Robust Satellite Techniques for monitoring TIR anomalies in seismogenic areas

Based on Thermal Infrared (TIR) satellite observations, previous studies have been suggesting for decades a relation between TIR anomalies and seismic activity. Among the others, a Robust Satellite data analysis Technique (RST) was proposed which provides a statistically based definition of ?TIR anomalies? and a suitable method for their identification even in very different local (e.g. related to atmosphere and/or surface) and observational (e.g. related to time/season, but also to solar and satellite zenithal angles) conditions. The possible applications of RST to satellite TIR surveys in seismically active regions was already tested in the case of tens of earthquakes occurred in four different continents. Among proposed genetic models, the increase of green-house gas (such as CO
₂
, CH
₄
, etc.) emission rates has been also suggested to explain the appearance of such anomalous TIR signal transients in some relation with the place and time of earthquake occurrence. The results so far achieved by applying the RST approach to seismic areas characterized by strong degassing did not contradict this hypothesis. In this work long term Meteosat-TIR images have been analyzed, according to RST procedure, in order to demonstrate how an enhanced greenhouse gas emission can not be excluded among the main causes of TIR anomalies appearance close to the time/location of earthquake occurrence. Boumerdes earthquake (Algeria, M
_b
~ 6.8, 21
^st
May 2003) and mud volcano eruptions in Azerbaijan have been considered in order to investigate TIR anomalies behaviour in presence of prevailing CH
₄
emissions. The comparison with results achieved in areas with prevailing CO
₂
emissions stress an actual dependence of space-time signature of observed TIR anomalies on the prevailing green-house gas emission: for CO
₂
dominated area, thermal anomalies generally respond to morphological lineaments (i.e. tectonic faults), as it is expected for diffusing gases heavier than air. The opposite, with not so well-marked overlapping, happens in the CH
₄
dominated areas as it is expected for diffusing gases lighter than air.