海底表层沉积物声速的环境因素影响特性

应用声速通用模型开展理论分析,结合温度-压力可控实验测量分析,研究地声反演、海底原位声学测量和采样样品声学测量3种主要的海底表层沉积物声学特性测量方法中,存在的环境因素影响机制和特性。理论计算与实验测量研究具有一致性,揭示温度和静水压力对海底表层沉积物的压缩波声速的影响机制主要是通过影响孔隙海水的密度、黏度、体积弹性模量体现的。在海底4000 m以内的表层海底沉积物通常存在的海底温度和静水压力范围内,发现声速比不为常数,随着温度升高和静水压力增大而呈现出细微减小趋势,理论计算海底沉积物与底层海水声速比波动度在2%以内,实验测量声速比波动度在2.73%以内。基于声速比不为常数,提出修正声速比校正模型,为减小温度和静水压力影响因素误差,更准确地实现不同原位、实验室环境状态下的海底沉积物声速的分析和比较提供了改进方法。 

Environmental factors affecting acoustic velocity of seafloor surface sediments

With the comprehensive analysis of measurement results by the temperature pressure controlled experiment and theoretical calculations with the general model of sound speed,the influence mechanism and characteristics of environmental factors affecting acoustic velocity of seafloor surface sediments are studied for the three main acoustic measurement methods including the geoacoustic inversion,the underwater in situ acoustic measurement and the sampling sample acoustic measurement.The consistency between theoretical calculation and experimental measurement reveals the main mechanism of the influence of temperature and hydrostatic pressure on the velocity of compressional wave of the surface sediments,which is achieved by their effect on the density,viscosity and bulk modulus of the pore water.At the same time,it is found that the sound velocity ratio isn’t constant and slightly decreases both with the increase of temperature and with that of hydrostatic pressure.In the normal range of temperature and hydrostatic pressure for the seafloor sediment at the depth of form 0 m to 4000 m,the fluctuation of acoustic velocity ratio of seafloor surface sediment and bottom sea water is within 2% by theoretical calculation and within 2.73% by experimental measurement.Based on the sound velocity ratio being not constant,a modified sound velocity ratio correction model is proposed,which provides a improved method to reduce the influencing error of temperature and hydrostatic pressure to more accurately realize the comparison and analysis of the sound velocity of the seafloor sediments under the different in situ and laboratory conditions.