lI£i\1io Hl<; EAilr1VIK~<; r£WAOVIK~<; ETOIpla<; TO~. XXXX, Bulletm of the Geological Society of Greece vol. XXXX, 2007 2007 Proceedings of Ihe 11 th InLernational Congress, Athens, May, npOKTlKQ 11°' 1IlE9vou<; Luv£opiou, A9~vo, MOlo<; 2007 2007 MORPHOTECTONICS OF THE PSATHOPYRGOS ACTIVE FAULT, WESTERN CORINTH RIFT, CENTRAL GREECE 2 3 Tsimi Ch.t, Ganas A.I, Soulakellis N. , Kairis 0. , and Valmis S.3 1 Institute ofGeodynamics, National Observatory ofAthens, 11810 Athens, Greece [email protected],gr 1 Department ofGeography, University ofthe Aegean, University Hill, 81100 Mytilene, Greece 3 Agricultural University ofAthens, Jera Odos 75, 11855 Athens, Greece Abstract The study area is located on the western part of the Gulf of Corinth which is considered as a paradigm ofan active rift system in Greece, This rift was formed by normal slip on big faults which extend the crust of the Earth in the N-S direction. The mOlphotectonic indices (hypsometric curve, hypsometric integral, drainage basin asymmetry, ratio of valley floor width to valley height) have been estimated using the 20-m digital elevation model of this area and the ARC software. The normalfaults ofthe study area have been extracted by use ofa DEMmosaic of20­ m pixel size, satellite images from Landsat 7 ETM+ and SRTM 90m. Our results highlight the recent activity ofthe Psathopyrgos normalfault on the basis ofa series ofmorphotectonic evidence and suggest the existence ofa single fault segment for a distance of 16 km. Key words: MOIphotectonics, Corinth rift, Psathopyrgos, active faults. n.EpiAr)4H l H 7rE;PlOxf; /ldsTlJC; c:iVo.L aTO (jVT/KO 6xpo TOV KOplvelOxoiJ avoiY/l(J.TOI;. 0 KOpIV()IOXOi; KOA7rOi; a7rOTE:f,ci xapaKT:IJPlaTlKO 7rapb.&ly,ua VWTE:KTOVIKOiJ jJve[a/laToi; aTOV E),),.17VlKO XcVpo. 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L;Tl7v sPyaaio. avrJj p<:J..<:TJj()7JKEi l6zairspa TO KaVOVlKG pf;YfJa rov PaOo7rVPYoU TO oiTO [0 )eElwuPyd Wi; j.da eVlaia, Eivspyf; OOfJI] fJf;KOV~ 16 XIALOj.l€TpOJV. At~E;l(;; ld.E:IOui: MOprpOTE:KTOVlKJ/, Koplv81aKo AVOLY/la., Pae07rVPYO~, €V£pyo P71YfJo.. Ψηφιακή Βιβλιοθήκη Θεόφραστος - Τμήμα Γεωλογίας. Α.Π.Θ. 1. Introduction The main aim of this work is the understanding of long-term tectonic processes in the Psathopyrgos area of the western Corinth Rift area through the construction of a series of digital maps showing the spatial distribution of the main morphotectonic indices. The morphotectonic analysis helps to identify tectonic processes at the surface (Keller and Pinter, 1996). Our objectives are a) the mapping of the spatial distribution of the morphotectonic indices over a total 2 area of 19.74 square kilometres (km , Fig. 1), b) the spatial relationship between the slip rate of the Psathopyrgos active fault and particular indices and c) the creation of a digital database of the geomorphology characteristics in the study region. In this paper we will present a fraction of our results around the Psathopyrgos area that have been validated in the field. In central Greece, large, shallow earthquakes (M>6) are found to rupture pre-existing fault scarps such as the 1981 earthquakes in the eastern end of the gulf of Corinth (Jackson et af. 1982). Every large earthquake creates a pennanent defonnation at the Earth's surface (Stein et af. 1988), resulting in the uplift of the foot\.Vall area and the subsidence of the hangingwall area, respectively. The key factor in shaping the landscape in such areas is the relation of the fault slip rate to the erosion rate, in other words in areas defonned by fast-moving faults the geomorphological signal will be much different from areas with slow-moving faults. The spatial criteria for the recognition of active uormal faults are (Jackson and Leeder 1994, Ganas 1997) a) the alignment of fault scarps aloug the base of mountain fronts b) the elliptical shape of the footwall area as observed in along-fault strike profiles c) the development of axial drainage in the hangingwall area and d) the development of trellis-type drainage in the foot\.Vall area with discharge of footwall catchments at both euds of segments. In this work we used a combination of techniques including use of orthorectified Landsat 7 image, a 20-m DEM mosaic and its by­ products (slope map, contours, TIN, shaded relief), a 90-m SRTM elevation model, geological data published in the literature and our own field work. 2. The study region The study area is the western part of the Gulf of Corinth which is considered to be a paradigm of an active rift system in Greece (fig. 1; De M31tini et al. 2004, Pavlides et al. 2004, Pantosti et al. 2004, Bernard et af. 2006). This rift was formed by normal slip on large, E-W striking faults which extend the crust of central Greece in the N-S direction. The length of Corinth rift is 130 km and the width is 20-40 km. The major depth is ~900 m and the major height of the mountains around the Gulf of Corinth is -2500 m. The south coast of the Corinth ri ft is uplifting whereas the north part is subsiding. From space geodesy we know that the Peloponuesus (southern part) moves faster towards southwest than the Greek mainland (Clarke et af. 1998). The result from this movement is that these two areas move away from each other with an average speed of I cm/year and increasing from east to west. The bedrock lithology is mainly limestone and the syn-rift rocks are Pliocene - Quaternary age sedimentary rocks such as marls, sandstones, conglomerates and alluvial fan deposits. In the study region, the active faults have normal kinematics. The area includes some of the most active faults in Greece that have already beeu studied by many researchers. For example, the Eliki Fault, which is approximately 40 km long ruptured during two important catastrophic earthquakes in 373 Be and in 1861 (Schmidt 1879). Moreover the study area has rugged relief, several major rivers flowing in the general N-S direction (Fig. I), many uarrow valleys and a lot of other interesting landforms. Within our study area the drainage is organized in fifty six (56) catchments. The catchments developed in the footwall area of the Psathopyrgos normal fault amount to fourteeu (14). The morphotectonic data for all catchments are presented in Table 1. Ψηφιακή Βιβλιοθήκη Θεόφραστος - Τμήμα Γεωλογίας. Α.Π.Θ. -11"' Lc!!cnd --Aklo ..._-- Streams ,(~~? ............... Faults • <4 --Old Faults ~ _ 'it -_. landslides ,~~ ~'~ ." .. ~ ~~:~. o Catchment .... '''; ~.I o 5.000 10.000 1MetefS Figure 1 - Map ofthe stndy area in Western Peloponnesus and Sterea Hellas. Numbers indicate main catchments. Note the E-W orientation of active faults and the N-S orientation of major rivers. Names of faults are after published literature or by the nearest village/town. Square box indicates the Psathopyrgos fault area Ψηφιακή Βιβλιοθήκη Θεόφραστος - Τμήμα Γεωλογίας. Α.Π.Θ. 3. Materials and Methods The software that was used was ArcGISTM v.B.I for Windows. From the available to us digital data, we digitized a) the catchments (56), b) the streams c) the landslides, d) the triangular facets developed on the footwall area of the large, nonnal faults and e) the normal faults as mapped by Doutsos and Poulimenos (1992), Roberts and Koukouvelas (1996) and by our own field work. The faults were located precisely by collecting fault plane coordinates using field GPS. The feature "active fault" includes 5 fieLds (attributes) namely the name of the fault, the length, the strike, the distance to the watershed (D to Divide) and the relief of each of them Hmax - Hillin (where Hmax is the maximum elevation in the footwall of the fault and Hmin is the minimum elevation in the hangingwall). The estimated morphometric indices of this study are the following: • Hypsometric curve and hypsometric integral (HI) HI =.Hmean - H min (1) H max -Hmin where H meon , Hmox and Hf/lm are the mean, maximum and minimum elevation, respectively. • Drainage basin asymmetry (AF) AF =100 *(Ar/ ) (2) / At where AI' is the size of area in the right sub-catchment of main river and At is the area of whole catchment. • Ratio of valley floor width to valley height (V) jW V = 2V (3) (hi -hJ+(h2 -h3 ) where V; IS the width of the valley floor, hi and h2 are the elevation ofthe right and left drainage basic line aud h3 is the elevation ofthe valley floor. In this paper we will present the results concerning the spatial distribution of the hypsometric integral (relation l), the basin asymmetry index (relation 2), and the variation of the slope of the triangular facets along the fault. We also discuss the implications of the above morphotectonic indices and in particular the Valley Height-width ratios (relation 3) for the Psathopyrgos fault.