Determining the fault parameters of an earthquake is fundamental for studying the earthquake physics, understanding the seismotectonics of the region, and forecasting future earthquake activities in the surrounding area. Dense crustal deformation data such as Interferometric Synthetic Aperture Radar (InSAR) are useful for fault parameter determination, but determining the dipping direction of a blind fault is often challenging when the size of the earthquake is not large ( M < 7) or when the coverage of the deformed area is limited to capture the details of rupture. The 5th April 2017, Mw 6.1 earthquake occurred near the city of Sefid Sang, northeast of Iran, provides an excellent case for exploring the potential of InSAR data for determining the dipping direction of a blind reverse fault. Using Advanced Land Observing Satellite-2 (ALOS-2) and Sentinel-1A interferograms of four different observation directions and a fault slip inversion method that allows thorough exploration of the fault geometry led to two candidates of reverse fault models, dipping either to the northeast or the south. The results show that the fault models of both dipping directions explain the data well, with a slight advantage in the northeast-dipping fault model in terms of the misfit when the atmospheric corrections were applied. The northeast-dipping fault model is, in addition, more consistent with the strike of the mapped active faults in the region and with the aftershock distribution, from which we infer that the 2017 Sefid Sang earthquake occurred on a northeast-dipping dextral-reverse fault. The preferred fault model has a strike angle of 314.8°, dip angle of 47.4° and rake angle of 130.3°, and a slip distribution of maximum 1.35 m at depth of 5 km equivalent to Mw 6.0. This study illuminates the difficulty of determining the dipping direction of blind faults even with InSAR measurements from multiple directions, but also that correcting for the atmospheric noise and comparing with other kinds of data can help infer the fault dipping direction.

中文翻译：

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InSAR盲逆断层倾角确定：以2017年伊朗东北部Sefid Sang地震为例

确定地震断层参数对于研究地震物理学、了解该地区的地震构造以及预测周边地区未来的地震活动至关重要。诸如干涉合成孔径雷达 (InSAR) 等密集地壳变形数据对于断层参数的确定很有用，但当地震规模不大 (M < 7) 或覆盖范围时，确定盲断层的倾斜方向通常具有挑战性变形区域的图像仅限于捕捉破裂的细节。2017 年 4 月 5 日，伊朗东北部 Sefid Sang 市附近发生的 Mw 6.1 地震为探索 InSAR 数据用于确定反向盲断层倾斜方向的潜力提供了极好的案例。使用高级陆地观测卫星 2 (ALOS-2) 和 Sentinel-1A 四个不同观测方向的干涉图以及允许彻底探索断层几何形状的断层滑动反演方法，产生了两个候选的反向断层模型，向东北倾斜或南方。结果表明，两个倾角断层模型对数据的解释较好，在应用大气校正时的失配性方面，东北倾断层模型略有优势。此外，东北倾断层模型与该地区绘制的活动断层走向和余震分布更加一致，由此推断2017年Sefid Sang地震发生在一条东北倾右旋逆断层上。 . 首选断层模型的走向角为 314.8°，倾角 47.4°，前角 130.3°，5 km 深度最大滑移分布 1.35 m，相当于 Mw 6.0。本研究阐明了即使使用多方向 InSAR 测量确定盲断层倾角方向的困难，而且校正大气噪声并与其他类型的数据进行比较有助于推断断层倾角方向。