通过编制全球数千次地震的地震速度图，他们还可以开始绘制地幔的温度和密度图。

By compiling a map of seismic velocities from thousands of earthquakes across the globe, they can also begin to map temperatures and densities throughout the mantle.

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但是在此之前，地球物理学者们认为，这种俯冲带大地震仅仅在年轻的海洋地壳挤入地幔处才可能发生。

But geophysicists had thought that great subduction-zone earthquakes happened only where younger oceanic crust scrapes its way into the mantle.

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最深的地震通常发生在板块边界的地方的地壳正在俯冲到地球的地幔。

The deepest earthquakes typically occur at plate boundaries where the earth's crust is being subducted into the earth's mantle.

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