Crustal Velocity Structure in Italy from Analysis of Regional Seismic Waveforms

Abstract

In this paper, we use regional seismic waveforms recorded by the recently-installed Istituto Nazionale di Geofisica e Vulcanologia (INGV) national network and the Mediterranean Very Broadband Seismographic Network (MedNet) stations to develop one-dimensional (1-D) crustal velocity models for the Italian peninsula. About 55,000 P -wave and 35,000 S -wave arrival times from 4,727 events are used to derive average seismic parameters in the crust and uppermost mantle. We define four regions, according to geological constraints and recent travel-time tomography results. Based on the average seismic parameters, we combine broadband seismic waveforms and travel-times of regional phases to model crustal structures for the four regions by applying the genetic algorithm. Our results indicate smooth velocity gradients with depth beneath the Apennines, and a deep Moho beneath the central Alps. Green’s functions from the regionalized 1-D velocity models are used to determine source depths and focal mechanisms for 37 events with magnitude larger than 3.5 by a grid search technique. Our results show that normal and strike-slip faulting source mechanisms dominate the Apenninic belt and most thrust faulting events occur in the Adriatic sea and the outer margin of the northern Apennines.