- Open Access
Frequency-dependent attenuation of S-waves in the Kanto region, Japan
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. 2009
Received: 18 December 2008
Accepted: 2 June 2009
Published: 10 November 2009
Apparent, scattering, and intrinsic S-wave attenuations (Q S −1 , Q scat −1 and Q int −1 ) of the upper lithosphere in the Kanto region of Japan were measured in the 1- to 32-Hz frequency range using Multiple Lapse Time Window Analysis (MLTWA) for 115 borehole seismograms of local earthquakes. A new set of time windows for MLTWA, in which multiple isotropic scattering is assumed, was proposed and employed to estimate the frequency dependence of S-wave attenuation parameters. Scattering attenuation was found to dominate intrinsic attenuation in the S-wave attenuation mechanism at low frequencies (<;2 Hz), whereas the opposite relation was observed at high frequencies. The transition is caused by the different frequency dependences of Q scat −1 (∝ f−1.5) and Q int −1 (∝ f−0.7) at this frequency. Interestingly, Q scat −1 is almost frequency independent at frequencies >8 Hz, which implies the self-similar nature of short-wavelength heterogeneities in the upper lithosphere. In terms of the upper lithosphere of the Kanto region, these results may indicate that the random heterogeneities characterized by the Gaussian autocorrelation function with a fractional fluctuation ε ≈ 10% and a correlation length a ≈ 2 km are superimposed on the weak background self-similar heterogeneity.