GEOLOGICA BALCANICA, 38. 1—3, Sofia, Dec. 2009, p. 23—33.

Morphotectonic characteristics of Lefkas Island during the Quaternary (Ionian Sea, )

George D. Bathrellos1, Varvara E. Antoniou2, Hariklia D. Skilodimou1

1 Department of Geography & Climatology, Faculty of Geology & Geoenvironment, National & Kapodistrian University of Athens, University Campus (Panepistimiopolis), Zografou, ZC 15784, Athens, Greece; e-mails: [email protected]; [email protected] 2 Department of Dynamic-Tectonic-Applied Geology, Faculty of Geology & Geoenvironment, National & Kapodistrian University of Athens, University Campus (Panepistimiopolis), Zografou, ZC 15784, Athens, Greece; e-mail: [email protected] (Submitted: 13.03.2008; accepted in revised form: 13.05.2009)

Abstract. This paper focuses on the study of the Quaternary morphotectonic evolution of the Lefkas Island using morphological and tectonic data. Based on our mainly morphological stud- ies, two principal tectonic structures have been distinguished: (i) the Nydri-Vasiliki Fault Zone (NVF) and (ii) the Ionian Zone overthrust onto the Paxos Zone, which both divide the island into three morphotectonic units of Karya (KMTU), Maradochori (MMTU) and Athani (AMTU). Paleogeographically, it has been suggested that the broader Lefkas area was dominated by a NE—SW to ENE—WSW compressional regime since the early Pliocene that continuous in our days, resulting in the uplift of the southwestern part of the island and the submergence of the northeastern part of the island. This deformation is characterized by principal fault structures of a N110°—130° strike. These structures, combined with a fault system of N40°—60° strike repre- senting an older Miocene fault zone, control the main morphological characteristics such as watersheds and streams and are responsible for the KMTU formation producing a northeast- ward plunging monoclinal en-echelon structure. During the Early Pleistocene, a shift of the compressional regime towards the east was re- sponsible for the formation of a N70°—90° strike fault system. These faults had a morphotectonic effect throughout the island, controlling the watersheds and stream evolution. The continuous compressional regime recorded in our days results in the formation of fault structures, striking N20°—40° and N170°—190° that bound almost exclusively the coastal area of the island.

Bathrellos, G. D., Antoniou, V. E., Skilodimou, H. D. 2009. Morphotectonic character- istics of Lefkas Island during the Quaternary (Ionian Sea, Greece). Geologica Balcanica 38(1—3), 23—33. Key words: surface analysis, drainage network, hydrological basins, morphotectonic units, Lefkas Island, Greece.

INTRODUCTION est elevation of 1158 m) with small intramountain- ous valleys and coastal basins. Its coastline has a to- The island of Lefkas is one of the seven Ionian Sea tal length of approximately 116.7 km and is steep in islands, the nearest one to the western coast of main- general. The western coasts present linear develop- land Greece, from which is separated by a narrow ment while the eastern, northern and southern coasts artificial straight, in the area of an extended shallow form many small elongated bays. lagoon (Fig. 1). The island has an elongated shape The island of Lefkas presents significant geolog- with principal development axis of N360° strike and ical for several reasons. First, to the west of the is- covers an area of approximately 300 km2. land, in the area of the Ionian Sea, the Hellenic The greater part of Lefkas Island can be charac- Trench (Fig. 1a) is bounded by the subduction of the terized as mountainous to semi-mountainous (high- Eastern Mediterranean lithosphere under the Aegean

23 Fig. 1a. Map of Greece showing the study area in the western margin of the Hellenic trench (from Mountrakis et al., 1986; Flotte et al., 2005 ) Le I = Lefkas Island, Am G = Amvrakikos Gulf, Sp = Sperchios. Fig. 1b. Map of western Greece showing the extension of the main geological zones of Hellenides (based on Sotiropoulos et al., 2003; Kamberis et al., 2005) and the location of the study area. lithosphere (Middle East, Eurasian lithospheric plate Fault distribution, linear morphological features such margin; McKenzie, 1972; Mountrakis et al., 1986; as the coastline, the watersheds and the streams of the Underhill, 1989; Le Pichon et al., 1995; Papazachos island have been analyzed and their statistical process- and Kiratzi, 1996; Sotiropoulos et al., 2003; Flotte et al., 2005; Kamberis et al., 2005; Kokinou et al., 2005). Second, the dominant geological formations of the southwestern part of the island are attributed to the most external geotectonic zone of the Hellenides Mountain belts, known as the Paxos Zone (Renz, 1940) or Pre-Apulian Zone (Aubouin, 1959) (Fig. 1 b). Third, in a great area of the island, mainly along its western coasts intense seismic activity has been recorded with numerous submarine active seismic epicenters, (Fig. 2, time period 1469—2003) that have generated earthquakes of small to medium focal depth (<40 km) with magnitude of >5R (Seismotec- tonic map of Greece, 1989; Kassaras et al., 1993; Hatzfeld et al., 1995; Papazachos and Papazachou, 1997; Louvari et al., 1999; Kokinou et al., 2006; Pa- padimitriou et al., 2006). Forth, the morphology of the island during the Qua- ternary presents interest mainly due to its alpine struc- ture and to its post-alpine active tectonics controlled directly from the Hellenic trench area processes char- acterizing it as an evolving morphotectonic structure. This paper focuses on the study of the morphotec- Fig 2. Seismic epicenter map (based on Kassaras et al., 1993; tonic evolution of the island during the Quaternary. Papadimitriou et al., 2006)

24 ing and correlation has been carried out in order to 1. Base maps from H.A.G.S. in 1:50000 scale, investigate the effect of the tectonic structures on them. “LEFKAS” sheet (1971) and “Ag. Petros” sheet (1971) The systematic correlation of the morphological from which the following elements were used: (a) the features with the tectonic elements determines indi- 20 m spacing contour lines, (b) the hydrographic rectly the effect of the tectonic activity on the devel- network and (c) the island coastline. opment of important morphological features in the 2. The geological map “LEFKAS” sheet (1963) in area, providing important information for its mor- 1:50000 scale, modified for the aims of the paper. photectonic evolution (Devi and Singh, 2006). 3. H.A.G.S. aerial photographs (scale 1:33000, The aim of this paper is to present principal mor- 1987) and Landsat satellite image 7 ETM+ (path/ phological features indicating diachronic shifts that row: 185/033, Date: 22-08-2000, Cloud=0% (cloud can be related or attributed to active tectonic struc- free), 7 multiphasmatic (analysis of 28 m) + 1 pan- tures as detected in Lefkas Island due to its proxim- chromatic (analysis of 15 m), mainly used to obtain ity to the Hellenic Arc. lineaments and to determine morphological charac- teristics that could not be identified on the base maps. 4. Field work focused on the certification of the DATA AND METHODOLOGY primary morphotectonic structures. The geographical data processing, the correlations We used the following sources for data collection and the construction of a digital elevation model and analysis and processing purposes of our study (DEM), followed by the production of a morpholog- in order to determine the morphotectonic structure ical gradients map are carried out with the use of of Lefkas Island during the Quaternary: Arc/GIS 9.0, while the processing of the satellite im-

Fig. 3. Geological map of Lefkas Island (modified from Bornovas, 1963, 1964)

4 Geologica Balcanica, 1—3/2009 25 age and the tectonic features is carried out with the tic sediments (pebbles, sands, marls, clays, etc). The use of ILVIS 3.3 Academic. thickness of these deposits varies from a few to sever- The data are recorded and processed based on al tenths of meters that in places exceeds 100 m. their linear characteristics and, more specifically, The orogenic Alpine phase was expressed on the based on their strike and length. For the investiga- Ionian Zone towards the end of the Oligocene and tion of the principal strikes of the linear elements resulted in intense tectonism of its formations with the calculation method of frequency is used and for folds and thrusts following a general direction of the investigation of their intensity the density meth- N350°—10°. According to Mercier et al. (1987), this od is used. The calculation method results are ex- phase was completed during the early Pliocene in the pressed with frequency and density rose diagrams most external region of the Hellenides mountain belts for every linear feature using Rockware/2004 Revi- with a NE compressional strain field (N40°—50°) sion 4.7.9. direction causing the overthrusting of the Ionian Finally, the principal trends of the linear features Zone on the Paxos Zone. are classified and characterized and the effect of the fault distribution on the morphological features is evaluated. RESULTS Tectonics GEOLOGY The Paxos Zone formations on the island are folded, Regarding the geological structure of the island, with inclined folds of a N20°—40° axial plane strike Alpine and post-Alpine formations and deposits are and 50° axial plane dip. The Ionian Zone forma- involved (Fig. 3). The Alpine formations include the tions are intensely folded, in closed inclined folds of Paxos Zone formations and the overthrusted forma- a N350°—20° axial plane strike and a 30°—50° axial tions of the Ionian Zone. plane dip. Also, they present a strong brittle defor- The Paxos Zone formations are located on the mation with the presence of many internal thrusts of southwestern part of Lefkas Island and are composed a N350°—10° strike and 40°—60° dip (Fig. 4). of a continuous sequence of Late Jurassic to Oli- The Ionian Zone overthrusts the Paxos Zone. The gocene carbonate rocks grading towards the upper thrust plane has a N330° strike and 40°—50° dip. At members to a Miocene sequence of siliceous lime- the base of this overthrust, intense tectonism was iden- stone (Bornovas, 1964; Stamatakis and Hein, 1993). tified with the presence of extensive slump structures. The Ionian Zone formations (Philippson, 1898; The Lefkas Island formations are faulted, mostly Nopcsa, 1921; Renz, 1940; Aubouin, 1959; Borno- from the neotectonic brittle deformation. The main vas, 1964; Dercourt et al., 1980) dominate the island faults or fault zones classification and prioritization and are composed of a series of Late Triassic — Late regarding frequency, density and type (Fig. 4) are Eocene carbonate formations grading into flysch presented in Table 1. The dip of the fault planes, formations (Late Eocene — Oligocene). The lower according to field work measurements, has a mean stratigraphic members of the carbonate series of the value of 60°. Ionian zone are composed of Triassic evaporites. Based on the distribution and evaluation of the The post-Alpine formations include Upper Mi- fault structures, the most important is that of Nydri- ocene molassic type formations and Quaternary de- Vassiliki Fault (NVF). It has a N40°—60° strike and posits. The Upper Miocene formations unconform- is characterized according to field work data as a ably overlie the Ionian Zone formations and are com- strike-slip fault. posed of conglomerates, sandstones, marls, marly lime- This dominant tectonic features along with the stones and breccia-conglomerates. The total thick- thrust structure, divide the island into three morpho- ness of these formations is approximately 500 m. The tectonic units: (a) the central-northern unit, (b) the Quaternary deposits are located on the mountainous southeastern unit and (c) the southwestern unit. For — semi-mountainous basins and on the coastal area the needs of this research the morphotectonic units mostly at the eastern coastal zone. These deposits are named from main villages which are located in include mainly fluvial and coastal deposits of clas- each unit. More specifically, the central-northern unit

Table 1 Frequency, density and character of the main fault systems in Lefkas Island

Principal Fault Classification Outcrop areas Character Strikes Frequency Density N20°–40° Medium Medium Coastal zone, Athani, Karya Oblique – normal N40°–60° Medium Medium Karya, Maradochori Strike slip N70°–90° Medium Major Coastal zone, Athani,,Maradochori Oblique strike slip N110°–130° Medium Major Karya Oblique – normal Coastal zone, Athani (primary), N170°–190° Major Medium Oblique – normal Maradochori, Karya

26 Fig. 4. Tectonic map of Lefkas Island with the rose diagram of faults as linear features (a: frequency, b: density) is named as Karya morphotectonic unit (KMTU), and locally tectonic mélange in the Miocene forma- the southeastern unit as Maradochori morphotec- tions. In several locations, these faults are intersect- tonic unit (MMTU) and the southwestern one as ed by the other fault systems. Based on the statistical Athani morphotectonic unit (AMTU). analysis, they are classified as medium distributed In Lefkas Island, five fault systems were identi- and are identified in KMTU and MMTU. In many fied with the following principal strikes: N20°—40°, locations these faults have a right-lateral oblique- N40°—60°, N70°—90°, N110°—130°, and N170°—190°. slip character such as Nydri-Vassiliki fault zone. The statistical processing of these fault systems was The N70°—90° striking faults are characterized as performed with the use of 192 linear features. oblique right-lateral faults presenting high-density The N20°—40° striking faults are characterized as compared to their frequency. They are identified in oblique/normal-slip faults, presenting lower density many locations on the island, mainly on the southern compared to their frequency. They are developed coastal zone of MMTU and AMTU, where they verti- parallel or sub-parallel to the main fold and thrust cally intersect the Alpine and Miocene formations. trends, with mostly counterbalancing dips. These The N110°—130° striking faults are characterized faults affect mainly the western coastal zones of as oblique/normal-slip faults. They present high-den- KMTU and AMTU and do not appear in the cen- sity in relation to their frequency in this direction tral area of the island. and are found mainly in KMTU, interrupting both The N40°—60° striking faults are characterized the Alpine formations of the Ionian Zone and the mainly as strike-slip faults. These faults interrupt the post-Alpine formations. Frequently, they are observed Alpine formations, the fold axes and thrusts, caus- as the margins of the Quaternary basins. The general ing intense tectonic deformation with fracture zones trend of these faults follows the main thrust trend. In

27 the area of Eglouvi-Lazarata-Lefkas (S to N), they sents a Miocene fault zone. The N70°—90° faults are form en-echelon monoclinal displacements essential- attributed to an intense compressional episode dur- ly forming three main surfaces of gentle slopes ing the Late Pleistocene (Mercier et al., 1987; Cush- (<10%) at 800—900 m (Eglouvi), 300—400 m (Lazar- ing, 1985; Sorel et al., 1988). The N110°—130° fault ata) and 0—100 m (Lefkas). A significant feature is system is related to the deformation of Early Pliocene, that these faults are not identified within AMTU while compressional regime (Sorel and Cushing, 1982; they affect only the northern section of MMTU where Cushing, 1985). The N170°—190° faults like the they locally intersect the NVF structure. N20°—40°, follow the fold and thrust structures, par- The N170°—190° striking faults are characterized allel to the trench axis. The above mentioned fault as oblique/normal-slip faults and although they have structures of different orientation represent an ex- a dominant frequency, they exhibit a very low-densi- pression of compressional tectonic regime that had ty (length). They are parallel to the main fold axes influence to the morphology of the island. and thrusts directions but mainly with counterbal- ancing dip. These faults are located on the coastal Geomorphology zones of AMTU, MMTU and KMTU, while they are absent from the central area of the island. Their re- In general, the relief of the island is steep, with the lation to the N20°—40° striking fault system could morphological slopes ranging from 10° to 65° (Fig. 5). not be identified. In the AMTU and MMTU the altitude is 700 m, while The N20°—40° faults follow the fold and the thrust in the KMTU is 1100 m. The higher morphological structures being parallel to the main development slope (65°) was observed at the west coastal zone of axis of the island. The N40°—60° fault system repre- the AMTU area. Gentle slopes (<10°) develop on the

Fig. 5. Morphotectonic units — morphological gradients map of Lefkas Island with the rose diagram of the coastline as linear features (a: frequency, b: density)

28 Table 2 Frequency, density and main outcrop areas, of coastline linear features of Lefkas Island

Principal Strike Frequency Density Outcrop areas N20°–40° Medium Medium Coastal zone, Karya N40°–60° Minor Minor Mainly Karya N70°–90° – – – N110°–130° – – – On the western (primary) and N170°–190° Major Major eastern coastal zone mountainous — semi-mountainous regions of Eglouvi The results of statistical processing of the coast- at altitude 800—900 m and in Lazarata and Marado- line using 198 linear features are presented in Ta- chori areas at 300—400 m. ble 2. It can be concluded that as far as the coast- The Englovi and the Lazarata plateau as well as line is concerned, the frequency follows the density the Lefkas lowland compose an en-echelon mor- with a primary N170°—190° strike and a secondary phological structure with a general direction to- N20°—40° strike (Fig. 5). The rest of the strikes con- wards the north. tribute scarcely on the coastline development. The hydrographic networks of the island are The plot of the streams on a frequency and density eroded in depth and their pattern is parallel and rose diagram is presented in Fig. 6. In Table 3 the rectangular type, while they mainly develop single- principal development directions are presented based streams. Only few hydrological networks, mainly in on their classification, character and area of appear- KMTU, present pattern of dendritic type on the ance. The statistical processing of the streams is car- Miocene formations. ried out with the use of 2064 linear features.

Fig. 6. Drainage basins map of Lefkas Island with the rose diagram of streams as linear features (a: frequency, b: density) and of watersheds as linear features (c: frequency, d: density).

29 Table 3 Frequency, density, character and main outcrop areas of the streams in Lefkas Island

Principal strikes Frequency Density Character Outcrop areas N20°–40° Minor Minor Tributaries Karya Main streams and N40°–60° Medium Medium Karya, Maradochori tributaries Single streams and Athani,Maradochori, N70°–90° Major Major tributaries Karya N110°–130° Medium Major Main streams Karya, Maradochori Maradochori, Karya, N170°–190° Minor Minor Mainly tributaries Athani

In all stream categories the frequency follows the 2. The N40°—60° strike, although it is medium for density. An exception is the N110°—130° striking the streams and watersheds in KMTU and MMTU, system that exhibits a greater density of streams com- has a minor participation on the KMTU coastline pared to its frequency, a fact that is attributed to and is absent from the AMTU and MMTU area. the main direction that the principal river branch- 3. The N70°—90° strike, although it is major for es follow. the streams (throughout the island) and medium/ Lefkas Island includes twenty drainage basins that major for the watersheds (KMTU, MMTU), is essen- present significant variety regarding their dimensions tially absent on the coastline. A notable observation and importance based on their morphological char- is the absence of watersheds in AMTU compared to acteristics (Fig. 6). From these twenty basins, the the significant stream evolution in that direction. number 13 and 15 essentially represent one drainage 4. The N110°—130° strike is medium for the wa- basin, since they are drained by the same stream to tersheds and medium/major for the streams (main the Vassiliki Bay. However, based on different struc- streams in KMTU and MMTU), while it is essential- tural and tectonic features they were separated in ly absent from the coastline. two. Most of the basins are open towards the sea. The 5. The N170°—190° strike, although it is major for exceptions are numbers 4, 12 and 14 that represent the coastlines of the western main and eastern coast- closed karstic basins. al zone of the island, appears as minor in streams The frequency and density rose diagrams of the and watersheds throughout the island. watersheds are presented in Fig. 6. In Table 4 their main evolution strikes are presented based on prior- Morphotectonic correlation itization, character and outcrop area. The statistical processing of the watersheds was performed with the The N20°—40° fault system, identified mainly on the use of 121 linear features. coastal zone, has contributed on the coastline for- The comparative study of frequency and density mation and scarcely on the stream development. The indicates that the watersheds of N70°—90° strike high density that it exhibits throughout the island present higher density than frequency while the op- and mainly in AMTU can be attributed to the fact posite is observed with the N20°—40° strike. In the that this direction mainly follows the fold and thrust rest of the strikes the frequency follows the density. structures. The comparison of the statistical processing of The N40°—60° strike-slip faults with the NVF as frequency and density among streams, watersheds dominant structure are scarcely expressed on the and coastlines indicates that: coastline, while they have significant presence on the 1. The N20°—40° strike, although it is major/me- main streams, tributaries and on the watersheds of dium for the watersheds (mainly in AMTU) with a the KMTU and MMTU. They are absent from minimum contribution on the streams (tributaries of AMTU. Along with the dominant tectonic fold struc- KMTU), appears as medium for the coastlines mainly tures and the thrust, they form basic watersheds and at the western coastal zone of Karya. streams. These faults could be considered important

Table 4 Frequency, density and outcrop area of the watersheds in Lefkas Island

Principal strikes Frequency Density Outcrop area N20°–40° Major Medium Athani, (mainly), Karya, Maradochori N40°–60° Medium Medium Karya, Maradochori N70°–90° Medium Major Karya, Maradochori N110°–130° Medium Medium Karya, Maradochori N170°–190° Minor Minor Karya, Athani, Maradochori

30 for the formation of the early morphotectonic struc- The N70°—90° fault system, according to Merci- ture of the island and for the dynamic compression- er et al. (1987), Cushing (1985) and Sorel et al. al strain distribution that dominates in KMTU, (1988), during the late Pleistocene was attributed to MMTU and AMTU. an intense compressional episode of a WSW—ENE The N70°—90° fault system identified throughout direction. This compression resulted in the devel- the island, with significant presence in the MMTU opment of a right-lateral horizontal slip and the and AMTU, forms watersheds (high-density) and formation of the E—W trending Sperchios-Amv- mainly streams. Moreover, it is not present on the rakikos fault zone (Fig. 1a). For many researchers, coastline. It is considered that the high-density of the Sperchios-Amvrakikos fault zone, which has a the system has contributed significantly to the in- significant right lateral horizontal slip, represents crease of the watersheds lengths, as well as to the the western projection of the North Anatolian Fault frequency and density of the streams. (Aubouin and Dercourt, 1975, Papanikolaou and The N110°—130° fault system having limited fre- Dermitzakis, 1981; Mariolakos et al., 1985). This quency and significant density forms watersheds and zone is regarded as an active structure (McKenzie, streams but it does not control the coastline. In gen- 1972; Lyberis, 1984, Lekkas et al., 2001). Based on eral, the KMTU area is morphotectonically control- the EBASCO (1979) map, the Sperchios — Amv- led by the geological and tectonic structure expressed rakikos zone was defined as an extensional rift, while through this system. Doutsos et al. (1987) suggested that the formation The N170°—190° fault system, showing high-fre- of Amvrakikos Bay is related to the action of nu- quency and low-density, controls mainly the western merous faults without systematic horizontal WNW— and the eastern coastline of the island and limited ESE direction. streams and watersheds. This fact leads us to suggest Since the N20°—40° fault strike coincides with that this system represents active structures under de- the fold axes strike and with the main development velopment. These faults follow the fold and thrust axis of the island, it can be suggested that this area structures and are parallel to the trench axis. is under compression and these faults represent The N40°—60° strike-slip faults caused the for- active structures as the result of strain release to- mation of the early morphotectonic structure of the wards the east and west. Moreover, based on the seis- island. The initial formation of these faults could be motectonic map of Greece, the most recent terres- related to the generation mechanism of the Miocene trial faults recorded on the western coasts of Lefkas molassic basins in the Ionian Zone. Towards this hy- Island are of middle Pleistocene — Holocene age pothesis, the outcrop of these faults as the margins and have a 0°—30° strike. of the Miocene formations is reinforcing. Reactiva- Finally, although the N170°—190° fault system tion of these faults as oblique strike-slip faults and relative correlation was not possible during the possibly as oblique right-lateral faults during the em- fieldwork, it can be considered that this system and placement on Paxos Zone should be considered since the N20°—40° fault system were active during the the Miocene formations on the NVF fault zone are same period. intensely tectonized and frequently outcrop under the Ionian Zone formations (Maradochori area). Moreover, along these fault zones the Ionian Zone CONCLUSIONS formations migrated further to the west interrupting the continuation of the thrust surface towards the Based on two principal tectonic surfaces, the NVF south. However, these faults do not displace the Pax- zone and the thrust, Lefkas Island was divided into os Zone formations. three main tectonic units that developed as morpho- Additionally, the N110°—130° faults that control tectonic units corresponding to the Karya (KMTU), watersheds and streams are frequently interrupted by Maradochori (MMTU) and Athani (AMTU). the N20°—40° fault system and for this reason they We suggest that the a large area of Lefkas Island are considered as older from the latter. Possibly, they was under a NE—SW to ENE—WSW directed com- were formed during the early Pliocene-early Pleis- pressional regime since the Early Pliocene till now. tocene, a period when, according to Sorel and Cush- It caused the uplift of Paxos Zone in the western ing (1982) and Cushing (1985), the tensional regime region and the parallel submergence of the Ionian was compressional. zone in the eastern region. Many researchers suggested that during the Qua- Therefore, after Early Pliocene emplacement on ternary the Lefkas Island was under compression of Paxos zone the continuous deformation caused fault a N40°—60° direction (Drakopoulos and Delibasis, structures of N110°—130° direction. These faults 1982; Cushing, 1985). Mercier et al. (1987) proposed along with the N40°—60° strike fault system, morpho- that this compressional phase dominates the area since tectonically formed the area of the Ionian zone for- the middle Pliocene. According to Cushing (1985), mations and mainly the KMTU. They controlled the this compressional regime gradually decreases in our watersheds and streams, while they shaped the KMTU days. Angelier et al. (1982) suggested that in the broad- to a monoclinal en-echelon structure of northeast- er area of the , the lower values of ex- ern plunge. This structure create three main surfaces tension can be recorded, â<1.0. of gentle slopes at altitude of 800—900 m, 300—400 m

31 and 0—100 m, resulting in the transgression of the The continuous compressional regime resulted in lower fault blocks from the sea on the northeastern the formation of fault structures with N20°—40° and area of the island. N170°—190° strikes that defined the coastal area. During the Early Pleistocene, the change of the direction of the compression from N40°—60° to N90°, Acknowledgment created the N70°—90° fault system. These faults mor- photectonically affected the island controlling the We would like to thank Professor G. Migiros for his watersheds and streams. constructive reviews on the manuscript.

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