3D crustal structure of the Irpinia region (Southern Apennines): constraints from the integration of subsurface data and local earthquake tomography

The Irpinia region in the Southern Apennines is one of the areas with the highest seismic hazard in Italy, as also testified by several recent and historical earthquakes ranging between M_w 6.6-6.9 (1694, 1732, 1930, 1980). The shallow crust structural setting of this area is characterized by multiple deformational stages, which caused the tectonic stacking of Meso-Cenozoic sedimentary sequences deposited in different paleogeographic domains. The overall structure of the chain still contends between the thin-skinned and thick-skinned models.
We present a 3D geological model of key stratigraphic and tectonic elements based on the analysis of 2D seismic reflection profiles, integrated with well data and surface geology information. We also computed a 3D velocity model of the upper crust (V_p and V_p/V_s) through a local earthquake tomography (LET) to provide inferences on the structure and rock properties of the deep Apulian tectonic stack, especially where this is poorly imaged by seismic reflection imaging. We propose an integrated interpretation of the deep structure based on the analysis of the CROP-04 deep seismic profile and Vp and Vp/Vs patterns.
Our results highlight the presence of a regional thrust separating a shallow domain, characterized by relatively low-angle thrust surfaces (Allochthonous domain), from a deeper domain characterized by high-angle buried thrusts that affect the Apulian carbonate platform. The Plio-Pleistocene Apulian compressional architecture seems to control the rock physical properties in the upper crust and the seismotectonic of the area related to NE-SW regional extension active since the Middle Pleistocene. We observed that background seismicity concentrates in high-V, high-V_p/V_s regions that follow the Apulian structural trends and strictly correlate with the main crustal ramp anticlines. Furthermore, our structural model provides new geological insight regarding the destructive 1980 Irpinia earthquake (M_w=6.9), which ruptured three main fault segments.
From a methodological point of view, the integration of 3D geological model and LET is suitable for future earthquake relocations based on a data-driven velocity model reconstruction that considers the 3D geological complexities.