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The seafloor in the Gulf of Corinth is divided into three physiographic provinces: shelf, slope and plain. (Fig.2.1) (Ferentinos et al 1988)
The shelf is characterized by low slope gradient (2o<) and extends as far as the 150m isobath. The slope along the southern margin is much steeper (20o- 40o) than that along the northern margin (10o- 20o) giving the gulf a distinct bathymetric asymmetry. The plain has a length of about 40km and a max width of about 14km.
The geomorphology of the onshore-offshore zone in the southern margin is controlled by the spatial geometry of the faults and the river drainage.
Fig.2.1 (a): Bathymetric map of the Gulf of Corinth (contour) every 50m
Fig.2.1 (b): 3-D bathymetric map
Western Gulf of Corinth
In the western part of the Gulf of Corinth between Egion and Akrata the coastal and offshore morphology is the direct result of the fault block terrain produced by the bounding faults. (Fig. 2.2) The faults control the development of the coastal plain, the shelf/slope morphology and deposition and influence the position of the rivers course in the plain.
The most prominent fault here is the Helike fault, a 40km long fault divided into two main segments, the western (W. Helike fault) and the eastern (E. Helike fault) separated by a right- stepping transfer zone at the Keranitis river. (Fig. 2.2) This fault defines the transition between the low lying coastal plain and the steeply sloped mountains. On the footwall block of this fault Gilbert type fan deltas, formerly deposited in a subsiding hangingwall position, currently being uplifted, have been formed. Superimposed on the uplifted fan deltas are more recent late Quaternary marine deposits which correspond to isotopic stages 5, 7 and 8 located on wave eroded platforms or terraces (McNeill and Collier 2004, McNeill et al 2006).
The other prominent faults, downbasin, are the onshore Egio fault and the offshore Valimitica and Diakofto faults. (Fig. 2.2) The latter two define the transition from the shelf to the plain and their fault-plane act as part of the slope. The structural relationship between the Egio and Helike faults produces a transfer zone that downflexes the step-over zone. (Fig. 2.2) This results in the continuous shifting of the Selinous and Keranitis rivers course. (Koukouvelas et al 2001 Pavlides et al 2004) This river migration produces a line-source sediment input over time resulting in the development of slope aprons at the base of the slope. (Fig. 2.2)
Central Gulf of Corinth
In the central part of the Gulf of Corinth, at Xylokastro, between the rivers Fonissa and Agiorgiticos, the Corinth fault controls the morphology of the shelf, slope and basin floor. (Fig. 2.3) The presence of the fault has resulted in a very narrow shelf and a very steep slope.
The fault plane of this fault acts as part of the slope forming a scarp that exceeds 580m in height and has an average gradient of between 25 and 40o . (Fig. 2.3) To the south on the footwall of the Corinth fault the Sithas, Agiorgiticos and Fonissa rivers incise the land producing river channels with 3o 5o and 10o gradient respectively. (Fig. 2.4) The steeply eroded canyons that dissect the shelf and the slope in front of the rivers are considered to be the offshore continuation of the Sithas, Agiorgiticos and Fonissa rivers. (Ferentinos et al 1988) (Fig. 2.4) The talweg axis of those canyons, dips more steeply than the corresponding onshore rivers, at 13o, 22o and 28o, respectively. This difference in the slope gradient is an indication of the youthful stage of the canyons and the high slip rate of the Corinth fault. (Fig. 2.4)
Fig. 2.3: 3-D illustration of the morphotectonic pattern and its influence on the sedimentation processes (From Ferentinos et al 1988)
Fig. 2.4: Topographic profiles along the Fonissa, Sithas and Agiorgitikos river-canyon systems 0o – no vertica.(From Ferentinos et al 1988)
Ferentinos G., Papatheodorou G. and Collins M. 1988. Sediment transport processes in an active submarine fault escarpment. Gulf of Corinth, Greece. Marine Geology, 83:43-61
McNeill L., and Collier R. (2004). Uplift and slip rates of the eastern Helike fault segment, Gulf of Corinth, Greece, inferred from Holocene and Pleistocene Terraces. Journal of Geological Society of London. 161:81-92
McNeill L., Collier R., Pantosti D., De Martini P., and D’Addezio C. 2006. Recent history of the eastern Helike Fault: Geomorphology, Palaeoseismology and Impact on Palaeoenviroment in Ancient Helike and Aegialeia – Archaeological Sites in Geologically Active Regions (eds D. Katsonopoulou S., Soter and I. Koukouvelas) Helike III, Athens 2005
Lyberis E., Papathedorou G., Hasiotis T., Ferentinos G. 1998. Submarine faults within the active tectonic graben of the Corinth Gulf. Four typical examples of modern tectonic control on morphology and sedimentation processes under the sea-level. 8th International Congress of the Geol. Soc. of Greece. Patras, Greece V. 2:223-234