Gravity Variation and Its Relationship with Earthquakes in Northeastern Margin of Tibet Plateau During 1998~2008

Abstract Gravity changes are often used in the study of hydrological environmental changes, but the gravity changes caused by earthquakes have also long been noticed. Significant anomalies of gravity changes have been observed before several strong earthquakes that occurred around the Tibetan Plateau. However, there are few studies on the complete gravity change processes before and after different earthquakes in the same area, and the characteristics of long-term background gravitational changes are not clear. Between 1998 and 2008, an extensive dataset of repeated gravity observation data was systematically collected across the Hexi Corridor in Gansu Province, China. This unique dataset, together with three earthquakes ( M ≥ 5) within the monitoring network during this period, provides an opportunity to study the complete gravity change process before and after the earthquakes. The gravity change data over a 10-year period indicate that the long-term background gravity changes in the region is negative within the Hexi corridor, possibly related to extraction of groundwater in the region. The M S 6.1 earthquake in 2003 and the M S 5.0 earthquake in 2008 were preceded by localized predominantly positive changes within 6 ~ 8 months prior to rupture. The earthquakes occurred during a process of gravity reversal recovery. This suggests that there may be an observational time window for the significant gravity positive changes prior to the earthquakes.