基于GPS观测研究中国东北地区现今地壳形变特征

基于中国东北和俄罗斯远东东南部2012—2017年的GPS观测数据, 利用包含年周期、 半年周期、 线性项和阶跃项的函数模型拟合GPS站坐标时间序列, 得到ITRF2014下的速度场, 并进一步转换到欧亚参考框架下得到相对欧亚板块的速度场。 基于多尺度球面小波方法解算应变率场, 并分析了其空间分布特征, 同时研究了各GPS站对2011年日本东北M_W9.0大地震的震后松弛响应特征和背景形变场特征。 结果表明: ① 若不扣除日本东北大地震的松弛效应, 相对欧亚板块中国东北主体上表现为东南方向运动, 在依兰—伊通断裂和嫩江断裂带之间, 地壳表现为逆时针旋转, 其他区域向东南方向运动, 方向一致性较好, 在敦化—密山断裂东侧速度大小明显增加。 敦化—密山断裂和依兰—伊通断裂两侧拉张量分别为3.96±0.04 mm/a和0.71±0.05 mm/a, 两条断裂的剪切运动不明显。 总体上, 面应变率显示出NW—SE向的拉张和NE—SW向的挤压, 面应变率显示出依兰—伊通断裂南端、 嫩江断裂带北端和俄罗斯远东东南部呈挤压状态。 在依兰—伊通断裂、 敦化—密山断裂南侧以及俄罗斯远东东南部最大剪应变率相对较大。 ② 各GPS测站对2011年日本东北M_W9.0大地震震后松弛的响应整体上表现为东南向运动, 松弛形变量随震中距增加而减小。 松弛效应的面应变率总体上表现为NW—SE向的拉张和NE—SW向的挤压, 面应变率显示出依兰—伊通、 敦化—密山断裂南端、 嫩江断裂带北端以及俄罗斯远东地区具有挤压特征, 其他地区表现为拉张特征。 中国与俄罗斯远东边界南端存在一个明显的最大剪应变率高值区。 ③ 扣除日本东北M_W9.0大地震引起的松弛变形后, 总体上面应变率仍然表现为NW—SE向的拉张和NE—SW向的挤压, 面应变率最大值仍然位于依兰—伊通断裂和敦化—密山断裂南端、 第二松花江断裂带以及俄罗斯远东和中国边界最南段。 在依兰—伊通断裂、 敦化—密山断裂南端, 中国与俄罗斯远东边界南端的最大剪应变率高值区仍然存在, 表明这些地区应变积累较快, 并且一直在持续。

The Current Crustal Deformation of Northeast China Deduced from GPS Observations

Using the GPS data observed from northeastern China and southeast of Russian Far East over the period of 2012—2017, we derived a velocity field within the ITRF2014, by fitting GPS time series with a multi-term functional model incorporating annual and semi-annual signals, linear trend as well as offsets. Subsequently, we transformed the velocity field into a Eurasia-fixed velocity field and analyzed its spatial characteristics. By taking the multi-scale spherical wavelet approach, we calculated strain rate tensors and analyzed the spatial distribution of various resolving scales. Meanwhile, we investigated the contribution due to the post-seismic relaxation of the 2011 M_W9.0 Tohoku earthquake, Japan and the background deformation field characteristics. The results show that if the relaxation effect of the great earthquake in northeastern Japan is not deducted, the velocity field relative to the Eurasian plate generally moved southwestward. The movements between Yilan-Yitong Fault and Nenjiang Fault is characterized by counter-clockwise rotation, but other regions moves southeastward with a good consistency in orientation and an increase in intensity east of Mishan-Dunhua Fault. The motions for the Dunhua-Mishan Fault and the Yilan-Yitong Fault are characterized by extensions of 3.96±0.04 mm/a and 0.71±0.05 mm/a, respectively. The fault-parallel motion is negligible for the two faults. Principal strain rates were dominated by NW-SE extension and NE-SW compression. The dilation rates show that it is undergoing compression for the southern portion of Yilan-Yitong Fault, northern end of the Nenjiang Fault and the southeast of Russian Far East. The deformations were generally oriented SE due to the post-seismic viscoelastic relaxation of the 2011 M_W9.0 Tohoku earthquake, inversely proportional with the epicentral distances. The corresponding principal strain rates were also characterized by NW-SE extension and NE-SW compression. The dilations were characterized as contraction for the southern segment of the Yilan-Yitong Fault and the Mishan-Dunhua Fault, the northern end of the Nenjing Fault and Russian Far East. Localized maximum shear rates were identified around the southern borderland between northeastern China and the southeast of Russian Far East. After the subtraction of the contribution due to the viscoelastic relaxation from the observed velocity, the principal strain rates were also characterized by NW-SE extension and NE-SW compression. The dilation rates were significant in the southern end of the Yilan-Yitong Fault and the Mishan-Dunhua Fault, over the Second Songhuajiang Fault and the southern borderland between northeast China and Russian Far East. The maximum shear rates are still significant for the above regions, indicative of fast and continuing strain buildup there.