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Thermal Infrared Anomaly Prior to Yiliang of Yunnan MS5.7 Earthquake

ZHANG Xuan1,ZHANG Yuan-sheng1,2,WEI Cong-xin1,2,TIAN Xiu-feng1,FENG Hong-wu1(1.Lanzhou Institute of Seismology,CEA,Lanzhou,Gansu 730000,China; 2.Lanzhou Base of Institute of Earthquake Prediction,CEA,Lanzhou,Gansu 730000,China)  
This study examines the thermal infrared anomaly occurring prior to the September 7,2012,MS5.7 earthquake in Yunnan Yiliang by analyzing infrared remote sensing brightness temperature data recorded by China Geostationary Meteorological satellite FY-2C/E.Infrared data of the prime time from 1:00 to 5:00 local Peking time was selected as the data source.Through data processing in which cloud data was disregarded,the power spectrum transform method was used to analyze and research the temporal evolution diagram of the earthquake thermal infrared anomalies and the timing curve of the brightness temperature average.The results show that 90 days prior to the earthquake,in approximately July 2012,a significant thermal anomaly area occurred near the epicenter,and exhibited irregular shapes.With the passage of time,the abnormal range gradually expanded along a particular direction of tectonic stress field,rapidly mutated,and gradually migrated from north to south.A large range of infrared anomaly up to hundreds of kilometers in length was recorded in the epicentral area,which is inconsistent with the temperature trend observed in the seismogenic zone.This abnormal area reached the maximum on September 1,2012,and gradually shrank after the earthquake occurred.The anomaly amplitude was rapidly reduced in the area near the seismogenic fault before disappearing.The earthquake thermal anomaly cycle was 64 days,and the thermal anomaly duration was more than 30 days.Prior to the earthquake,the magnitude of relative change was more than 10 times,for a maximum of the previous five years.From mid-July 2012 to the seismogenic day,the average increased sharply,and abnormal peaks appeared during the four days prior to the earthquake.After the earthquake occurrence,the characteristic amplitude gradually reduced,and anomalies dissipated step by step.Moreover,we determined that the brightness temperature anomaly exhibited zonal distribution along the fault,which should be related to the distribution of active tectonics.The thermal infrared anomalies observed prior to the earthquake were fairly obvious and persistent,lasting through two stages of initial and strengthening warming.The abnormal area shifted,expanded along the fault direction,and rapidly increased.The epicenter of this earthquake was not in the abnormal maximum area but approached the fault near the edge of the anomaly area.This situation is consistent with the results of most earthquake cases and may be related to the geological structure and the underground environment of the epicenter.These characteristics can provide some clues in determining future seismogenic time and tracking the location of the epicenter.Because the current understanding of the genetic mechanism of earthquake thermal infrared anomalies is not yet complete,future research should include shock cases and law summaries.However,the highlights of the thermal infrared anomaly occurring prior to this earthquake presented in this study are indeed authentic.
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