Investigation of earthquake cloud and thermal changing precursor in finding earthquake caused fault Case Study: Mohammad-Abad-e-Rigan (January 27, 2011)

Hence Iran locates on Alpine-Himalayan seismic belt and it has high seismicity, Study of earthquake seismology is necessary. Part of alpine-Himalayan seismic belt is Iran plateau that demonstrates high seismicity behavior and it has unique deformation.
Seismotectonic studies indicate very density of active fault existence in this plateau. In all of Iran seismotectonic regime, east of Iran seismotectonic zone due to presence of strike slip fault system and occurrence of large earthquake has a great importance. Happening of destructive earthquakes such as Bam (2003) 6.6 Mw and Rigan (2010) 6.7 Mw reveal high potential of occurring. Intended area in this study is Rigan that locates in Kerman province, Iran. This area has important faults such Kahurak, Bam, Nosratabad, Shahdad, Guk, Golbaf, Sirch and Sabzevaran that they are have high seismicity.
In this paper, we considered cloud formation as earthquake precursor for Mohammad Abad Rigan earthquake (2011) that ever known less. Also thermal precursor was considered in this study. According to existing theories, raises in stress can produce initial fracture in region. So with raising in temperature, water evaporation in pore of stone is created. When vapor has appropriate condition (for example; lower temperature and existing enough water), it convert to clouds. One of fantastic feature of this phenomena is these clouds can’t move in presence of wind Because of steady source of their generation. This fact is a distinguishable thing for recognizing of this cloud among other clouds. In first part, panchromatic images of 62 days before the event was got and then these row images was georeferenced. So earthquake clouds digitally extracted and the result superposed on topography map of intended region. Also it should be mentioned that earthquake clouds, 10 days prior to earthquake (17th January) was detected. 10 days is suitable time for decision in determiner organization for example; Governorates, Municipalities and etc. for good conclusion about earthquake occurring, verdict based on cloud earthquake is not enough and it is necessary that we applied other precursors. One of them is thermal infrared that has great results.
In another part of study, temperature content of thermal bands (bands 31 and 32) of MODIS is extracted and Land Surface Temperature (LST) time series was created. Temperature variations is always considered as an important and effective factor in earthquake phenomenon studying. Thermal anomaly can be seen within 1-24 days before earthquake and the temperature increases 5-12 degrees and then returned to the previous mode after the earthquake. Some other researchers presented the increase of 2-10 degrees. The idea that earthquake may interrelated with temperature proved by applying it in Russia, China and Japan. However, notice that thermal anomaly may occur due to other reasons except earthquake. When it is because of earthquake, actually it is because of the stress exists in underground layers and change in soil properties. Zuji et al. (1990) proved that gases such as methane, carbon dioxide and hydrogen released from soil cracks before earthquake which lead to intensification of chlorofluorocarbons (CFC) and magnetic fields of the earth. There are some other theories about this phenomenon such as piezoelectric and expansion forces of the elastic strain that increase temperature.
After getting images from NASA website and preprocessing, by deduction of Air temperature time series from LST time series, atmosphere effects that exist because of air weather condition, is eliminated. Obtained signal was some noisy. In the next step, the wavelet as a powerful filter is applied on time series. For extracting Interpretable results, Statistical test such as standard deviation must be perform on filtered time series. Standard deviation (ST) can create normal limited area. By using limited area that produced by ST, thermal anomaly is detected 2 days prior to earthquake. Also with colorization of thermal images and then creation of visual time series, strike of fault line is found.
Finally, by Comparison between earthquake cloud line, focal mechanism and high temperature zone, high correlation was found. These results show that observed cloud related to Rigan earthquake and also show that high temperature zone related to earthquake event, too.
Results of this study can be used in two aspects. One of these is application in early warning system. Other aspect is application in geology usage. Second usage helps geophysicist and geologist to detect hidden and caused fault.