Abstract
We applied the CCA method, a technique of analysis recently developed by ourselves, to a set of microtremor seismograms from an array of vertical-motion sensors, installed around a miniature circle of radius 0.3 m. Rayleigh-wave phase velocities were identified with reasonable accuracy up to wavelengths of several ten meters or, in some cases, well in excess of 100 m. This suggests that, when combined with Konno and Kataoka's (2000) approximate method to associate Rayleigh-wave phase velocities with average shear velocities of the shallow soil, the use of miniature circular arrays provides the opportunity to make a quick appraisal of surface soil properties by way of simple microtremor measurements. This approach presents a groundbreaking advantage over existing microtremor methods, in the sense that a tiny patch of ground, well within the arms reach of a single observer, is sufficient for the estimation of average shear velocities down to depths of several ten meters. We applied the proposed approach to array seismograms of microtremors obtained at three different sites in Tsukuba City, Ibaraki Prefecture. The average shear velocities to depths of 10, 20 and 30 m, inferred with the proposed method, were indeed consistent with available PS logs and known geologic structures.
