Inventario delle faglie attive tra i fiumi Po e Piave il Lago di Como (Italia settentrionale)

Abstract

This paper illustrates the inventory of active faults located the sector of Northern Italy between the Po and Piave rivers and lake Como and which pertain to the interval ranging from the Middle Pleistocene up to the Holocene (700,000 B.P. to the Present). The first part of the paper reviews the various definitions of "active fault" in the geological literature, explains the definition adopted here, and specifies the criteria applied in the inventory. The basis for the inventory consists in a detailed and accurate analysis of the neotectonic literature according to the following stages of research: preliminary fault selection, bibliographic research on the individual faults, compilation of a "Map of active faults" and of the fault data sheets. The "Map of active faults", on the scale of 1 : 500,000, contains the various faults which have been numbered, classified as "active" or "held to be active" and subdivided into "outcropping" or "buried". The data sheets for each fault or group of faults contain information on the location, name, neotectonic references, fault-type, attitude, displacement, lenght, trace features, period of activity, classification, degree of activity (determined by the average slip rate) according to three classes, and any additional notes. Overall, 144 faults were inventoried and mapped; 24 were classified as "active" and 120 as "held to be active". The Authors also analyze the distribution and features of the faults inventoried and present a "Degree of activity map". One may observe from the map that the major elements in the eastern area showed a Class II degree of activity (average slip rate ranging from 0.1 to 1 mm/year). In the Garda sector, the faults identified were found to have both Class II and Class III degrees of activity (average slip rate of less than 0.1 mm/year). In both sectors, an average slip rate greater than 1 mm/year (Class I degree of activity) was observed locally. After comparing these data with the findings of the most recent neotectonic studies, the authors conlcude that the isolated reliefs in the upper part of the Brescia plain are not part of the pre-Alpine neotectonic sector and that the degree of activity in the area North of lake Garda has been understimated in detailed studies due to the absence of definite markers for dating fault activity. Furthermore, the authors also consider the Holocene tectonic activity in the Adda river basin and in the Dolomites to be more widespread than has been indicated as yet. In addition, the Authors stress the necessity for more detailed and standardized studies that are also more coordinated with the various disciplines dealing with neotectonics. It is indispensable that a data bank be established for the collection of data on active tectonic elements; this study is intended as a first step in that direction.