Relationship of Stress Changes and Anomalies in OLR Data of the Wenchuan and Lushan Earthquakes

The Longmenshan fault zone in southwest China has produced two large earthquakes within the last few years: the Wenchuan earthquake with magnitude scale (Ms) 8.0 on May 12, 2008, and the Lushan earthquake with Ms 7.0 on April 20, 2013. In this paper, we investigate the Coulomb stress changes, the data from the strainmeters and pendulum tiltmeter which detected stress changes before the Wenchuan and Lushan earthquakes, and the anomalies in the outgoing longwave radiation (OLR) data observed by National Oceanic and Atmospheric Administration Satellites. We do this using our proposed new change detection method, tested through examination of ten strong earthquakes in China, which can effectively reveal changes in OLR data before and after earthquakes. Our investigation suggests that the positive coseismic Coulomb stresses of Wenchuan may have increased the probability of the earthquake occurring. The pre-earthquake synchronous increments in stresses detected by strainmeters and the pendulum tiltmeter in several seconds can be viewed as slow earthquakes and thus may have triggered the Wenchuan and Lushan earthquakes. Our study indicates that there are larger OLR anomalies in fault zones than nonfault zones and those larger anomalies were generated before the Wenchuan than Lushan earthquakes. There were also larger increments in vertical pendulum tiltmeter and four-component borehole strains before the Wenchuan earthquake than before the Lushan earthquake. Our results suggest that larger stress changes may trigger larger earthquakes and cause larger anomalies in OLR data.