GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.1 73 Galli P., Peronace E., Bramerini F., Castenetto S., Naso G., Cassone F., Pallone F., 2016; The MCS intensity distribution of the devastating 24 August 2016 earthquake in central Italy (MW 6.2) . ������ �� ����������� �� Annals of Geophysics, 59 Grünthal G., 1998); European Macroseismic Scale 1998 (EMS-98), Center Europèen de Géodynamique et de Séismologie, Luxembourg Italian Department of Civil Protection, 2017; http://www.protezionecivile.gov.it/jcms/it/terremoto_centro_italia_ 2016.wp Luzi L., Puglia R., Russo E. & ORFEUS WG5, 2016; Engineering Strong Motion Database, version 1.0. Istituto Nazionale di Geofisica e Vulcanologia, Observatories & Research Facilities for European Seismology. doi: 10.13127/ESM Quantum GIS Development Team, 2017; Quantum GIS Geographic Information System. Open Source Geospatial Foundation Project. http://qgis.osgeo.org Sabetta F., Pugliese A., 1996; Estimation of response spectra and simulation of Non-stationary earthquake ground motion , Bulletin of the Seismological Society of America, 86(2):337-352. Back azimuth determination of regional earthquakes using colocated measurements of ground rotations and translations during the 2016 central Italy seismic sequence A. Simonelli 1,2 , H. Igel 1 , J. Wassermann 1 , J. Belfi 2 , A. Di Virgilio 2 , N. Beverini 2 , G. De Luca 3 , G. Saccorotti 3 1 Ludwig-Maximilians-Universitaet, Münik, Germany 2 Istituto Nazionale di Fisica Nucleare, Pisa, Italy 3 Istituto Nazionale di Geofisica e Vulcanologia, Italy Introduction. On August 24, 2016, at 01:36:32 UTC a Mw=6.0 struck the central sector of the Apennines chain (Italy), causing almost 300 casualties and extensive destruction. During the following two months, both rate and energy of aftershocks decreased progressively. On October 26, 2016, the activity renewed with two energetic events (Mw=5.4 and Mw=5.9) until climaxing, four days later, with a Mw=6.5 shock. The colocated observation of ground translations and vertical rotations permits, with a single station approach, to estimate the Back azimuth (hereinafter BAZ) of the incoming wave-field generated by seismic events. The measurements that are object of this study are obtained my means of a large ring laser gyroscope named Gingerino and characterized in (Belfi et al. , 2017). This instrument is located, as shown in Fig. 1, inside the underground laboratory of the INFN in Gran Sasso and on top of his granite frame is located a broadband seismometer. We selected 33 events with the criterion of the best s/n ratio and we studied systematically the relative BAZ with a novel method based on rotation- to-translation comparison. Method. The classical seismological observations are based on the data recorded by seismometers, this sensors provide a measure of the ground displacement. During the transit of a seismic wave by the way the ground is not only translating but it also rotates; this means that the standard seismometer recordings of an earthquake are not a complete measure of the real ground motion. The experiment Gingerino permits to directly measure the vertical ground rotation rate. A comparison with the seismometer data, performed with the processing described below, allow an estimation of the direction of the incoming wavefield for S-waves horizontally polarized and Lg waves. The direct measure of the direction of the wavefield, based on physical principles, is of great importance itself as a property of the seismic event and can help to highlight geological/structural effects that can cause anomalous off-path propagation of the seismic waves. We assume the plane-wave propagation and we process the data set in order to get an experimental estimation of the events back azimuth. We compare this results to the theoretical