First evidence for Late Pleistocene to Holocene earthquake surface faulting in the Eastern Monferrato Arc (Northern Italy): Geology, pedostratigraphy and structural study of the Pecetto di Valenza site

摘要: Abstract The W Po Plain (Northern Italy) is commonly regarded as a region characterized by low seismicity hazard, due to the lack of historical and instrumental record strong earthquakes. Nevertheless, recent studies performed in Monferrato hills provide evidence active faulting possible paleoseismicity occurred Middle Pleistocene Holocene times. Therefore, for verifying seismic potential this area, we firstly revised available geological geophysical information. We selected area between Valenza Alessandria (Eastern Arc), which show best structural, geomorphic, stratigraphic setting documenting tectonic deformation faulting. Therein, identified, first time, earthquake surface displacement Late Quaternary pedosedimentary sequence exposed at Pecetto di Valenza. outcropping section has been logged investigated according an approach integrating sedimentological micropedological data with structural analyses radiocarbon dating. This allowed reconstructing evolution paleoseismic history site. From bottom, consists Miocene marly bedrock, whose weathering started Marine Isotopic Stage (MIS) 7 or 5 interglacials. A colluvial deposit follows, formation can be attributed MIS 5e. upper part two loess covers, showing different degrees weathering, possibly ca. 30 ka BP deepest (ca. 4 BP) uppermost one. accretion therefore older likely associated 3 2 glacial phases. Each records induced reverse warping, giving constraints events that In fact, 2D balanced retrodeformation section, pedostratigraphic constraints, identifying least phases deformation, more than five fault scarp-forming events, caused total net 4.8 m during past 40 ka. Our highlighted interaction tectonically aeolian deposition, allowing small drainage basin. results analysis reinforce conclusion previous Authors Arc should viewed gap, earthquakes (Mmax ∼6.5) long recurrence interval (in order several thousands years). relevant implications hazard assessment, must checked further trench investigations along mapped thrust faults affecting western Plain.