Normal faults associated with volcanic activity arc |
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| Authors: | B C Papazachos and D G Panagiotopoulos |
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| Institution: | Geophysical Laboratory, University of Thessaloniki, P.O.Box, 352-1, GR 54006, Thessaloniki, Greece |
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| Abstract: | Volcanic centers (volcanoes, fumaroles or solfatara fields), epicenters of strong shallow earthquakes (with focal depths up to 20 km) and epicenters of intermediate depth strong earthquakes (with focal depths between 120 and 160 km) in the southern Aegean volcanic arc can be grouped into five, well defined, linear clusters trending about N60°E. This lineation of shallow earthquakes and volcanic activity is attributed to five corresponding normal faults which are named after the five corresponding volcanic centers (Sousaki, Methana, Milos, Santorini and Nisyros). This is supported by a similar trend of the geomorphological features (grabens and islands) and of geophysical features (Bouguer anomalies), as well as by other seismological data (fault plane solutions and the origins of tsunamis) and geological information on the Santorini caldera. The greater volcanic activity in the eastern volcanic centers (Santorini and Nysiros) compared to the western volcanic centers (Sousaki, Methana and Milos) is attributed to the higher rate of extensional crustal deformation. In the eastern part of the volcanic arc it is 26 mm/yr: in the west it is 2 mm/yr. The delineation of the epicenters of the intermediate depth earthquakes along the same five lines indicates the existence of five corresponding rupture zones in the lower (leading) part of the descending lithospheric slab (at depths of 120–180 km). These deep zones are probably the sources of hot material which is ascending vertically upwards and intrudes into the crust along its fracture zones. The orientation of these zones explains the focusing of the macro-seismic results of these deep shocks at narrow regions of the sedimentary arc (Peloponnesus, Crete, etc). |
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