Multiscale Ambient Noise Tomography of Short-Period Rayleigh Waves across Northern Taiwan

Abstract

Abstract Using the ambient noise cross-correlation technique, we derived empirical Green’s functions (EGFs) of short-period Rayleigh waves from the continuous vertical component of data recorded by 34 seismic stations in northern Taiwan. We measured the group velocity of the EGFs in the frequency range of 0.2–0.5 Hz. The derived EGFs and group velocity measurements were carefully examined, and only quality results were used for the tomographic inversion. We implemented a wavelet-based multiscale inversion technique to construct the group velocity map for 0.35-Hz Rayleigh waves in northern Taiwan. The resulting model shows excellent correlation to the surface topography and geological units. To compare with models derived from traditional body-wave tomography, we calculated the group velocity maps and their fit to the noise-derived EGFs for two recent body-wave models. The comparison indicates that body-wave velocities, particularly V S , at shallow depth in the west coast plain are overestimated in two recent body-wave-derived models, and/or a much higher V P / V S ratio may exist for this area. Our results suggest that the noise-derived short-period EGFs may provide important constraints on shallow Earth structure, in complement to that provided by body waves.