GPS观测的2015年尼泊尔M_S 8.1级地震震前应变积累及同震变形特征  

Pre-seismic strain accumulation and co-seismic deformation of the 2015 Nepal M_S 8.1 earthquake observed by GPS

作　　者：苏小宁[1,2] 王振 孟国杰[1] 徐婉桢 任金卫[1] 

机构地区：[1]中国地震局地震预测研究所地震预测重点实验室,北京100036 [2]同济大学测绘与地理信息学院,上海200092 [3]Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan

出　　处：《科学通报》2015年第22期2115-2123,共9页Chinese Science Bulletin

基　　金：国家自然科学基金(41174004,41461164004);国家国际科技合作专项(2015DFR21100,2010DFB20190);中国地震局地震预测研究所基本科研业务专项(2012IES010302)资助

摘　　要：2015年4月25日,在印度板块与欧亚板块交界区的喜马拉雅地震带上发生了尼泊尔MS 8.1级大地震.震前GPS速度场和应变率场显示,喜马拉雅地震带整体表现为15.94±1.82 mm/a的压缩特征,同时还具有分段活动特征.此次地震发生在速度场顺时针旋转和逆时针旋转的分界带,该处最大主压应变率的量值在喜马拉雅地震带并非最大.GPS观测的同震位移场揭示了尼泊尔MS 8.1级地震引起的地壳变形特征,分别有9和6个测站观测到明显的水平向和垂向同震位移,其水平分量的运动方向整体表现为南向运动,位于震中东南侧的3个测站垂直分量表现为上升,其余测站为下降.中国境内距离震中最近的5个测站的垂向同震位移显示,此次地震造成珠穆朗玛峰的沉降量约为4mm.依据GPS观测到的同震位移场,利用非负最小二乘方法反演震源断层面上的滑动分布.反演结果表明最大滑动量为6.84 m,滑动量较大的区域分布在加德满都附近及其以北区域的下方,这可能是造成加德满都地区具有较大破坏的原因之一,该滑动分布模型能够很好地解释GPS观测到的同震位移.利用此滑动分布模型计算的地震矩为8.21×1020 N m,对应的矩震级为MW7.9.On April 25th, 2015, an Ms 8.1 earthquake hit Nepal on the Himalayan seismic zone at the junction of Indian Plate and Eurasian Plate. The pre-earthquake GPS velocity and strain rate fields show that the Himalayan seismic zone was characterized by compression of 15.94±1.82 mm/a and contrast activities in its diverse segmentations. This earthquake happened at the dividing region of the clockwise and counterclockwise rotation rate, where the largest principal compressive strain rate is not highest in the whole Himalayan seismic zone. The coseismic displacements registered by GPS depicted the major feature of crust deformation caused by the Ms 8.1 earthquake. We observed noticeable horizontal and vertical displacements in nine and six GPS stations, respectively. The horizontal coseismic displacements were generally directed southward, whereas vertical deformation showed a site-specific pattern. The 3 stations south-east to the epicenter captured the vertical coseismic displacement moving upward, while the stations in other quadrants recorded downward movement. Within Chinese borderland, the 5 stations closest to the epicenter recorded vertical coseismic displacements of about -4 mm. The faulting slip distribution was inverted by the approach of non-negative least squares with the coseismic displacements. The result showed that the largest faulting slip was 6.84 m, and the relatively large slips were distributed in subsurface near Kathmandu and its neighbouring area north to it. This might be one of the major reasons for the severe destruction in the Kathmandu region. This slip distribution model well explained the coseismic displacements observed by GPS. The slip model gave a seismic moment of 8.21×10^20 N m, with a moment magnitude of Mw 7.9.

关 键 词：尼泊尔MS8.1级地震 GPS应变率场 同震位移 滑动分布 珠穆朗玛峰 

分 类 号：P315.7[天文地球—地震学]