GROUND EFFECTS IN THE SEPTEMBER-OCTOBER 1997 UMBRIA-MARCHE (CENTRAL ITALY) SEISMIC SEQUENCE AND THEIR SIGNIFICANCE FOR SEISMIC HAZARD ASSESSMENT

摘要

The September-October 1997 seismic sequence in the Umbria-Marche region of Central Italy (main shocks on September 26th, Mw 5.7 and 6.0, and on October 14th, Mw 5.6) left significant ground effects, which were mainly concentrated in the Colfiorito intermountain basin. These effects included surface faulting, ground cracks and settlements, rock falls, slides, hydrological and gas anomalies. Of special interest was the observation of surface ruptures generated along segments of a system of normal faults already mapped as capable, with end-to-end lengths of 12 kilometers and maximum displacements of 8 cm. In this paper it is emphasized that surface faulting due to the 1997 event can be used to infer the threshold magnitude for surface faulting in Central Apennines, allowing to calibrate palaeoearthquake size from fault offsets as seen in trench investigations.