In order to define seismic hazard with sufficient accuracy required for engineering applications, we initiated a multidisciplinary geoscientific study offshore western Peloponnese, focusing on the Kyparissiakos Gulf. Multibeam swath bathymetry localised unstable coastal slopes, which were later investigated by high resolution seismic profiles. Sediments and crustal structures were studied by multi-channel seismic recordings and active large-offsets seismic profiling. We established an onshore/offshore local seismic array that recorded 3500 micro-earthquakes in two months, and combined the results with historical and digital seismicity data in order to understand the active crustal deformation. These findings were further combined with geological mapping and tectonic observations from onshore Peloponnese and available offshore data. All this geologic and tectonic information was coupled with evidence from the analysis of historical and recent seismicity with the aim of identifying the seismogenic sources. We have defined nine seismogenic zones in western Peloponnese that are significantly different from those published in the literature. The new zonation addresses more accurately the deformation of the crust and sediments, and is the basis for a reliable seismic hazard analysis and seismic risk assessment. We identified a large area of the northern Peloponnese and the Ionian islands of Letkas, Cephalonia, Zakynthos and Strophades, to be involved in a SW-ward oriented crustal extrusion, dominated by two major dextral deforming strike slip faults: Cephalonia and Andravida with their offshore prolongation. Some changes with respect to the Greek zonation in the literature have been introduced in the region surrounding the new nine seismogenic zones to reach a homogeneous cover of the whole Peloponnese.