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Simulation study on oblique in situ acoustic longitudinal wave measurement of seafloor inhomogeneous sedimentary layer
WANG Ying, TAO Chunhui, ZHANG Guoyin, ZHOU Jianping, SHEN Honglei
Journal of Marine Sciences ›› 2023, Vol. 41 ›› Issue (4) : 57-69.
PDF(5319 KB)
PDF(5319 KB)
Simulation study on oblique in situ acoustic longitudinal wave measurement of seafloor inhomogeneous sedimentary layer
Acoustic characteristics of seafloor sediments are the basic elements of marine sound field calculation and engineering geological evaluation. In situ measurement is an effective means to accurately obtain acoustic characteristic parameters. The structure stratification characteristics and the existence of geological anomalies such as boulders lead to vertical and lateral heterogeneity, and the existing acoustic in situ measurement system is difficult to detect and recognize the nonuniform features, and there is a lack of discrimination reference for the identification of stratigraphic non-uniformity. In this study, an oblique acoustic in situ longitudinal wave measurement method based on the heterogeneity of seafloor deposition was proposed, and a simulation study on the oblique acoustic in situ measurement of sediments within a hundred meters was carried out by using the finite element method. According to the data of regional geological engineering exploration data in the East China Sea, three models of uniform sedimentary layer, stratified sedimentary layer, and a sedimentary layer containing the boulder were constructed, and a simulation of acoustic velocity measurement in the sedimentary layer was carried out based on oblique in situ measurement method. The results show that the oblique in situ measurement method was effective in identifying the inhomogeneity in the large-depth sedimentary layer. By introducing the concept of equivalent offset, the original acoustic velocity calculation formula was improved, effectively improving anomaly identification accuracy. The oblique acoustic in situ measurement method proposed in this study was an effective extension of the existing in situ measurement methods of sedimentary layers, which will help to promote the further application of in situ measurement in marine engineering surveys.
seafloor sedimentary layers / oblique acoustic in situ measurement / acoustic characteristic / simulation
| [1] |
陶春辉. 海底沉积物声学原位测试和特性研究[D]. 杭州: 浙江大学, 2005.
|
| [2] |
潘国富. 南海北部海底浅部沉积物声学特性研究[D]. 上海: 同济大学, 2003.
|
| [3] |
孟祥龙. CT探测技术在跨海顶管孤石群探测的应用研究[J]. 铁道建筑技术, 2021(1):150-154.
|
| [4] |
刘保华, 阚光明, 李官保. 海底沉积物声学特性测量技术与应用[M]. 北京: 科学出版社, 2019:38-50.
|
| [5] |
王景强, 李官保, 阚光明, 等. 深海海底沉积物声学特性原位测量试验研究[J]. 地球物理学报, 2020, 63(12):4463-4472.
由于实验室测试环境条件与深海海底的原位温压环境存在较大的差异，取样测量的沉积物声学参数通常偏离海底原位状态的真实值.该文利用深水型压载式沉积声学原位测量系统，在水深超过5000 m的西太平洋海域开展了沉积物声学原位测量试验，准确获取了深海底原位状态下沉积物的声速和声衰减系数，并同步采集了沉积物柱状样品.结果显示，实验室测量的沉积物声速、声衰减系数均高于原位测量结果.通过温压校正和数据—模型对比表明，实验室声速比与原位声速比存在较大的差异，难以通过温压校正模型和频散模型完全改正，这可能与深海沉积物的结构扰动有关.较之浅海沉积物，软弱的深海沉积物结构更易受到采样过程的扰动，因而深海沉积物的声学特性测量更为困难，这表明在深海海底声学研究采用原位测量技术具有必要性.该研究标志着我国海底声学研究由浅海走向深海，对推动海底声学的深入研究具有重要意义.
|
| [6] |
陶春辉, 金肖兵, 金翔龙, 等. 多频海底声学原位测试系统研制和试用[J]. 海洋学报:中文版, 2006, 28(2):46-50.
|
| [7] |
|
| [8] |
|
| [9] |
In situ measurements of compressional and shear wave speed and attenuation were collected 30 cm below the water-sediment interface in Currituck Sound, North Carolina at two field locations having distinctly different sediment types: medium-to-fine-grained sand and fine-grained sand with approximately 10% mud content. Shear wave measurements were performed with bimorph transducers to generate and receive horizontally polarized shear waves in the 300 Hz to 1 kHz band, and compressional wave measurements were performed using hydrophones operated in the 5 kHz to 100 kHz band. Sediment samples were collected at both measurement sites and later analyzed in the laboratory to characterize the sediment grain size distribution for each field location. Compressional and shear wave speed and attenuation were estimated from the acoustic measurements, and preliminary comparisons to the extended Biot model by Chotiros and Isakson [J. Acoust. Soc. 135, 3264–3279 (2014)] and the viscous grain-shearing theory by Buckingham [J. Acoust. Soc. 136, 2478–2488 (2014)] were performed.
|
| [10] |
|
| [11] |
|
| [12] |
|
| [13] |
阚光明, 刘保华, 韩国忠, 等. 原位测量技术在黄海沉积声学调查中的应用[J]. 海洋学报, 2010, 32(3):88-94.
|
| [14] |
|
| [15] |
The acoustic lance is an instrument developed to obtain in situ compressional wave velocity and attenuation (Q−1) profiles for a sedimentary layer of several meters thickness at the sediment–seawater interface. The self-contained instrument consists of ten independent recording channels with a linear array of receivers embedded in the seafloor below a broadband acoustic source. It provides in situ recording of full waveforms to determine interval velocity and attenuation. The system can be attached to a gravity corer or to a specially designed probe. A comprehensive experiment was carried out in Mid-Atlantic Ridge sediment ponds where the lance made in situ measurements, and core samples were recovered. Core data agree well with in situ data in one location, but disagree in other locations. Lance data indicate that the sediment ponds have similar in situ velocity distributions, with an acoustic channel much thinner than that predicted by earlier investigators.
|
| [16] |
|
| [17] |
Knowledge of sediment sound speed is crucial for predicting sound propagation. During the Shallow Water '06 experiment, in situ sediment sound speed was measured using the Sediment Acoustic-speed Measurement System (SAMS). SAMS consists of ten fixed sources and one receiver that can reach a maximal sediment depth of 3m. Measurements were made in the frequency range 2–35kHz. Signal arrival times and propagation distances were recorded, from which sediment sound speed was determined. Preliminary results from three deployments show that SAMS was capable of determining sediment sound speed with uncertainties less than 1.6%. Little dispersion in sediment sound speed was observed.
|
| [18] |
刘伯胜, 黄益旺, 陈文剑, 等. 水声学原理[M].第三版. 北京: 科学出版社, 2020:65-83.
|
| [19] |
周志远, 高金耀, 吴招才, 等. 东海莫霍面起伏与地壳减薄特征初步分析[J]. 海洋学研究, 2013, 31(1):16-25.
收集、整理大量由地震剖面提供的沉积层厚度资料,得到东海沉积层等厚图。对完全布格重力异常进行沉积层重力效应改正后,得到剩余重力异常,利用地震资料揭示的莫霍面深度值来约束界面反演得到东海莫霍面埋深。结果表明,东海陆架盆地莫霍面深度在25～28 km之间平缓变化,地壳厚度为14～26 km,西厚东薄;冲绳海槽盆地莫霍面深度为16～26 km,地壳厚度为12～22 km,北厚南薄。东海陆架盆地东部与冲绳海槽盆地南部地壳减薄明显,拉张因子分别达到2.6和3。初步分析认为冲绳海槽地壳以过渡壳为主,并未形成洋壳。
|
| [20] |
李红星. 杭州湾沉积物原位声学特性分析及浅表低速层研究[D]. 长春: 吉林大学, 2008.
|
| [21] |
周建平, 吕文正, 陶春辉. 海底柱状沉积物超声测量[J]. 东海海洋, 2003, 21(4):26-33.
|
| [22] |
张慧. 花岗岩声波波速与岩体弹性模量的统计分析[J]. 低碳世界, 2016(2):110.
|
| [23] |
|
| [24] |
|
| [25] |
李倩宇, 陶春辉, 周建平, 等. 海底沉积物声学原位信号自动拾取方法研究[J]. 杭州电子科技大学学报:自然科学版, 2019, 39(2):18-21,39.
|
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