中国大陆科学钻探主孔流体地球化学异常与远强震的关系

2001年11月14日发生的昆仑山口西 M_s 8.1级地震和2004年12月26日发生的印度尼西亚苏门答腊 M_s 8.7级地震前后,中国大陆科学钻探(CCSD)主孔流体组成出现明显的异常。两次远强震前后的流体异常幅度很大,并具有相似的演化趋势。异常始于震前2-7天,He、N_2/O_2、He/Ar、N_2/Ar 为负异常,Ar/O_2为正异常。远强震前后流体异常特征与 CCSD附近小震前后流体异常特征具有明显的区别,表明昆仑山口西 M_s 8.1级地震前后和苏门答腊 M_s 8.7级地震前后的 CCSD 主孔流体异常可能与两次远强震相关。认为 CCSD 主孔中的 He、N_2、Ar 是记录远强震的敏感载体,可能记录了震前长周期波传播至 CCSD 主孔时激发的流体变化,反映了震源区的应力变化,也可能反映了区域构造活动乃至地球深部构造活动产生的场兆、源兆信息。

The gas anomalies in the CCSD borehole associated with two distant strong earthquakes: the 2001 West Pass of Kunlun Mountains earthquake (Ms 8.1) and the 2004 Sumatra-Andeman earthquake(Mw 9.3)

Based on the research of the fluid compositions in the mud of Chinese Continental Scientific Drilling Hole,short-term anomalies before and after two distant big earthquakes,the Nov.14,2001 West Pass of Kunlun Mountains Earthquake with M_s 8.1 and the Dec.26,2004 Sumatra-Andeman earthquake with M_s 8.7 (M_w 9.3),were recognized.The values of the concentration of He and the N_2/O_2,He/Ar,N_2/Ar ratios had changed significantly 2-7 days before the two distant earthquakes occurred.The abnormalities of the two earthquakes changed in the similar trends.The abnormalities of the concentration of He and the ratios of N_2/O_2,He/Ar and N_2/Ar show obviously negative,however,the ratio of Ar/O_2 changed reversely.The gas anomalies before and after the two distant earthquakes show very different from those of small earthquakes near the CCSD horehole.The evidence suggests that the concentration and ratio of compositions in the fluid of CCSD might be sensitive to the occurrences of distant strong earthquake.It might be the transmitting of long period wave during the event which triggered the changes of the concentration and ratio of fluid compositions. On the other hand,the anomalies might reflect the focal precursors and field precursors produced by a regional or deep tectonic activity.