Near‐fault fling steps might cause severe damage to near‐fault structures such as bridges or base‐isolated buildings. Therefore, the accurate simulation of ground displacements including fling steps based on fault models is an important issue not only for seismological but also for engineering purposes. The discrete wavenumber (DWN) method (e.g., Bouchon, 2003) has been established as a method to calculate complete elastic wavefield, including permanent displacement for a homogeneous or a layered half‐space. However, the accuracy of the permanent displacements calculated by the DWN method is influenced by the selection of parameters, such as the imaginary part of the complex frequency and the subfault size in the case of extended sources. The objective of this study is to clarify the requirement for these parameters for the accurate simulation of fling‐step displacements to further enhance the use of the DWN method. Honda and Yomogida (2003) also addressed the issue of calculating fling‐step displacements using the DWN method; however, their study was focused on cases in which a large amount of seismic moment is released at depth. This study was focused on fling‐step displacements due to rather shallow slip, in which the fault distance was as small as several meters in an extreme case, motivated by recent damaging earthquakes such as the 2016 Kumamoto, Japan, earthquakes. The ground displacements including fling steps were calculated by the DWN method and compared with the analytical solutions for the static displacements (Okada, 1985, 1992), both for point sources and extended sources in a homogeneous half‐space. According to the results, following recommendations were made. For the imaginary part of the complex frequency, ωc=ω−λi⁠, λ=ξπ/Tw with ξ≥2.0 can be recommended, with the understanding that the waveforms are effective only within the range of [0,Tw/ξ]⁠. For extended sources, the subfault size should be as small as 0.5 times the fault distance to accurately simulate fling steps.

中文翻译：

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用离散波数法估算的近断层跳阶位移精度

接近故障的跳动步骤可能会严重损坏接近故障的结构，例如桥梁或基础隔离的建筑物。因此，基于故障模型对包括位移步骤在内的地面位移进行精确模拟不仅是地震学上的问题，而且是工程上的重要问题。离散波数（DWN）方法（例如，Bouchon，2003年）已建立为一种计算完整弹性波场的方法，包括均匀或分层半空间的永久位移。但是，通过DWN方法计算的永久位移的精度受参数选择的影响，例如在扩展源的情况下，复数频率的虚部和子故障大小。这项研究的目的是弄清对这些参数的要求，以便精确模拟侧移位移，以进一步增强DWN方法的使用。Honda和Yomogida（2003）也解决了使用DWN方法计算侧向位移的问题。但是，他们的研究集中在深度释放大量地震矩的情况下。这项研究的重点是由于滑动较浅而导致的阶跃位移，在极端情况下，断层距离小至几米，这是由于最近发生的破坏性地震（例如2016年日本熊本地震）引起的。用DWN方法计算了包括抛掷台阶在内的地面位移，并与静态位移的解析解进行了比较（Okada，1985，1992），均质半空间中的点光源和扩展光源。根据结果​​，提出了以下建议。对于复数频率的虚部，可以推荐ωc=ω-λi⁠，建议λ=ξπ/ Tw，ξ≥2.0，前提是波形仅在[0，Tw /ξ]⁠范围内有效。对于扩展源，子故障的大小应小至故障距离的0.5倍，以准确模拟跳动步骤。