HOW AN EARTHQUAKE HAPPENS.
An earthquake usually occurs at a fault, a fracture in Earth's crust that separates two large, constantly moving slabs of rock. As the slabs push against each other, intense pressure builds. When the pressure becomes extreme, rocks on either side of the fault suddenly shift. The point where the slabs first shift is called the focus (1). Massive waves of energy released by the rupture travel upward from the focus, making land shake, toppling buildings (Gujarat, India, top), and loosening soil to cause landslides (Santa Tecla, El Salvador, bottom).The spot on Earth's surface directly above the focus is called the epicenter (2).
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|Article Type:||Brief Article|
|Date:||Mar 12, 2001|
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