2004 Mw 9.3 Sumatra-Andeman earthquake and gas geochemistry anomalies in CCSD borehole: A possible ultra-remote linkage
CCSD在线流体监测捕获的气体地球化学异常与2004年9．3级苏门答腊地震可能的超远程关系

We report unusual gas geochemical anomalies in response to the Dec. 26, 2004 MW 9. 3 Sumatra-Andeman earthquake in a distance more than 4100 km. The gas anomalies were captured by continuous real-time monitoring the geochemistry for the gases extracted from the drilling mud of the Chinese Continental Scientific Drilling (CCSD) project. The gas anomalies started at 11:30 pm on Dec. 24, 2004 ( Beijing Local Time) , and were possibly enhanced by the passage of surface waves of the 2004 Sumatra-Andaman Earthquake. Dramatic changes in gas geochemistry occurred at 7:30 am on Dec. 26, 2004, an hour and a half before the 2004 Sumatra-Andeman earthquake, and ended abruptly on Dec. 29, 2004. As compared with those gases before 7:30 am, Dec 26, gases from 7 :30 am, Dec 26 to 7 :30 pm, Dec 29 , 2004 are extraordinary. The 2004 Sumatra-Andaman earthquake is the most extraordinary recorded events in that it has about >500 s duration of high frequency energy radiation, > 1200 km along-strike rupture length, and > 200 km downdip rupture length. The gases anomaly observed during the CCSD drilling can be induced by either coseismic changes in static strain or passage of seismic waves. However, the CCSD drilling site is more than 4100 km away from the epicenter of the 2004 Sumatra-Andaman Earthquake, more than three times its rupture length. Such a long distance leads to coseismic static strain too smaller to trigger the opening of fractures; instead, the passage of transient seismic waves may induce changes in the mechanical properties or permeability of small sealed fractures and metamorphic rocks in the CCSD drilling site, and in turn enhance the release of gas or fluids that are trapped within the sealed fractures or rocks, and resulted in the dramatic shift in the trends of He-Ar systematics. Therefore, we suggest that the anomalous gas geochemical signals were enhanced by the passage of surface waves of the 2004 Sumatra-Andaman earthquake.