汶川M_S 8.0震前区域重力场变化与震质中研究

Regional gravity variation before Wenchuan M_s8. 0 earthquake and epicentroid research

青藏高原东缘地区地震灾害频发,2008年汶川Ms8.0地震给我国人民带来了巨大的灾难.汶川地震发震构造位于龙门山断裂带上,该断裂带在发震前长期闭锁,在汶川震中附近没有明显的小震活动和地表位移等前兆现象.本文以1998年至2005年的四期流动重力测网资料为基础,应用重力位场方法反演下地壳密度变化,开展深部孕震过程研究,结果表明:在汶川震前以震中200 km范围内,马尔康测点重力变化最大,超过100×10^(-8)m/s^2,并在2004～2005年间有聚集性小震群活动.根据本文反演的下地壳密度变化结果,判断其震质中位于该区附近,与汶川震中不重合.该区孕震期间重力场显著变化值与深部莫霍面结构相关性强,大范围明显的重力场变化预示着深部动力学环境的改变,可作为地震前兆异常深入研究.

There are lots of earthquakes in the region of eastern Tibet margin. Wenchuan Ms8.0 earthquake on 2008 gave our people huge disaster. This earthquake＇s epicenter is on the fault region of Longmenshan. However, this fault was in the long-term blocking state before earthquake. There are no distinct small earthquakes activity and ground surface displacement and others seismic forerunners near epicenter. In this paper, we based on the mobile gravity survey dataset, applied on the gravity inversion method to research the lower crust＇s density variation for reveal seismogenic process in deep earth. The results show that the gravity variation of Maerkang area was the largest in the Wenchuan epicenter 200 km range. The variation was more than 100 mGal and it happened clustered small earthquakes between 2004 to 2005. In accordance with the density inversion result of lower crust, we estimate the hypocentroid in the near Maerkang, but it is not coincidence with the Wenchuan epicenter. Moreover, the gravity variation is strong dependence on the Moho structure. The gravity variation with wide range indicates the geodynamic environment changing. It may be as earthquake precursor with further research.