选取2004年12月26日印尼苏门答腊Mw9.0地震的余震分布空间范围为研究区域,该区域位于缅甸小板块中部,纬度范围为2°N～15°N.根据USGS地震目录,研究了2004年印尼苏门答腊Mw9.0地震前地震频次的时空变化,并分析了地震活动与地球自转的关系.结果显示:1)在余震区域范围内,地震频次自2000年开始出现了明显的上升趋势变化,反映了地震活动的增强过程,临近地震发生前,地震频次有一定幅度的回落；2)通过地震频次空间扫描,发现震前在震中附近区域地震活动增强显著；3)在1990～2004年的15年中,单位时间内发生的地震数在地球自转季节性变化减速时段与加速时段之比值rda在震前出现明显的上升过程:1998年～2002年rda缓慢上升,2002年底rda快速上升达最高值,之后,rda呈现下降趋势,直至苏门答腊Mw9.0地震发生；4)2000年1月～2004年11月间,在纬度1°N～7°N的空间范围内的震中附近地区,5.5级以上地震都发生在地球自转季节性变化减速时段内；5)地震活动累积年频次相对于其长期平均值的变化量△N与地球自转“十年起伏”变化关系表现为地球自转减速时△N上升,地震活动增强,加速时△N下降,地震活动减弱.这些现象并非偶然,可能预示着地球自转减速与苏门答腊Mw9.0地震之间存在着某种联系,这些结果对地震孕育过程的认识和地震预测研究具有一定的价值.%The region where the aftershocks of the December 26, 2004 Indonesia Sumatra earthquake of MW9. 0 are distributed is selected for research in this spaper. It is located in the central part of the Myanmar plate, with a latitude range from 2°N to 15°N. The data of the earthquake catalogue pubulished by the United States Geological Survey is used to study the temporal and spatial variations of the earthquake frequency before the 2004 MW9. 0 Indonesia Sumatra earthquake, and to analyze the relationship between the seismicity and the earth rotation. The results are as follows: 1)A very clear gradually increasing variation of the earthquake frequency within the region of aftershocks began from 2000, reflecting the enhanceing process of the seismicity. The earthquake frequency decreased to a certain extent prior to the imminency of the main shock. 2) Through the spacial mapping analyse of the earthquake frequency , it is found that a significant increasing region of seismic activity was located near the epicenter before the main shock. 3) The rda value, defined as the ratio of earthquake number cuurring in a unit time in the deceleration period of the earth rotation to that in the acceleration period of the earth rotation, increased significantly before the MW9. 0 earthquake. It increased slowly from 1998 to 2002, and reached to the maximum at the end of 2002, and then decreased until the occurrence of the main shock. 4) The M≥5. 5 earthquakes occurring in the region with latitude range from 1°N to 7°N near the epicenter almost all happened in the deceleration period of the seasonal change of the earth rotation. 5) When it is in the deceleration period of the seasonal change of the earth rotation, AN, defined as the deference between the cumulative annual frequency of seismic activity and its mean, increases, which shows that the seismic activity enhanced. When it is in the acceleration period, AN decreases, and the seismic activity becomes weak. This phenomenon is not accidental, maybe reveals the relation of the MW9. 0 Indonesia Sumatra earthquake to the deceleration of the earth rotation. These results are valuable to us for further understanding the process of earthquake pregnancy and researching earthquake prediction.
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