earthquake![click to hear](/images/speaker.jpg)
Sudden tremor in a region of the Earth’s crust caused by one rock mass sliding against another.
focus ![click to hear](/images/speaker.jpg)
Point in the Earth’s crust where an earthquake is triggered. Also called the hypocenter.
seismic wave ![click to hear](/images/speaker.jpg)
Series of vibrations generated at the focus that disperse in all directions, causing shaking of the Earth’s surface.
Earth’s crust ![click to hear](/images/speaker.jpg)
Solid layer at the Earth’s surface whose thickness varies from 6 mi beneath the oceans to 35 mi beneath the mountains.
isoseismal line ![click to hear](/images/speaker.jpg)
Curved line connecting the points on the Earth’s surface that have been subject to tremors of the same intensity.
epicenter ![click to hear](/images/speaker.jpg)
Point on the Earth’s surface located directly over the focus, where the most violent tremors are felt.
depth of focus ![click to hear](/images/speaker.jpg)
Distance between the focus and the epicenter; it can reach 430 mi.
fault ![click to hear](/images/speaker.jpg)
Fracture in the Earth’s crust separating two blocks that slide against one another during an earthquake.