地震折射层析法在红壤关键带地层划分中的应用研究
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中国工程院咨询研究项目(2019-XZ-24)、国家自然科学基金项目(41771251)和国家重点研发计划政府间国际科技创新合作重点专项项目(2018YFE0107000)资助


Application of Seismic Refraction Tomography in Stratigraphic Division of Critical Zones in Red Soil Area
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Consulting Research Project of Chinese Academy of Engineering(2019-XZ-24), the National Natural Science Foundation of China (No. 41771251), The National Key Research and Development Program is the Key Special Project of Inter-governmental International Scientific and Technological Innovation Cooperation(2018YFE0107000)

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    摘要:

    地球关键带结构的识别对于理解关键带系统中发生的地球物理化学过程有重要意义,以往基于钻井和剖面来研究关键带地下结构的方法不足以充分反映关键带地下构造全貌,近些年地震折射层析方法在浅层地表勘探中兴起。为探究关键带地下结构的空间变异特征,本研究以红砂岩基岩的鹰潭孙家流域和板岩基岩的长沙沿江阶地为研究区,通过高精度地震折射层析(SRT)方法,绘制了关键带地层剖面速度图,将关键带划分为覆盖层、半风化层、基岩层。基于钻井实测数据定量评估地震勘探反演精度。结果表明:(1)红壤关键带深度为8.2~22.9 m,半风化层上界面深度为3.0~13.2 m,红壤关键带基岩面对应的地震波纵波速度在2 000~2 400 m·s-1之间。(2)含水层中的地下水会使地震折射法划分的关键带覆盖层厚度偏小;地下水水位与地震纵波1 000 m·s-1速度等值线有一定协同关系。(3)鹰潭研究区覆盖层下界面预测值与观测值的均方根误差(RMSE)为1.7 m,长沙研究区覆盖层下界面预测值与观测值的RMSE为2.4 m;鹰潭研究区基岩面预测值与观测值的RMSE为7.0 m,长沙沿江阶地基岩面预测值与观测值的RMSE为0.9 m。综上所述,地震折射层析方法在预测关键带覆盖层深度上效果较好,而在预测关键带基岩面深度尤其是鹰潭孙家流域基岩面深度上效果有待进一步提升。

    Abstract:

    [Objective] It is of great significance to identify structure of the critical zones (CZs) of the earth for better understanding the geochemical, ecological and hydrological processes occurring in the CZs. However, previous studies relied mainly on borehole drilling and profiles, which is far from enough to help draw a full picture of the underground structure of the CZs. To overcome this problem, in this study, attempts were made to combine borehole drilling with the seismic refraction tomography (SRT) method to test if the seismological method can effectively detect the structure of CZs of highly weathered regolith.[Method] To that end, case studies were carried out of the Sunjia Catchment of Yingtan and the terraces of slat bedrock along the Yangtze River in Changsha. The study areas are both located in the red soil region, but different in bedrock composition. The bedrock is red sandstone in the Sunjia Catchment and sedimentary slate in the terraces along the Yangtze River. Ten seismic lines were arranged in the two study areas, and each had a detection depth ranging between 25~30 m. In addition, a total of 13 boreholes were drilled in the two study areas. In the field investigation recognition capability and error range of the SRT method were evaluated.[Result] Results show:SRT can effectively discern propagation velocity of p-wave at different depths in the CZs, and determine depth of key interfaces. In Yingtan, the identified lower boundary of the Overburden layer varies in the range of 3.0~5.2 m, with root mean square error (RMSE) being 1.7 m, and the identified bedrock surface does in the range between 8.2 and 22.0 m, with RMSE being 7.0 m. In Changsha, the identified lower boundary of the first layer falls in the range of 8.1~13.2 m, with RMSE being 2.4 m, and the identified bedrock surface does between 18.8 and 22.9 m, with RMSE being 0.9 m. The prediction is in good agreement with the drilling observation. The seismic wave travels at 2400 m/s in red sandstone and at 2 000 m·s-1 in sedimentary slate. Under flat terrain the overburden and bedrock are stable, while under sloping terrain, the overburden is thick on the top slope, and gets thinner on the mid slope. Landfills reduce the precision of seismograph in predicting underground structure for they have great impacts on the structure of the overburden layer, but not much on the structure of the deep underground. Groundwater in aquifers makes the overburden of the critical zones divided with the seismic refraction method tend to be thinner.[Conclusion] The longitudinal wave traveling through the subterranean layers of the CZs varies in velocity with the layer, which is the key to identification of the structural layers of the CZs by seismograph. SRT can not only improve the efficiency of field investigations, but also advance the development of the CZ three-dimensional mapping.

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钟陈,宋效东,杨顺华,张甘霖.地震折射层析法在红壤关键带地层划分中的应用研究[J].土壤学报,2022,59(1):92-104. DOI:10.11766/trxb202008080247 ZHONG Chen, SONG Xiaodong, YANG Shunhua, ZHANG Ganlin. Application of Seismic Refraction Tomography in Stratigraphic Division of Critical Zones in Red Soil Area[J]. Acta Pedologica Sinica,2022,59(1):92-104.

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  • 收稿日期:2020-08-08
  • 最后修改日期:2020-10-29
  • 录用日期:2020-11-12
  • 在线发布日期: 2020-12-10
  • 出版日期: 2022-01-11