Carbon Monoxide Anomalies for the 2013 Mw =6.7 Lushan Earthquake Using MSSA-RST Approach

This article deals with the spatial-temporal investigation of the possible relationship of the carbon monoxide (CO) anomalies with the 2013 Mw =6.7 Lushan earthquake. The complexity of the seismogenic environment contributes to the irregular spatial distribution of CO background. Accurate estimation of the spatial reference background is crucial for precisely detecting seismic-related anomalies. In this study, we proposed an improved Robust Satellite Techniques (RST) approach, in which long-term spatial common variation was incorporated into reference background using multichannel singular spectrum analysis (MSSA) together with spatial clustering. Using the MSSA-RST approach, we detected CO anomalies associated with the Lushan earthquake, utilizing MERRA-2 data spanning from 180 days before to 90 days after the mainshock, and compared the results with those obtained using typical RST. The cumulative CO anomalies exhibited two accelerated growths in the form of a sigmoidal trend: from −51 to −40 days, and from −26 days to 15 days after the mainshock. Spatially, CO anomalies were distributed around the epicenter and along fault zones. Subsequently, we analyzed seismic events and deformation to explore the association between CO anomalies and the Lushan earthquake. The lithospheric Benioff strain also displayed two sigmoid accelerations preceding the mainshock, consistent with cumulative CO anomalies. Some high-value regions in the GPS velocity field were aligned with CO anomaly clusters surrounding Longmenshan, Xianshuihe, Zemuhe, and Anninghe faults. Furthermore, the spatial correspondence and temporal sequence of multiple parameters provide additional support for the potential seismic origin of most atmospheric CO anomalies detected by the new approach, which can be explained by lithosphere-atmosphere–ionosphere coupling (LAIC) models.