Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/2153
AuthorsHunstad, I.* 
Anzidei, M.* 
Cocco, M.* 
Baldi, P.* 
Galvani, A.* 
Pesci, A.* 
TitleModelling coseismic displacements during the 1997 Umbria-Marche earthquake (central Italy)
Issue DateNov-1999
Series/Report no.2/139(1999)
URIhttp://hdl.handle.net/2122/2153
KeywordsCentral Apennines, coseismic displacements, GPS data, normal faulting
Subject Classification04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution 
AbstractWe propose a dislocation model for the two normal faulting earthquakes that struck the central Apennines (Umbria-Marche, Italy) on 1997 September 26 at 00:33 (Mw 5.7) and 09:40 GMT (Mw 6.0). We fit coseismic horizontal and vertical displacements resulting from GPS measurements at several monuments of the IGMI (Istituto Geografico Militare Italiano) by means of a dislocation model in an elastic, homogeneous, isotropic half-space. Our best-fitting model consists of two normal faults whose mechanisms and seismic moments have been taken from CMT solutions; it is consistent with other seismological and geophysical observations. The first fault, which is 6 km long and 7 km wide, ruptured during the 00:33 event with a unilateral rupture towards the SE and an average slip of 27 cm. The second fault is 12 km long and 10 km wide, and ruptured during the 09:40 event with a nearly unilateral rupture towards the NW. Slip distribution on this second fault is non-uniform and is concentrated in its SE portion (maximum slip is 65 cm), where rupture initiated. The 00:33 fault is deeper than the 09:40 one: the top of the first rupture is deeper than 1.7 km; the top of the second is 0.6 km deep. In order to interpret the observed epicentral subsidence we have also considered the contributions of two further moderate-magnitude earthquakes that occurred on 1997 October 3 (Mw 5.2) and 6 (Mw 5.4), immediately before the GPS survey, and were located very close to the 09:40 event of September 26. We compare the pattern of vertical displacements resulting from our forward modelling of GPS data with that derived from SAR interferograms: the fit to SAR data is very good, confirming the reliability of the proposed dislocation model.
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