Moving from the RETIRA to the RETIRSA index in the application of Robust Satellite Techniques to short-term seismic hazard forecast: the case of the Italian region

Robust Satellite Techniques have been applied to the analysis of long-term satellite TIR (Thermal InfraRed) radiances to identify those anomalous transients (in the spatial/temporal domain) possibly associated with the occurrence of major earthquakes. A possible limitation associated to the used RETIRA (Robust Estimator of TIR Anomalies) index is related to the spatial distribution over the scene of meteorological clouds which affect the computation of the average thermal background that is used to remove those, large-scale temperature variations, due to warm/cold fronts and or anticipation/delay of seasonal behaviors (e.g. Aliano et al., 2008). In order to take into account such possible effects, also simplifying the process of thermal anomalies identification, a new index RETIRSA (Robust Estimator of TIR Slope Anomalies) has been introduced, which allows for taking into account possible large-scale meteorological forcing, without the need to estimate ground thermal conditions at the large scale. Such an index allows for investigating the “nocturnal heating” effect - already proposed by Bleier et al. (2009) as a potential precursor of major earthquakes – by an RST-based approach. In this work, the known ability of the RST methodology to discriminate anomalous TIR transients possibly related to seismic events from those TIR variations related to other causes (e.g. meteorological) has been verified by comparing previous results based on the RETIRA index with those achievable by using the new RETIRSA index. Preliminary results of such a comparison over a long (June 2004 - December 2014) time-series of MSG/SEVIRI TIR observations over Italy will be presented