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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.
The earthquake disaster on the eastern margin of the Qinghai-Tibet Plateau caused a great disaster for the people of our country in 2008. The Wenchuan earthquake seismogenic structure was located on the Longmen Shan fault zone, which was blocked for a long time before the earthquake There are no obvious precursory phenomena such as small earthquakes and surface displacements near the Wenchuan epicenter.In this paper, based on the data of four mobile gravity networks dating from 1998 to 2005, the gravity field method is used to invert the changes of the lower crustal density and carry out deep seismogenic The results show that within 200 km of the epicenter before the Wenchuan earthquake, the maximum change of the gravitational force at the Malcolm point exceeds 100 × 10 -8 m / s 2 and there is a small collection of small earthquakes between 2004 and 2005 Based on the results of the inversion of the lower crust density, we can conclude that its seismic mass is located near the area and not coincident with the Wenchuan epicenter.The significant change of gravitational field during the earthquake seismogenic period is strongly related to the deep Moho structure, The large-scale change of the gravitational field indicates the change of the deep dynamic environment and can be used as an in-depth study of the anomalous earthquake precursors.