Effects of soil-moisture content on shallow seismic data

Abstract

Repeated shallow‐seismic experiments were conducted at a site on days with different near‐surface moisture conditions in unconsolidated material. Experimental field parameters remained constant to ensure comparability of results. Variations in the seismic data are attributed to the changes in soil‐moisture content of the unconsolidated material. Higher amplitudes of reflections and refractions were obtained under wetter near‐surface conditions. An increase in amplitude of 21 dB in the 100–300 Hz frequency range was observed when the moisture content increased from 18% to 36% in the upper 0.15 m (0.5 ft) of the subsurface. In the time‐domain records, highly saturated soil conditions caused large‐amplitude ringy wavelets that interfered with and degraded the appearance of some of the reflection information in the raw field data. This may indicate that an intermediate near‐surface moisture content is most conducive to the recording of high‐quality shallow‐seismic reflection data at this site. This study illustrates the drastic changes that can occur in shallow‐seismic data due to variations in near‐surface moisture conditions. These conditions may need to be considered to optimize the acquisition timing and parameters prior to collection of data.