Abstract: Geomorphic offsets displaced by coseismic surface rupture can be analyzed to identify earthquake recurrence behavior. Therefore, obtaining a sufficient and precise along-fault offset dataset is vital to identify long-term earthquake recurrence behavior. Furthermore, knowledge of along-fault slip distribution during a single-earthquake or multi-earthquakes is important for other reasons, including a better understanding of the relationship between earthquake size and coseismic displacements, fault kinematics and fault mechanics. A recent flourish of offsets-measuring software and high-resolution topographic data together offer an unprecedented opportunity to measure high-density fault offsets. Here, we introduce and compare two kinds of most popular software, LaDiCaoz and 3D_Fault_Offsets. We describe the workflow and principle of the two codes by taking a fault-offset example on the eastern Altyn Tagh Fault. LaDiCaoz iterates over the channel morphology and position parameters and determines the summed absolute elevation difference Σ[Δ(elevation)] between both transverse profiles. The optimal horizontal offset is defined by the parameter combination that results in the least mismatch between two profiles. Compared with LaDiCaoz, the principle of 3D_Fault_Offsets is more complicated by measuring the offset in three dimensions. It mathematically identifies and represents nine of the most prominent geometric characteristics of common sublinear markers along faults in three dimensions, such as the streambed(minimum elevation), top, free face and base of channel banks or scarps(minimum Laplacian, maximum gradient, and maximum Laplacian), and ridges(maximum elevation). By calculating best fit lines through the nine point clouds on either side of the fault, the code computes the lateral and vertical offsets between the piercing points of these lines onto the fault plane, providing nine lateral and nine vertical offset measures per marker. Through a Monte Carlo approach, the code calculates the total uncertainty on each offset. Although both 3D_Fault_Offsets and LaDiCaoz are developed based on the Matlab platform, there are significant differences in principles, linear marker, software interface, repeatability, input-file types, degree of automation, adaptability, output file types, etc. In this part, we compare and summarize their features, advantages, and disadvantages. Finally, we calculate the correlation of two groups of fault-offset data derived from the two methods along the eastern ATF. By doing this, we try to explore if the two methods can be crosschecked and to study how sinuosity of the linear geomorphic markers affect the measuring results. By discussing and comparing the accuracy of the two measuring methods, we consider that LaDiCaoz is better than 3D_Fault_Offsets in accuracy aspect. In our opinion, there exist some disadvantages in the both software, and higher automation and introduction of artificial intelligence will be the future development direction.

Key words: eastern Altyn Tagh Fault, co-seismic offset, cumulative Offsets, LaDicaoZ, 3D_Fault_Offsets, high-resolution topographic data

摘要： 测量地表的断层位移对于恢复同震位移和长期累积位移分布非常重要。 近年来, 编程软件的不断更新和高精度地形数据(例如激光雷达探测与测量和无人机航空摄影测量)的积累为测量密集的断层位移数据提供了前所未有的机会。 文中主要对2款比较常用的断层位移测量软件--LaDiCaoz和3D_Fault_Offsets进行介绍。 首先, 基于阿尔金断层东段石包城铁矿附近的1个位移测量实例分别说明这2款软件的工作原理; 然后, 分别对比和总结了其在目标地貌标志、 界面、 输入文件类型、 自动化程度、 适应性、 可重复性和输出文件类型等方面的差异和优劣; 最后, 基于2种软件在阿尔金断裂东段获得的2组断层位移数据的相关性研究, 探讨2种软件的结果是否相互验证, 以及线性地貌标志的弯曲程度对测量结果的影响。 通过对2种软件所得测量结果与野外地质测量结果的对比, 以及对软件测量结果的可靠性和地质意义的讨论, 我们认为目前这2款软件都存在自动化程度较低和人为因素影响较大等不足之处, 高度自动化和人工智能的引入可能是断层位移测量方法的发展方向。

关键词: 同震位移, 累积位移, LaDiCaoz, 3D_Fault_Offsets, 高精度地形数据, LiDAR