The Gulf of Corinth: an active half graben?
Introduction
The Gulf of Corinth area (Fig. 1) has been studied for a long time, since its southern shore exposes spectacular outcrops and because it is the most seismically active zone of the European Union. However, until recently, subsurface data, from both offshore and onshore, were not available. Consequently, because synrift deposits crop out only along the southern shore of the Gulf, the models about the extensional processes in the area were build up on a small amount of data. Subsurface data have been collected offshore by Hellenic Petroleum, the National Centre of Marine Research (NCMR) and the Patras University, and more recently onshore by the cluster of European projects called “CRL” (Corinth Rift Laboratory, Moretti et al., 2002). This new data have lead to a better-constrained structural model of the Gulf that will be discussed in the following section. Through the CRL project, extensive field works have also been carried out around the Aigion area, together with detailed analyses of cuttings and cores collected on land as well as offshore. The CRL also has set-up the installation of few networks (seismic, GPS, strain meters, geochemical…) which have allowed the monitoring of the area and the recollection of a large mass of information. Our work suggests that the Gulf of Corinth is the result of a longer and more complex deformation history than the simple half graben, bordered southward by an unique active fault, often described in the literature.
Section snippets
Geological setting
Extension in the Aegean Sea started in Miocene times (Le Pinchon & Angelier, 1979, Jolivet et al., 1994, Armijo et al., 1996). This extension is thought to be due to both gravitational collapse of the thick crust inherited from earlier mountain building (Jolivet, 2001) and lithospheric thinning in the Aegean back arc region (Doutsos et al., 1988). The extension rate is fast, about 3 cm/year, with respect to Eurasia (Kahle et al., 2000, Jolivet, 2001) and progressively migrates to the south.
Fault activity
The faults exposed along the southern shore of the Gulf often dissect the synrift sediments and therefore have been often described (Doutsos & Poulimenos, 1992, Roberts et al., 1993 and many others). However, faults are numerous on both sides of the Gulf and available data show that some of the south dipping faults located on (or near) the northern shore are still active.
The activity of the Delphi fault (Fig. 3d), for example, has been recorded for more than 3000 year by repetitive destructions
Kinematics of the Gulf opening
Ori (1989) divides the Gulf of Corinth's evolution into two main phases. During the first phase the proto-Gulf of Corinth was filled with continental and shallow-water deposits. During the second phase, the Gulf of Corinth acquired its current orientation and sedimentation was characterised by the deposition of Gilbert-type deltas along the southern shore and by turbidites within the Gulf itself. Ori (1989) suggested that the first phase could be rather “old” and related to the Aegean Sea
Block tilting in the Gulf of Corinth
Tilted blocks usually exist in rifts, and have been described worldwide on seismic lines as well as in the field. Often the blocks are at the scale of the upper crust, as in the Gulf of Suez (Moretti and Colletta, 1988), and the tilt process is due to the rotation of rigid blocks. In the case of domino on planar faults, extension does not imply any absolute uplift of the crest of the blocks (Angelier and Colletta, 1983). In the case of listric faults, the crest may be effectively uplifted by
Uplift
As there is no evidence of block tilting, the uplift of the area cannot be caused by the rotation or by elastic rebound of a tilted block. On the eastern part of the Gulf, Armijo et al. (1996) interpret the uplift of marine terraces, outcropping between Corinth and Xylocastro, as the elastic rebound of the footwall of a major fault. They reached the conclusion that the required synrift sediment thickness for such an uplift (800 m in 350 000 years) was in the range of 10 km and the elastic
Conclusions
The data summarized here allow us to confute some of the previous simple models which have been proposed for the evolution of the Gulf of Corinth. In particular it has been assessed that:
- 1.
The Gulf of Corinth is not an asymmetric simple half graben. There are active normal faults on both sides of the Gulf and the depocenters depend on the place northward, at the center or southward. The maximum water depth is measured almost everywhere in the central sector of the basin.
- 2.
There is no evidence of
Acknowledgments
This study has been founded by the EEC (Vth PCRD) through the projects 3F-Corinth (ENK6-CT-2000-00056) and DG-Lab (EVR1-CT-2000-40005), G. Ollier and J. Schuppers being the scientific advisers. We are very grateful to F. Ghisetti, L. Vezzani and R. Sibson who mapped the Aigion area. We also thank D. Sorel, T. Doutsos and I. Koukouvelas who spent some of their time with us in the field, and G. Ferentinos and A. Stefanos for stimulating discussions and for access to their onshore seismic data.
References (68)
- et al.
Tectonics and sedimentation in the gulf of Corinth and the Zakynos and Kefallinia channels, western Greece
Tectonophysics
(1984) - et al.
Sequence stratigraphy of (?) Pliocene–quaternary synrift, Gilbert-type fan deltas, northern Peloponnesos, Greece
Marine and petroleum Geology
(1994) - et al.
Geometry and kinematics of active faults and their seismotectonic significance in the western Corinth-Patras rift (Greece)
J. Struct. Geol.
(1992) - et al.
Seismicity, normal faulting, and geomorphological development of the Gulf of Corinth (Greece)the Corinth earthquake of february and march 1981
Earth and Planetary Science Letters
(1982) A comparison of geodetic and finite strain pattern in the Aegean, geodynamic implications
Earth and Planetary science letters
(2001)- et al.
The terraces of Corinth [Greece]—a detailed record of eustatic sea-level variations during the last 500,000 years
Marine Geol.
(1987) - et al.
Quantification de la déformation associée à la faille d'Aigion (Golfe de Corinthe, Grèce) par l'étude des dépôts du Pleistocène supèrieur et de la transgression marine holocène
CRAS
(2002) - et al.
Thinned continental crust below northern Evoikos Gulf, central Greece, detected from deep seismic soundings
Tectonophysics
(2001) - et al.
Fault-block tiltingthe Gebel Zeit example, Gulf of Suez
J. of Struct. Geology
(1988) - et al.
How does a block tilt?
Tectonophysic
(1988)
Alternating marine and lacustrine sedimentation during late Quaternary in the Gulf of Corinth rift basin, central Greece
Mar. Geol.
The relationship between the geometry of normal faults and that of sedimentary layers in the hanging walls
J. Structural. Geology
Tension fractures and extensional tectonics
Nature
Quaternary evolution of the Corinth Rift and its implications for the Late Cenozoic evolution of the Aegean
Geophys. J. Int.
The Ms=6.2, June 15, [1995] Aigion earthquake (Greece): evidence for low angle normal faulting in the Corinth rift
J. Seismol.
Geodetic determination of tectonic deformation in Central Greece from 1900 to 1988
Nature
Active deformation, of the gulf of Korinthos, Greece: results from repeated GPS surveys between 1990 and 1995
JGR
Rates of uplift in the Corinth and Megara basins, central Greece
Tectonics
High sediement yields and cool, wet wintersrest of past glacial paleoclimates in the northern Mediterranean
Geology
Geodetic strain of Greece in the interval 1892–1992
J. Geophys. Res.
Late Cenozoic extension of the Alpine collisional orogen, northeastern Greeceorigin of the north Aegean basin
GSA Bulletin
The Corinth-Patras rift as the initial stage of the continental fragmentation behind an active island arc [Greece]
Basin Research
Deformation of tilted blocks, consequences on block geometry and extension measurements
Bull. Soc. Geol. France
Attemps to date Pleistocene normal faults of the Corinth-Patras Rift (Greece) by U/Th method and tectonic implication
Geophysical resaerch metters
3D kinematics of extension in the Aegean region from the early Miocene to the present, insights from the ductile crust
Bul. Soc. Geol. France
GPS-derived strain rate field within the boundary zones of Eurasian, African, and Arabian Plates
JGR, v 105
The Hellenic arc and trench systema key to the neotectonic evolution of the eastern Mediterranean area
Tectonophysics
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