Repeated earthquake cycles produce topography, fault damage zones, and other geologic structures along faults. These geomorphic and structural features indicate the presence of co‐seismic permanent (inelastic) surface deformation, yet a long‐standing question in earthquake research is how much of the co‐seismic deformation field is elastic versus inelastic. These questions arise in part because it is unclear what measurable co‐seismic characteristics, such as off‐fault or distributed surface deformation and cracking, represent true unrecoverable deformation. One emerging descriptor of permanent co‐seismic deformation is surface strain magnitudes inferred from imaging geodesy observations. In this study, we present the surface strain field of the 2013 Mw7.7 Baluchistan strike‐slip earthquake in southern Pakistan. We invert co‐seismic displacement fields generated from pixel‐tracking of SPOT‐5 and WorldView optical imagery for co‐seismic surface horizontal strain tensors. We observe that co‐seismic strain field is dominated by negative dilatation strains, indicating that the co‐seismic fault zone contracted during the earthquake. We show that co‐seismic inelastic failure exhibits a relatively consistent width along the rupture that is localized to a zone 100–200 m wide on the hanging wall side. The width of co‐seismic permanent deformation does not correlate with variations in off‐fault deformation or surface geology. Based on comparisons to other recent earthquakes, we posit that the permanent surface strains reflect inelastic deformation of the faults inner damage zone, and that the width of this zone reflects fault maturity.

中文翻译：

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基于高分辨率表面应变分析的2013年巴基斯坦Bal路支Mw7.7地震的永久同震形变

重复的地震周期会沿着断层产生地形，断层破坏带和其他地质结构。这些地貌和结构特征表明存在同震永久（非弹性）表面变形，但是在地震研究中一个长期存在的问题是同震变形场中有多少是弹性的还是无弹性的。之所以出现这些问题，部分原因是目前尚不清楚什么可测量的同震特征（如断层或分布的表面变形和裂缝）代表了真正的不可恢复的变形。永久同震变形的一种新兴描述是从成像大地测量观测推论得出的表面应变大小。在这项研究中，我们介绍了巴基斯坦南部2013年Mw7.7 uch路支斯坦走滑地震的地表应变场。我们将SPOT-5和WorldView光学图像的像素跟踪生成的同震位移场求出，用于同震表面水平应变张量。我们观察到，同震应变场主要由负膨胀应变控制，这表明同震断层带在地震期间收缩了。我们表明，同震非弹性破坏沿破裂方向显示出相对一致的宽度，该宽度在悬挂壁一侧的宽度为100-200 m。同震永久变形的宽度与断层变形或地表地质的变化不相关。根据与其他近期地震的比较，我们假定永久性表面应变反映了断层内部破坏带的非弹性变形，而该区域的宽度反映了断层的成熟度。