| A | B |
|---|
| fault | surfaces along which rocks break and move; rocks on either side of a fault move in different directions relative to the fault surface |
| earthquake | the movement of the ground, caused by waves from energy released as rocks move along faults |
| normal fault | a pull-apart (tension) fracture in rocks, where rocks that are above the fault surface drop downward in relation to rocks that are below the fault surface |
| reverse fault | a compression fracture in rocks, where rocks that are above the fault surface are forced up over the rocks that are below surface |
| strike-slip fault | a break in rocks due to shearing forces, where rocks on either side of the fault move past each other without much upward or downward movement |
| seismic waves | in an earthquake, the energy waves that move outward from the earthquake focus and make the ground quake |
| focus | the point in earth's interior where earthquake energy is released |
| primary wave | waves of energy, released during an earthquake, that travel through earth by causing particles in rocks to compress and stretch apart in the direction of the wave |
| secondary wave | waves of the energy, released during an earthquake, that travel through Earth by causing particles in rocks to move at right angles to the direction of the wave |
| epicenter | the point on Earth's surface directly above an earthquake's focus |
| surface wave | waves of energy, released during an earthquake, that reach Earth's surface and travel outward from the epicenter in all directions; travel through Earth by giving rock particles an elliptical and side-to-side motion |
| inner core | the dense, solid center of Earth, formed mostly of iron and nickel |
| outer core | the liquid layer of Earth's core that surrounds the solid inner core and is comprised of iron and nickel |
| mantle | the thickest layer inside Earth; it lies between the outer core and the crust and is described as plasticlike; formed mostly of silicon, oxygen, magnesium, and iron |
| crust | the outermost layer of Earth, varying in thickness from more than 60km to less than 5 km |
| moho discontinuity | the boundary between Earth's crust and the mantle; seismic waves travel faster below the Moho and slower above it |
