Onshore and offshore compressional tectonics in the eastern Betic Cordillera (SE Spain)

Abstract

This study concerns the northern terminal splay of the Eastern Betic Shear Zone (Betic Cordillera, SE Spain), where the Bajo Segura Basin lies, and its offshore prolongation along the western Mediterranean margin. We have integrated seismic reflection profiles with gravimetry, seismicity, wells and outcrop data from the Bajo Segura Basin and the Alicante shelf in order to determine the current geodynamic setting of the area. The results indicate that the same compressional structures in Upper Miocene–Quaternary rocks are observed both on- and offshore. In the onshore Bajo Segura Basin, there are ENE–WSW growth folds related to reverse faults in the basement. In the Alicante shelf, the main structure is an ENE–WSW anticlinorium which deforms Upper Miocene–Quaternary syntectonic deposits. These compressional structures are still active at present, as shown by the offshore seismicity. From the structural analysis and focal mechanisms of the earthquakes we conclude that the Bajo Segura Basin and its adjacent shelf have been subject to NNW–SSE compression since Late Miocene until the Present. Folding and reverse faulting of the Upper Miocene–Quaternary sedimentary cover and of its basement have accommodated this compression. The main active structures onshore, located in the Bajo Segura Basin, extend eastwards into the Mediterranean Sea. This fact is interpreted as the Eastern Betic Shear Zone continues offshore to the east.