Earthquake Basics and Types of Faults
An earthquake occurs when Earth's lithosphere (the crust and upper mantle) moves along a fault. Every earthquake has three main parts: the fault (the crack where movement happens), the focus (the underground starting point), and the epicenter (the point directly above the focus on Earth's surface).
Faults form when Earth's crust breaks or cracks, creating planes along which movement occurs. The rock above the fault plane is called the hanging wall, while the rock below is the footwall. How these walls move determines the type of fault: normal faults occur when the hanging wall moves downward (caused by divergent boundaries), reverse or thrust faults happen when the hanging wall moves upward (from convergent boundaries), and strike-slip faults involve horizontal movement (from transform boundaries).
Earthquakes can cause devastating effects including tsunamis (massive ocean waves from underwater quakes) and aftershocks (smaller tremors following the main earthquake). The Richter Magnitude scale measures earthquake strength—the higher the number, the more extensive the damage.
Remember This: The epicenter is not where the earthquake begins underground—that's the focus! The epicenter is the point on Earth's surface directly above the focus.