Gravity changes before and after the 2010 Ms7.1 Yushu earthquake

Absolute and relative gravity observations from 1998 -2010 from the China Crustal Movement Ob- servation Network, a major national scientific project, have been used to model the gravity field and its varia- tions associated with the April 14, 2010 Ms7.1 Yushu earthquake. The evolution of the regional gravity field and its relationship with seismicity before and after the Yushu earthquake are studied. The observed gravity changes are closely related to the active Ganzi-Yushu Fault, and gravity measurements can be used to observe the migration of material accompanying active faults and crustal tectonics. The dynamic variation of the gravity field reflects its evolution prior to and during the Yushu earthquake. The gravity measurements near its epicen- ter are as large as 80 × 10-s m/s2.and they show wave-like increases with time prior to the Yushu earth- quake.

Gravity variation before Kunlun mountain pass western M_s=8.1 earthquake

The relation between the gravity variation features and Ms=8.1 earthquake in Qinghai-Xizang monitoring area is analyzed preliminarily, by using spatial dynamic variation results of regional gravity field from absolute gravity and relative gravity observation in 1998 and 2000. The results show that: 1) Ms=8.1 earthquake in Kulun mountain pass western occurred in the gravity variation high gradient near gravit/s high negative variation; 2) The main tectonic deformation and energy accumulation before Ms=8.1 earthquake are distributed at south side of the epicenter; 3) The range of gravity's high negative variation at east of the Ms=8.1 earthquake epicenter relatively coincides with that rupture region according to field geology investigation; 4) Gravity variation distribution in high negative value region is just consistent with the second shear strain's high value region of strain field obtained from GPS observation.

Coseismic gravity and displacement changes of Japan Tohoku earthquake(Mw 9.0)

The greatest earthquake in the modern history of Japan and probably the fourth greatest in the last 100 years in the world occurred on March 11, 2011 off the Pacific coast of Tohoku.Large tsunami and ground motions caused severe damage in wide areas, particularly many towns along the Pacific coast. So far, gravity change caused by such a great earthquake has been reported for the 1964 Alaska and the 2010 Maule events. However, the spatial-temporal resolution of the gravity data for these cases is insufficient to depict a co-seismic gravity field variation in a spatial scale of a plate subduction zone. Here, we report an unequivocal co-seismic gravity change over the Japanese Island, obtained from a hybrid gravity observation（combined absolute and relative gravity measurements）. The time interval of the observation before and after the earthquake is within 1 year at almost all the observed sites, including 13 absolute and 16 relative measurement sites, which deduced tectonic and environmental contributions to the gravity change. The observed gravity agrees well with the result calculated by a dislocation theory based on a self-gravitating and layered spherical earth model. In this computation, a co-seismic slip distribution is determined by an inversion of Global Positioning System（GPS） data. Of particular interest is that the observed gravity change in some area is negative where a remarkable subsidence is observed by GPS, which can not be explained by simple vertical movement of the crust. This indicated that the mass redistribution in the underground affects the gravity change. This result supports the result that Gravity Recovery and Climate Experiment（GRACE） satellites detected a crustal dilatation due to the 2004 Sumatra earthquake by the terrestrial observation with a higher spatial and temporal resolution.

Gravity observation at continental borderlands (Russia, Primorie, Cape Shults)

The paper is focused on different kinds of gravity results obtained in Shults Cape Observatory for 2010 -2015. Gravity observation is interpreted together with GPS observation data which was obtained from 2012 to 2015 at the same station, The station is situated on Gamov peninsular （42.58° N, 131.15° E, Russia） at the coast of Japan Sea, This region constitutes the eastern boundary of Eurasia. This major continental tectonic feature is associated with a seismic activity, high heat flow and anomalous thickness of earth＇s crust. The goal of the observation was the investigation of gravity variation with time and seismicity situation monitoring. Gravity observation was developed at special basement by absolute gravimeter （GABL type） and by spring gravimeter （SCINREX CG-5and gPhone type）. Tidal models were tested by results of observation with spring gravimeters. Reduction task was solved, as the experimental data received from different points of Shults Cape Observatory was used. Applied reduction coefficient is 203.3 12Gal m l, and agrees with theoretical calculation. Next goal was studying structure of earth＇s crust by means of gravity models. Gravity anomaly varied from 30 mGal to 46 mGal, which also depend on difference reference system, Experimental results were used for testing of the structure of continental boundary, which also depends on the sea bottom flexion. Thickness of elastic layer was estimated from 12 km to 18 km by using different models.