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earthquake ![click to hear : earthquake click to hear : earthquake](../../../images/speaker-vert.gif)
Sudden tremor in a region of the Earth’s crust caused by one rock mass sliding against another.
focus ![click to hear : focus click to hear : focus](../../../images/speaker-vert.gif)
Point in the Earth’s crust where an earthquake is triggered. Also called the hypocenter.
seismic wave ![click to hear : seismic wave click to hear : seismic wave](../../../images/speaker-vert.gif)
Vibrations generated at the focus that disperse in all directions, causing shaking of the Earth’s surface.
Earth’s crust ![click to hear : Earth’s crust click to hear : Earth’s crust](../../../images/speaker-vert.gif)
Solid layer at the Earth’s surface whose thickness varies from 10 km beneath the oceans to 60 km beneath the mountains.
isoseismal line ![click to hear : isoseismal line click to hear : isoseismal line](../../../images/speaker-vert.gif)
Curved line connecting the points on the Earth’s surface that have been subject to tremors of the same intensity.
epicenter ![click to hear : epicenter click to hear : epicenter](../../../images/speaker-vert.gif)
Point on the Earth’s surface located directly over the focus, where the most violent tremors are felt.
depth of focus ![click to hear : depth of focus click to hear : depth of focus](../../../images/speaker-vert.gif)
Distance between the focus and the epicenter; it can reach 700 km.
fault ![click to hear : fault click to hear : fault](../../../images/speaker-vert.gif)
Fracture in the Earth’s crust separating two blocks that slide against one another during an earthquake.