球对称有限水体气泡振荡模型及其对陆地水体气枪研究的意义  

A spherically symmetric model of bubble oscillation in finite water bodies and its implications for air gun studies in onshore water bodies

作　　者：徐逸鹤 王宝善[1,4] 王伟涛[1] XU YiHe;WANG BaoShan;WANG WeiTao(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Department of Earth Sciences,University of Cambridge,Cambridge CB30EZ,United Kingdom;Geophysics Section,School of Cosmic Physics,Dublin Institute for Advanced Studies,Dublin D02Y006,Ireland;School of Earth and Space Science,University of Science and Technology of China,Hefei 230026,China)

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]英国剑桥大学地球科学系,剑桥CB30EZ [3]爱尔兰都柏林高等研究院宇宙物理学学院地球物理学分部,都柏林D02Y006 [4]中国科学技术大学地球和空间科学学院,合肥230026

出　　处：《地球物理学报》2022年第9期3374-3385,共12页Chinese Journal of Geophysics

基　　金：国家重点研发计划(2018YFC1503200);国家自然科学基金(41804054,41904084,41790463)联合资助。

摘　　要：在陆内水体内激发气枪震源,利用其气泡振荡产生的地震波可以研究地下结构及速度变化.与海洋激发环境不同,陆内有限水体会影响气泡的振荡过程.本文利用有限元方法,对球对称情况下气泡在有限水体内的振荡过程进行了数值模拟分析,发现气枪震源在陆内水体内的气泡振荡存在临界大小,与气枪激发时产生的激波有关.模拟结果表明,水体较大时(半径大于100 m),可以继续使用无限水体模型;当水体较小时(半径小于50 m),固液边界反射的激波会改变气泡处的压力,进而改变气泡振荡过程,显著地提高气泡振荡的频率,降低振荡的幅度.相关数值模拟结果与实验观测相符,为陆内小水体中气枪的高频源场信号特征提供了合理的解释.基于有限水体的气泡振荡过程分析有助于提升对陆内水体气枪激发过程的理解,为气枪选址、设计、优化提供理论依据.Air gun sources,which generate seismic waves via bubble oscillations in the water,can be used in onshore water bodies to study the structure and velocity changes in the Earth.Compared to air guns in oceans,the limited volume of the onshore water bodies will change the oscillation of the bubbles.In this paper,we simulated the bubble oscillations in finite water bodies in case of spherical symmetry.Using 1-D explicit finite-element method,we found there is a threshold in terms of the size of the water body under which the behavior of the bubble oscillation is strongly affected by shock waves generated when air guns shot.In large water bodies(radius>100 m),classical air gun models developed for infinite water bodies are still applicable,while in water bodies(radius<50 m),the frequency of the bubble oscillation increases and the amplitude decreases due to shock waves.When the shock waves arrive the vicinity of the bubble after bouncing back from the fluid-solid interface at the boundary of water bodies,they modify the pressure field near the bubble,thus changing the bubble oscillation.The results of simulations show consistent patterns with previous air gun experiments.This study offers a reasonable explanation for the high-frequency content from air guns in small water bodies.It also helps improve the knowledge of the process of air gun sources in the onshore water bodies,providing a theoretical evidence for the site selection,design and optimization of air gun sources.

关 键 词：气枪 有限水体 震源 主动源 气泡振荡 

分 类 号：P315[天文地球—地震学]