地球低阶重力场系数J_2异常变化与地震活动的关系研究

The relationship research between the anomalous change of the low degree gravity field coefficient J_2 and the seismic activity

1992—2011年地球低阶重力场系数J2先后发生了两次异常变化,时间段约为1997—2000年、2007—2010年;根据中国地震台网(CSN)公布的地震目录,收集1990—2012年间发生在中国大陆MS≥3.0的所有地震资料,初步分析了J2异常变化与地震活动的关系。文中分别对浅源(深度范围0≤h≤70km)MS≥5.0、MS≥6.0和中源(深度范围70≤h≤300km)MS≥3.0、MS≥3.5、MS≥4.0地震总数进行了统计分析,建立了地震活动频次随时间变化的时间序列。文中将地震频次时间序列与地球低阶重力场系数J2长期变化作对比分析,结果显示:(1)浅源地震活动存在3个明显的峰值,第一个峰值和第二个峰值出现的时间段分别和"98异常"、"07异常"时间段吻合,第三峰值时间段和地球自转速率转变时刻吻合;(2)中源地震活动与浅源地震活动存在差异,前者仅存在两个明显的峰值,第一峰值出现的时间段和"98异常"吻合,第二峰值相对于"07异常"出现后移现象,然而小波多分辨率分析显示地震频次时间序列的小波细节系数发生显著变化的时段和"07异常"非常吻合;(3)中国大陆发生的7级以上的地震,62.5%位于J2异常变化期间、纬度集中分布于J2节点线35.3°附近。这些结果表明:J2异常变化可能会对中国大陆地震活动产生较显著的影响;地球自转速率转变的时刻对浅源地震活动产生较显著影响,而对中源地震活动影响不明显。最后从地球重力学以及J2变化与地球自转的关系方面分析J2异常变化与地震活动的关系。研究显示:1992—2011年间J2发生的两次异常变化的时间间隔大致为10a,这和地球自转"10a起伏"变化相吻合,这些结果对中国大陆地震孕育过程规律的认识以及地震预测研究具有一定的价值。

There were two anomalous changes that happened in the low degree gravity field coefficient J2during the 1992-2011,in two periods of about 1997-2000and 2007-2010;according to the earthquake catalog that reported by CNS,all the MS≥3.0seismic data in China Mainland during 1990-2012have been collected to make the preliminary analysis of the relationship between the J2anomalous change and the seismic activity.This paper makes statistical analysis of the total number of the shallow-focus MS≥5.0,MS≥6.0earthquakes（0≤h≤70km）and of the intermediate focus MS≥3.0,MS≥3.5,MS≥4.0earthquakes（70≤h≤300km）respectively to establish the time series of frequencies of earthquakes.This paper has made detailed comparison between the time series of frequencies of earthquakes and J2,and the results are as follows：（1）the shallowfocus earthquake activity has three peaks,the first peak time and the second peak time are consistent with＂98anomalous＂and＂07anomalous＂respectively,and the third peak time is consistent with the transition period of Earth＇s rotation rate;（2）there are differences between the intermediate focus and shallow-focus earthquake activity,the former has only two obvious peaks,and the first peak time is consistent with＂98anomalous＂,the second peak time appears the delay phenomenon relative to＂07anomalous＂,however,the wavelet multiresolution analysis shows that the wavelet detailed coefficients of the time series of frequencies of earthquakes changed significantly in the time period that is perfectly consistent with＂07anomalous＂;（3）the ratio of MS≥7.0earthquakes that happened during the time of J2 anomalous changing is 62.5%,and their latitude distribution is almost near the node line of J2about 35.3°N.These results show that J2anomalous change may lead to strong seismic activity in China Mainland,the transition of Earth＇s rotation rate could significantly affect the shallow-focus earthquake activity but not the intermediate-focus earthquake activity.In the end,this paper studies the relationship between J2variations and seismic activity from the aspects of Earth gravity and the relationship between J2and the Earth rotation.The results are valuable to us for further understanding the process of earthquake pregnancy and researching earthquake prediction.