Robust satellite techniques for seismically active areas monitoring: a sensitivity analysis on september 7th 1999 Athens’s earthquake.

Space-time TIR anomalies, observed from months to weeks before the occurrence of earthquakes, have been suggested, by several authors, as pre-seismic signals. A robust approach (RAT) has recently been proposed (and successfully applied in the field of monitoring major natural and environmental risks) which permits a statistically based definition of TIR anomaly even in the presence of highly variable contributions from atmospheric (e.g. transmittance), surface (e.g. emissivity and morphology) and observational (time/season, but also solar and satellite zenithal angles) conditions. In this paper the actual potential of satellite TIR surveys is evaluated on the basis of several years of NOAA/AVHRR and METEOSAT observations over Europe. TIR anomalies, possibly associated to the Athens's earthquake which occurred on September 7, 1999, have been particularly considered in order to evaluate the capability of the proposed approach to filter-out noisy contributions to the measured TIR signal due to variable, observational and meteorological, conditions. This study demonstrated the capability of the proposed method to isolate (if any) possible pre-seismic anomalous TIR patterns from the most important noisy contributions to the measured signal. The advantages offered by the use of geo-stationary (quite doubling the achievable signal-to-noise ratio) instead of polar satellite packages result also quite evident after the tests performed in the case of Athens's earthquake. Even if it was not the aim of this paper to confirm or confute the existence of pre-seismic TIR anomalies (an extended number of test-cases should be analyzed before), results here achieved surely encourage the continuation of the studies in this direction permitting, moreover, to devise suitable strategies in order to obtain more firm answers to this fascinating hypothesis