ALBERT

Description: The Mediterranean Ridge is an accretionary wedge consisting of a large pile of tectonically deformed sediments. In the past the Mediterranean Ridge has been interpreted as a prism related to Hellenic subduction. However, geophysical evidence (Pasiphae cruise, 1988) has indicated the presence of a high-velocity body southward of the Hellenic trench, which was subsequently interpreted as an extended continental backstop. During the recent IMERSE project, coincident wide-angle and normal-incidence seismic data were collected over the ridge along the NE–SW MEDRIFF corridor (Explora cruise, 1994). The objectives of the IMERSE project were to acquire the seismic observations necessary for a high-resolution structural model of the western Mediterranean Ridge, including the structure of the newly interpreted continental backstop. Here we present the results of recent re-modelling of two-ship, expanding spread, seismic refraction data (ESP-8 and -9) recorded during the Pasiphae cruise. The modelling of these data has allowed an approximate constraint on the position of the juncture between the Mediterranean accretionary complex and its buttress. Also presented are processing and modelling results of the recently acquired IMERSE wide-angle data. Travel-time modelling of these data has allowed the construction of six, multi-azimuth, velocity–depth models. These models show the existence of high-velocity material at depth (P-wave velocity〉5 km/s), inferred to be extended backstop, and constrain its southward extent. All models show the presence of a Messinian evaporite layer near the surface. The evaporite layer is observed to vary in thickness (from 0 to 2.0 km), with the existence of local thickening and thinning, due to depositional factors, tectonism and salt dissolution. In addition, combined analysis of the wide-angle velocity models with coincident seismic reflection and swath bathymetry data indicates that the geometry of the continental backstop varies laterally as a consequence of transform faulting, possibly related to the southward rotation of the Peloponnesus thrust sheet and backstop emplacement.