| 基于地震层析速度模型分析海滩地下结构:以青岛石老人海水浴场为例 |
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| 引用本文： | 高福建,邹志辉,王永红.基于地震层析速度模型分析海滩地下结构:以青岛石老人海水浴场为例[J].地学前缘,2022,29(5):275-284. |
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| 作者姓名： | 高福建 邹志辉 王永红 |
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| 作者单位： | 1.中国海洋大学 海洋地球科学学院/海底科学与探测技术教育部重点实验室, 山东 青岛 2661002.青岛海洋科学与技术国家实验室 海洋矿产资源评价与探测技术功能实验室, 山东 青岛 266061 |
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| 基金项目： | 国家重点研发计划项目(2018YFC0603604);国家重点研发计划项目(2021YFE0108800);中央高校基本科研业务费项目(201964017);中国海洋大学研究生教育质量提升计划建设项目(HDJG19006);中国海洋大学本科教学研究项目(2021JY043);中国海洋大学本科教学研究项目(2022JY028) |
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| 摘 要： | 对海滩地下结构的认识是海岸带研究的一个重要方面,也是海滩保护和开发的基础。目前对于海滩的研究大多集中在表面动态变化监测和研究,而对于海滩内部结构和基底形态研究还非常有限。现有的钻探和探测手段一般只能研究表层砂体,难以探测到砂体的底部,无法建立海滩的整体结构模型,不利于分析砂的储量和研究海滩的演化。因此,需要一种探测手段,以便快速有效地开展砂体结构的大范围探测。本文把多尺度地震层析成像方法应用于海滩结构研究,以山东半岛东南部花岗岩石质海岸的一个典型海滩—青岛石老人海水浴场为例,对石老人海滩下方从地表到结晶基底的整体结构开展研究。通过采用新研制的重锤震源得到较高信噪比的地震数据,使用多尺度地震层析成像方法对海滩地下结构进行建模,建立了青岛石老人海水浴场海滩下方深达50 m的速度结构模型。所建立的速度结构模型与该区域已有的对砂体厚度的认识,以及海滩钻孔取样得到的柱状样品的砂粒度变化曲线吻合。该速度结构模型显示,测线下方砂体北厚南薄,在后滨的厚度约为15 m,而在前滨仅有5 m左右。我们推测,海滩下方的砂体中可能存在直立的岩石和未风化完全的岩石,海滩下方的不均匀风化作用导致其下方基底呈现下凹的形态,这种基底形态可能具有稳定砂体的作用。本文方法能够快速有效地构建海滩下方速度结构模型,并且可以方便地推广到其他海滩的结构探测,对于研究海滩结构、演化过程和沙滩保护具有重要意义。
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| 关 键 词： | 地震层析成像 海滩 砂体 重锤震源 青岛石老人海水浴场 |
| 收稿时间： | 2021-03-10 |
Subsurface structure of seabeach revealed by seismic tomographic velocity model: An example of the Qingdao Shilaoren beach |
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| GAO Fujian,ZOU Zhihui,WANG Yonghong.Subsurface structure of seabeach revealed by seismic tomographic velocity model: An example of the Qingdao Shilaoren beach[J].Earth Science Frontiers,2022,29(5):275-284. |
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| Authors: | GAO Fujian ZOU Zhihui WANG Yonghong |
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| Institution: | 1. College of Marine Geosciences, Ocean University of China/Key Lab of Submarine Geosciences and Prospecting Techniques, MOE, Qingdao 266100, China2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China |
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| Abstract: | Understanding the subsurface structure of seabeach is an important part of coastal zone research and fundamental to seabeach protection and coastal development. Current seabeach researches are mainly focused on beach surface dynamics, but the internal structure and basement morphology of seabeach is little studied. Although drilling and other conventional exploration methods can be used for structural analysis of shallow sand, they are inadequate for building a complete seabeach model from surface to the bottom of basement. Without such a model it is difficult to calculate the sandbody volume or study seabeach evolution; therefore, a wide-range, effective detection method is needed for the structural analysis of sand body. Here, as an example, we apply multiscale seismic tomography to the Qingdao Shilaoren beach, a typical seabeach on the granite rocky coast of southeastern Shandong Peninsula, to investigate its detailed subsurface structure from surface to the crystalline basement. By using the newly developed heavy hammer source, we obtained the seismic data with high signal-to-noise ratio at offset as far as 150 m under noisy beach environment. The multiscale seismic tomography method performed well in modeling the subsurface structure of the seabeach, which allowed us to establish a velocity model to a depth of ~50 m below the Qingdao Shilaoren beach for interpreting the internal structure of sand body. The resulting velocity structure model fits well with the previously reported sand depth and particle size variation results obtained from drilling experiments. The inverted velocity structure shows that the sand body beneath the north end of the survey line (coastal side) is thicker than that beneath the south end near the shoreline, with ~15 m thickness beneath the backshore and only 5 m beneath the foreshore. We infer that there may be underground vertical rocks and partially weathered rocks in the sand body. The uneven weathering resulted in a concave-shaped basement that might have stabilized the sand body. Our method can be used to quickly and effectively build velocity models of subsurface sand body and other subsurface structures of seabeach, which is significant to the study of seabeach structure and evolution and beach protection. |
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| Keywords: | seismic tomography beach sand body seismic hammer source Qingdao Shilaoren beach |
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