Anomalous land surface temperature and outgoing long-wave radiation observations prior to earthquakes in India and Romania

Cumulative stress energy in an earthquake preparation zone under operating tectonic force manifests various observable signs of the impending earthquake, i.e., earthquake precursors. This energy transformation may result in enhanced transient thermal infrared (TIR) emission, which can be detected through satellites equipped with thermal sensors like AVHRR (NOAA), MODIS (Terra/Aqua). This paper presents observations made using NOAA-AVHRR data–derived land surface temperature (LST) and outgoing long-wave radiation (OLR) values in case of two moderate earthquakes (22 July 2007, Yamnotri earthquake, India and 27 October 2004, Vrancea earthquake, Romania) using anomalous TIR signals as reflected in LST rise and high OLR values can be seen conspicuously and following similar growth pattern spatially and temporally. In both the cases, data analysis revealed a transient thermal infrared rise in LST ranging 5–10°C around epicentral areas. The thermal anomalies started developing about 7–8 days prior to the main event depending upon the magnitude and focal depth and disappeared after the main shock. Similarly, the OLR values ~30–45 W/m² higher than the normal were observed 7–8 days prior to the main event. The rise in LST can be attributed to enhanced greenhouse gas emission from the squeezed rock pore spaces and/or to the activation of p-holes in stressed rock volume and their further recombination at rock-air interface. OLR is temperature and humidity dependent, and any change in these variables may be responsible for anomalous OLR values.