Deformed stratigraphic markers in the shallow subsurface of the Po Plain: possible indicators of recent tectonic activity?

The Po Basin is a wedge-top basin developed atop a system of blind thrusts. These structures were originally considered to be inactive. Geomorphological and geophysical studies have supported the hypothesis of a recent activation of several blind thrusts. This hypothesis has been confirmed for some areas by two M=6 earthquakes that struck Emilia-Romagna in 2012. This research program is an attempt to use Late Pleistocene and Holocene stratigraphic markers as possible indicators of recent tectonic activity. Through accurate identification and mapping of deformed stratigraphic markers, the aim of the research is to understand the extent to which tectonics may influence Quaternary stratigraphy on short temporal scales and explore the possible use of high-resolution Quaternary stratigraphy to help predict the spatial distribution of future damaging earthquakes in the study area. Distinct types of stratigraphic markers include: (i) Paleosols. Two weakly developed paleosols were mapped in the Po Plain: the paleosol formed at the onset of the Last Glacial Maximum (29-24 ky) and the paleosol related to the Yonger Dryas cooling event (12.9-11.7 ky). (ii) Peat layers and lagoonal horizons (9-6 ky). Brackish deposits, in particular, are the most reliable stratigraphic markers, as they represent horizontal layers at time of deposition. (iii) Fossiliferous sand body that extends continuously in S-N direction, parallel to the shoreline. A wedge-shaped sediment body formed in response to coastal progradation, during the MIS 5e highstand was mapped in the Po Plain. In this work we demonstrate that areas of maximum deformation of Late Pleistocene- Holocene stratigraphic markers are strikingly coincident with the epicenters of historic and instrumental seismicity dating back to the last five centuries. This research shows that the accurate sedimentological and stratigraphic analysis of shallow buried depositional systems used in conjunction with conventional seismic stratigraphy can help assess a decipherable record of near-surface tectonic deformation.