Megathrusts are created in subduction zones—land plate boundaries where two plates converge.

超级强震产生于俯冲带——两个板块交汇的陆地板块边界。

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The geology of this part of the Andes is a result of the eastward subduction of the Nazca tectonic plate underneath South America.

该区域安第斯山脉的地质结构是纳斯卡板块向东俯冲，下穿垫在南美版块之下。

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The major earthquakes and active volcanoes occurring there are caused by the westward movement of the Pacific tectonic plate and other plates leading to subduction under Asia.

由于太平洋构造板块及其他几个板块的向西移动，导致其向亚洲板块之下俯冲，从而会在这一带引发大地震和火山活动。

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Instead of occurring at a plate boundary along an area called a subduction zone, where one tectonic plate is diving beneath another, this earthquake occurred in the middle of an oceanic plate, where the faults in the crust essentially moved from side to side instead of up and down.

MSN: Why this Indonesia quake didn't spark a monster tsunami

But on that fateful Friday, when the North American plate slid over the Pacific plate along a subduction zone running 130km (80 miles) off the Pacific coast of northern Japan, the shock leapt from the first segment to a second and on to a third, extending the fault zone some 400km and increasing its intensity more than 30-fold.

ECONOMIST: The myth and reality of the Japanese earthquake

Although they are sometimes produced by landslides on the seafloor, significant tsunamis are typically created by subduction earthquakes, when one massive oceanic plate suddenly lurches deeper beneath another plate, shoving up a huge section of the seafloor.

MSN: Why this Indonesia quake didn't spark a monster tsunami