Detailed Bathymetric Survey in the Sea Region of the Estimated Source Area of the 1771 Yaeyama Earthquake Tsunami and Consideration of the Mechanism of Its Occurrence
Detailed Bathymetric Survey in the Sea Region of the Estimated Source Area of the 1771 Yaeyama Earthquake Tsunami and Consideration of the Mechanism of Its Occurrence
复制标题
1771年八重山地震海啸推算震源区海域的详细水深测量及其发生机制的思考
DOI：
10.4294/zisin1948.45.4_417
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
M. Kimura
中科院分区：
文献类型：
--
作者：
Takeshi Matsumoto;M. Kimura
历史记载显示，1771年4月24日，琉球地区最西部的宫古岛和八重山群岛海域发生了由大地震引起的大规模海啸，被称为“大地震海啸”或“八重山地震海啸”，海啸淹没了岛屿内部。1990年11月、1991年4月、1992年1月和4月，利用KAIYO号和YOKOSUKA号研究船上的SEABEAM和HS-10系统，在这一区域进行了条带测深测量。完成了22 40' N-24 10' N，122 50' E-126 20' E范围内的精确地形等高线图，包括琉球海沟最西端和海啸震源区（约24.0 N，124.3 E）。将测区划分为五个不同的地形域，并按带状排列。这些原则是：1区：北纬24 00'以北，八重山群岛南部沿海沿着分布着发育良好的海底峡谷。第二区：23 40' N-24 00' N，124 10' E-124 20' E附近，以深海扇为特征，以陡崖为边缘的大规模沉降为特征。观测到的凹陷相对高度约为200-300 m。三区：在北纬23 40'以南的海沟向陆坡上，地形相当复杂，有多个陡崖、山脊和波谷，其走向尚不清楚。4区：沟轴区，深度约6500- 6600 m，以开阔平原为特征。轴向平原的最大宽度约为40公里。第五区：海沟的向海坡，在冲绳以南海域以地垒和地堑同分布为特征。地垒和地堑的走向在宫古群岛附近为NW-SE，在八重山群岛附近为NW-SE。认为1771年明治大海啸是由深海扇的大规模沉降引起的，而深海扇是由其北部海底峡谷的软质沉积物组成的，波浪可能从海啸源位置沿沿着传播。
Historical record shows that a large-scale tsunami named "the Great Meiwa Tsunami" or "the Yaeyama Earthquake Tsunami" occurred on 24th April 1771 in the sea region of Miyako and Yaeyama Islands, westernmost part of Ryukyu District caused by a large earthquake and the tsunami inundated up to the inside of the islands. Swath bathymetric survey in this area was conducted by the use of SEABEAM and HS-10 systems on board the Research Vessels KAIYO and YOKOSUKA, in November 1990, April 1991, January and April 1992. Precise topographic contour map was completed in the area of 22 40' N-24 10' N, 122 50' E-126 20' E, including the westernmost part of the Ryukyu Trench and tsunami source area (around 24.0 N, 124.3 E). The survey area is classified into five different topographic domains which are arranged zonally. Those are: Zone 1: north of 24 00' N, which is characterised by the distribution of well developed submarine canyons along the southern coasts of Yaeyama Islands. Zone 2: 23 40' N-24 00' N, which is characterised by deep sea fans and its large-scale subsidence edged by steep scarp near 23 55' N-24 00' N, 124 10' E-124 20' E. The observed relative height of the depression is about 200-300 m. Zone 3: south of 23 40' N on the landward slope of the trench, which is characterised by quite complicated topography such as several escarpments and ridges and troughs of which trend is not clearly recognized. Zone 4: trench axis area with depth about 6500-6600m, which is characterised by broad plain. Maximum width of the axial plain is about 40km. Zone 5: seaward slope of the trench, which is characterised by horsts and grabens which are samely distributed in the sea area of the south of Okinawa Island. The strike direction of the horsts and grabens is NW-SE off Miyako Islands, and WNW-ESE off Yaeyama Islands. The 1771 Meiwa Tsunami is considered to be originated by the large-scale subsidence of the deep sea fans which is composed of soft sediment derived from the submarine canyons just north of the fans, and the wave might be propagated along the canyons from the position of the tsunami source.