Quaternary Faults and Seismic Hazard in the Lake Garda Area

Evidence of active tectonic shortening in the Lake Garda area (Northern Italy) has been very well described in the geological literature for at least 40 years, mainly due to the extensive research conducted during the siting of nuclear power plants in Lombardia in the 80's. This area includes in fact the causative faults for some of the largest seismic events ever occurred in Northern Italy, i.e. the two medieval earthquakes of January 3rd, 1117 (Verona, Io = IX-X MCS) and the 25th of December, 1222 (Brescia, Io = IX-X MCS). More recently, two "twin" moderate events occurred at Salò on October 30th, 1901 (Io = VIII MCS) and November 24th, 2004 (Ml = 5.4). This is therefore a critical area for understanding the relationship between tectonic structures and earthquake source parameters in the Po Plain. We address this issue through new field data and airphoto interpretation, morphobathymetric investigations in South Lake Garda, and a systematic revision of published data. A new map of Quaternary faults is presented, that shows a good correlation between Quaternary deformations, major regional tectonic structures, and macroseismic information derived from local strong seismic events. Style and rates of activity of the proposed capable faults allow us to infer the typical seismogenic features of the characteristic seismic event for the Lake Garda region, which can be regarded as the controlling earthquake for the seismic hazard of the central part of the Po Plain.