GRACE卫星观测到的尼泊尔8.1级地震前后的重力变化

Gravity Variations before and after the M8.1 Nepal Earthquake Observed by the GRACE

利用GRACE卫星重力资料,计算尼泊尔地震震中及周缘重力和地表密度时空变化,并获取震源域特征点重力变化时间序列。结果表明,青藏高原内部、印度北部及华南块体东侧重力以增加为主,喜马拉雅与缅甸弧形带重力呈逐年减少趋势;尼泊尔地震发生在正负重力变化梯度带上,且重力变化在2015年具有明显的时间分段性特征,1~3月及地震发生的4月重力均以减小为主,5~9月以增加为主,12月以后以减小为主逐渐恢复;特征点时序揭示震源域重力呈长期减少趋势,并在2013~2016年呈现出"增加-减少-增加-发震-减小"的变化特征;地表密度变化较好地反映出地表质量迁移与重力变化的关系,为进一步理解尼泊尔地震的大陆动力学机制提供参考。

Variations of the gravity and the ground density of Nepal and its surrounding area are calcu- lated from the GRACE satellite gravity observations; furthermore, the time series of gravity changes at typical points around seismic sources in the region are also obtained. The results show that the ob vious negative gravity change rate is concentrated in the Himalaya and Burma arc regions, while the internal Tibetan plateau, northern India and the eastern Southern China block mainly present the significantly positive gravity change rate. The Nepal earthquake occurred in the transfer zone between the positive and the negative gravity changes. The gravity change rate has obvious time segmentation features during 2015： gravity changes decreased from January to April, increasing from May to September, but the gravity changes gradually recovered to increased tendency after December, 2015. Time series of typical points reveals that the gravity around the seismic sources region of the Nepal earthquake overall show long-time decreased feature, the gravity change rates mainly present the characteristics of ＂increase-decrease-increase-earthquake occurred-decrease＂ from 2013 to 2016. The chan- ges of the ground density can well reflect the relationship between the ground mass migration and the gravity change rate, which also provides an important reference for understanding the dynamic mechanism of the Nepal earthquake.