Evidences of Active Faulting in Thrace Region (Northeastern Greece)

Abstract

Active oblique to strike-slip faults were identified in southern Thrace (northeastern Greece), on the basis of field observations, geological mapping, analysis of geometrical and dynamic characteristics of recent tectonic structures as well as evaluation of their seismic potential. The seismic activity refers mainly to strong earthquakes occurring under the sea, while a minor number of seismic epicenters have been registered on land. According to the historic and recent data, most seismic destructions in this region are due to the influence of the North Anatolian Fault and North Aegean Trough system. The diachronic activity of several faults and the changes in the movement type from clearly normal to oblique-normal or strike-slip, have left clear signs on the existing polished fault planes. Among the numerous faults determined in Thrace, some of them can be characterized as active, according to their geological and morphotectonic characteristics. Taking in to account the faults length, the specific seismotectonic conditions prevailing over the Hellenic territory and the existed empirical relationships, the maximum displacement in case of seismic reactivation was estimated.

The Greek Database of Seismogenic Sources (GreDaSS): state-of-the-art for northern Greece

“…Extensional faulting has occurred since at least the Miocene, and the striations bear evidence of at least three tectonic phases [Lybéris 1984, Lybéris andSauvage 1985]. The trace has been well mapped by several researchers [Ly-béris 1984, Rondoyanni et al 2004. Based on the sea bottom seismic reflection profiles [Martin 1987], the structure probably continues offshore westwards, within the Gulf of Kavala.…”

“…The fault barriers between the segments are due to change in strike and dip, generating an overall zig-zag geometry. The dip appears to progressively decrease towards the west [Mountrakis and Tranos 2004, Mountrakis et al 2006, Rondoyanni et al 2004]. This probably implies that the maximum depth of the fault zone also progressively decreases westwards, if we assume that the dimensional proportion of the comprised segments remains constant and that the possible listric geometry of the fault plane, which is the usual occasion for the normal faults in the Aegean, should create shallower structures.…”

“…This probably implies that the maximum depth of the fault zone also progressively decreases westwards, if we assume that the dimensional proportion of the comprised segments remains constant and that the possible listric geometry of the fault plane, which is the usual occasion for the normal faults in the Aegean, should create shallower structures. The slip vectors measured on fault outcrops indicate a generally dip-slip normal kinematics, although oblique-slip displacements prevail locally [Lybéris 1984, Mountrakis et al 2006, Rondoyanni et al 2004]. The calculated slip-per-event for each fault segment ranges from 0.55 to 0.90 m. Taking into account the characteristics of the geometrical barriers, and assuming the possibility of a dynamic triggering model, the worst case scenario implies the contemporaneous rupture of more than one segment.…”

“…The 'softest' barrier (i.e. the easiest to break during an earthquake) is probably the one between the Xanthi and Iasmos segments, which some authors have already described as a unique struc- ture [Lybéris 1984, Rondoyanni et al 2004. Assuming 44 km of total length, the empirical relationship of magnitude versus rupture area [Wells and Coppersmith 1994] indicates a maximum expected magnitude of 7.0.…”

Trace element contents in uncultivated surface soils in the Kavala area, northern Greece

“…The main rock types in the area are: a) gneisses, schists and amphibolites (Permian-Eocene), b) marbles (Permian-Eocene), c) granitic and granodioritic rocks (Cretaceous-Oligocene), and d) sedimentary deposits (MioceneHolocene). The intense plutonism of the Rhodope is represented by granites, granodiorites, monzonites, quartz monzonites and diorites of Eocene, Oligocene, and Miocene age (Kilias and Mountrakis 1998, Christofides et al 2001, Rondoyanni et al 2004. Additionally, the PyriteBlende-Galena (PBG), Au, Cu, Μη, and Fe mineralizations and ore deposits are widespread in the study area (Maratos and Andronopoulos 1966, Filippidis et al 1996, Vavelidis et al 1996, 1997.…”