Multi-beam bathymetry and high-resolution low-penetration seismic reflection profiles of the offshore extensions of the Betic Internal Zone off Sierra de Cartagena-La Union margin along its south side and the Mar Menor margin along its east side, the Mazarron Escarpment forming its southern boundary and the adjacent oceanic Algero-Balearic basin have provided images of the neo-tectonic structures of the region equal to those provided by subaerial photography. For the first time we mapped with unprecedented detail the Mazarron Escarpment and the Southeast margin of Iberia.The first-order structures of the region are due to the consequence of the collision of the African and Eurasian plates during the Alpine orogeny in late Oligocene-Middle Miocene, the westward migration of the Alboran plate in the Middle Miocene and the desiccation of the Mediterranean in the Messinian (Late Miocene) that led to the deposition of evaporites in the Algero-Balearic basin and erosion of the Mazarron Escarpment, the Sierra de Cartagena-La Union shelf, the Mar Menor margin and the adjacent coast. Our data images second order tectonic features (neo-tectonic features) superimposed on the larger structures. These include the deformation of the strata in the Algero-Balearic basin by the gliding of the Plio-Quaternary sediments on Messinian halite on the margins of the basin and sediment loading in its center, the Late Miocene-Quaternary deformation of the area north of the Mazarron Escarpment resulting from the continuous oblique convergence of the African and Eurasian plates in a NNW-SSE direction, the Miocene to Pleistocene volcanic edifices and pinnacles (dikes), the pockmarks formed by the extrusion of gas/water via faults and the massive gravitational failure of the Mazarron Escarpment triggered by this plate convergence. The data also show in detail features formed on the Mazarron Escarpment during the Messinian, Pliocene and Pleistocene regressions and those on the shelf formed during the Pleistocene glacially induced regressions/transgression and sediment drifts generated by modern currents.