水中气枪声源激发的地震波场波动成分及其能量占比特性

Wave Components and Energy Ratio Characteristics of Seismic Wave Field Motivated by Airgun Source in Shallow Water

为分析水中声源激发的海底地震波场波动成分组成及其能量占比特性,开展了理论推导、数值仿真与试验研究。基于高阶交错网格有限差分法对分层浅海模型中声源激发的海底地震波场进行数值模拟仿真,理清海底地震波场波系及其组成成分;采用τ-p法对仿真的海底地震波场波动成分进行分离,分析不同海底底质条件下气枪声源激发的地声波动成分能量及其占比特性;开展一次湖试和两次海试,验证了仿真结果。研究表明:水中声源激发的海底地震波可分为纵波、横波、水中声波、表面波4个波系;τ-p法能有效分离气枪声源激发地海底地震波场波动成分;通过处理气枪声源激发的浅海海底地震波阵列信号,可以比较准确地获得海域底质特性;硬海底利于激发海底地震波、表面波和横波,软海底利于激发纵波,异常软的底质难以激发出表面波。

The fluctuation components and their energy ratio characteristics of seismic wave field motivated by airgun source in shallow water are analyzed through theoretical derivation,numerical simulation and experiment.The layered model of shallow water is simulated using high-order staggered-grid finite difference method,and the wave systems and components of seabed seismic wave field are given.Wave components of the simulated seabed seismic wave field are separated usingτ-p method,and the fluctuation components and their energy ratios of seismic wave field are simulated and analyzed.A lake trial and two sea trials were made to validate the theoretical and simulated results.The results demonstrate that the seabed seismic wave motivated by airgun source in water is divided into longitudinal wave,transversl wave,underwater acoustic wave,and surface wave,τ-p method can be used to separate the wave components of seismic wave field,and the sea bottom characteristics can be obtained from the signals received by the seismic array.The seabed seismic wave,interface wave and transversal wave are easily motivated on hard seabed,the longitudinal wave is easily motivated on soft seabed,and the interface wave is difficultly motivated on very soft seabed.