新疆及邻近地区重力场变化特征研究

Variation Characteristics of a Recent Gravity Field in Xinjiang and its Adjacent Regions

摘要:

首次利用1998-2010年共6期全国地壳运动网、数字地震网和陆态网络重力观测数据，通过整理计算平差，分别绘制了新疆及周边部分地区（西藏、甘肃、青海和宁夏）2~3年尺度重力场差分变化和累计变化图像，并结合动力构造环境和强震活动，剖析该地区重力变化特征及与强震孕育之间的响应关系。分析表明：新疆及周边地区重力场变化较明显，重力异常变化值较大，2~3年为尺度的重力变化值最大达到-140×10-8 ms-2；地震发生在重力变化转折、高梯度带附近和主要控制构造交汇部位；新疆及周边地区重力变化具有明显的分区特征，重力变化机制的差异与构造环境密切相关。

Abstract:

By calculating six stages of gravity data from 1998 to 2010，we obtained images of the differences and the cumulative changes in the gravity field within 2~3 year periods in Xinjiang and its adjacent areas （Tibet，Gansu，Qinghai，and Ningxia）.We then analyzed the corresponding relationship between the gravity changes and strong earthquake preparation through the dynamic structural environment and earthquake activity in Xinjiang.The results showed that the gravity field in Xinjiang changed obviously with a maximum of about -146×10-8 ms-2 within two to three years；earthquakes usually happened in a high gradient belt and in the main structural section；and the changing mechanism and differential of the gravity field were strongly related to the structural environment.In order to obtain dynamic changing images of the gravity field in Xinjiang and its adjacent region and the corresponding relationship between gravity change and strong earthquake preparation，this paper selected 100 gravity points （four to six absolute points and more than ninety solute points）which formed a monitoring network spread throughout Xinjiang，Tibet，Gansu，Qinghai and Ningxia via the China Seismological Bureau，the Zongcan Bureau，the Chinese Academy of Sciences and the state bureau of surveying and mapping unit.The data was processed with LGADJ software from the China Earthquake Administration.First，we selected relative and stable points to adjust the calculation process and address a few errors arising from a more significant and gross error，then proceeded with processing to reasonably determine the prior variance of each instrument.When we used the absolute gravity data to adjust the calculation process，we calibrated the weight in the 5×10-8 ms-2 precision relative gravity measurement data with the instruments used，by iterative computation.The results showed the accuracy to be within（8～12）× 10-8 ms-2 and the gravity change accuracy to be 15×10-8 ms-2.We found the anomaly region of the gravity field to usually have a high spatial gradient.Through our study on the evolution process in Xinjiang and its adjacent region，study results also revealed that an earthquake with an MS of 6.0 happened in this region.Due to an accumulation of stress, strain，and various physical features during earthquake preparation，Tianshan was pressed by the Tibetan plateau and Pamir with gravity decreasing in negative areas.The gravity value shows that the Tarim basin descended in the northwest，being pressed and accumulating in this region.