Study on thermal anomalies of earthquake process by using tidal-force and outgoing-longwave-radiation

Four earthquakes above magnitude 5.0 in Yunnan and Tibet, China occurred from 2010 to 2011. By calculating the tidal-force changes induced by celestial bodies in this region, we found that the earthquakes occurred when tidal-forces continuous¬ly grew from low to peak levels and approached the maximum amplitude phase, which indicated a tidal-force that had a trigger or inducing effect of active tectonic earthquakes when the ground stress reached a critical point. At the same time analyzing the abnormal changes of outgoing longwave radiation (OLR), along with the tidal cycle, indicated that the regional distribution of the enhancement region of OLR anomalies was closely related to geologic structure, especially ac¬tive faults. The OLR radiation anomaly evolved: an initial infrared rise, followed by an enhancement reaching peak, attenuation, and then a return to normal. The entire process was similar to changes observed in rock-breaking process under stress loads. Our investigation showed that the tidal-force changes caused by ce¬lestial bodies could trigger an earthquake when tectonic stress reached its critical breaking point, and the OLR anomaly was the radiation signature of the change in seismic tectonic stress. Therefore, the method of combining measurements of the tidal-force changes induced by celestial bodies with those of thermal-anomaly changes has some practical value for detecting the precursor state of impending earthquakes