The major event of the 1997 Umbria-Marche (Italy) sequence: what could we learn from DInSAR and GPS data?

The main event of the Umbria-Marche (Central Italy) sequence was an MW= 6 earthquake following another MW= 5.7 event that had occurred a few hours before. Two kinds of geodetic data enable us to image the coseismic displacement field related to these two earthquakes: GPS measurements over several points in the area and the vertical displacement field provided by DInSAR interferometry with respect to a preseismic stage. Both measurements were taken approximately 15 days after the main shock. Other two MW> 5 earthquakes occurred nearby, 6 and 9 days after the main shock, also contributed to the observed displacement field. The present study of the main structure involved in this sequence is based on the comparison between a dislocation model that is as simplified as possible and both kinds of deformational data. The seismogenic structures involved in the four events were described by several studies, made before the present one, where reference is also made to seismological evidence. The previously obtained inferences of fault geometry (length, width and slip heterogeneity) concerning the main event of the Umbria-Marche sequence are used here as a starting model. Compared with previous analyses of the same measurements, the present study identifies to what extent each fault parameter is constrained by the data, quantifying the uncertainties associated with its estimated value.