海沟（trench）是位于海洋中的两壁较陡、狭长的、水深大于5000m（如毛里求斯海沟5564m）的沟槽。其中海底最深的地方，最大水深可达到10000米以上（如马里亚纳海沟11034m）。

A trench is in the ocean with two steep and narrow walls and a water depth greater than 5,000m (e.g. Mauritius Trench 5,564m). The deepest part of the seafloor can reach a maximum depth of more than 10,000 meters (e.g., Marianas Trench 11,034m).

海沟是一种深度超过5000米的狭长的海底凹地。两侧坡度陡急，如太平洋的菲律宾海沟、大西洋的波多黎各海沟等。海沟多分布在大洋边缘，而且与大陆边缘相对平行。对于海沟的定义，科学家有许多不同的观点。有人认为，水深超过6000米的长条形洼地都可以叫做海沟。另一些人则认为真正的海沟应该与火山弧相伴而生。世界大洋约有30条海沟，其中主要的有17条。属于太平洋的就有14条。 在地质学上，海沟的产生被认为是海洋板块和大陆板块相互作用的结果。密度较大的海洋板块以30度上下的角度插到大陆板块的下面，两个板块相互摩擦，形成长长的"V"字型凹陷地带。另外，科学家还认识到所有的海沟都与地震有关。环太平洋的地震带都发生在海沟附近。这是因为海沟区的重力值比正常值要低，它意味着海沟下面的岩石圈被迫在巨大的压力作用下向下沉降。

A trench is a narrow submarine depression with a depth of more than 5,000 meters. The slope is steep on both sides, such as the Philippine Trench in the Pacific Ocean and the Puerto Rico Trench in the Atlantic Ocean. Trench is mostly located at the edge of the ocean and is relatively parallel to the continental margin. Scientists have many different views on the definition of a trench. Some believe that any long depression with water depth over 6,000 meters can be called a trench, while others believe that a true trench should be accompanied by a volcanic arc. There are about 30 trenches in the world’s oceans, 17 of which are major. Those belonging to the Pacific Ocean alone are 14. In geology, the creation of trenches is thought to be the result of the interaction of oceanic and continental plates. The denser oceanic plate plunges beneath the continental plate at an angle of 30 degrees, and the two plates rub against each other, forming a long “V” shaped depression. In addition, scientists have recognized that all trenches are associated with earthquakes. The seismic zones of the Pacific Rim all occur near trenches. This is because the gravity value in the trench area is lower than normal, which means that the lithosphere beneath the trench is forced to sink downward under tremendous pressure.

海沟是岩石圈板块的汇聚型板块边界（消亡边界），大洋岩石圈板块在此俯冲、消亡。主要分布于环太平洋地区，也见于印度尼西亚以西的印度洋和加勒比海域。在太平洋西部和印度洋，海沟与岛弧平行排列；在太平洋东部，海沟与陆缘火山链相伴随。海沟有以下特征：

A trench is a convergent plate boundary (extinction boundary) of lithospheric plates where oceanic lithospheric plates subduct and extinguish. They are mainly found in the Pacific Rim, but also in the Indian Ocean and the Caribbean Sea west of Indonesia. In the western Pacific Ocean and Indian Ocean, trenches are aligned parallel to island arcs; in the eastern Pacific Ocean, trenches are accompanied by chains of land margin volcanoes. The trenches have the following characteristics:

①海沟长一般在500～4500千米，宽40～120 千米。地球上最深的马里亚纳海沟深达11,034米。海沟在平面上大多呈弧形向大洋凸出，横剖面呈不对称的V字型，近陆侧陡峻，近洋侧略缓。

① Trench is generally 500 to 4,500 km in length and 40 to 120 km in width. The deepest trench on earth, the Marianas Trench, is 11,034 meters deep. Most of the trenches are arc-shaped horizontally and protrude into the ocean, with an asymmetrical V-shaped cross-section, steep near the land side and slightly slower near the ocean side.

②海沟两侧普遍具有阶梯状的地貌，地质结构复杂，发育蓝闪石片岩相高压低温变质带。海沟中的沉积物一般较少，主要包括深海、半深海相浊积岩。海沟是大洋地壳与大陆地壳之间的接触过渡带。

② The trench is generally characterized by stepped landforms on both sides, complex geological structure, and the development of high-pressure low-temperature metamorphic zones in the blue amphibole schist phase. The sediments in the trench are generally small, mainly including deep-sea and semi-deep-sea phase turbidites. The trench is a contact transition zone between oceanic crust and continental crust.

③海沟的两面峭壁大多是不对称的"V"字型，沟坡上部较缓，而下部则较陡峭。平均坡度为5度到7度。偶尔也会遇到45度以上的斜坡。

③ The two sides of the trench are mostly asymmetrical “V” shaped, and the upper part of the trench slope is gentle, while the lower part is steeper. The average slope is 5 degrees to 7 degrees. Occasionally, slopes of 45 degrees or more are encountered.

④海沟为重力负异常带，自由空间异常值可低至－200毫伽以下，热流值仅为1HFU左右，低于地壳平均热流量。

④ The trench is a negative gravity anomaly zone, with free space anomaly values down to below -200 mG, and heat flow values of only about 1HFU which is lower than the average heat flow in the crust.

⑤沿海沟分布的地震带是地球上最强烈的地震活动带。震源通常自洋侧向陆侧加深，构成自海沟附近向大陆方向倾斜的震源带（见贝尼奥夫带）。

⑤ The seismic zone distributed along the trench is the most intense seismic activity zone on earth. The seismic sources usually deepen from the ocean side to the land side, constituting a seismic zone that tilts from the vicinity of the trench toward the continent (Benioff zone).

在现代海沟的研究基础上，古海沟的鉴定有3个主要标志：蛇绿岩套；高压低温变质带，以蓝闪石片岩为特征，发育挤压和剪切构造；混杂岩。板块俯冲作用常被用于解释海沟成因。但海沟的形成与俯冲的机理相当复杂，仍有待于深入综合研究。

Based on studies of modern trenches, paleotrenching has been identified by three main markers: ophiolite suites; high-pressure and low-temperature metamorphic zones characterized by blueschist schist, developing extrusive and shear structures; mictites. Plate subduction is often used to explain trench genesis. However, the mechanism of trench formation and subduction is quite complex and still needs to be studied in depth and comprehensively.

参考文献：

[1] 朱俊江, 丘学林, 詹文欢,等. 南海东部海沟的震源机制解及其构造意义[J]. 地震学报, 2005, 27(003):260-268.

[2] 赵根模, 姚兰予. 东亚大陆的地震迁移(一)——从西太平洋海沟到中国大陆内部的巨震及火…[C]// 中国地震学会第五次学术大会论文摘要集. 1995:P.440-447.

供稿者：马归宜 硕士研究生

审核导师：傅鹏程 教授