FAULTING DEFORMATION OF THE MESOHELLENIC TROUGH IN THE KASTORIA-NESTORION REGION (WESTERN MACEDONIA, GREECE) (original) (raw)
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Geological Society, London, Special Publications, 2006
Northern Greece is an intracontinental region behind the Hellenic subduction zone, with widespread seismic activity (ranging from low to high), with strong destructive earthquakes of Mg6.0 in historical to recent times. Geological and seismological data indicate that recent seismic activity is mainly localized along large, inherited, fault zones, which have transected Northern Greece since Oligocene-Miocene times. The main active fault zones in Thrace, and Eastern and Central Macedonia strike approximately east-west, with lengths of 40-120 km. Fault segments strike WNW-ESE to ENE-WSW and range from 10 to 30 km in length. In Western Macedonia the main active fault zones strike NE-SW to ENE-WSW with lengths of 40-60 km and consist of 10-30 km segments. The region's strong earthquakes are usually associated with reactivation of these fault segments and are estimated at M=5.6-6.5. Focal mechanisms and fault-slip data from the fault zones indicate a change in the trend of extension axes from NNE-SSW in Eastern Macedonia-Thrace to NNW-SSE in Western Macedonia. Thus, neotectonic and seismological data suggest that variations in fault patterns, as determined from the large inherited fault zones transecting Northern Greece, are the major factor governing this change in the trend of maximum extension. This interpretation is consistent with the long-lived arcuate shape of the Hellenic subduction zone.
The 13 May J995 (M. ,., 6.6) earthquake occurred in a l'ery /uw seismicity area in northern Greece. The area ;s dominated by many fault! (mainly NE -SW trending) that were activated during Quaternary. The most impressive and typical fault Is the Aliabnon river (or Servia) ENE trending structure. The length of the typical seismic fault traces observed is J0 /0 15 km (N 6ff -7(f) between Polaeochori • Sarakina -Nisi. while the total length ofthe main normalfault activated during the earthquake is believed to be about 30 Icm from its ENE edge (Rymnio village). 'Tht! seismogenic area was affected by many other reactivated antithetic or synthetic. parallel, sub-parallel and obliq~faults. landslides and rock falls, not necessarily of tectonic origin. The most characteristic are the northern anlithetlc lilU! of Chromion and the SSW dipping Felli branch at the WSWedge of the main seismic fault It co~ers an area at least 50 km long and 30 /cm with. Surface traces follow pre-existlng structures, showing an imbricate-like fan geometry.
Seismic fault geometry and kinematics of the 13 May 1995 western Macedonia (Greece) earthquake
During the devastating earthquake of 13 May 1995, in the Kozani-Grevena area (Western Macedonia, Greece), many surface ruptures formed in the epicentral area. Most of these fractures were due to faulting, but some were secondary ground ruptures and landslides. Geological field work in the area has shown that the Aliakmon river neotectonic fault consists of several (three or more) fault strands: the Servia, the Rymnio and the Paleochori-Sarakina strands. Using geological criteria, all of these fault strands were judged to be active faults affecting recent (Holocene) deposits and scree. The main new surface fractures caused by the earthquake, and particularly those clearly of tectonic origin, follow systematically the traces of the last two neotectonic fault strands, forming a new fracture line. This tectonic line, trending ENE-WSW (N70°), coincides with the focal mechanism solution and the satellite image major lineament. Both the geological and instrumental seismological data sugges...
In the present work a detailed seismotectonic study of the broader area of the Mygdonia basin (N. Greece) is performed. Digital data for earthquakes which occurred in the broader Mygdonia basin and were recorded by the permanent telemetric network of the Geophysical Laboratory of the Aristotle University of Thessaloniki during the period 1989-1999 were collected and fault plane solutions for 50 earthquakes which occurred in the study area were calculated with a modified first motions approach which incorporates amplitude and radiation pattern information. Fault plane solutions for the 3 main shocks of Volvi (23/05/78, M W = 5.8 and 20/06/78, M W = 6.5) and Arnaia (04/05/95, M W = 5.8) events and the 1978 aftershock sequence were additionally used. Moreover, data from two local networks established in the Mygdonia basin were also incorporated in the final dataset.
Deformation and stress regimes in the Hellenic subduction zone from focal Mechanisms
Journal of Seismology, 2005
Fault plane solutions for earthquakes in the central Hellenic arc are analysed to determine the deformation and stress regimes in the Hellenic subduction zone in the vicinity of Crete. Fault mechanisms for earthquakes recorded by various networks or contained in global catalogues are collected. In addition, 34 fault plane solutions are determined for events recorded by our own local temporary network on central Crete in 2000-2001. The entire data set of 264 source mechanisms is examined for types of faulting and spatial clustering of mechanisms. Eight regions with significantly varying characteristic types of faulting are identified of which the upper (Aegean) plate includes four. Three regions contain interplate seismicity along the Hellenic arc from west to east and all events below are identified to occur within the subducting African lithosphere. We perform stress tensor inversion to each of the subsets in order to determine the stress field. Results indicate a uniform N-NNE direction of relative plate motion between the Ionian Sea and Rhodes resulting in orthogonal convergence in the western forearc and oblique (40-50°) subduction in the eastern forearc. There, the plate boundary migrates towards the SE resulting in left-lateral strike-slip faulting that extends to onshore Eastern Crete. N110°E trending normal faulting in the Aegean plate at this part is in accordance with this model. Along-arc extension is observed on Western Crete. Fault plane solutions for earthquakes within the dipping African lithosphere indicate that slab pull is the dominant force within the subduction process and interpreted to be responsible for the roll-back of the Hellenic subduction zone.
The strain pattern in the western Hellenic arc deduced from a microearthquake survey
Geophysical Journal International, 1990
More than loo0 earthquakes recorded during 7 weeks in 1986 in the Peloponnese and surrounding areas show shallow seismicity spread over a wide area bounded by the Hellenic trench. The highest level in the energy release is for clusters located along the Hellenic trench, where changes in the morphology are seen. A few clusters are also observed, as at the intersection between the Gulf of Corinth and the Gulf of Patras, near the Lake Trikhonis, or between Kythira and Crete. In the Peloponnese, the shallow earthquakes do not define single faults, but are diffusely distributed. A higher concentration and a deepening of the foci (within the whole crust) towards the west seem to reflect a higher strain rate there. Fault plane solutions exhibit a scattered pattern for earthquakes shallower than 11 km, but for earthquakes deeper than 11 km, they show some consistency in the orientation of P-, T-, and B-axes. Gently dipping nodal planes are seen all over the Peloponnese, with the conjugate vertical plane striking in various directions, and with no consistency in the sense of motion. These earthquakes are located between 8 and 18 km deep and could reflect a decoupling between the lower and the upper crust. Reverse faulting is seen in the Gulf of Kefallinia and the western Peloponnese. The P-axes trend NE-SW to E-W. Normal faulting is seen in the Gulf of Corinth and in central Peloponnese with the T-axes trending N-S, and in the southern Peloponnese, where the T-axes trend NW-SE. The deformation over the western Hellenic arc, revealed by fault plane solutions of earthquakes with depth between 11 and 40 km, appears to be the superposition of two phenomena. First, throughout the Aegean, crustal extension with orientation roughly parallel to the trench dominates, with crustal shortening and subduction along the Aegean arc. Superimposed on this is a more local effect of the collision between the Aegea and Apulia which seems to induce horizontal compression roughly perpendicular to the Aegean arc west of the Peloponnese and Epirus. The compression due to this decays eastward, at a distance comparable with the width of the collision zone. The deepening of the brittleductile transition is likely to be due to an increase of the strain field towards the Ionian islands. AJ McK AJ McK AJ McK AJ AJ J J J AJ AJ LC FEgpre l 2 . Map of the style of deformation observed in the western Hellenic arc. Compression is seen from the trench to western Peloponnese. Fault plane solutions are taken from the literature and referenced in . The transition between compression and extension is sharp, and in some place we observe strike-slip mechanisms within the extensive stress field. The three shaded areas are the three dense clusters of seismicity. The transition between compression and extension occurs where the Hellenic trench is less defined.
International Geology Review, 2010
The Movri Mountain earthquake (Mw 6.4), western Greece, was likely caused by dextral‐slip along a blind high‐angle fault, and generated a complex pattern of co‐seismic surface ruptures southwest of the Gulf of Corinth. The mapped Nisi, Michoi, and Vithoulkas rupture segments have similar lengths (5–6 km) and vertical offset on the order of 25, 10, and 5 cm, respectively. They are commonly expressed as straight or jagged linear traces with secondary cracks radiating from the main segments. Horizontal slip vector analysis indicates extensional faulting processes for all rupture segments. Although these faults exert some control on the fluvial drainage pattern and at least one of them was ruptured during past events, their escarpments are poorly preserved. The indistinct topographic expression of the studied faults and their complex rupture patterns can be attributed to the distribution of the deformation over a blind fault.