How Do We Know about Layers Deep within Earth?
ES0402  Seismic Tomography

In addition to showing the overall layered structure of Earth, earthquake waves can be analyzed to reveal finer-scale features within the mantle. By combining the data from many earthquakes, subtle changes in wave speed have been identified. Areas through which waves move quickly tend to be cooler or consist of denser rock. Areas where waves move slowly indicate warmer or less dense rock. Regions of upwelling and downwelling of material in the mantle have been mapped using this method of seismic tomography.

The globe on the left shows surface topography. The globe on the right shows shallow mantle tomography. On the tomographic model, cooler areas are shown in blue and warmer areas are shown in red.

  !   After the file loads, click the arrow buttons to turn the globes. Examine how cool and warm areas are related to continent location.

Paul Morin, University of Minnesota with data from
NOAA and Zang Yu-Shen and T. Tanimoto.
Global topography compared to shallow mantle tomography.

10. Where are the cool and the hot regions of the mantle located?

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