晚全新世中国古海啸研究

发布时间：2018-03-23 11:40

本文选题：海啸　切入点：海啸沉积　出处：《中国科学技术大学》2017年博士论文

【摘要】：本文以东海陆架泥质沉积物为研究对象,通过识别沉积序列中的异常突变,来研究东海的古海啸事件。沉积学证据和历史资料证明公元1076年南海曾发生过一次强烈海啸,东海沉积物中在850 yr BP和1150 yr BP存在粒度突然变粗的两段,从时间上看850 yrBP的一段可能是受南海海啸影响形成的。东海表层沉积物的整体分布趋势和南海海啸的数值模拟分析证明了这一点:海啸波沿着表层沉积由粗到细的方向传播,来自远海的粗颗粒表层沉积向近海搬运。这一过程在沉积物的粒径变化序列中得到了体现。1150 yr BP附近北半球存在一段突然变冷的时期,东亚冬季风在此时增强,通过对东海沿岸流的影响使沉积物中粗颗粒物质相对含量上升,引起粒径变粗。因此,沉积序列中的两个突变层位分别对应了南海古海啸和更老的一次北半球降温事件。数值模拟结果表明南海海啸引起的东海海面变化很小,而沉积记录中的粒径波动是整段沉积中最强的,因此东海在过去两千年没有受到大型海啸的袭击,否则沉积序列中会出现更强的记录。虽然历史文献中有广东潮州沿海在公元1076年被海啸袭击的记载,但是这次海啸给沿海地区造成了怎样的损失却没有详细的记录。南澳岛在古代归潮洲管辖,这里2015年才建成跨海大桥,在这之前岛上和大陆的联系均依靠船运,因此受人类活动的影响小,是研究古海啸的理想区域。对岛上东南沿岸的沉积序列的研究表明沉积物中有一层具有海啸沉积特征的砂层,其形成的年代与南海海啸的发生时间非常接近。结合潮州曾被海啸袭击的历史记载,可以确定这层沉积就是海啸在南澳留下的地质证据。在沉积层中还散乱分布着宋瓷碎片,而且仅有宋瓷,不存在其他朝代的历史遗迹。对南澳岛出土的文物和岛上遗留的建筑遗迹进行了统计,发现他们的时代大多分布在海啸发生之前的唐代、宋代初期和1575年之后的明代末期、清代,属于中间五百年的物品的数量很少。南澳在1575年正式设县建镇,在这之后进入了繁荣的发展阶段。从这之前五百年文物和遗迹的数量来看,南澳在海啸之后经历了很长一段时间的文化衰退期,甚至一度出现空白。这说明南海海啸对这个岛屿的影响是灾难性,而南澳岛上可能埋藏了大量的宋代历史遗迹。这个例子也说明了海啸灾害的多样性和复杂性,及海啸不仅可以破环海岸带的设施、经济、生态系统,当条件合适时也可能对文化造成影响,引起文化发展的衰退甚至空白。海啸沉积虽然是研究古海啸的主要载体,本文的两个例子己经表明单靠沉积学的方法不易获得对古海啸事件完整、清晰的理解,多种方法结合使用是研究古海啸的更好的途径。
[Abstract]:In this paper, the paleo-tsunami events in the East China Sea are studied by identifying abnormal mutations in the sedimentary sequence of the muddy sediments of the East China Sea shelf. The sedimentological evidence and historical data prove that a strong tsunami occurred in the South China Sea in 1076 AD. In the sediments of the East China Sea, there are two sections with sudden coarsening grain size at 850yr BP and 1150 yr BP. From the point of view of time, a section of 850#en0# may be influenced by the South China Sea tsunami. The overall distribution trend of surface sediments in the East China Sea and the numerical simulation analysis of the South China Sea tsunami prove this: the tsunami wave propagates along the direction of surface sediments from coarse to fine. The coarse-grained surface sediments from the far sea are transported to the offshore sea. This process is reflected in the grain size change sequence of sediments. There is a period of sudden cold in the Northern Hemisphere near .1150yr BP, and the East Asian winter monsoon is strengthened at this time. The effect on the coastal current of the East China Sea increases the relative content of coarse particles in sediments and results in coarser grain size. The two abrupt layers in the sedimentary sequence correspond to the ancient tsunami of the South China Sea and an older northern hemisphere cooling event, respectively. The numerical simulation results show that the sea surface changes caused by the tsunami in the South China Sea are very small. The grain size fluctuations in the sedimentary records are the strongest in the entire section, so the East China Sea has not been hit by a large tsunami in the past two thousand years. Otherwise, there will be stronger records in the sedimentary sequence. Although the historical literature records that the coastal area of Chaozhou, Guangdong, was hit by a tsunami in 1076, But how much damage the tsunami caused to coastal areas is not well documented. Nanao Island, which was administered by Guichao Island in ancient times, did not build a bridge to cross the sea until 2015, before the island and the mainland relied on shipping. Therefore, the study of sedimentary sequences along the southeast coast of the island shows that there is a layer of sand with tsunami sedimentary characteristics in the sediment. The age of its formation is very close to the time of the South China Sea tsunami. Combined with the historical records of Chaozhou being hit by the tsunami, it can be ascertained that this layer of sediment is geological evidence left by the tsunami in South Australia. In the sedimentary layer, there are also scattered pieces of Song porcelain. Besides, there are only Song porcelain, and there are no other historical relics of the dynasties. According to the statistics of the cultural relics unearthed from Nanao Island and the architectural remains left on the island, it is found that most of their times were distributed in the Tang Dynasty before the tsunami. In the early Song Dynasty and the late Ming Dynasty after 1575, in the Qing Dynasty, the number of articles belonging to the middle 500 years was very small. Nanao officially established counties and towns in 1575. After that, we entered a stage of prosperity. Judging from the number of cultural relics and relics in the past 500 years, Nanao experienced a long period of cultural decline after the tsunami. There was even a gap. This shows that the impact of the South China Sea tsunami on the island was disastrous, while Nanao Island may have buried a large number of historical relics of the Song Dynasty. This example also illustrates the diversity and complexity of the tsunami disaster. And tsunamis can not only destroy coastal facilities, economies, ecosystems, but may also have an impact on culture when the conditions are appropriate, leading to a decline or even a blank in cultural development. Although tsunami deposition is the main carrier for studying ancient tsunamis, The two examples in this paper have shown that it is difficult to obtain a complete and clear understanding of the ancient tsunami events by sedimentology alone, and the combination of many methods is a better way to study the ancient tsunami.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P731.25

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