Seismic imaging for an ocean drilling site survey and its verification in the Izu rear arc
Seismic imaging for an ocean drilling site survey and its verification in the Izu rear arc
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伊豆弧后大洋钻探现场地震成像及其验证
DOI：
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发表时间：
2017
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通讯作者：
S. Kodaira
中科院分区：
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作者：
M. Yamashita;N. Takahashi;Y. Tamura;S. Miura;S. Kodaira
为了评估国际海洋发现计划（International Ocean Discovery Program）提出的钻探地点的地壳结构，日本海洋地球科学技术机构（Japan Agency for Marine-Earth Science and Technology）在2006年至2008年期间，利用“海轮”（Kaiyo）和“海轮”（Kairei）两艘科考船，在伊豆岛弧后方进行了地震调查。由三种反射测量组成的高分辨率密集网格测量生成了清晰的地震剖面，并通过地震折射测量获得了地震速度图像。在本文中，我们将地震剖面与钻井获得的地质柱进行了比较。在地震折射速度成像得到的纵波速度5 km/s和6 km/s等高线以上的地震反射剖面中，确定了5个火山碎屑沉积单元。然而，从地震图像中解释的一些单元边界在钻探岩心中无法识别，这突出了仅从地震图像识别火山岩地区地质目标的困难。钻探获得的地质岩心由7个岩性单元组成（标记为I至VII）。单元1 ~ V的年龄在0 ~ 9 Ma之间，单元6、VII的年龄在海底1320 ~ 1806.5 m （mbsf）之间，为9 ~15 Ma之间。通过网格测量线之间的交叉光谱分析，通过相干性确定了U1437钻井点下方火山沉积物的强非均质性。我们的研究结果表明，在火山弧后情况下的海洋钻探现场调查中，使用密集网格配置是重要的，以便识别非均质地壳结构，例如来自不同来源的沉积物。为了评估一个拟议的海洋钻探地点的地壳结构，在日本伊豆后弧进行了高分辨率密集地震调查。我们的研究结果表明，在火山弧后的情况下，为了识别不均匀的地壳结构，例如来自不同来源的沉积物，使用密集网格配置是很重要的。
To evaluate the crustal structure of a site proposed for International Ocean Discovery Program drilling, the Japan Agency for Marine-Earth Science and Technology carried out seismic surveys in the Izu rear arc between 2006 and 2008, using research vessels Kaiyo and Kairei. High-resolution dense grid surveys, consisting of three kinds of reflection surveys, generated clear seismic profiles, together with a seismic velocity image obtained from a seismic refraction survey. In this paper, we compare the seismic profiles with the geological column obtained from the drilling. Five volcaniclastic sedimentary units were identified in seismic reflection profiles above the 5 km/s and 6 km/s contours of P-wave velocity obtained from the velocity image from the seismic refraction survey. However, some of the unit boundaries interpreted from the seismic images were not recognised in the drilling core, highlighting the difficulties of geological target identification in volcanic regions from seismic images alone. The geological core derived from drilling consisted of seven lithological units (labelled I to VII). Units I to V were aged at 0–9 Ma, and units VI and VII, from 1320–1806.5 m below seafloor (mbsf) had ages from 9 to ~15 Ma. The strong heterogeneity of volcanic sediments beneath the drilling site U1437 was also identified from coherence, calculated using cross-spectral analysis between grid survey lines. Our results suggest that use of a dense grid configuration is important in site surveys for ocean drilling in volcanic rear-arc situations, in order to recognise heterogeneous crustal structure, such as sediments from different origins. To evaluate the crustal structure of a site proposed for ocean drilling, high-resolution dense seismic surveys were carried out in the Izu rear arc, Japan. Our results suggest that use of a dense grid configuration is important in volcanic rear-arc situations, in order to recognise heterogeneous crustal structure, such as sediments from different origins.