Construction of fault geometry by finite-fault inversion of teleseismic data
Construction of fault geometry by finite-fault inversion of teleseismic data
复制标题
通过远震数据有限断层反演构建断层几何
DOI：
10.1093/gji/ggaa501
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发表时间：
2020
影响因子：
2.8
通讯作者：
Fukahata Yukitoshi
中科院分区：
文献类型：
--
作者：
Shimizu Kousuke;Yagi Yuji;Okuwaki Ryo;Fukahata Yukitoshi
传统的震源反演估计假设的断裂面上的地震破裂过程，这是先验确定的。由于地震震源反演技术的非线性，如何同时获得断层几何信息和破裂过程一直是个难题。在这项研究中，我们通过对我们之前发表的有限断层反演分析(Shimizuet等人)的阐述，提出了一种从远震P波数据中估计断层几何形状和地震破裂过程的反演方法。)。这种方法不同于传统的方法，它用五个基双偶分量来表示断层面上的滑动，用势密度张量来表示，而不是用两个与断层方向相容的双偶分量来表示。由于由势密度张量得到的滑动方向应与断层方向相容，因此可以得到与破裂过程一致的断层几何形状。在实践中，我们依赖于迭代过程，首先假设断层平面平坦，然后利用所获得的势密度张量中包含的信息来更新断层几何。在构造非平面模型-断层表面时，为了简单起见，我们假定断层方向只在走向或倾向上改变。在通过合成测试验证了所提方法的有效性后，我们将其应用于发生在几何复杂断裂系统上的巴基斯坦俾路支省MW7.72013级地震和尼泊尔戈尔喀市MW7.92015级地震。俾路支省地震的模拟断层是一条向东南凸起的弯曲走滑断层，这与观测到的地表破裂是一致的。模拟的高尔卡地震断层是一条具有斜坡-平坦-斜坡结构的逆断层，这也与由大地测量和地质资料得出的断层几何学相一致。结果表明，该方法能很好地约束地震断层的几何形状。
Conventional seismic source inversion estimates the earthquake rupture process on an assumed fault plane that is determineda priori. It has been a difficult challenge to obtain the fault geometry together with the rupture process by seismic source inversion because of the nonlinearity of the inversion technique. In this study, we propose an inversion method to estimate the fault geometry and the rupture process of an earthquake from teleseismicPwaveform data, through an elaboration of our previously published finite-fault inversion analysis (Shimizuet al. ). That method differs from conventional methods by representing slip on a fault plane with five basis double-couple components, expressed by potency density tensors, instead of two double-couple components compatible with the fault direction. Because the slip direction obtained from the potency density tensors should be compatible with the fault direction, we can obtain the fault geometry consistent with the rupture process. In practice we rely on an iterative process, first assuming a flat fault plane and then updating the fault geometry by using the information included in the obtained potency density tensors. In constructing a non-planar model-fault surface, we assume for simplicity that the fault direction changes only in either the strike or the dip direction. After checking the validity of the proposed method through synthetic tests, we applied it to theMW7.7 2013 Balochistan, Pakistan, andMW7.9 2015 Gorkha, Nepal, earthquakes, which occurred along geometrically complex fault systems. The modelled fault for the Balochistan earthquake is a curved strike-slip fault convex to the south-east, which is consistent with the observed surface ruptures. The modelled fault for the Gorkha earthquake is a reverse fault with a ramp-flat-ramp structure, which is also consistent with the fault geometry derived from geodetic and geological data. These results exhibit that the proposed method works well for constraining fault geometry of an earthquake.