DISS 3.2.GreDaSS: Seismogenic Source GRCS072 - Ptolemaida

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COMMENTS The fault zone of Ptolemaida Composite Source bounds the northwestern lakeshore of Vegoritida Lake and consists of two segments: the Vegora (GRGG072) and Vegoritida (GRGG073) Faults. Many authors support the segmentation. Goldworthy and Jackson (2000, 2001) suggest the existence of a gap between the two segments, while Sakellariou et al. (2001), after carrying out a geophysical survey in Vegoritida Lake producing more than 200 km of high resolution Boomer profiles, suggest a partial angular overlap being intercepted by an almost E-W trending fault. Many authors have investigated the fault zone. Most of geometric and kinematic parameters derive from geological-morphotectonic mapping and field measurements and observations by Pavlides (1985) and Pavlides and Mountrakis (1987). Maximum depth is based on the cross-section of the Ptolemaida Basin proposed by Pavlides and Simeakis (1987/1988) showing the geometry of the faults. Strike is based on geological and morphotectonic mapping from all previous authors. Dip range is according to field measurements (Pavlides, 1985; Pavlides and Mountrakis, 1987) and the schematic cross section across the major fault zones of Ptolemaida Basin proposed by Pavlides and Simeakis (1987/1988). Rake derives from kinematic indicators measured by Pavlides (1985) and Pavlides and Mountrakis (1987). Taking into account the total length of the zone, assuming that both fault segments can be co-seismically reactivated (worst case scenario), and using the empirical relationships of Pavlides and Caputo (2004), a maximum expected magnitude of 6.7 (± 0.5) is suggested. OPEN QUESTIONS It is not clear how the fault zone ends to the SE. The existence of the antithetic Chimaditis Fault (GRGG075) in the SE continuation of the fault implies either the end of the fault’s propagation southeasternwards or the possible continuation southern of Chimaditis Fault forming a horst. It is also unknown whether the fault zone interacts at depth with the Amyndeo CS (GRCS070) forming a large detachments zone. SUMMARIES Pavlides (1985) The author carried out a geological and morphotectonic mapping as well as meso-structural analyses of the Ptolemaida Basin. One of the investigated tectonic structures is the Ptolemaida CS. After field descriptions and measurements, the suggested length, strike and dip of the fault are 12 km, 30-40° and 60° to the SE, respectively. At the southwestern end of the fault zone (Vegora ISS-GRGG072), the division into two branches is suggested. The first branch starts from Vegora village following the previous direction, while the second one forms an angle with the previous one, crossing the Filotas village and ending at the Perdikas village. Along the second branch the author measured striated fault scarps on limestone which outcrops between Neogene and Quaternary sediments. A minimum total vertical displacement of 200 m is suggested from field observations near to the Vegora village and northeast from Aghios Panteleimonas village. Visible displacement is vanished near the Aghios Panteleimonas village, but it is estimated to ca. 500 m from the depth of the limestone on the hanging-wall. Many striated fault scarps were observed on limestone, some of them near Vegora village and many other smaller in a quarry near the Aghios Panteleimonas village with tenths of centimetres of displacement and three generations of slickenlines. The most recent generation is mainly of normal component. Pavlides and Mountrakis (1987) The authors carried out a meso-structural analysis in the broader area of the Florina-Ptolemaida Basin, producing a geological-morphotectonic map. They suggest that the geomorphologic features of the basin (partitioned into smaller sub-basins, including the local four lakes, separated by ridges) are tectonically controlled mainly by large normal faults, striking NE-SW and reaching a length up to 30 km. The most important are: 1. the Petron-Nymfaeon Fault (corresponding to Amyndeo Composite Source-GRCS070 of this database) which strikes N30°E, dips SE and is more than 30 km long, 2. the Vegoritis Fault (corresponding to Ptolemaida Composite Source-GRCS072 of this database) which strikes N40°E, dips to the SE and counts 20 km of length, 3. the Chimaditis-Anargiri Fault (corresponding to Chimaditis-GRGG075 Fault of this database) which strikes N30°E, dips NW and is more than 10 km in length, and 4. the group of parallel NE-SW normal faults of the Mt Vermio-Komnina valley and Ptolemais-Proastio subsidence which extend for over 50 km. The authors suggest that all previous faults are active inherited structures because they cut both the pre-Neogene formations (mainly Mesozoic limestones of the basin margins) and the unconformably overlying Neogene-Quaternary sediments. They also support the proposal of recent activity on the well developed tectonic geomorphology along the strike of the faults. Concerning the kinematics of the fault, two superimposed sets of striation on the limestone fault scarp were observed, verifying the implication of a relative succession in fault’s reactivation history. After the meso-structural analysis, they conclude that West Macedonia has been under widespread extension divided in at least two phases since Miocene, all related to normal faulting. The older one is the Late Miocene-Pliocene phase with a NE-SW direction of extension and the most recent one is the Quaternary to present phase with a NW-SE direction of extension. Goldsworthy and Jackson (2000, 2001) The authors investigate the correlation of the parallel faults of Amyndeo CS (GRCS070), Ptolemaida CS (GRCS072) and Peraea Fault (GRGG074). Based on morphotectonic evidence, a gradual activity migration from Amyndeo CS to Peraea Fault is suggested. Measurements on striated fault surfaces of the Ptolemaida Composite Source indicate a consistent slip vector in the direction ca. 130°, with an inclination of ca. 55°. A gap is also suggested between the two fault segments of the zone, the Vegora (GRGG072) and Vegoritida (GRGG073) Faults. Sakellariou et al. (2001) The authors carried out a geophysical survey in Vegoritida Lake producing more than 200 km of high resolution Boomer profiles in order to investigate the neotectonic movements, sedimentation and the water-level fluctuation of the lake during the Upper Quaternary. Based on geomorphologic criteria they suggest a minimum vertical displacement across the Vegoritida Fault Zone of about 600-700 m. They recognize two fault segments along the fault zone, the boundary of which is near to the Ag. Panteleimon village. They traced the northern segment along the steep western lakeshore which tilts the lakebed westernwards together with the lacustrine deposits. According to the authors, in this part the fault has formed a rough relief causing slope instability phenomena and in addition with the tilting of the lakebed and the sediments, they suggest that the fault is still active. On the contrary, the southern segment shows weaker evidences of recent activity. The authors ascribe the segmentation to the existence of a very steep (almost vertical) south dipping and almost E-W trending fault, named after the village of Ag. Panteleimon. The fault is observed in the Boomer profiles where it shows a 1-2 m-high scarp on the lakebed and a gradual increase of displacement in the underlying sediments according to depth. Near to the fault scarp sediments are also shown folded. Taking into account the morphology of the footwall and hanging-wall, the deformation of the sediments and the fact that the fault crosses the Vegoritida and Nymfaeo Petron Fault Zones to the west, the authors suggest that the Ag. Panteleimon Fault is a dextral strike-slip structure with a minor normal component. Also many NE-SW trending secondary faults are observed affecting the lakebed and the sediments below as well as N-S up to NE-SW trending faults along the eastern side of the lakeshore that are considered as antithetic to the large fault zone. Diamantopoulos and Dimitrakopoulos (2004) The authors carried out a geological and morphotectonic study in order to explore the morphology and the sub-surface structure of the pre-Tertiary basement of Ptolemaida-Kozani graben. According to them, Vegoritis-Ptolemais-Kozani graben represents a composite post-orogenic and active graben, which is separated in a couple of elongated perpendicular grabens, characterized by different stratigraphic evolution and sub-surface morphology. They present a map showing the morphology and the sub-surface structure of the pre-Tertiary basement based on drillings, geophysical and hydrogeological data of PPC (Public Power Corporation). Mountrakis et al. (2006) The authors carried out a geological and morphotectonic mapping in the Ptolemaida Basin. Along with the two major fault zones bounding the northwestern and southeastern margins of the basin, many other secondary faults were mapped. One of the latter is the Ptolemaida Composite Source. However, no further information and description is given for the secondary structures. Xanthopoulou (2006) The author carried out a morphotectonic investigation using various morphometric parameters which indicate high activity for both segments of the Ptolemaida Composite Source.