Research and Application of Interpretation Technology of Gravity Magnetic and Seismic Joint Inversion

Abstract:

We take the Wenchuan earthquake in 2008 as an example, to explain the effectiveness of joint inversion for solving the problem of geological and geophysical interpretation. Which can also be used in the research of Nepal Earthquake in 2015.We use boundary identification and Euler deconvolution to inverse Longmenshan gravity anomaly before earthquake. Fault distribution features and the general depth about the fault top of Long Men-shan and its adjacent area before earthquake has been obtained. Figure 1 is the faults been divided. Among them, F₅, F₆, F₇are the main faults of Longmenshan, and the depth of these three faults are all above 20km.We use gravity, seismic joint inversion to analyze the formation mechanism of Wenchuan earthquake for the complex study area. Morphology difference and possible earthquake formation have been analyzed through the Euler deconvolution result of gravity anomaly measured section before and after the earthquake. Finally, we present 2D human-computer interaction joint inversion according to the existing seismic and gravity measurement results. Figure 2 shows that, the subsurface formation of Songpan - Ganzi has changed after the earthquake. According to the reduced bouguer gravity anomaly and the formation changes after the earthquake, we conclude that the change is due to the material migration which has a squeeze on Songpan-Ganzi region. While almost no change has taken place before and after the earthquake in Sichuan basin, which is due to the protection of the rigid crust.Through the research, we get the cause of the wenchuan earthquake: the movement of Indian plate, make the material into the margin of northeastern of qinghai-tibet plateau, which results to the strong activity and deformation of the northeasten edge of plateau, and deep material migrate to the east along the channel formed by large strike-slip fault system; Longmenshan fault zone is the main output channels of the material, so there are thrust nappe structure, while material continually flows to the east. The flows is cut off by the sichuan basin which is a hard crust block, so the matter migrate to the north west to dive;In a long time under the action of extrusion, the stress concentrating and deep matter and energy strongly accumulating, which finally lead to the earthquake.