ESTIMATION OF CRUSTAL STRUCTURE FROM OBSERVED GROUP VELOCITIES OF PL-WAVES IN JAPAN

Forward modelling of the crustal structure of the eastern Honshu Island, Japan, was made based on the group velocities of PL-waves in the period range of 20-30 s. The observed values of group velocity were obtained by applying the multiple filter technique to the seismograms for earthquakes with the epicentral distance ranging from 500 to 1000 km. The theoretical values were calculated using Oliver and Major's method to find the best fit dispersion curve in the least-squares sense. The obtained structural model has considerably high crustal velocities compared to other previous models. It was shown that the PL-wave group velocity in the period range of interest was most sensitive to seismic velocities of the center of the crust. Numerical experiments confirmed the applicability of the approximation methods employed to obtain both observed and theoretical group velocities.