The spatial variation of ground motion is determined for high-frequency P- and S-waves in the New Madrid Seismic Zone at a site near Mooring, TN. An L-shaped array consisting of 19 seismometers and having arm lengths of 600 m located on Holocene fluvial sediments of the Mississippi River was used to examine wave coherency appropriate for many sites throughout the Mississippi embayment and other sediment sites associated with large rivers. Data from local and regional earthquakes within a distance range of 300 km show that coherency within the frequency band of 0.5 to 16 Hz degrades with inter-station distance across the array according to an empirical exponential model. Vertical component P-waves are coherent over nearly 2 horizontal wavelengths. However, the coherency for horizontal component S-waves degrades more rapidly than the vertical component P-waves. S-waves become significantly incoherent at distances of only 0.2 horizontal wavelength and become completely incoherent after 0.5 wavelength. The results of this study show clear and quick decay of wave coherence likely to occur in strong ground motions from nearby earthquakes. The observed incoherence can be a significant factor for the response of structures having foundation lengths of even 100 m.

在田纳西州Mooring附近的新马德里地震带中，针对高频P波和S波确定了地面运动的空间变化。L形阵列由19个地震仪组成，臂长600 m，位于密西西比河全新世河床沉积物上，用于检查适用于密西西比河河堤整个过程中许多地点和与大河有关的其他沉积物地点的波相干性。来自300 km距离范围内的局部和区域地震的数据表明，根据经验指数模型，在0.5至16 Hz频带内的相干性会随着整个阵列的站点间距离而降低。垂直分量P波在近2个水平波长上是相干的。然而，水平分量S波的相干性比垂直分量P波的衰减更快。S波在仅0.2个水平波长的距离处显着变得不相干，而在0.5个波长之后变得完全不相干。这项研究的结果表明，在附近地震引起的强地面运动中，波的相干性可能会迅速明显衰减。观察到的不连贯性可能是基础长度甚至为100 m的结构响应的重要因素。