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Evolution of the offshore western Gulf of Corinth

Rebecca E. Bell^,1, Lisa C. McNeill¹, Jonathan M. Bull¹ and Timothy J. Henstock¹

¹ National Oceanography Centre, Southampton, University of Southampton Waterfront Campus, European Way, Southampton SO14 3ZH, United Kingdom

View larger version (36K): [in this window] [in a new window]   Figure 1. Framework of the Gulf of Corinth. The locations of major onshore and offshore faults are taken after Stefatos et al. (2002), Leeder et al. (2005), McNeill et al. (2005b), and this study. Topography is from the Shuttle Radar Topography Mission (http://srtm.usgs.gov), and bathymetry is reproduced from the GEBCO Digital Atlas published by the British Oceanographic Data Center on behalf of Intergovernmental Oceanographic Commission (IOC) of UNESCO and the International Hydrographic Organization (IHO), 2003. Inset—Summary of Aegean regional tectonics. Arrows are north coast GPS velocity vectors for a stationary southern coastline, from Clarke et al. (1998) (Fig. 16).

View larger version (36K): [in this window] [in a new window]   Figure 2. Extent of the swath bathymetry (dotted) and seismic reflection profiles (solid lines) collected by the MV Vassilios in 2003 (McNeill et al., 2005b). Sedimentation-rate calculations at the labeled sites are given in Table 3. AIG—Aigion fault; WEF—West Eliki fault; EEF—East Eliki fault; DER—Derveni fault.

View larger version (47K): [in this window] [in a new window]   Figure 3. (A) MCS data from the Eratini sub-basin (location identified in Fig. 2). (B) Four clinoform packages (arrowed) are identified within the basin. The shallowest clinoform within each package marks the end lowstand shoreline, formed before the Rion sill flooded during marine transgression. Unnumbered lines represent interpreted marine to lacustrine transitions. (C) Horizons can be correlated with the eustatic sea-level curve of Siddall et al., (2003) to estimate horizon age. After McNeill et al. (2005b).

View larger version (42K): [in this window] [in a new window]   Figure 4. (A) Close-up of the stratigraphy within the Eratini sub-basin (box in Fig. 3B). (B) Unit III shows a clinoform configuration associated with lacustrine delta progradation during sea-level lowstand. The parallel reflections at the base of the unit are probably highstand and transgressive sediments.

View larger version (54K): [in this window] [in a new window]   Figure 5. (A) MCS data from the central western Gulf (location shown in Fig. 2) (B) Seismic stratigraphic interpretation showing the two main sediment packages, A and B, and horizon correlation with the sea-level curve of Siddall et al. (2003) modified for the level of the Rion sill.

View larger version (93K): [in this window] [in a new window]   Figure 6. (A) MCS data from the E-W Gulf profile (location shown in Fig. 2). (B) Seismic stratigraphic interpretation showing the two main sediment packages, A and B, and horizon correlation with the sea-level curve of Siddall et al. (2003) modified for the level of the Rion sill.

View larger version (40K): [in this window] [in a new window]   Figure 7. Interpreted major faults in the western Gulf of Corinth. Positions of faults are constrained by the seismic profiles and swath bathymetry used in this study and that by McNeill et al. (2005b), and are supplemented by interpretations from Zelt et al. (2004) and Goodliffe et al. (2003). AIG—Aigion fault; WEF—West Eliki fault; EEF—East Eliki fault; DER—Derveni fault; WCF—West Channel fault; ECF—East channel fault; SEF—South Eratini fault; NEF—North Eratini fault; AKR—Akrata fault.

View larger version (46K): [in this window] [in a new window]   Figure 8. (A) TWTT depth to the basement-sediment contact and (B) TWTT sediment thickness isopach. Produced using the basement interpretations of our MCS study and additional basement interpretations from deep seismic reflection profiles from the R/V Maurice Ewing cruise EW0108/2001 (Zelt et al., 2004; seismic images accessed through the Marine Seismic Data Center at http://www.ig.utexas.edu/sdc/).

View larger version (52K): [in this window] [in a new window]   Figure 9. (A) MCS data from the west of the study area (location in Fig. 7). (B) Structural interpretation of the sub-bottom structure and inset line drawing showing basement depth for this location from Figure 8.

View larger version (57K): [in this window] [in a new window]   Figure 10. (A) MCS data from the center of the study area (location in Fig. 7). (B) Structural interpretation of the sub-bottom structure and inset line drawing showing basement depth for this location from Figure 8.

View larger version (54K): [in this window] [in a new window]   Figure 11. (A) MCS data from the east of the study area (location in Fig. 7). (B) Structural interpretation of the sub-bottom structure and inset line drawing showing basement depth for this location from Figure 8.

View larger version (25K): [in this window] [in a new window]   Figure 12. (A) Comparison of the average depth of buried clinoform slope breaks, C1–C4 (Fig. 3) with the eustatic sea-level curve of Siddall et al. (2003). (B) Subsidence rates at the fault plane averaged within each time step between shoreline formation. Results suggest that subsidence was relatively constant within the Late Pleistocene but has increased within the Holocene, assuming sill depth, lowstand level, and water depth of formation are approximately constant and accurate.

View larger version (30K): [in this window] [in a new window]   Figure 13. (A) Subsided shoreline, total basement throw, and stratigraphic offset measurement methods used in the determination of estimated slip rates for different time periods. (B) Summary of the estimated slip rates, in mm/yr, for each fault over different time periods, using the three measurement methods described in (A). Slip rates in white boxes have the highest confidence level; those in light-gray boxes are associated with uncertainty in unknown paleotopography, and those in black have been determined using the interpolated basement structure of Figure 8.

View larger version (24K): [in this window] [in a new window]   Figure 14. (A–J) Stratigraphic interpretations for the MCS data set in the western Gulf of Corinth. Basement depths are observed directly from the MCS data or derived from the regional grid in Figure 8A (see Basement Structure section for method).

View larger version (27K): [in this window] [in a new window]   Figure 14. Continued.

View larger version (48K): [in this window] [in a new window]   Figure 15. (A) Uninterpreted and interpreted MCS data for the boxed region in Figure 14B. Post–ca. 0.4-Ma sediments show a southward tilt toward the East Eliki fault and Akrata fault at the south end of the profile. (B) Uninterpreted and interpreted MCS data for the boxed region in Figure 14F. Sediments to the south show a preferred southward tilt toward the onshore East Eliki fault, whereas those to the north dip toward the S-dipping West Channel fault. Intense minor faulting exists between sediments dipping with a preferred north and south orientation. (C) Uninterpreted and interpreted view of the East Channel fault from the central western gulf (Fig. 14D). The East Channel fault is a complex fault zone with activity pre-ca. 125 ka (horizon 2) being concentrated on a buried fault to the south of the East Channel fault. Note exaggerated vertical scale compared to Figures 15A and 15B.

View larger version (28K): [in this window] [in a new window]   Figure 16. Maps to show major active faults and possible positions of the coastline during the development of the western Gulf of Corinth, together with schematic cross sections. (A) Pre-ca. 2 Ma, a number of faults were active leading to the subsidence of a wide basin with unknown northern extent. (B) During the Early Pleistocene, the rift was controlled primarily by the Mamousia-Pirgaki fault in the south and the West Channel-East Channel fault system to the north. (C) Within the last ca. 1 Ma, activity has become focused on the Aigion fault/East Eliki fault along the southern margin and ca. 0.5-Ma activity on the northern margin transferred onto the South Eratini/North Eratini faults. South coast rift geometry after Collier and Jones (2003).

View larger version (27K): [in this window] [in a new window]   Figure 17. Summary of evidence concerning the geometry and interaction of western Gulf of Corinth faults at depth. Inset shows the position of the transect and locations of Ms >5 seismicity in the area from Ambraseys and Jackson (1990) and Bernard et al. (1997). Faults observed on the southern coastline are from Collier and Jones (2003) and offshore faults from this study. Faults have been projected with dips of 60° down to the probable depth of the brittle-ductile transition as dashed lines. The position of the detachment surface proposed by Sorel (2000) and Rigo et al. (1996) have been projected onto this line. Note that these are distinct features at very different depths. The best-fit modeled fault plane for the 1995 Aigion earthquake from Bernard et al. (1997) is shown.