Sensitivity of coseismic gravity changes to source slip parameters: case study on the 2004 Sumatra earthquake

Abstract

Earthquakes are often accompanied by changes in the surface gravitational field during the preparation and occurrence. Inversion of source parameters by coseismic gravity changes can provide a foundation for understanding the characteristics of seismicity. In order to improve the accuracy of source slip parameters inversion by coseismic gravity changes effectively, this paper designed a set of methods to characterize the sensitivity of coseismic gravity changes to different source slip parameters quantitatively. Firstly, based on dislocation theories, the coseismic gravity changes under different source slip parameters can be obtained through forward modeling. Then, the dimensionless sensitivity analysis method is introduced to calculate the sensitivity factors of coseismic gravity changes to different slip parameters. Based on the fault model of the 2004 Sumatra earthquake, this paper evaluated the sensitivity of coseismic gravity changes to four independent source slip parameters quantitatively, namely depth, dip, slip and rake. The results show that the sensitivity of the coseismic gravity changes decreases in the order of slip, rake, depth and dip of the 2004 Sumatra earthquake. Because the sensitivity to slip is much higher than that to dip, small slip inversion deviation can cause large dip inversion deviation. Therefore, it is necessary to pay more attention to determine the slip and rake which rank ahead in the inversion process. In addition, even though the method designed in this paper is also applicable to other earthquakes, the sensitivity of coseismic gravity changes to each sliding parameter will be different in different earthquakes.