DEVELOPMENT OF REMOTE SENSING BASED GEOTHERMIC TECHNIQUES IN EARTHQUAKE STUDIES

Abstract

Earthquakes, the most unexpected and perhaps the most devastating natural calamity on earth, have imbibed interest in scientists from time immemorial. Studies on mechanism, cause, measurement of intensity and magnitude and not to mention prediction of earthquakes are still ambiguous. Generally, it is true that earthquakes cannot be predicted, but then devastating earthquakes keep coming and foster challenges to researchers world over. While analyzing past earthquakes and their characteristics perhaps a better understanding about this complex phenomenon can be made. That tectonics play a major role as the causative force behind an earthquake is now clear. Plate boundaries and fault zones are the most seismically active regions on the earth's crust and almost all past major earthquakes have been located along plate margins. Any pressure built-up due to tectonic activities, and also associated subsurface degassing due to closing of micro-pores with increasing stress, might create changes in the temperature regime near land surface. Charge carriers in rocks can be free electrons or deficient electrons (positive hole pairs or PHPs). PHPs dissociate under high pressure. When p-holes arrive at the earth's surface, they recombine by taking electrons from the surrounding and release heat. If by any technique, this change in thermal regime is detected, it can perhaps provide important clue to some impending earthquake activity. If earthquakes forewarn us before they strike, it is of utmost importance that we understand and pick up the clues. Satellite based radiometers, which can sense the thermal emission originating from the earth's surface and the intervening atmosphere, can be used to study any thermal anomaly developing near surface of the earth. Such satellite-derived detection of land surface temperature (LST) anomaly related to an earthquake is an important breakthrough for earthquake research. The concept that prior to earthquakes the LST increases has been validated by the study of 12 recent past earthquakes around the world. In the present study, LST maps derived from thermal NOAA-AVHRR data sets have been prepared and used to study the thermal scenario for the earthquakes in Bhuj (India) [26 January 2001 (Mw 7.7)], Boumerdes I (Algeria) [21 May 2003 (Mw 6.8)], Bam [26 December 2003 (Mw 6.6)] and Zarand in Iran [22 February 2005 (Mw 6.4)], Southeast Iran [13 March 2005 (Mw 6.0)] and in Banda-Aceh (Sumatra) [26 December 2004 (Mw 9.0)]. The earthquakes in Xinjiang [24 February 2003 (Mw 6.4)] and Zhangbei [10 January 1998 (Mw 6.2)] (China), Izmit / Kocaeli (Turkey) [17 August 1999 (Mw 7.6)], two earthquakes in Hindukush (Afghanistan) [3 March and 25 March 2002 (Mw 7.4 and 6.1)], and Kalat (Pakistan) [4 March 1990 (Mw 6.1)], have been studied using passive microwave SSM/I data sets. The Bhuj earthquake (India) has been analyzed using both AVHRR and SSM/I data sets. It has been observed that for all the above earthquakes studied, there were decipherable short-term temporal anomalies in the LST maps before the earthquakes. This thermal anomaly went away along with the earthquake events. The anomalies appeared a few days to a few hours preceding the earthquakes. The increase in temperature varied from 5-13° C than the usual temperature of the region around the epicentral area and also varied from earthquake to earthquake. Air temperature collected by meteorological stations situated near and around the epicentral area was obtained for the earthquake in Bhuj (India) and the several earthquakes in Iran. Temperature variation curves (TVC) were constructed using these data sets. The TVCs for these earthquakes also showed peaks of temperature increase before the earthquakes, which became normal again after the earthquakes. Air temperature normals were also constructed for the earthquakes in India and Iran, averaging data of several years. The amplitude of variation from normal was analyzed and was observed that the temperature was normal in all those years, unlike in the year in which the earthquake occurred. It has also been observed that the generation of thermal anomalies, their spatial extent, intensity and the days of their appearance prior to an earthquake depends on the magnitude, focal depth of the earthquake, terrain and meteorological conditions etc.