Propagation of dispersed compressional and Rayleigh waves on the Texas coastal plain

Abstract

During a refraction profile on the Texas coastal plain, a strong surface wave with predominant frequencies between 2 and 10 Hz and group velocities near 1.9 km/sec was observed to ranges as great as 64 km. This dispersed wave, with velocities near the compressional wave speed of near‐surface sediments, corresponds to the “leaky” compressional or PL wave. PL dispersion can be predicted from the theory of the normal modes of a layered liquid medium. Efficient propagation of the PL wave is related to the high Poisson ratio of the unconsolidated sediments in the shallow subsurface, and additional examples from the published literature show that the PL wave is commonly excited by shallow sources both on land and offshore. In addition to the PL waves, dispersed waves with group velocities between 0.3 and 0.7 km/sec were observed at ranges less than 10 km. These are identified as Rayleigh waves (LR). Smoothly varying P and S velocity structures for the upper 1 km are obtained by fitting theoretical dispersion curves to the observed PL and LR data.