The earthquake focus is the point wherein the rocks start to crack, and where pressure is released. For earthquakes occuring on the ocean floor, this is the point where schock waves originate.
The epicenter is the point on the Earth's directly vertically above the focus. This is where the shock is strongest since pressure is released directly below it.
For earthquakes occuring on the ocean floor, waves grow larger as it moves farther from the epicenter. That is, waves are largest at the sea shores.
(Not sure but we are currently studying those)
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