The coseismic ground deformations of the 1997 Umbria-Marche earthquakes: a lesson for the development of new GPS networks

Abstract

After the occurrence of the two main shocks Mw=5.7 (00.33 GMT) and Mw=6.0 (09:40 GMT), on September 26, 1997, which caused severe damaged and ground cracks in a wide area of the Umbria Marche region [Tosi et al., 1999], the Istituto Nazionale di Geofisica in cooperation with the Istituto Geografico Militare Italiano, with the aim to detect the coseismic ground deformations, reoccupied 13 geodetic monuments placed across the epicentral area, belonging to the first order Italian GPS network IGM95 [Surace, 1993] and to the Tyrgeonet [Anzidei et al., 1995].The comparison between the 1995 coordinate set and those obtained during the surveys performed in the early days of October 1997 in the Umbria Marche earthquake epicentral area, shown maximum deformation values at the closest stations to the epicentres, up to 14.0±1.8 and 24.0±3.0 cm in the horizontal and vertical components, respectively. The availability of the IGM95 stations allowed translating geodetic data into relevant geophysical results. The estimation of postseismic coordinates at 13 vertices provided, for the first time in Italy, the evidence of significant displacements during a seismic sequence.