Simulation of Horizontal Ground Motions with Spatial Coherency in Two Orthogonal Horizontal Directions

Most available spatial coherency models are for the excitations along the same orientation. However, the coherency for excitations in two orthogonal horizontal directions may not be neglected, at least for recording stations with a separation distance, Δ, greater than 100 m. An assessment of this coherency using the records from a dense array in Taiwan with Δ < 100 m is presented and an empirical model is suggested. Use of the model to simulate spatial varying excitations is presented by applying the spectral representation method with both Cholesky and square-root decompositions, and the method by adjusting the phase angle to match the coherency characteristics.