Abstract: The gravity field is one of the basic physical fields of the earth. The non-tidal time-space dynamic changes of the gravity field have full and clear physical meaning, which can reflect the material change and deformation process in the earth and are closely related to earthquakes that occur in the crust. Therefore the changes of the gravity field before earthquakes are often considered as a physical precursor. Variations of gravity at certain spatial and temporal scales can be obtained by campaign gravity observations. Usually, in such surveys the distribution of measurement sites are not uniform due to the natural conditions of the land surface. So the variation of the gravity field over time and the measurement error are largely at the same level. Because of dominant relative gravimeters, the changes of segment differences in relative site values are more reliable. Considering these issues, this work designs a method to represent the segment differences in gravity changes and defines a new parameter of G value to evaluate the changes of the gravity field. Using this approach, we examine the changes of gravity during 2009 to 2015 before the 21 January 2016 Menyuan M_S6.4 earthquake. The results show that the method proposed in this work can effectively describe the changes of the gravity field in the seismic area, which can provide a new line of thought for the quantitative description of the gravity precursor associated with earthquakes.

Key words: Menyuan earthquake, campaign gravity measurement, segment difference, earthquake precursor, quantitative analysis

摘要： 地震前的重力场变化现象常被认为是一种物理前兆。通过陆面流动重力观测，可以获得一定时空尺度的区域重力场变化。通常流动重力观测网络由于受陆面自然条件限制，测点空间分布不均匀；重力场随时间的动态变化量与测量误差基本在同一水平；由于测量设备以相对重力仪为主，测量段差变化比点值变化更可靠。基于以上3点文中设计了流动重力段差的表示方法，并定义了1个评价区域测网重力场变化显著性程度的G值定量化新参数。文中应用该方法跟踪研究了2016年1月21日门源M_S6.4地震前2009—2015年的多期重力年变化，结果显示该方法可以有效地刻画区域重力场变化程度，能够为地震重力前兆的定量描述提供1条新思路。

关键词: 门源地震, 流动重力测量, 段差变化, 地震前兆, 定量分析