What is the difference between the focus and the epicenter?

• A. The focus is the surface point above the earthquake; the epicenter is underground.
• B. The epicenter is where rocks rupture occurs; the focus is the surface location above.
• C. The focus is where rocks rupture occurs in the crust; the epicenter is the surface location above.
• D. The focus and epicenter are always at the same depth.

Answer: (C)

The main idea is understanding where an earthquake starts versus where you feel it on the surface. The focus is the point inside the Earth where rocks break and energy is released. The epicenter is the point on the Earth's surface directly above that rupture. The choice that says the focus is where rocks rupture occurs in the crust and the epicenter is the surface location above matches this relationship, since it ties the underground origin to the surface point above it. Keep in mind the focus can be in the crust or deeper, and the epicenter remains the surface point directly above that underground origin.