At present time, ground-motion prediction models neglect the directionality observed in horizontal components of earthquake ground motions, that is, the important changes in ground-motion intensity that occur with changes in azimuth. This study presents an investigation of the directionality of a recently proposed measure of ground-motion intensity during the 6 February 2023, Mw 7.8 Pazarcık and Mw 7.5 Elbistan earthquake doublet in the Kahramanmaraş region of Türkiye, which resulted in the collapse of more than 35,000 buildings and caused almost 60,000 fatalities. The studied intensity measure is referred to as FIV3, which has been shown to be better correlated with structural collapse than the spectral acceleration at the fundamental period of the structure. The improved intensity measure is period-dependent and is computed as the sum of the three largest incremental velocities with the same polarity obtained from the area under segments of a low-pass filtered ground acceleration time series. The following aspects are studied in this article: variation of FIV3 intensity with changes in the orientation; variation of FIV3 intensity with changes in the period of vibration; attenuation of FIV3 intensities with increasing distance; and spatial distribution of the orientation of maximum FIV3 intensity. This study is based on 231 pairs of records from the Mw 7.8 main event and 222 pairs of records from the Mw 7.5 event. Similarly to the directionality of spectral ordinates, it is found that the directionality of FIV3 intensity also increases with increasing period. Strong directionality occurred not only in the near field but up to distances as large as 400 km from the epicenter. The orientation of maximum FIV3 intensity is found to occur close to the transverse orientation, consistent with observations for the orientation of maximum spectral ordinates during strike-slip earthquakes.

中文翻译：

---

2023 年 2 月 6 日土耳其卡赫拉曼马拉什地震双重地震期间 FIV3 地面运动强度的方向性

目前，地震动预测模型忽略了地震地震动水平分量中观察到的方向性，即地震动强度随方位角变化而发生的重要变化。本研究对最近提出的 2023 年 2 月 6 日期间地面运动强度测量的方向性进行了调查，Mw7.8 帕扎尔茨克和Mw土耳其卡赫拉曼马拉什地区埃尔比斯坦 7.5 级地震造成 35,000 多座建筑物倒塌，造成近 60,000 人死亡。研究的强度测量被称为 FIV3，它已被证明与结构倒塌的相关性比结构基本周期的谱加速度更好。改进的强度测量与周期相关，并且被计算为从低通滤波地面加速度时间序列的片段下的区域获得的具有相同极性的三个最大增量速度的总和。本文主要研究以下几个方面：FIV3强度随方向变化的变化；FIV3强度随振动周期变化的变化；FIV3 强度随着距离的增加而衰减；以及最大 FIV3 强度方向的空间分布。本研究基于 M 的 231 对记录w7.8主赛事和M的222对记录w7.5 事件。与光谱坐标的方向性类似，发现FIV3强度的方向性也随着周期的增加而增加。强方向性不仅发生在近场，而且发生在距离震中长达 400 公里的地方。发现 FIV3 最大强度的方向接近横向方向，与走滑地震期间最大谱坐标方向的观测结果一致。