Large seismic faults in the Hellenic arc

Abstract

Using information concerning reliable fault plane solutions, spatial distribution of strong earthquakes (Ms³ 6.0) as well as sea bottom and coastal topography, properties of the seismic faults (orientation, dimension, type of faulting) were determined in seven shallow (h < 40 km) seismogenic regions along the convex part of thc Hellenic arc (Hellenic trench) and in four seismogenic regions of intermediate depth earthquakes (h = 40-100 km) along the concave part of this arc. Except for the northwesternmost part of the Hellenic trench, where the strike-slip Cephalonia transform fault dominates, all other faults along this trench are low angle thrust faults. III thc western part of the trench (Zante-west Crete) faults strike NW-SE and dip NE, while in its eastern part (east Crete-Rhodos) faults strike WNW-ESE and dip NNE. Such system of faulting can be attributed to an overthrust of the Aegean lithosphere on the eastern Mediterranean lithosphere. The longest of these faults (L = 300 km) is that which produced the largest known shallow earthquake in the Mediterranean area (21 July 365, Ms = 8.3) which is located near the southwestern coast of Crete. The second longest such fault (L = l 70 km) is that which produced a large earthquake (December 1303, Ms = 8.0) in the easternmost part of the trench (east of Rhodos island). Both earthquakes were associated with gigantic tsunamis which caused extensive damage in the coast of many Eastern Mediterranean countries. Seismic faults of the intermediate depth earthquakes in the shallow part of the Benioff zone (h = 40- 100 km) are of strike-slip type, with a thrust component. The orientations of these faults vary along the concave part of the arc in accordance with a subduction of remnants of all old lithospheric slab from the convex side (Mediterranean) to the concave side (Aegean) of thc Hellenic arc. The longest of these faults (L = 220 km) is that which produced the largest known intermediate depth earthquake in the whole Mediterranean area (12 October 1856, M = 8.2) north of Crete. The second longest such fault (L = 160 km) produced a large earthquake (26 June 1926, M = 8.0) in the easternmost part of the concave part of the arc (near Rhodos). Both earthquakes caused very serious damage in several Eastern Mediterranean countries but were not associated with tsunamis.