Crustal attenuation characteristics of S-waves beneath the Eastern Tohoku region, Japan

Abstract

Abstract An inversion method was applied to crustal earthquakes dataset to find S-wave attenuation characteristics beneath the Eastern Tohoku region of Japan. Accelerograms from 85 shallow crustal earthquakes up to 25 km depth and magnitude range between 3.5 and 5.5 were analyzed to estimate the seismic quality factor Q s. A homogeneous attenuation model Q s for the wave propagation path was evaluated from spectral amplitudes, at 24 different frequencies between 0.5 and 20 Hz by using generalized inversion technique. To do this, non-parametric attenuation functions were calculated to observe spectral amplitude decay with hypocentral distance. Then, these functions were parameterized to estimate Q s. It was found that in Eastern Tohoku region, the Q s frequency dependence can be approximated with the function 33 f 1.22 within a frequency range between 0.5 and 20 Hz. However, the frequency dependence of Q s in the frequency range between 0.5 and 6 Hz is best approximated by Q s (f) = 36 f 0.94 showing relatively weaker frequency dependence as compared to the relation Q s (f) = 6 f 2.09 for the frequency range between 6 and 15 Hz. These results could be used to estimate source and site parameters for seismic hazard assessment in the region.

Keywords

• Tohoku
• Generalized inversion technique
• Non-parametric attenuation function
• Seismic quality factor
• S-wave