Application of MASW technology to identification of tidal flat stratigraphy and its geoenvironmental interpretation
Application of MASW technology to identification of tidal flat stratigraphy and its geoenvironmental interpretation
复制标题
MASW技术在潮坪地层识别及地质环境解释中的应用
DOI：
10.1016/j.margeo.2008.03.007
复制
发表时间：
2008
期刊：
影响因子：
2.9
通讯作者：
S
中科院分区：
文献类型：
--
作者：
Watabe;Y. and Sassa;S
潮间带是海洋环境的关键要素；它们由具有丰富生物活性的区域组成，也有助于水的净化。近年来，潮间带底栖生物的活动与地球环境特征密切相关。本研究的目的是探讨受地球环境特征强烈影响的潮滩地层。本文采用多通道表面波分析（MASW）的表面波方法研究了潮间滩的剪切波速/刚度结构，以识别和描述滨岸和滨岸潮滩地层。利用夏季春潮时天然滩涂、天然泥滩和人工层状沙泥滩暴露的时间，进行了野外调查。事实证明，MASW是一种非常有用的方法，可以有效地测量各种类型潮间带的地层。这种方法被自然界广泛接受，因为它没有任何有害的影响。MASW获得的潮滩地层与相应地球环境动力学下表现出来的形态土壤结构相一致。在沙地中，通过MASW（剪切波速/刚度的分布）以及土壤采样和物理土壤试验（孔隙比的分布）获得的地层形成可归因于在潮汐引起的地下水位波动下，土壤受到各种吸力动力的循环弹塑性收缩。在泥滩中，虽然观察到孔隙结构的变化与颗粒大小分布有关，但土壤刚度非常均匀，因为土壤中没有发生吸力。在小规模人工层状滩涂中，通过砂盖疏浚泥土，对人工层状滩涂地层进行了清晰的识别。地下水位动态与自然大尺度沙场相当，表明该沙场具有层状砂泥地层，但成功还原了其地质环境特征。
Intertidal flats are key elements in marine environments; they consist of regions with rich bioactivity and also contribute to water purification. Recently, it has been demonstrated that benthic activities in intertidal flats are closely related to geoenvironmental characteristics. The purpose of this study is to investigate the tidal flat stratigraphy which should be strongly affected by the geoenvironmental characteristics. We examined the shear wave velocity/stiffness structures of intertidal flats by a surface wave method called the multichannel analysis of surface waves (MASW) in order to identify and describe the cross-shore and alongshore tidal flat stratigraphy. Field surveys were carried out on a natural sandflat, natural mudflat, and artificial layered sand–mud flat during the spring tides in summer when these flats were exposed. The MASW has proved to be a very useful method to effectively survey the stratigraphy of various types of intertidal flats. This method is widely acceptable to nature because it does not have any harmful impacts. The tidal flat stratigraphy obtained by the MASW was consistent with the morphological soil structures that manifested themselves under relevant geoenvironmental dynamics. In the sandflat, the formation of stratigraphy obtained by the MASW (as distributions of the shear wave velocity/stiffness) and by soil sampling and physical soil tests (as distributions of the void ratio) can be attributed to the cyclic elastoplastic contraction of the soils that are subjected to various suction dynamics under tide-induced groundwater table fluctuations. In the mudflat, although a variation in the void structure was observed in association with grain size distributions, the soil stiffness was extremely homogeneous because suction did not occur in the soil. In the small-scale artificial layered sand–mud flat, which contained dredged muddy soil with a sand capping, the artificially layered tidal flat stratigraphy was clearly identified by the MASW. The groundwater table dynamics were equivalent to those in the natural large-scale sandflat, indicating that the geoenvironmental characteristics were successfully recreated, even though it had a layered sand–mud stratigraphy.