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  • Seismological Society of America (SSA)  (3)
  • 1
    Publication Date: 2015-06-09
    Description: On 30 October 1930, an M w  5.8 earthquake hit the northern Marche coastal area (central Italy), causing significant damage ( I 0 VIII–IX degree Mercalli–Cancani–Sieberg) along a 40 km stretch of the Adriatic coast between Pesaro and Ancona, centered on the town of Senigallia. This area is characterized by relatively infrequent and moderate-sized earthquakes and by elusive active faults. In spite of the presence of well-known northwest–southeast-trending, northeast-verging fault-propagation folds forming the outer thrusts of the Apennines, the current level of activity, and the kinematics of these coastal structures are still controversial. We present a multidisciplinary analysis of the source of the 30 October 1930 Senigallia earthquake, combining instrumental and macroseismic data and elaborations with available evidence from geological and tectonic investigations. We determine the main seismic parameters of the source, including the earthquake location, its magnitude, and, for the first time, its focal mechanism, providing the first instrumental evidence for thrust faulting along the northern Marche coastal belt. Our findings provide conclusive evidence for the current activity of the northern Marche coastal thrusts. As such they have significant implications for the seismic hazard of the area, a densely populated region that hosts historical heritage, tourism facilities, industrial districts, and key transportation infrastructures. Online Material: Description of method used for moment tensor computation, tables of focal mechanisms and recording stations, and figures of seismic flux and uncertainty maps for macroseismic epicenters.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 2007-12-01
    Description: 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.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 3
    Publication Date: 2005-04-01
    Description: 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 (sub 0) of 25 stronger twentieth-century events in Switzerland from surface-wave amplitude measurements. These M (sub 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 (sub 0) estimates exist. The surface-wave amplitudes were measured at empirically determined distance varying reference periods T (sub Delta ) . For amplitudes measured at T (sub Delta ) , the distance attenuation term of the surface-wave magnitude relation S(Delta ) = log (A/T) (sub max) + 1.66 log Delta is independent of distance. For log M (sub 0) = M (sub S) + C (sub E) , we get log M (sub 0) = S(Delta ) + 14.90. Uncertainties of + or -0.3 for the 14.90-constant correspond to a factor of 2 M (sub 0) uncertainty, which was verified with independent data. Our relation allows fast, direct M (sub 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 (sub Delta ) and actual measurement periods. The resulting magnitudes range from M (sub 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.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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