Markos D. Tranos

Thessaloniki–Gerakarou Fault Zone (TGFZ): the western extension of the 1978 Thessaloniki earthquake fault (Northern Greece) and seismic hazard assessment

Abstract Active faulting and seismic properties are re-investigated in the eastern precinct of the city of Thessaloniki (Northern Greece), which was seriously affected by two large earthquakes during the 20th century and severe damage was done by the 1759 event. It is suggested that the earthquake fault associated with the occurrence of the latest destructive 1978 Thessaloniki earthquake continues westwards to the 20-km-long Thessaloniki–Gerakarou Fault Zone (TGFZ), which extends from the Gerakarou village to the city of Thessaloniki. This fault zone exhibits a constant dip to the N and is characterised by a complicated geometry comprised of inherited 100°-trending faults that form multi-level branching (tree-like fault geometry) along with NNE- to NE-trending faults. The TGFZ is compatible with the contemporary regional N–S extensional stress field that tends to modify the pre-existing NW–SE tectonic fabric prevailing in the mountainous region of Thessaloniki. Both the 1978 earthquake fault and TGFZ belong to a ca. 65-km-long E–W-trending rupture fault system that runs through the southern part of the Mygdonia graben from the Strymonikos gulf to Thessaloniki. This fault system, here called Thessaloniki–Rentina Fault System (TRFS), consists of two 17–20-km-long left-stepping 100°-trending main fault strands that form underlapping steps bridged by 8–10-km-long ENE–WSW faults. The occurrence of large (M≧6.0) historical earthquakes (in 620, 677 and 700 A.D.) demonstrates repeated activation, and therefore the possible reactivation of the westernmost segment, the TGFZ, could be a major threat to the city of Thessaloniki. Changes in the Coulomb failure function (ΔCFF) due to the occurrence of the 1978 earthquake calculated out in this paper indicate that the TGFZ has been brought closer to failure, a convincing argument for future seismic hazard along the TGFZ.

Structural characteristics of two strong earthquakes in the North Aegean: ierissos (1932) and Agios Efstratios (1968)

Abstract Structural analysis has been carried out on the volcanics of the island of Agios Efstratios and along the highly faulted zone of SE Chalkidiki, south and north of the North Aegean Trough, respectively (northern Greece). The areas have been affected by strong earthquakes and a comparison is made between the available structural and seismological data, together with new seismotectonic information. At Agios Efstratios, the earthquake of 1968 (M7.1) occurred on a principal displacement zone with dextral strike-slip movement, while the fault geometry of the whole area supports the view of transtensional deformation. The strong (M7.0) earthquake of 1932 at Ierissos was directly connected with an E—W-trending normal fault. Striations on the seismic fault surfaces and the corresponding fault mechanism indicate a N-S direction of active extension. The hangingwall is also affected by smaller antithetic E-W- and NW-SE-trending structures.

Neotectonic and seismological data concerning major active faults, and the stress regimes of Northern Greece

Abstract 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 M ≥ 6.0 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.

Transtensional origin of the NE–SW Simitli basin along the Strouma (Strymon) Lineament, SW Bulgaria

Several depocentres have developed along the NNW–SSE-striking Strouma (Strymon) Lineament since the Miocene, forming the Strouma/Strymon graben system. Some of these basins, including the Dzherman and Simitli, strike at high angles to the lineament. The rhomboid-shaped Simitli basin is limited in the south by the NE–SW-striking, seismically active Kroupnik fault and contains terrestrial clastic sediments, which have been deposited since the Sarmatian. Its formation is attributed to ‘wrench-dominated transtension’ (DB event) which activated the basins NE–SW-striking boundary faults as left-lateral strike-slip structures during the Early–Middle Miocene. This deformation was associated with NNE–SSW contraction and WNW–ESE extension and succeeded the NNE–SSW contraction caused by ‘pure shear-dominated transpression’ (DA event), which governed the region in Late Oligocene–Early Miocene times. During the Middle–Late Miocene, the DB event was followed by WNW–ESE ‘pure shear-dominated extension’ (D1 event), which caused further widening of the basin. The transtensional origin of the Simitli basin is explained by lateral extrusion of the crustal mass squeezed between the Apulian–Adriatic microplate and the European foreland towards the North Aegean Sea. The subduction retreat of the Hellenic orogen possibly enhanced this lateral extrusion, and from the Late Miocene onwards the NE–SW-oriented back-arc extension balanced the continuing retreat.

Geometry and kinematics of deformation in the Albanian orogenic belt during the Tertiary

Abstract Geological survey and structural analysis across the Central and Northern Albanides allows us to establish the kinematic and strain history of the Albanian orogenic belt from the time of the Tertiary continental collision between the Apulian and European plates. Four main deformation events are distinguished: D1 occurred during the Eocene–Oligocene, causing SW vergent imbrication of the External Albanides associated with NE-ward back thrusting. During D1 compression, the Korabi zone of the Internal Albanides together with the overlying Mirdita ophiolites, overthrust onto the External Albanides. Crustal thickening accompanied D1 deformation. D2 took place during the Oligocene–Miocene and was related to crustal thinning and extensional exhumation of the footwall External Albanides, while plate convergence continued and compression migrated SW-ward to the more external parts of the Albanides. During D2 extension, Mirdita ophiolites detached downwards to SW, covering parts of the External Albanides. A younger D3 NE-SW shortening followed during the Middle–Late Miocene. Finally, high angle D4 normal faults strongly modified from the Miocene onwards the pre-existing deformation geometry of the Albanides. The Tertiary kinematic evolution of the Albanides is in good agreement with the Tertiary kinematics history of the Hellenides, revealing that the same geodynamic processes affected both regions during the Tertiary.

The recent crustal deformation of the Hellenic orogen in Central Greece; the Kremasta and Sperchios Fault Systems and their relationship with the adjacent large structural features [Die rezente Krustendeformation des Hellenischen Orogens im zentralen Griechenland; die Kremasta- und Sperchios- Störungssysteme und ihre Verhältnisse zu den benachbarten großen Bruchstrukturen.]

Kilias, A.A., Tranos, M.D., Papadimitriou, E.E. & Karakostas, V.G. (2008): The recent crustal deformation of the Hellenic orogen in Central Greece; the Kremasta and Sperchios Fault Systems and their relationship with the adjacent large structural features. (Die rezente Krustendeformation des Hellenischen Orogens im zentralen Griechenland; die Kremasta- und Sper- chios-Storungssysteme und ihre Verhaltnisse zu den benachbarten grosen Bruchstrukturen.) - Z. dt. Ges. Geowiss., 159: 533-547, Stuttgart. Abstract: The 70 km long WNW-ESE trending Kremasta and Sperchios Fault Systems cutting at high angle the Pindos Mountain range in Central Greece have been defi ned and mapped in detail. The geometry and kinematics of both fault sys- tems including normal faults that have been reactivated since Quaternary defi ne a contemporary N-S extensional stress re- gime. In more regional scale, both the Kremasta and Sperchios Fault Systems represent an underlapping extensional zone between the Cephalonia Transform Fault and the North Anatolia Fault and form with the Corinth Gulf Fault System in Cen- tral Greece antithetic domino-type trailing faults in respect to the SSW-wards motion of the Aegean block. Kurzfassung: Es wurden die 70 km langen WNW-ESE streichenden Kremasta- und Sperchios-Storungssysteme, die schrag mit einem hohen Winkel das Pindos-Gebirge im zentralen Griechenland schneiden, ausfuhrlich untersucht und kartiert. Die Geometrie und Kinematik beider Storungssysteme, die aus wahrend des Quartars reaktivierten Abschiebungen bestehen, defi nieren ein modernes N-S streichendes Extensions-Spannungsregime. Im regionalen Masstab sind die Kremasta- und Sperchios-Storungssysteme als eine Extensions-Verbindungsbruchzone zwischen den Kephalonia- und nordanatolischen grosen dextralen Blattverschiebungen anzusehen. Die Kremasta- und Sperchios-Storungssysteme bilden zusammen mit dem Abschiebungssystem des Golfs von Korinth ein antithetisches Dominotyp-Storungssystem im Zusammenhang mit der nach SSW gerichteten Bewegung des Agaischen Blocks ab.

GEOMETRY, KINEMATICS AND MORPHOTECTONICS OF THE YANQING-HUAILAI ACTIVE FAULTS (NORTHERN CHINA)

Field studies along the Huailai and Yanqing mutually parallel neotectonic fault zones lead to a description of morphotectonics and palaeoseismicity, as well as the geometry and segmentation of these structures. The study emphasizes the kinematics of the region. The faults belong to the tectonic interaction between the Shanxi rift system and the North China fault system. Although the general strike of the zones is NE–SW, the Yanqing fault is divided into five segments of NNE–SSW, ENE–WSW and E–W trends, and the Huailai fault into three segments of ENE–WSW and E–W trends. They are mainly pure dip-slip normal faults, while less often they show oblique-slip components. The mesostructural quantitative palaeostress analyses (local neotectonic–active stress pattern) indicate a regional NNW–SSE-oriented extension (σ3), locally deviated to N–S, NW–SE, WNW–ESE, depending on the fault segment strike. The great deviation of fault strikes from the mean and their relation with the basement joint and thrust systems lead to the hypothesis that the neotectonic faults, which have a capacity for strong earthquakes, follow pre-existing inherited structures.

Major active faults of SW Bulgaria: implications of their geometry, kinematics and the regional active stress regime

Abstract Southwest Bulgaria is an intracontinental region between the Dinaro-Hellenic and Balkan mountain ranges that has experienced infrequent, but strong and destructive earthquakes. The general geometric and kinematic characteristics of the major faults, mainly the active ones, are investigated, as the seismic activity is insufficient to describe thoroughly the active crustal deformation associated with the faulting. The results suggest a major rupture zone with a length of more than 50 km. The east-west-striking Kochani-Kroupnik-Bansko ‘rupture zone’ was potentially associated with the large 1904 Kroupnik earthquakes, and has been found to transect the region joining the Kochani, Kroupnik and Bansko faults. In addition, a long-term slip rate ranging from 0.14 to 0.7 mm a−1 has been estimated for some large faults in the region using morphotectonic features. The most active faults are normal ones striking WNW-ESE to ENE-WSW, whereas the NNW-SSE- to NW-SE-striking faults tended to act as barriers to the growth of the former faults, as they do not exhibit much indication of recent reactivation. The stress regime determined is extensional with the least principal stress axis (σ3) subhorizontal and oriented north-south. The fact that the active faults show geometric and kinematic characteristics, as well as estimated long-term slip rates, similar to those of the active faults of central and eastern Macedonia and Thrace (Northern Greece) suggests that both of these regions share a single contemporary stress field.

Slip preference analysis of faulting driven by strike-slip Andersonian stress regimes: an alternative explanation of the Rhodope metamorphic core complex (northern Greece)

Slip preference analysis (SPA) is accomplished by examining fault activation driven by different Andersonian strike-slip stress regimes. Strike-slip regimes favour the activation of strike-slip faults striking as high as 45° from the trend of the σ1 axis, thus favouring the predominance of R shears over P shears in a strike-slip shear zone. Reverse and normal faults cannot be activated simultaneously by a common strike-slip stress regime, and their activations depend on the stress ratio. The SPA provides new constraints on stress inversion methods that take into account only the misfit angle minimization criteria. Insights from the SPA give rise to an alternative explanation of the origin of the Tertiary Rhodope metamorphic core complex exposed in the inner part of the Hellenic orogen, which attributes the activation of the associated extensional shear zones and detachments to an Andersonian, transpression–strike-slip (TRP–SS) to strike-slip (SS) stress regime, and not to an extensional one as widely assumed. The variation from TRP–SS to SS is critical for the activation of the extensional structures and is attributed to the local and at-depth increase of the vertical crustal stresses owing to the ascent and emplacement of large plutonic bodies.

Geology of Ammouliani Island (Northern Greece) – implications for the tectono-magmatic evolution of the Serbo-Macedonian Massif

Ammouliani Island is located in Northern Greece with its exposed rocks belonging to the Serbo-Macedonian Massif of the Hellenic hinterland. Its geology is of great importance because it lies in an area where a striking change in trend of the orogenic fabric from NW-SE to ENE-WSW occurs. For this purpose, a geological map at a scale of 1:10,000 is presented based upon detailed fieldwork and the interpretation of satellite imagery. In addition, special interest has been paid to the tectonic elements of the map units. This detailed mapping results in the definition of a new unit, the Ammouliani Unit, which is placed between the underlying Kerdilion and the overlying Vertiskos Unit of the Serbo-Macedonian Massif. The main features of the Ammouliani Unit are the predominance of leucosomes and the intense migmatization and strong shearing. Three main folding events (F1, F2 and F3) have been defined in the exposed rocks of the island with the first related to intense migmatization and shearing, whereas the last two are progressive to each other and are related to Mesozoic orogenic processes. In addition, NE-ENE striking shear zones were observed with the Ammouliani granite placed parallel to these. The bending of the orogenic fabric from NW-SE to ENE-WSW is younger than the F2 and F3 folding events and is related to Tertiary orogenic (tectono-magmatic) processes due to the convergence between Apulia and Eurasia and the ongoing retreat of the Hellenic subduction zone.