玉树和汶川地震前后区域水平形变的空间分布

以1999—2007年和2009—2010年两个时间段的GNSS观测资料为基础, 借助于多核函数解析、 滤波和应变场的无偏算法以及区域无旋转基准, 在运动场连续变化的条件下获得了玉树M_S7.1和汶川M_S8.0地震前后青藏高原东南地域运动与形变场, 并得到如下基本认知: ① 玉树和汶川地震前震源区构造活动在空间和较长时间上明显弱化, 最大正应变和最大剪切应变均处在区域构造活动的最低水平。 ② 与地震破裂相应的旋剪形变最大部位既不位于震源区也不远离震源区, 似乎存在某种协调有序活动, 玉树地震发震构造断裂带基本上处在区域右旋活动与左旋活动的过渡区上, 而左旋活动最大条带却为平行于该断裂带且相距约150 km的东北构造活动区内; 汶川地震发震构造断裂虽处在右旋活动的龙门山断裂带上, 但右旋活动最大条带为平行于该断裂带且相距约200 km的西北活动区内。 ③ 玉树地震震时较大水平形变的范围较小, 汶川地震震后水平形变仍较突出。 ④ 理塘—德巫断裂带的北段及周边地区应给予关注, 面应变为象限分布图像, 最大正应变和最大剪切应变均显示闭锁的迹象。

Spatial Distribution of Regional Horizontal Deformations before and after the Yushu and Wenchuan Earthquakes

Based on GNSS observation(from 1999 to 2007,and from 2009 to 2010) and continuous variation of deformation field,this study employed filtering and analysis of multi-kernel function and an unbiased algorithm of strain field to obtain movement and deformation field of the southeastern of Qinghai-Tibet Plateau before and after the MS7.1 Yushu and MS8.0 Wenchuan earthquakes.The observations showed: ① Tectonic activities of seismic source were significantly weakened at spatial and relative long time level before the Yushu and Wenchuan earthquake.The maximum positive strain and shear strain fell to the lowest level of regional tectonic activities.② Spin shear deformation corresponding to the earthquake rupture was neither in nor far from the seismic source region,and there seemed an orderly coordinated action.The tectonic fault zone of Yushu earthquake was in the intermediate of regional right-lateral and left-lateral movements,while the largest stripe of left-lateral movement was 150 km away from the northeast of tectonic activity region,paralleling with the fault zone.Although structural fracture of Wenchuan earthquake was in the Longmen Mountain fault zone of right-lateral movement,the largest band of right-lateral movement was paralleled with this fault zone and in the northwestern activity zone with 200 km distance.③ The range of large co-seismic horizontal deformation of the Yushu earthquake was actually small,while the post-seismic horizontal deformation of the Wenchuan earthquake remains significant.④ The North and the surrounding of Litang-Dewu fault zone should be given more attentions because plane-strain was presented in the image of quadrant distribution,and both the maximum positive strain and maximum shear strain were showing sign of being locked.