OLR anomalies of the Dezhou M_S5.5 earthquake in Shandong Province based on FY-3E satellite data

Based on the periodic variation of tidal forces, outgoing longwave radiation (OLR) data from the FY-3E satellite were used to analyze the daily variations of OLR from June 30 to August 30 in 2023 over a large area (17°N～55°N, 73°E～136°E) of the Chinese mainland. In addition, correlations between tidal forces, OLR, and the M_S5.5 earthquake that occurred in Pingyuan County, Dezhou on August 6, 2023 were discussed. Analysis of OLR changes and the synchronous tidal force cycle revealed that: ① During the periods without earthquake tidal force changes (cycles A and B before the earthquake and D after the earthquake), OLR exhibited no significant variations near the epicenter, whereas continuous OLR anomalies were observed during the earthquake period (cycle C), accompanied by continuous variation in tidal force from trough to peak to trough. OLR anomalies show the stage characteristics of initial warming, strengthening, peak attenuation, and gradual calming, which are synchronous in time. ② OLR anomalies were closely distributed around the Liaocheng-lankou fault, indicating that seismic tectonic movement was the main cause of OLR anomalies associated with the earthquake, and the evolution of OLR anomalies during the earthquake represent the radiation of seismic tectonic stress changes. ③ The earthquake occurred near the peak phase point of cycle C, synchronous with the enhanced characteristics of the OLR anomalies. Therefore, when accumulated seismic tectonic stress exceeded the critical state of rock fracture and sliding, the sudden change in the size and direction of the tidal force promoted the instability of the Liaocheng-lankou fault and induced the earthquake. These results also show that the OLR products of the FY-3E satellite are useful for identifying seismic infrared anomalies.