417 words used in the labs.

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Term

Focus

Also written: Hypocentre

The point within Earth where an earthquake rupture starts, also called the hypocentre. Rupture can then spread across a much larger fault surface. The epicentre is the point directly above it at the surface.

What to look for

USGS seismometer installation in Puerto Rico. Wave arrival times and recorded ground motion are used to estimate an earthquake's focus, epicentre and magnitude; none of those buried locations is visible in this photograph.

Related labs

Earthquakes →

Mark understood

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Explore further with USGS water glossary · USGS volcano glossary · NPS glacial geology · NASA Earth facts. Photograph acknowledgements are collected on the Image credits page.