Analysis of seismicity patterns for the Italian territory: monitoring and validation issues

Abstract:

A reliable characterization of possible pre-earthquake processes requires their rigorous formalization and testing, first in retrospect, and then in an experimental real-time mode.

Nowadays Italy represents the only region of moderate seismic activity where rigorous prospective testing of seismicity patterns at the intermediate-term middle-range scale is ongoing since more than a decade. Specifically, two different algorithms are simultaneously applied, namely CN and M8S, which are based on general concepts of pattern recognition that permit to deal with multiple sets of seismic precursors. These methods make use of detectable inverse cascade of seismic process to allow for a diagnosis of the periods of time when a strong event is likely to occur inside a given region. The results from experimental testing, regularly updated every two months since 2003, permit a routine validation of the considered patterns at the intermediate space-time scale.

The reduction of uncertainties about location (where) and time (when) a strong earthquake has to be expected requires the use of additional information, which may be eventually provided by different observables (e.g. GPS, gravity, geochemical and other geophysical evidences), other methods (e.g. PI), as well as by relatively lower magnitude seismicity data from high quality local catalogs. The possibilities for an integrated analysis of different data are exemplified, focusing on the North-eastern part of Italy. In particular, a formal analysis of accurate local bulletins, compiled at OGS since 1977, is carried out based on nearest-neighbor distances of events in space-time-energy domain, with the aim to verify possible pre-earthquake features of seismic clusters in the area.

The issues related with prospective testing of the applied methodologies are discussed, including problems with space-time homogeneity of input data, illustrating the results obtained for the recent strong earthquakes in Italy.