Possible thermal seismic precursors along Western boundary of Lut plate (IRAN)–Kerman area



So far a number of works on the heat flux anomalies of the earth surface based on the satellite images and underground water as seismic precursors have been carried out. In this paper the soil temperature data at 1m depth (deep enough to filter temperature variation due to high frequency meteorological forcings) has been considered to see if there are connections between earthquakes in Bam and Zarand (Kerman province) and seismic activities. Bam and Zarand are situated near the active faults; hence the activities of these faults may lead to thermal anomalies recorded at the soil temperature monitoring stations (Iranian Meteorological Organization). Usually near the surface soil temperature changes very rapidly by the meteorological forcing as daily variations of surface temperature due to changes of solar heating , but at deeper depth, say more than 0.5 m the changes are nearly negligible. Temperature data of different soil depth, namely, 10, 20, 30, 50, and 100 cm at 03, 09, and 15 universal times for years 1996-2005 are obtained from the Metrological Organization for Bam and 2003-2005 for Zarand stations. By analyzing the penetration of daily heat waves into the ground, the damping depths indicate that temperature deeper than 10 cm is usually unaffected by surface temperature variations. Hence we used temperature records of 100 cm and try to see if there are any anomalous changes prior to the major earthquakes in these two regions. The anomalies are deviation of temperature records from the mean trends of temperatures at these stations. The time lags between the time of troughs of anomalous signals and the time of minimum temperatures of the month earthquake occurred, were also estimated indicating that they are about 4-7 days. From the vertical temperature graients in the deeper soil, thermal diffusivity of the soil at and around of the time of the events were also calculated, indicating some changes. Also the water levels of some wells at these two stations indicated some changes, going down or up rather suddenly. All these changes show that there may be some variations prior and after the earthquakes. From these the actual temperature changes more vividly. Mean daily soil temperatures at 1m depth at these stations were analyzed, showing decrease (about 1.5 degrees) before the strong earthquakes and larger increase (about 2.5 degrees) after them. These changes may be due to seismic effects near the active zones.