|Titolo:||From high temporal resolution to enhanced radiometric resolution: Night Thermal Gradient results|
|Data di pubblicazione:||2014|
|Abstract:||Anomalous thermal infrared (TIR) emissions have been widely detected by satellite sensors prior to major earthquakes. A recent processing technique for data from geostationary satellites, here demonstrated for the case of the April 06, 2009 magnitude 6.3 L’Aquila earthquake, allows us to identify areas of enhanced TIR emission around the epicentral region within a distance of about 100 kilometres. The index, called Night Thermal Gradient (NTG) identifies TIR anomalies by following the temperature trend during the night, when the surface of the Earth normally cools. However, leading up to the earthquake, an anomalous warming trend was observed. We compare the anomalous NTG pattern to the expected normal trend, taking into account the overall tectonic setting, the seismogenic faults and lithological spatial features, the orography, and the world stress map for the epicentral region. While a certain lithological selectivity can be recognized, the main stress field and known seismogenic faults seem to be less important than topographic heights, which are to be classified as non-seismogenic. The strong correlation between topography and TIR anomalies agrees with the proposed physical mechanism for the generation of TIR anomalies, namely the role played by stress-activated positive hole charge carriers, which tend not to stay in the valleys but to spread to mountain tops. This relation is apparent in the association of two tectonic features with thrust, where strong – horizontal – compressive stresses seem to be provide favorable conditions for the generation of TIR anomalies. The modification of these stress fields prior to the L’Aquila event have triggered the failure of the Paganica Fault. It is important to note that the distances, over which the TIR anomalies occurred, are an order of magnitude larger than the estimated length of the main fault rupture. Pixel-by-pixel time series comparisons between the maximum TIR anomaly area and the epicentre of the main shock show that the increase in radiative emission was associated with the areas of highest TIR anomalies, not with the area immediately surrounding the epicenter.|
|Tipologia:||4.2 Abstract in Atti di convegno|
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