Gravity Changes Associated with the Ms8.0 Wenchuan Earthquake Detected by GRACE

Abstract

AbstractTime‐varying gravity field and surface density distribution on and around Chinese Mainland are calculated by the GRACE satellite gravity data. Time series of gravity changes at typical locations are also obtained. At the same time, time series of displacements at GPS fiducial stations of WUSH, LHAS, KUNM and LUZH are obtained in the regional reference frame. Results from GRACE gravity observations indicate that there was significant negative gravity change along the Himalaya arc after the Sumatra earthquake, particularly during the period of 2006 to 2008. Meanwhile there was also obvious negative gravity change along the northwestern boundary of the Xiyu block. While there appeared an arc with positive gravity change along the northern and eastern boundaries of the Tibetan plateau in 2007. And positive gravity change was remarkable in the southern and middle segments of the North‐South seismic belt in 2008. This trend of gravity variation after the Sumatra earthquake began to change only after the Wenchuan earthquake. Displacements at four GPS stations recorded co‐seismic signals of the great Sumatra earthquake, and then the horizontal displacement vectors at WUSH, LHAS and KUNM showed significant changes in their general trend until the occurrence of the Ms8.0 Wenchuan earthquake. The changes in the ground mass in the Tibetan plateau and its surrounding areas as revealed by the GRACE satellites have provided new observation approach and data for the explanation of the dynamic mechanism of the Wenchuan earthquake. A preliminary explanation and discussion on the characteristics of the time variable changes in the gravity field observed by GRACE and the dynamic mechanism of the Wenchuan earthquake are presented in this paper by combining the features of regional tectonic movements and displacements of GPS observations.