SUMMARY In contrast to global observations in stable continental crust, the present-day orientation of the maximum horizontal stress in Western Australia is at a high angle to plate motion, suggesting that in addition to large-scale plate driving forces, local factors also play an important role in stress repartitioning. As a reliable stress indicator, full waveform moment tensor solutions are calculated for earthquakes that occurred between 2010 and 2018 in the southern Yilgarn Craton and the adjacent Albany-Fraser Orogen in southwestern Australia. Due to regional velocity heterogeneities in the crust, we produced two geographically distinct shear wave velocity models by combining published crustal velocity models with new ambient noise tomography results. We applied a full waveform inversion technique to 15 local earthquakes and obtained 10 robust results. Three of these events occurred near Lake Muir in the extreme south of the study area within the Albany-Fraser Orogen. The focal mechanism of the 16th September 2018 Lake Muir event is thrust; two ML≥ 4.0 aftershocks are normal and strike-slip. Our results are consistent with field observations, fault orientations inferred from aeromagnetic data and surface displacements mapped by Interferometric Synthetic Aperture Radar which are all consistent with reactivation of existing faults. The other seven solutions are in the southeastern Yilgarn Craton. These solutions show that the faulting mechanisms are predominantly thrust and strike-slip. This kinematic framework is consistent with previous studies that linked active seismicity in the Yilgarn Craton to the reactivation of the NNW–SSE oriented Neoarchean structures by an approximately E–W oriented regional stress field. Our results suggest that the kind of faulting that occurs in southwest Australia is critically dependent on the local geological structure. Thrust faulting is the dominant rupture mechanism, with some strike-slip faulting occurring on favourably oriented structures.

中文翻译：

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改进的澳大利亚西南部克拉通板内地震全波形矩张量反演

总结 与稳定大陆地壳的全球观测相比，目前西澳大利亚最大水平应力的方位与板块运动呈高角度，这表明除了大尺度的板块驱动力外，当地因素也起到了一定的作用。在应力重新分配中起重要作用。作为可靠的应力指标，计算了 2010 年至 2018 年间发生在南伊尔加恩克拉通和澳大利亚西南部奥尔巴尼-弗雷泽造山带的地震的全波形矩张量解。由于地壳中的区域速度异质性，我们通过将已发表的地壳速度模型与新的环境噪声断层扫描结果相结合，产生了两个地理上不同的剪切波速度模型。我们将全波形反演技术应用于 15 次局部地震，并获得了 10 个稳健的结果。其中三起事件发生在奥尔巴尼-弗雷泽造山带研究区最南端的缪尔湖附近。2018年9月16日缪尔湖事件的震源机制是推力；两次ML≥4.0余震为正常走滑。我们的结果与现场观测、从航磁数据推断的断层方向和干涉合成孔径雷达映射的表面位移一致，这些都与现有断层的重新激活一致。其他七个解决方案位于伊尔加恩克拉通东南部。这些解决方案表明，断层机制主要是逆冲和走滑。这种运动学框架与先前的研究一致，这些研究将伊尔加恩克拉通的活跃地震活动与通过近似 E-W 方向的区域应力场重新激活 NNW-SSE 方向的新太古代结构联系起来。我们的研究结果表明，澳大利亚西南部发生的断层类型严重依赖于当地的地质结构。逆冲断层是主要的断裂机制，一些走滑断层发生在有利定向的构造上。