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| | Abstract | | Tachikawa fault is one of the most activity faults in the Tokyo metropolitan area and when large earthquake will occur by this fault in the near future, it is expected that large economic and human loss will happen around this area. However, three dimensional subsurface structural model is not clear still enough for the estimation of the strong ground motions in this area. In this study, we estimated deep and shallow S-wave velocity structures using the Rayleigh wave phase velocities from the obtained records of the microtremor array explorations. Rayleigh-wave phase velocity at periods from 0.5 to 5.0 seconds from large array was estimated from a frequency-wave number spectral method analysis of the microtremors. And also Rayleigh-wave phase velocity at periods from 0.03 to 0.3 seconds from small array was estimated from a spatial autocorrelation method analysis of the microtremors. We identified the subsurface structural model using inversion based on the simulated annealing method. Based on numerical experiments it is indicated that thickness of individual layers are inverted very well. The results indicate that a basement depth in those profiles at down-thrown side of the fault is larger than that at up-thrown side with a difference of about 2km. |
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