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.
capable fault
ITHACA PROJECT AND CAPABLE FAULTS IN THE PO PLAIN (NORTHERN ITALY)
The use of the term “capable fault” instead of the more generic “active fault”, is to be preferred when dealing with faults, that, more than being simply active, have the capability to cut or deform the ground surface, generally in association, but not exclusively, with seismic events. Such faults are the most relevant from the societal hazard viewpoint, for the damage they can cause directly or indirectly (e.g., interaction between capable fault and high risk facilities) by offsetting the ground and by shaking (surface ruptures commonly accompany earthquakes above magnitude 6).
Recognition of presence of capable faults and assessment of their potential for surface rupturing is fundamental in the siting process of highly hazardous and strategic structures and, more generally, in land use planning and management of infrastructures, especially during emergencies.
So, being the Italian territory crossed by a large number of potentially capable faults, more than a decade ago the ITHACA (ITaly HAzard from CApable faults) project was initiated, to map and describe all faults recognized or suspected of being capable. The database, that contains more than 1500 faults (with a wide range of variability of the level of reliability of the input data), is managed by the Geological Survey of Italy, department of ISPRA.
In the Po Plain territory, ITHACA displays many of such structures. Despite the modest expected displacement (tens of centimeters at most) for each event along these faults, the high, and still growing, grade of human occupancy of this land makes the risk associated to seismicity and capable faulting a growing factor of anxiety. To begin a process of risk attenuation, specific norms in urban planning are needed to regulate development along capable faults, with special care when dealing with hazardous plants.