Yunma Xu

China Earthquake Administration, Peping, Beijing, China

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Publications (2)1.96 Total impact

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    ABSTRACT: Although it is well known that coseismic gravity changes take place during an earthquake, previous research has not yielded convincing evidence demonstrating that significant gravity changes occur before large earthquakes. Furthermore, even if we suspect that gravity changes occur before large earthquakes, we have yet to demonstrate how to consistently observe these changes for useful earthquake forecast that would bring benefits to society. We analyzed ground gravity survey data obtained in 1998, 2000, 2002, and 2005 at stations of the Crustal Movement Observation Network of China (CMONOC) and examined gravity changes before the occurrence of nine large (M s ⩾6.8) earthquakes that ruptured within or near mainland China and Taiwan from November 2001 to August 2008. Results from this analysis show that significant gravity changes occurred across a large region before each of these nine large earthquakes, and these changes were detected by repeated ground gravity surveys through CMONOC. Although these gravity changes were significant, more research is needed to investigate whether these gravity changes could be viewed as precursors of large earthquakes. Limitations and uncertainties in the data include sparseness of the gravity monitoring network, long time intervals between consecutive gravity surveys, inevitable measurement errors, hydrological effects on gravity, and effects of vertical crustal movements on gravity. Based on these observations, we make several recommendations about possible future directions in earthquake-related research using gravity monitoring data. Keywordsearthquake–gravity–seismology–China–Wenchuan–geodesy–GIS
    Geo-spatial Information Science 01/2011; 14(1):1-9. DOI:10.1007/s11806-011-0440-0
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    ABSTRACT: It was recognized 50 years ago that coseismic gravity changes take place during a large earthquake. In the past 30 years, there have been research efforts devoted to investigating possible associations between gravity variations and earthquakes in China. Before the Wenchuan (M(w) 7.9) earthquake, a group of researchers at the Second Crust Monitoring and Application Center of China Earthquake Administration noticed significant gravity changes in a region covering the well-known south-north earthquake belt in China and suggested in 2006 that the possibility for a major earthquake to occur near Wenchuan in either 2007 or 2008 was high. These researchers used gravity changes as the primary earthquake precursor to make the suggestion. In this article, we report the method used for repeated regional gravity survey, the procedures for gravity survey data analysis, and the characteristics of gravity variations before the Wenchuan earthquake that ruptured on 12 May 2008. Although gravity changes at a number of locations in the region surrounding Wenchuan were significant, more research is needed to investigate whether these gravity variations could be viewed as a precursor of the Wenchuan earthquake. Uncertainties in the reported gravity variations include inevitable measurement errors related to ground gravity surveys covering a large region, hydrologic effects on gravity, and the effects of vertical crustal movements on gravity. Other limitations of the data are that the density of the gravity observation stations is coarse and that the time intervals of the surveys were two to three years long. Based on these observations, we make several recommendations about data collection and data analysis procedures that would enhance future earthquake research using gravity monitoring data in China.
    Bulletin of the Seismological Society of America 10/2010; 100(5B):2815-2824. DOI:10.1785/0120100081 · 1.96 Impact Factor