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

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