1. College of Geo-exploration Science and Technology, Jilin University, Changchun 130026, China;
2. Shandong Geophysical and Geochemical Exploration Institute, Jinan 250013, China;
3. Guangdong Geological Survey Institute, Guangzhou 510000, China

The spatial autocorrelation method is a traditional microtremor survey method. The autocorrelation coefficients and the dispersion curves are obtained by the spatial autocorrelation method in different radii combinations with double circular observation array. The authors compare the dispersion curves of different radii, and then combine some previous research results to summarize the characteristics. The large radius combination method has higher reliability in the low frequency part, whereas the small radius combination method has higher reliability in the high frequency part. Therefore, the authors use the methods of sub-band fitting Bessel function and fractional average dispersion curve into different frequency bands to widen the available frequency range and improve the detection accuracy. Finally, the effectiveness of the method is verified through field experiments.