Discovery of spatial-temporal causal interactions between thermal and methane anomalies associated with the Wenchuan earthquake

Abstract

Few studies have determined the relationship between the thermal and methane anomalies associated with earthquakes. In this study, National Center for Environmental Prediction (NCEP) air temperature data and Atmospheric Infrared Sounder (AIRS) total column CH₄ data were used to extract the thermal anomalies and methane concentration anomalies before 2008 Wenchuan earthquake. The Granger causality test is then used to support or disprove some conjectures that describe the relation between thermal anomalies and methane anomalies The results show that thermal anomalies appeared from May 5 to 14, 2008, and that methane anomalies appeared from May 12 to 28. Spatially, thermal anomalies occurred to the south of the epicentre in the area with the maximum secular block motion before the earthquake, and the methane anomalies occurred along the Longmenshan Fault as well as the south of the epicentre. The Granger causality results indicate that change in crustal stress caused the thermal anomalies, creating the escaping channels for the underground gases, and then lead to the methane anomalies. In terms of the lag of the methane anomalies, the methane anomalies are unlikely to have been the main cause of the thermal anomalies. However, in the area with large block motion before the earthquake and in the surface rupture area, the methane anomalies may have also influenced the local temperature.