The average depth of the Atlantic with its adjacent seas, is 3,339 metres (1,826 fathoms; 10,955 ft); without them it is 3,926 metres (2,147 fathoms; 12,881 ft). The greatest depth, Milwaukee Deep with 8,380 metres (4,580 fathoms; 27,490 ft), is in the Puerto Rico Trench. The trench is situated on the boundary between the Atlantic and the Caribbean Sea. It's 800 km (497 mi) long. If an earthquake occurs along this fault zone, it can generate a powerful tsunami. For example, a Puerto Rico earthquake of 1918 triggered a significant tsunami which swept the west coast of the island if Puerto Rico, which lies immediately to the south of the fault zone.

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