Depth and morphology of reflectors from the non‐linear inversion of arrival times and waveform semblance data. Part II: modelling and interpretation of real data acquired in Southern Apennines, Italy

Abstract

ABSTRACTIn order to retrieve a 2D background velocity model and to retrieve the geometry and depth of shallow crustal reflectors in the Southern Apennines thrust belt a separate inversion of first arrival traveltimes and reflected waveforms was performed. Data were collected during an active seismic experiment in 1999 by Enterprise Oil Italiana and Eni‐Agip using a global offset acquisition geometry. A total of 284 on‐land shots were recorded by 201 receivers deployed on an 18 km line oriented SW–NE in the Val D'Agri region (Southern Apennines, Italy).The two‐step procedure allows for the retrieval of a reliable velocity model by using a non‐linear tomographic inversion and reflected waveform semblance data inversion. The tomographic model shows that the P wave velocity field varies vertically from approximately 3 km/s to 6 km/s within 4 km from the Earth's surface. Moreover, at a distance of approximately 11 km along the profile, there is an abrupt increase in the velocity field. In this zone indeed, an ascent from 2 km depth to 0 km above sea level of the 5.2 km/s iso‐velocity contour can be noted. The retrieved velocity can be associated with Plio‐Pleistocene clastic deposits outcropping in the basin zone and with Mesozoic limestone deposits. The inversion of waveform semblance data shows that a P‐to‐P reflector is retrieved at a depth of approximately 2 km. This interface is deeper in the north‐eastern part of the profile, where it reaches 3 km depth and can be associated with a limestone horizon.