An algorithm for identifying the svrface waves, Love-and Rayleigh-waves, in microtremors has already been developed as a new exploration technique which can determine S-wave velocity structure. A practical use of the technique has been designed and also examined at two experimental sites in an urban area, Morioka city in northen Honshu, Japan. The technique involves the measurement of the dispersion of both surface waves in microtremors by using a specially-designed circular seismic array consisting of more than three tri-axial seismometers that are equally spaced on acircle and one at the circular center. In determination of phase velocities of Love-and Rayleigh-waves, the newly-modified spatial auto-correlation method has been used. The method can provide not only the dispersion of Rayleigh waves, but also that of Love waves. The dispersion of Love waves is directly convertible to the S-wave velocity structure. Estimated phase velocities of Love wave using microtremors at the experiment site of Iwate University were in the range of 750 to 200m/s corresponding to the frequency range from 2.8 to 10Hz. The phase velocities determined from horizontal microtremors were in good agreement with those calculated by the structure model which were derived from the phase velocities of Rayleigh waves. Estimated phase velocities of Love wave in microtremors were in the range of 450 to 200m/s corresponding to the frequency range from 1 to 2.9 Hz at the experiment site of Morioka technical high-school. These results of two experimental sites show that the newly-modified spatial auto-correlation method is applicable to estimation of Love wave phase velocities using microtremors.
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