extends well beyond the territory of switzerland, covering the southwestern parts of Germany, the western parts of Austria, the adjacent parts of northern Italy and n...
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