Neotectonic study of Western Crete and implications for seismic hazard assessment

Demosthenis Mountrakis, A. Kilias, A. Pavlaki, C. Fassoulas, E. Thomaidou, C. Papazachos, C. Papaioannou, Z. Roumelioti, C. Benetatos, and D. Vamvakaris

A detailed study has been realized in the framework of a large-scale seismotectonic survey in Western Crete (Southern Greece), for the creation of a revised neotectonic map in a scale of 1:50.000, including the recognition and mapping of the main neotectonic faults and the evaluation of their seismic potential. For this reason, the faults under investigation were distinguished as active, possible active and inactive. Kinematic data and striations were used to estimate the corresponding stress field geometry. Two distinctive stress phases were recognized, operating after the Middle Miocene extensional exhumation of deep crustal rocks. The first N-S extension phase (D1) took place during Mid-Upper Miocene to Lower Pliocene, forming large normal faults, trending mainly E-W, that bound the large Neogene basins. The second phase (D2) took place during late Pliocene-Quaternary times, forming medium-to-large normal faults that trend mainly N-S, related to an E-W extension. In the E-W trending D1 faults, a younger strike-slip striation usually occurs, compatible with the later D2 kinematics. Smaller, mainly NE-SW trending faults, with significant lateral displacement, indicate a kinematic compatibility to the more recent D2 phase. Some of these faults act as transfer zones between the larger N-S trending D2 faults. Considering the fault length and the using several geological criteria for their seismic risk evaluation, we recognized 13 large major fault zones in the study area, six of which were considered as active, while three as possible active faults. Results obtained from the analysis of fault plane solution information verify both the determined active (D2 phase) stress field results, as well as the local kinematic behavior of the neotectonic faulting. Moreover, a detailed seismic hazard analysis, involving both probabilistic and deterministic approaches, shows a significant spatial variation of the various hazard measures, with the seismic hazard of the westernmost part of study area being controlled by the neighboring higher seismicity neotectonic faults.