| A | B |
|---|
| stress | A force that acts on rock to change its shape or volume |
| compression | Stress that squeezes rock until it folds or breaks |
| normal fault | A type of fault where the hanging wall slides downward; caused by tension in the crust |
| footwall | The block of rock that forms the lower half of a fault |
| strike-slip fault | A type of fault in which rocks on either side move past each other sideways with little up or down motion |
| syncline | A downward fold in rock formed by compression in Earth’s crust |
| earthquake | The shaking that results from the movement of rock beneath Earth’s surface |
| epicenter | The point on Earth’s surface directly above an earthquake’s focus |
| S waves | secondary seismic waves; waves that move the ground up and down or side to side |
| Mercalli scale | A scale that rates earthquakes according to their intensity and how much damage they cause at a particular place |
| Richter scale | A scale that rates an earthquake’s magnitude based on the size of its seismic waves |
| moment magnitude scale | A scale that rates earthquakes by estimating the total energy released by an earthquake |
| P waves | primary seismic waves; compresses and expands the ground |
| seismograph | A device that records ground movements caused by seismic waves as they move through Earth |
| magnitude | The measurement of an earthquake’s strength based on seismic waves and movement along faults |
| surface waves | A type of seismic wave that forms when P waves and S waves reach Earth’s surface |
| plateau | A large area of flat land elevated high above sea level |
| anticline | An upward fold in rock formed by compression of Earth’s crust |
| reverse fault | A type of fault where the hanging wall slides upward; caused by compression in the crust |
| hanging wall | The block of rock that forms the upper half of a fault |
| shearing | Stress that pushes masses of rock in opposite directions, in a sideways movement |
| tension | Stress that stretches rock so that it becomes thinner in the middle |
| seismogram | The record of an earthquake’s seismic waves produced by a seismograph |
| aftershock | An earthquake that occurs after a larger earthquake in the same area |
| tsunami | A large wave produced by an earthquake on the ocean floor |
