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Simple assessment of shallow velocity structures with small-scale microtremor arrays: interval-averaged S-wave velocities

This article describes a method for processing microtremor records from a small-scale seismic array that allows interval-averaged S-wave velocities to be estimated for 10-m depth ranges down to a depth of 30 m. The method was applied to microtremor data obtained in the town of Mashiki, Kumamoto Prefecture, Japan, and the analysis results were evaluated through a comparison with available PS logs and sections obtained by surface-wave methods. It turned out that the interval-averaged S-wave velocity estimates may be subject to errors of up to 20–30% in absolute values, but it was shown that the method can help evaluate relative spatial variations in those S-wave velocities. In view of the simplicity of analysis, the analyser-independent nature of the results and the limitations of analysis accuracy, the interval-averaged S-wave velocity estimation method presented here could be used as an effective tool for the preliminary analysis of microtremor data from small-scale seismic arrays. This article describes a simple method for estimating interval-averaged S-wave velocities for 10-m depth ranges down to a depth of 30 m. Possibilities and limitations of this method are examined by using the analysis results of the microtremor data obtained in the town of Mashiki, Kumamoto Prefecture, Japan.