Stress field and kinematics for diffuse microseismicity in a zone of continental transpression, South Island, New Zealand
Stress field and kinematics for diffuse microseismicity in a zone of continental transpression, South Island, New Zealand
复制标题
新西兰南岛大陆变形带弥散微震的应力场和运动学
DOI：
10.1002/2017jb013942
复制
发表时间：
2017
期刊：
影响因子：
--
通讯作者：
T. Stern
中科院分区：
文献类型：
--
作者：
E. Warren‐Smith;S. Lamb;T. Stern
我们分析了新西兰阿尔卑斯断裂附近的浅层(0-20 公里)微震活动，那里存在澳大利亚板块和太平洋板块的斜向会聚。对155次地震(2012年6月至2013年10月)的震源机制进行了反演，以确定应力场的方向。这产生了一个主要的水平压力轴，SHmax = 114° ± 10°，这不能用全球定位系统观测到的板块会聚引起的构造载荷和重力应力的总和来解释。各个震源机制的滑动向量的方位与板块会聚向量垂直和平行。然而，这些断层从应力反转到SHmax方向约45°，表明摩擦系数很低。地震滑动方向可能是运动学控制的，以适应板块在有限的一组断裂上的会聚，类似于沿阿尔卑斯山断裂的新构造断裂的分段，阿尔卑斯断裂在1-10 公里的尺度上被划分为走滑和逆冲段。我们建议对我们计算的最大方位角进行两种可能的控制。首先，地震的SHmax估计可能有轻微的顺时针偏差；与应力反转方法假设的相比，在更有限的裂缝范围内可能会发生滑动，尽管这种影响可能相对较小(±5°)。更重要的是，在大地震过程中，不同时间尺度的应力场分量可能被解除，导致在几次大地震的时间尺度上，残余应力场变化很大(±15°)。
We analyze shallow (0–20 km) microseismicity adjacent to the Alpine Fault in New Zealand, where there is oblique convergence of the Australian and Pacific plates. Focal mechanisms for 155 earthquakes (June 2012 to October 2013) are inverted to determine the orientation of the stress field. This yields a principal horizontal axis of compression, SHmax = 114° ± 10°, which cannot be explained in terms of the sum of stress from tectonic loading due to plate convergence, indicated by GPS observations, and gravitational stresses. The azimuth of slip vectors for individual focal mechanisms cluster perpendicular and parallel to the plate convergence vector. These faults, however, strike at ~45° to SHmax from the stress inversion, suggesting a very low coefficient of friction. The earthquake slip directions may be kinematically controlled, accommodating the plate convergence on a limited set of fractures, similar to the segmentation for neotectonic faulting along the Alpine Fault, which is partitioned into strike‐slip and thrust segments at a 1–10 km scale. We suggest two possible controls on our calculated SHmax azimuths. First, there may be a slight clockwise bias in the estimates of SHmax from earthquakes; slip may be occurring on a more limited range of fractures than assumed by the stress inversion method, although this effect is likely to be relatively small (±5°). More importantly, the components of the stress field may be relieved at different timescales during big earthquakes, resulting in a residual stress field that varies significantly (±15°) on timescales of several large earthquakes.