KINEMATIC EVOLUTION OF THE MARTANA FAULT (UMBRIA-MARCHE APENNINES, ITALY) DURING PLEISTOCENE-HOLOCENE TIMES

Abstract

The Martana Fault exhibits a characteristic ""Jc" -shape plan view, with the longer fault segment trending N-NNW and the shorter one striking around Nl00°E. Ongoing activity of this fault is indicated by fresh and prominent fault scarps, interaction of faulting with drainage systems, and displacement of alluvial fan apexes. The structural-geological and geomorphic data indicate a recent polyphase kinematic evolution. After developing as a nor­mal fault in the Early Pleistocene, the N-NNW Martana Fault segment underwent a phase of dextral reactivation that extended from the Early-Middle Pleistocene boundary until around 0.39 Ma. The establishment of a stress field with a NE-ENE-trending o3 axis and NW-NNW o1 axis in the Late Pleistocene-Holocene resulted in a relevant component of sinistrai faulting along N­NNW-trending fault segments and almost pure normal faulting on newly formed NW-SE faults, which mostly formed in the Massa Martana area as pull-apart structures in the overlapping area between a pair of N-S-trending transtensional sinistral faults. The active -mainly left-lateral- transtensional kinematic along N­NNW-trending fault segments is also shown by the sinistral off­set of the E-W-trending Decumanus road at the ruins of the Roman town of Carsulae.