Fabrizio Bernardi

Crustal Velocity Structure in Italy from Analysis of Regional Seismic Waveforms

Abstract In this article, 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 1D crustal velocity models for the Italian peninsula. About 55,000 P -wave and 35,000 S -wave arrival times from 4727 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 a depth beneath the Apennines and a deep Moho beneath the central Alps. Green’s functions from the regionalized 1D velocity models are used to determine source depths and focal mechanisms for 37 events with a 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 that most thrust faulting events occur in the Adriatic Sea and the outer margin of the northern Apennines.

Seismic Moment from Regional Surface-Wave Amplitudes: Applications to Digital and Analog Seismograms

Accurate, consistent earthquake size estimates are fundamental for seismic hazard evaluation. In central Europe, seismic activity is low and long-term seismicity, available as intensities from written historical records, has to be included for meaningful assessments. We determined seismic moments M 0 of 25 stronger twentieth-century events in Switzerland from surface-wave amplitude measurements. These M 0 can be used to calibrate intensity-moment relations applicable to preinstrumental data. We derived the amplitude-moment relation using digital data from 18 earthquakes in and near Switzerland where independent M 0 estimates exist. The surface-wave amplitudes were measured at empirically determined distance varying reference periods T Δ . For amplitudes measured at T Δ , the distance attenuation term of the surface-wave magnitude relation S (Δ) = log ( A / T ) max + 1.66 log Δ is independent of distance. For log M 0 = M S + C E , we get log M 0 = S (Δ) + 14.90. Uncertainties of ±0.3 for the 14.90-constant correspond to a factor of 2 M 0 uncertainty, which was verified with independent data. Our relation allows fast, direct M 0 determination for current earthquakes, and after recalibration of the constant, the relation can be applied anywhere. We applied our relation to analog seismograms from early-instrumental earthquakes in Switzerland that were collected from several European observatories. Amplitude measurements from scans were performed at large amplifications and corrected for differences between T Δ and actual measurement periods. The resulting magnitudes range from M w = 4.6 to 5.8 for the largest earthquake in Switzerland during the twentieth century. Uncertainties for the early-instrumental events are on the order of 0.4 magnitude units. Online material : Moment-tensor analysis of 14 recent earthquakes.

Correction to “Moment tensor inversion of early instrumental data: application to the 1917 High Tiber Valley, Monterchi earthquake” by F. Bernardi et al.

This article corrects: F. Bernardi, M.G. Ciaccio, B. Palombo and G. Ferrari, Moment tensor inversion of early instrumental data: application to the 1917 High Tiber Valley, Monterchi earthquake, Annals of Geophysics, 59 (3), 2016, S0318; doi:10.4401/ag-6850.