Physically Based Modeling of Spatially Variable Seismic Ground Motions

地震地面运动的空间变化对桥梁、管道等生命线的响应有重要影响；与结构支承承受相同的地震运动相比，它可能会在结构中产生显著的附加荷载。地震地面运动的空间变化是由于地面上波形的明显传播及其在支撑结构不同位置的形状差异所致。在先前的一项研究中，PI开发了另一种方法来研究在密集仪器阵列上记录的空间可变的地震地面运动。它将地震运动模拟为正弦函数的叠加，由其幅度、频率、波数和相位来描述。对台湾罗东SMART-1台阵记录的数据进行的分析表明，共同相干分量与实际运动的近似程度非常令人满意，空间变异性是由与波在场地地形中向上传播有关的台站到达时间延迟以及共同分量特征周围运动的幅度和相位的变化引起的。它应用于记录的数据，识别出运动的相干近似周围的幅度和相位变化之间的相关模式；这一观察结果可能导致在描述空间变异性方面的重大发展。然而，该方法只适用于一个场地，为了推广其结果，有必要将其应用于不同的地震场地。因此，本研究使用了大量的岩土场地记录的附加数据。根据地震震级进行区分：调查同一地点的小震和大震(如主震和余震)。还考虑了站点(“湿”和“干”站点)的地下水位的影响。

The spatial variation of seismic ground motions has an important effect on the response of lifelines, such as bridges and pipelines; it may induce significant additional loads in the structure than the ones obtained if the structure's supports are subjected to the same seismic motions. The spatial variation of seismic ground motions results from the apparent propagation of the waveforms on the ground surface and the differences in their shape at the various locations of the supporting structure.In a previous study, the PI developed an alternative methodology for the investigation of spatially variable seismic ground motions recorded at dense instrument arrays. It models the seismic motions as superpositions of sinusoidal functions, described by their amplitude, frequency, wavenumber and phase. The application of the methodology to data recorded at the SMART-1 array in Lotung, Taiwan, revealed that the common, coherent component approximates to a very satisfactory degree the actual motions,and that the spatial variability is caused by arrival time delays at the array stations associated with the upward traveling of the waves through the site topography, and by variabilities in both the amplitudes and phases of the motions around the common component characteristics.The developed methodology considers simultaneously the amplitude and the phase variation in seismic motions. Its application to recorded data recognized correlation patterns between amplitude and phase variabilities around a coherent approximation of the motions; this observation may lead to significant developments in the description of spatial variability. However, the methodology has been applied to one site only, and, for the generalization of its results, it is necessary that it be applied at different sites subjected to various earthquakes.Therefore, the present study uses extensive additional sets of data recorded at rock and soil sites. Differentiation is made in terms of the earthquake magnitude: small and large events (e.g., main event andaftershocks) at the same site are investigated. The effect of the water table at the sites ('wet' and 'dry' sites) is also taken into consideration.