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

2004 Mw 9.3 Sumatra-Andeman earthquake and gas geochemistry anomalies in CCSD borehole:A possible ultra-remote linkage.

中国大陆科学钻探工程在线流体地球化学监测在2004年12月10至2005年1月10日之间捕获到一段重要的气体地球化学异常。该异常从2004年12月24日晚上11点半开始到12月29日晚上7点半结束,其中在12月26日早上7点半到29日晚7点半这段异常非常特殊,表现出流体地球化学的剧烈变化。具体表现为流体组分从基本上不含Ar、He及N2跳跃到富含Ar、但亏损He和N2。该异常发生在2004年9.3级苏门答腊地震前1个半小时。由于CCSD现场离苏门答腊地震震中距离大于4170公里,大于该地震破裂长度1200公理的3倍,该地震在CCSD现场产生的静态应力变化微乎其微,不足以导致CCSD现场深部岩石或封闭破裂的岩石物理性质剧烈变化,因而可以排除静态激发效应的作用。在我国的云南和广东等地所观测到的地震异常和地下水位变化等表明2004年苏门答腊地震的动态激发效应主要沿东北方向,这和大地震的动态激发具有方向性一致。而CCSD现场就位于该方向上。我们推测2004年苏门答腊地震所产生的面波在CCSD现场激发的动态效应,导致库仑型失稳,增进深部岩石或破裂带的渗透率,释放富含Ar但亏损He和N2的流体,产生CCSD所观测到的气体异常。

We report Unusual gas geochemical anomalies in response to the Dec. 26, 2004 M-w 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 pill 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 scaled 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.