Inference of Q-values below 1 Hz from borehole and surface data in the Osaka basin by three-component waveform fitting

The quality factor of the shear waves Q(s) below 1 Hz in the Osaka sedimentary basin, Japan, is inferred from borehole earthquake-motion recordings and surface earthquake-motion recordings by three-component waveform fitting. Assuming quality factor of S waves Q(s) to be a function of the frequency f and the shear-wave velocity V-s in meters in the form AV(s)f(11), the waveform fitting of borehole data reveals that coefficient A is approximately 0.24, and exponent n is less than or equal to zero. To verify Q(s)-values from borehole data and, if possible, to confine Q(s)-values to a narrow range, we infer the Q(s)-values from surface earthquake-motion recordings by fitting them with earthquake motions simulated by the finite-difference method. It indicates that Q(s)-values are negatively frequency dependent and that the lower limit of Q(s)-values is approximately 0.24V(s)f(-1).