Development of Coherency Models From Finite Element Simulations at a Hard Rock Site in Busan, Korea

ABSTRACT Spatial variability in ground motion is commonly represented with empirical coherency functions derived from recordings collected by dense seismic arrays. The deployment of such arrays is costly and requires long‐term operation. This study explores whether site‐specific coherency functions can be obtained through numerical simulations using spatial variability parameters derived from in‐situ tests, which include the coefficient of variation (CV) and correlation length (CL). Two‐dimensional finite element analyses were conducted for a hard rock site in Busan, Korea. Geophysical tests, including surface wave analysis and ambient noise recordings, provided CV and CL values that were used to generate two‐dimensional shear wave velocity Gaussian random fields. The outputs from time history analyses were processed to develop both lagged coherency and plane‐wave coherency models, which were then validated against the dense array derived empirical functions at the same site. The close agreement between the numerical and empirical coherency models demonstrates that, when site‐specific spatial variability parameters are available, numerical simulations can supplement or even replace ergodic coherency models.