Spatial spectral variations of microtremors and electrical resistivity tomography surveys for fault determination in southwestern Crete, Greece

The horizontal to vertical spectral ratio (HVSR) technique using microtremors and electrical resistivity tomography (ERT) surveys reveal a potentially seismic active source in southwestern Crete located within the outer forearc of the Hellenic subduction zone in one of the most seismically active deformed regions in Europe. The combined approach is applied on the Pahia Ammos coast southwest of the Paleohora peninsula and reveals an almost E-W-striking fault crosscutting the dense populated area. Spatial HVSR variations in the fundamental frequencies and HVSR shapes using microtremors pattern the effects of surface and subsurface structure on seismic ground motion and are capable of delineating fault zones. One clear HVSR peak in the low frequencies is related to the thickness of the alluvial deposits. Two amplified frequencies are attribute to lateral heterogeneities/irregularities induced by the fault zone and thickness variations of the geological column overlying the lateral irregularities of near-subsurface structure. Dipole-dipole and Wenner-Schlumberger configuration arrays are conducted to model the surface and subsurface structure variations. The identified fault zone striking E-W inland is capable of enhancing ground seismic motion and significantly contributes to the seismic hazard assessment of the studied area. Geophysical results are cross-correlated, verifying the validity of the research outcome.