The 1997 Umbria-Marche (Italy) earthquake sequence: analysis of the data recorded by the local and temporary networks |
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| Authors: | M Cattaneo P Augliera G De Luca A Gorini A Govoni S Marcucci A Michelini G Monachesi D Spallarossa L Trojani Xgums |
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| Institution: | (1) Dipartimento Scienze della Terra, n, Università di Genova, Viale Benedetto XV, 5, 16132 Genova;(2) GNDT-CNR, Via Nizza 128, 00198 Roma;(3) Dipartimento di Fisica, Università dell'Aquila, Via Vetoio, 67010 Coppito di L'Aquila;(4) Servizio Sismico Nazionale, Via Curtatone 3, 00185 Roma;(5) Osservatorio Geofisico Sperimentale, Trieste, P.O. Box 2011, 34016 Trieste;(6) Osservatorio Geofisico Sperimentale, Macerata, Viale Indipendenza 180, 62100 Macerata;(7) GNDT-CNR, Via Nizza 128, 00198, Roma;(8) Present address: ING, Via di Vigna Murata, 605, 00143 Rome, Italy |
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| Abstract: | We present some preliminary results obtained from thejoined analysis of the data collected by the permanentand the temporary networks operating in the area ofthe earthquake sequence that followed (andanticipated) the 26 September, Central Italy, mainshocks. In particular, these earthquake data haveallowed us to determine a well constrainedwave-velocity model (both P and S) with stationcorrections which demonstrated to produce robusthypocentral locations. These velocity modelswith station corrections have been used forre-locating the whole September 1997–July 1998subset of data of the permanent network, and theprevious background seismicity, starting from May1996. The focal mechanisms of the largest events werealso obtained from an analysis of the first-motionpolarities.Our results indicate that 1) the seismic activityaligns on a SE-NW trend for a total length of about50 km of extension; 2) the focal depth of theseevents is restricted to the range 0–9 km; 3) mostevents can be related to sub-parallel SW dipping faultplanes; 4) focal mechanisms of the largest shocks(ML > 4) show a coherent behaviour, withnormal fault solution on SSE-NNW striking, SW dippingplanes; 5) the space-time evolution of the activitydisplays a discontinuous mode of energy release, withdifferent episodes of activation and an apparentclustering of aftershocks at the edges of the areaswhich presumably ruptured in the main shocks. |
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| Keywords: | Aftershocks distribution Apennines earthquake location propagation models seismic sequences |
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