Abstract
To better define the seismic velocities of the shallow crust in central Italy, in the area affected by the 1997 Colfiorito, 2009 L’Aquila and 2016–2018 Amatrice–Norcia seismic sequences, we selected all deep wells with available sonic logs from the Apennine belt to the related Adriatic foredeep. Sonic logs are among the most important in situ measurements of rock properties and provide a reliable image of physical conditions at depth. By analysing the wave train transit times, we inferred the P-wave velocity within depth intervals displaying homogeneous sonic log properties, and estimated the rock density by applying an empirical relationship between the sonic velocity and density in sedimentary rocks. We compared these results with the main litho-stratigraphic units in stratigraphic profiles of the wells. From the density estimates, we inferred the trends of the vertical stress magnitude in the belt, eastern front and foredeep geodynamic domains. This work is a contribution to better interpretation of physical conditions at depth and provides data that can be applied to define more complete seismological, gravity and magnetic models. We provide data uncertainties that must be considered to ensure proper use of data and to evaluate the spatial resolution of the models derived from those data.
Highlights
Information on P-wave velocity (Vp) data and the velocity model obtained from that information represent a first step, within the limits of geological and geophysical data, to constrain the tectonic structure of the crust in complex regions
In the northern Italy area including the Po Plain, the Apennine belt and Adriatic foredeep, a five-layer Vp model was gathered by the analysis of 64 deep wells; the overburden stress magnitude was calculated for each well, for the first time, in a wide area of Italy
Lithostatic gradients range from ~26 to 21 MPa/km from the belt through the Po Plain to the foredeep, with values of 130–105 MPa lithostatic pressure, at 5 km depth[7]
Summary
Information on P-wave velocity (Vp) data and the velocity model obtained from that information represent a first step, within the limits of geological and geophysical data, to constrain the tectonic structure of the crust in complex regions. In central Italy (Fig. 1) immediately after the Mw 6.0 24 August 2016 Amatrice earthquake[4,5], additional borehole data on the stratigraphic profiles and sonic logs were obtained in the belt very close to the Amatrice area (two wells) and, to the east, along the Adriatic foredeep (two wells)[6]. In this part of Italy, the lithostatic gradient gradually changes from ~26 MPa/km close to Amatrice to less than 23 MPa/km along the foredeep. Previously[3], Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143, Roma, Italy. *email: paola.montone@ ingv.it www.nature.com/scientificreports/
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