As stresses following rupture are dissipated continuous measurements of postseismic surface deformation provide insight into variations of the frictional strength of faults and the rheology of the lower crust and upper mantle. Due to the difficulty of capturing the earliest phase of afterslip, most analyses have focused on understanding postseismic processes over timescales of weeks to years. Here we investigate the kinematics, moment release, and frictional properties of the earliest phase of afterslip within the first hours following the 2016 M_w 7.1 Kumamoto earthquake using a network of 5‐minute sampled continuous Global Positioning System (GPS) stations. Using independent component analysis to filter the GPS data, we find that (1) early afterslip contributes only ~1% of total moment release within the first hour and 8% after 24 hr. This suggests that the lack of a coseismic slip deficit, which we estimate using standard geodetic data sets (e.g., InSAR, GPS, and pixel offsets) and which span the first 4 days of the postseismic period, is largely reflective of the dynamic rupture process and we can rule out contamination of moment release by early afterslip. (2) Early afterslip shows no evidence of a delayed nucleation or acceleration phase, where instead fault patches transition to immediate deceleration following rupture that is consistent with frictional relaxation under steady state conditions with dependence only on the sliding velocity. (3) There is a close correlation between the near‐field aftershocks and afterslip within the first hours following rupture, suggesting afterslip may still be an important possible triggering mechanism during the earliest postseismic period.

中文翻译：

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解决2016年Mw 7.1熊本地震后头几个小时内早期后滑的运动学和力矩释放：对地震蠕变的浅滑赤字和摩擦行为的影响

由于消除了破裂后的应力，对地震后表面变形的连续测量可以洞悉断层的摩擦强度以及下地壳和上地幔的流变性。由于很难捕捉到后滑的最早阶段，因此大多数分析都集中于了解数周至数年时间范围内的地震后过程。在这里，我们研究了2016 M _w之后的最初几个小时内滑移最早阶段的运动学，力矩释放和摩擦特性。使用连续5分钟采样的全球定位系统（GPS）站点网络进行的7.1熊本地震。使用独立分量分析来过滤GPS数据，我们发现（1）早期后滑仅在第一个小时内占总力矩释放的1％左右，而在24小时后占8％。这表明缺乏同震滑移赤字，这是我们使用标准的大地测量数据集（例如，InSAR，GPS和像素偏移量）估计的，并且其覆盖了震后周期的前四天，这在很大程度上反映了动态破裂过程并且我们可以排除滑移后早期释放瞬间的污染。（2）滑倒后早期没有迹象显示成核或加速阶段延迟，取而代之的是，断层在破裂后过渡到立即减速，这与稳态条件下的摩擦松弛一致，仅取决于滑动速度。（3）在破裂后的最初几个小时内，近场余震与后滑之间存在密切的相关性，这表明在地震后的最早阶段，后滑仍可能是重要的触发机制。