Research on Polarization of Earthquake Ground Motion and Application to Strong Motion Prediction

分析了密集台阵系统(千叶台阵)记录的17个地震的加速度图，以研究地面运动的极化特征。得出如下结论：1.台阵各观测点的低频地震动极化方向基本相同，但高频地震动的极化方向相差很大。2.每个观测点都有其高频地震动的首选方向。场地对极化特征的局部影响是由于地表地震反应的方向差异，这可能是由于地表的各向异性。4.地震动极化随着震级的增加而减弱。震中距离和频度。台阵场地的平均偏振特征随地面震动频率的不同而变化，不能直接反映震源地震波的辐射模式。用经验格林函数法从小震记录合成大震地震动时，应注意上述第4项和第5项。

Accelerograms of 17 earthquakes recorded by a dense array system (Chiba array) have been analyzed to investigate polarization characteristics of ground motions. The followings are concluded.1.Polarization directions of low frequency ground motions are almost the same for all observation points of the array, but those of high frequency ground motions are very different from one another.2.Each of the observation points has its preferred direction of ground shaking at high frequency.The local site effect on polarization characteristics is caused by the directional difference in seismic response of surface layrs, which may be due to anisotropy of the surface layrs.4.Polarization of ground motion becomes weak with the increase in earthquake magnitude, hypocentral distance and frequency.Average polarization characteristics of the array site vary with the frequency of ground shaking and do not directly reflect the radiation pattern of seismic waves at the earthquake source.The above items 4 and 5 should be noted in synthesizing ground motions due to large earthquakes from records of small earthquakes by the empirical Green's function method.