Seismic imaging of the shallow and deep structures in the Ancona landslide area

Abstract

Following the large 1982 Ancona landslide, which affected a densely populated district with many man-made infrastructures, a big effort was made by the scientific community to study the area and a great amount of geophysical and geotechnical data were acquired. The region is part of the external domain of Central Apennine resulted by Neogene compressive deformations. The tectonic processes have resulted in instabilities along the entire central Adriatic coasts of Italy, marked today by large-scale gravitational phenomena. An early Pleistocene regional uplift formed a slope subject to glacioeustatic sea-level oscillations, with erosion and water infiltration, favouring instability and movements under the action of gravitational driving forces. Sliding surface formation and roto-translational displacements have occurred until the recent reactivations of earth-flows and chaotic mounds at the slope break in correspondence with the formation of the Peri-Adriatic basin. In this paper, we present images of seismic sections obtained from the processing of two sea-land reflection profiles and offshore very high-resolution prospecting. Our paper intends to reinforce the importance of a multi-disciplinary approach integrating geophysical data to geological, morphological and engineering methods. The seismic survey of the two sea-land sections considered a joint land–sea acquisition to image the subsurface in the transitional zone. Composite sections were obtained from the processing of differently recorded sub-datasets, which depended on the type of land and marine sources and sensors in combination with the unique frequency content, source strength and noise, such as the propagation of surface-waves or air-gun bubbles. The properly acquired and processed data yielded post-stack migrated depth converted seismic sections, reflecting interfaces down to approximately 1400 m depth, where the top of Messinian evaporites has been encountered. The final sections reveal the deep structural settings and the importance of the still active anti-Apennine transfer faults.The offshore Boomer high-resolution profiles show only the near sea-bottom sequences. These fluvio-deltaic Plio-Quaternary deposits represent the final filling phase of the foreland basins, exposed to sub-aerial erosion during the last glacial period and to submersion during the subsequent sea-level rise of approximately 120 m.The final sections reveal the deep structural settings and the importance of the still active anti-Apennine transfer faults.