Variations of multiple gaseous emissions associated with the great Sumatra earthquakes in 2004 and 2005

Three-dimensional (3D) temporal variations and correlation analysis of CO, CH4 and O3 concentrations associ-ated with the 26 December 2004 Sumatra-Andaman MW 9.1 Earthquake and 28 March 2005 Sumatra-Nias MW 8.6 Earthquake offshore of Sumatra, Indonesia were investigated using satellite data from AQUA AIRS in order to understand the lithospheric and atmospheric interactions during seismic activities. These great earthquakes occurred in the subduction zone northwest of the Sumatra Island. It was observed that large amounts of gases were emitted from the Earth's crust into the atmosphere before, during and after the earthquakes compared to the earthquake-free periods and background areas. Anomalies in CO, CH4 and O3 concentrations occurred along the NW-trending Sumatra fault system and peak values were found in the epicenter areas. Temporally, the anomalies occurred from 3 months before the Sumatra-Andaman Earthquake to 1 month after the Sumatra-Nias Earthquake and they lasted for 7 months. The correlation coefficients between the gas parameters increased with the period closer to the earthquake occurrence. More CO and CH4 were emitted from the epicenter area and O3 was produced in the background area during earthquake preparation period and occurrence reflected in the correlation analysis. The data indicated that the gaseous anomalies were most probably attributed to the gas emissions caused by the two great earthquakes that were accompanied by intense tectonic activities and fractures produced in the crust. After the underground gases were emitted into the atmosphere, they underwent a series of physical (diffusion, convection, etc.) and chemical reactions, which consequently lead to the gases (e.g. CO, CH4 and O3) anomalies at different altitudes in the atmosphere. The results are helpful in improving the judgment ability to understand geochemical earthquake anomalies and understanding the mechanism of lithosphere-coversphere-atmosphere-ionosphere coupling (LCAIC).