This paper discusses the spatial correlation structure of earthquake ground motion in a small field across a distance of the order of structures. The data from Chiba Array is analysed to obtain the empirical correlation coefficients, which present nonstationarity. For a small field, where the wave propagation effect can be negligible, the main shock or an impulsive motion tends to cause higher correlation than the coda part The vertical motion shows difference in coherency depending on the earthquake characterizing parameters, while the horizontal component reflects predominancy of the local soil effect
