Question

which of the following are true of earthquakes?
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an earthquake builds up strain in the rock.
an earthquake originates at the focus.
an earthquake is always preceded by aftershocks.
an earthquake originates at the epicenter.
an earthquake occurs after strain has built up in the rocks.

Explanation:

• Earthquakes occur when strain (caused by tectonic forces) builds up in rocks beyond their elastic limit. The rocks then fracture, releasing energy. The point where the earthquake originates underground is the focus (hypocenter). Aftershocks follow an earthquake, not precede it. The epicenter is the point on the Earth's surface directly above the focus.

Answer:

• An earthquake originates at the focus.
• An earthquake occurs after strain has built up in the rocks.