Abstract: The seismic method based on elastic wave characteristics of rock is the most important method in geophysical exploration. The propagation velocity of elastic wave in rock is an effective bridge connecting physical and mechanical characteristics of rock with geology. In terms of biogenetic coral reef limestone in the sea, the characteristics of elastic wave is an effective way to find out the whole internal properties of coral reef. This study shows that the elastic longitudinal wave velocity of coral reef limestone has a linear positive correlations with dry density and rebound value, but has a linear negative relationship with porosity. The elastic wave features of coral reef limestone with various structural types present significant difference. For example, coral skeleton limestone and coral gravel limestone have good uniformity, whereas coral gravel limestone and coral sand limestone have distinct dispersion. Based on the relationships between longitudinal wave velocity and dry density, porosity and rebound value of coral reef limestone, a classification standard of the quality grade is proposed for coral reef limestone, combined with the rebound values of drilling core along the depth of a coral reef and the optical detection results of core sheets. It has certain reliability and applicability. A modified time-average formula is established by using the basic principle of two-phase rock model. In addition, Remo Hunter-Gardner equation is suitable for elastic wave characteristics of coral reef limestone with different structural types.

Key words: coral reef limestone, structural type, elastic waves, porosity, quality grade