The September 26, 1997 Colfiorito, Italy, earthquakes: modeled coseismic surface displacement from SAR interferometry and GPS

The largest events of the 1997 Umbria-Marche seismic sequence were the two September 26 earthquakes of Mw=5.7 (00:33 GMT) and Mw=6.0 (09:40 GMT), whic h caused severe damage and ground cracks in a wide area around the epicente rs. We created an ERS-SAR differential interferogram, where nine fringes ar e visible in and around the Colfiorito basin, corresponding to 25 cm of cos eismic surface displacement. GPS data show a maximum horizontal displacemen t of (14 +/- 1.8) cm and a maximum subsidence of (24 +/- 3) cm. We used the se geodetic data and the seismological parameters to estimate geometry and slip distribution on the fault planes. Modeled fault depths and maximum sli p amplitudes are 6.5 km and 47 cm for the first event and 7 km and 72 cm fo r the second one, in good agreement with those derived from the seismologic al data.