Earthquake ground motions (GMs) may display distinct characteristics in all directions within the horizontal plane. However, the causes of GM polarization are still not fully understood. Structural designs use maximum rotated intensity measures (IM_RotD100) to accommodate variations of the GM with orientation, but the orientation associated with IM_RotD100, β, is not easily predictable. This study investigates the influence of linear site response to observed GM variability with direction. We analyze GMs recorded at the surface and at depth from four stations in the Japanese database, KiK-net. Selected events have moment magnitudes ranging 3–5, and rupture distances within 100 km. Findings provide evidence that site effects contribute to GM directionality, and that directional resonance can be observed at sites lacking significant topographic features. Additionally, values of β at depth are not correlated to the orientation corresponding to their expected polarization (from S-wave radiation patterns), which provides evidence of non-negligible path contributions to GM directionality observed at our study sites.

地震地震动（GM）可能在水平面内的所有方向上显示出不同的特性。但是，GM极化的原因仍未完全理解。结构设计使用最大旋转强度量度（IM _RotD100）来适应GM随方向的变化，但方向与IM _{RotD100相关}β很难预测。本研究调查线性位点响应对观察到的GM方向变异性的影响。我们分析了日本数据库KiK-net中四个站点在地面和深处记录的GM。选定事件的矩量级为3-5，破裂距离在100 km之内。这些发现提供了证据表明位点效应有助于GM的方向性，并且在缺乏明显地形特征的位点可以观察到方向性共振。此外，深度处的β值与对应于其预期极化的方向（来自S波辐射图）不相关，这提供了在我们的研究地点观测到的对GM方向性不可忽略的路径贡献的证据。