Earthquake ground surface ruptures provide insights into faulting mechanics and inform seismic hazard analyses. We analyze surface ruptures for 11 historical (1968–2018) moment magnitude (Mw) 4.7–6.6 reverse earthquakes in Australia using statistical techniques and compare their characteristics with magnetic, gravity, and stress trajectory data sets. Of the total combined (summative) length of all surface ruptures (∼148 km), 133 km (90%) to 145 km (98%) align with the geophysical structure in the host basement rocks. Surface rupture length (SRL), maximum displacement (MD), and probability of surface rupture at a specified Mw are high compared with equivalent Mw earthquakes globally. This is attributed to (1) a steep cratonic crustal strength gradient at shallow depths, promoting shallow hypocenters (∼1–6 km) and limiting downdip rupture widths (∼1–8.5 km), and (2) favorably aligned crustal anisotropies (e.g., bedrock foliations, faults, fault intersections) that enhanced lateral rupture propagation and/or surface displacements. Combined (modeled and observed) MDs are in the middle third of the SRL with 68% probability and either the ≤33rd or ≥66th percentiles of SRL with 16% probability. MD occurs proximate to or directly within zones of enhanced fault geometric complexity (as evidenced from surface ruptures) in 8 of 11 earthquakes (73%). MD is approximated by 3.3 ± 1.6 (1σ) × AD (average displacement). S-transform analyses indicates that high-frequency slip maxima also coincide with fault geometric complexities, consistent with stress amplifications and enhanced slip variability due to geometric and kinematic interactions with neighboring faults. Rupture slip taper angles exhibit large variations (−90% to +380% with respect to the mean value) toward rupture termini and are steepest where ruptures terminate at obliquely oriented magnetic lineaments and/or lithology changes. Incremental slip approximates AD between the 10th and 90th percentiles of the SRL. The average static stress drop of the studied earthquakes is 4.8 ± 2.8 MPa. A surface rupture classification scheme for cratonic stable regions is presented to describe the prevailing characteristics of intraplate earthquakes across diverse crustal structural-geophysical settings. New scaling relationships and suggestions for logic tree weights are provided to enhance probabilistic fault displacement hazard analyses for bedrock-dominated intraplate continental regions.

中文翻译：

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板内逆断层地震的表面滑移分布和几何复杂性

地震地表破裂提供了对断层力学的见解，并为地震危险性分析提供了信息。我们使用统计技术分析了澳大利亚 11 次历史 (1968-2018) 矩震级 (Mw) 4.7-6.6 反向地震的地表破裂，并将其特征与磁、重力和应力轨迹数据集进行比较。在所有地表破裂的总组合（累计）长度（~148 公里）中，133 公里（90%）至 145 公里（98%）与主基岩中的地球物理结构一致。与全球等效 Mw 地震相比，在指定 Mw 下地表破裂长度 (SRL)、最大位移 (MD) 和地表破裂概率较高。这归因于 (1) 较浅深度处陡峭的克拉通地壳强度梯度，促进浅震源（约 1-6 公里）并限制下倾破裂宽度（约 1-8.5 公里），以及 (2) 有利地排列的地壳各向异性（例如，基岩叶理、断层、断层交叉点）增强横向破裂传播和/或表面位移。组合（建模和观察）MD 位于 SRL 的中间三分之一，概率为 68%，SRL ≤33rd 或 ≥66th 百分位数，概率为 16%。在 11 次地震中的 8 次 (73%) 中，MD 发生在断层几何复杂性增强的区域附近或直接发生在其中（从表面破裂证明）。MD 近似为 3.3 ± 1.6 (1σ) × AD（平均位移）。S 变换分析表明高频滑动最大值也与断层几何复杂性一致，由于与相邻断层的几何和运动相互作用，应力放大和滑动变异性增强。破裂滑移锥角向破裂终点表现出很大的变化（相对于平均值 -90% 至 +380%），并且在破裂终止于倾斜取向的磁力线和/或岩性变化时最为陡峭。增量滑移近似于 SRL 的第 10 个和第 90 个百分位数之间的 AD。所研究地震的平均静应力降为 4.8 ± 2.8 MPa。提出了克拉通稳定区的地表破裂分类方案，以描述不同地壳结构地球物理环境中板内地震的主要特征。