In relation to sea-bottom pseudo reflection face and methane hydrate in seismic exploration records, fundamental experimental studies have been made. In order to get a handhold to elucidate phenomena accompanying methane hydrate, the studies have investigated wave propagation behavior of rock samples and sandy sediments under medium and low temperature conditions. The experiments have used a constant-temperature cooling water circulating equipment to control temperatures of each sample. The samples were placed in a cooler box with the vibration transmitter and receiver fixedly installed, and changes of the waves against temperature change were measured. Sand-stones and two kinds of tuffs were used as rock samples for the measurement. Artificial sand sample soaked in water was used as a substitute for a methane hydrate layer. As a result of the experiments, the relation between the hydrate layer and the gas layer was comprehended. In addition, the blanking phenomenon was thought occurring as a result of the nearly whole substance presenting the speed of ice due to freezing of the sediments, rather than by what is described in the ground homogeneousness theory. 5 refs., 9 figs.