INTRODUCTION

Physical property models of gas hydrate-bearing sediments are important basis of seismic studies of marine gas hydrates［1］.The relationships between physical properties of gas hydratebearing sediments and concentration of gas hydrates are useful for the recognition of the geophysical characters and the estimates of the quantity of gas hydrates.There have been more studies of P wave velocity and less studies of S wave velocity and Poisson's ratio.Some models have been proposed to describe the relationship of the velocity and the concentration such as porosity reduction model［2］，time-average equation model［3］，weighted time-average and Wood's equation model［3］，the model based on seismic wave propagation theory in three-phase medium［4］and elastic modulus model［5］.The simple models are less rigorous in theory compared with complex models，but simple models can be easily used.The relationships between elastic properties and gas hydrate/free gas concentration are presented based on such models as weighted time-average and Wood's equation［3］，seismic wave propagation in three-phase effective medium［4］and elastic moduli［5］.The AVA characters of different models are calculated and analyzed，while the role of amplitude-versus-offset（AVO）analysis of bottom simulating reflector is discussed.(https://www.daowen.com)