Subsurface 3D modeling of Giumentina Valley (Majella, Abruzzo, Italy) trough multi-methodic geophysical surveys

International audienceInto an archeological study of Giumentina Valley, near Caramanico Terme (Majella, Abruzzo, Italy), we performed a multi-methodic geophysical survey with the aim to delineate the geological setting. This is an ancient valley-basin whose riverbed was carved in Cenozoic limestone and has been filled with fluvial, lacustrine and slopes detrital sediments. Its geological history is closely connected to the evolution and the morphogenesis which affected the northern side of the Majella Massif in the last million years. In fact, the Giumentina Valley is a hanging valley originated as a consequence of paleogeographic variations that have led to the formation of lakes and marshes as well as the formation of endorheic karstic structures in some points of the abandoned riverbed. In order to reconstruct the stratigraphy along the valley we planned 6 Electrical Resistivity Tomographies and 24 single station passive seismic surveys. The ERT allowed to obtain 6 2D sections of the subsurface, longitudinally and orthogonally respect to the valley; trough HVSR survey we collected few points above the lines (to estimate an average shear velocity value of the alluvial and lacustrine deposits) and others scatter across the valley (away from the lines) to estimate the top marly-limestone bedrock depth. We utilized also a borehole log (located at north of the valley) to constrain the ERT interpretation and HVSR direct modeling. Trough the thickness of the different deposits units detected by geophysical surveys and starting from the actual DTM (digital terrain model), we calculated respective paleo-DTM of the marly-limestone bedrock and lacustrine top unit. The spatial localization of the 2D ERT and HVSR, performed by an RTK GPS survey, allows to know the spatial position of subsurface limits for the different deposit units. Trough an appropriate interpolation of these points is possible to generate the DTM representing different geological surfaces detected. Geophysical surveys performed, allowed to discriminate the stratigraphic sequence because of the different resistivity values for the lacustrine and alluvial deposits with a maximum thickness away from Morrone mountain. Furthermore the ERT method showed a buried doline at the center of the valley in accord with other similar forms into the area. With the actual knowledge is not possible to interpret more about carbonatic formation also with visible different resistivity. The initial aim, stratigraphic reconstruction of the deposits and 3D subsurface geometry of the valley, has been performed with a degree of uncertainty due to the geophysical spatial sampling, respect to the geological variability. However, it is possible to sustain that for this purpose, the spatial distribution of the 2D ERT and HVSR realized allowed to delineate the geological setting of the Giumentina Valley. It is under evaluation a seismic reflection/refraction survey to better delineate lithological and structural shapes of Giumentina Valley