Neotectonic faulting, uplift and seismicity in the central and western Swiss Alps
Michaela Ustaszewski, O. Adrian Pfiffner, 2008. "Neotectonic faulting, uplift and seismicity in the central and western Swiss Alps", Tectonic Aspects of the Alpine-Dinaride-Carpathian System, S. Siegesmund, B. Fügenschuh, N. Froitzheim
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Our study aims to characterize the post-glacial neotectonic activity by finding surface expressions of recently active tectonic faults. The central and western Swiss Alps were chosen as the study area because surface uplift rates are very high, indicating ongoing uplift of the external basement massifs. Moreover, the Valais area coincides with enhanced seismic activity. Active faults were searched by mapping lineaments on aerial photographs and subsequent field studies. Three main types of faults could be distinguished: gravitational faults (i.e. faults related to mass movements); tectonic faults; and composite faults (i.e. tectonic faults with a component of gravitational and post-glacial rebound-related reactivation). A large number of tectonic faults were found (over 1700), but only two unequivocally post-glacially active tectonic faults could be distinguished. Indications for their post-glacial (re-)activation are displaced Quaternary landforms or sediments. Large gravitational faults, as well as composite faults often correlate with deep-seated gravitational slope deformations (DSGSD). The latter occur mainly along valley slopes, particularly where a pervasive foliation strikes parallel to the valley. Fault orientations show correlations either with the regional main foliation (e.g. Aar and Gotthard massif), the orientation of valleys (e.g. Bedretto and Urseren valley), or pre-existing tectonic structures (e.g. faults parallel to joints that are perpendicular to the strike of major structures in the Helvetic nappes). Comparisons of fault orientations with orientations of nodal planes of earthquake focal mechanisms of the last 20 years show a poor indicative correlation. The central and western Swiss Alps host a large number of faults prone for reactivation in today's stress field. However, for most of these faults, no indications of their last phase of activity exist. The low number of unambiguously active tectonic faults suggests that the current strain is either predominantly aseismic or, alternatively, cumulated seismic moment is too low for producing surface rupture.
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The Alps, Carpathians and Dinarides form a complex, highly curved and strongly coupled orogenic system. Motions of the European and Adriatic plates gave birth to a number of ‘oceans’ and microplates that led to several distinct stages of collision. Although the Alps serve as a classical example of collisional orogens, it becomes clearer that substantial questions on their evolution can only be answered in the Carpathians and Dinarides. Our understanding of the geodynamic evolution of the Alpine-Dinaride-Carpathian System has substantially improved and will continue to develop; this is thanks to collaboration between eastern and western Europe, but also due to the application of new methods and the launch of research initiatives. The largely field-based contributions investigate the following subjects: pre-Alpine heritage and Alpine reactivation; Mesozoic palaeogeography and Alpine subduction and collision processes; extrusion tectonics from the Eastern Alps to the Carpathians and the Pannonian Basin; orogen-parallel and orogen-perpendicular extension; record of orogeny in foreland basins; tectonometamorphic evolution; and relations between the Alps, Apennines and Corsica.