A procedure to identify objectively active seismotectonic structures

The scope of the present work is to present a procedure capable of identifying objectively seismically active tectonic structures. The procedure is essentially based on finding spatial clusters of seismicity on the basis of bidimensional filtering of seismic catalog epicentral. data, and has to take account of the fact that catalog reliability and resolving power are functions of time and position. These problems, which can potentially lead to an incorrect regionalization, can be attributed to catalog incompleteness. The effects of the latter are estimated and corrected through a new approach which determines the completeness interval and measures the degree of incompleteness from the plot of the cumulative number of events. The resulting procedure for assessing completeness is very simple, but achieves a far better accuracy than common methods such as the contingency table and Stepp's method. While, obviously, it is not possible to fully correct the catalog for data which are faulty or missing in the original sources, all the information can be used in contour mapping by an appropriate weighting of incomplete parts. On the other hand, the choice of the weighting factors involves some arbitrary judgement and therefore introduces a bias. In Order to reach an objective result, different weighting schemes covering all feasible choices are tried and the final regionalization is concluded to be valid only if it is stable. Active tectonic structures are then easily identified by comparison with geologic maps. An application to the southern Calabria-Sicily region is presented.