Abstract
Seismic interferometry has been extensively used to estimate group velocities of long period surface-wave with the long time series of mirotremors obtained at distant stations. For subsurface exploration in a relatively-narrow area, however, the seismic interferometry should be used in a wide frequency range with short time series of microtremors as possible. We conducted observations of microtremors with six stations distributed along an about 10 km survey line for 2 days, and verified the feasibility of using the seismic interferometry with the short time series of microtremors. We first discussed theoretically about estimation of Rayleigh-wave group velocities by using seismic interferometry as a function of wavelength and station distance. Next, we analyzed the observed microtremors by the seismic interferometry and estimated the Rayleigh-wave group velocities. Examination on the amplitudes of cross correlation functions indicated that the surface-wave signals could be retrieved in the cross correlation functions even if the data length is short. However, the group velocities were estimated appropriately only in the range suggested by the theoretical consideration of wavelength between about 1/2 and 1/50 of station distances. We finally concluded that the data at stations pairs with the short separation provides the surface-wave group velocities in short-period range.
