| A | B |
|---|
| seismic waves | carry energy from and earthquake away from the focus |
| earthquake | the shaking that results when rocks move inside Earth |
| focus | the place where rocks break and cause an earthquake |
| epicenter | the point on the surface directly above the focus |
| 3 kinds of seismic waves | P waves, S waves, surface waves |
| P waves | move rocks back and forth; fastest seismic waves; arrive first |
| S waves | move rocks up and down; travel more slowly than P waves; arrive second |
| surface waves | waves that travel along Earth's surface; the slowest seismic waves that cause the most damage |
| 3 methods of measuring earthquakes | Mercalli scale, Richter scale, moment magnitude scale |
| Mercalli scale | measurement based on the amount of damage an earthquake does |
| Richter scale | measurement based on the size of the seismic waves |
| seismograph | an instrument that measures the size of seismic waves |
| moment magnitude scale | measurement based on the amount of energy an earthquake releases |
| epicenter | the point on Earth's surface that lies directly above an earthquake's focus |
| finding the location of the epicenter | to do this, you need seismographs in three different places |
| seismograph readings | these can tell you whether an earthquake is closer or farther away |
| instruments that monitor faults | these measure changes in Earth's elevation, tilting of the land surface, and ground movements along faults |
| clues that an earthquake might happen | ground movements near a fault |
| instruments tht monitor faults | tiltmeters, creep meters, GPS satellites |
| tiltmeter | shows how much the Earth is tilting or tipping |
| tiltmeter | this instrument measures when the ground tilts; water inside a glass bulb shows how much tilting there is |
| creep meter | this instrument shows how far the sides of a fault have moved in the opposite directions |
| creep meter | this instrument uses a wire stretched across the fault; the wire gets longer when the two sides move apart |
| GPS satellites | markers are put on both sides of a fault do detect tiny movements in any direction along a fault |
| a place where an earthquake is likely | when stress builds up at faults where rocks do not move easily |
| what happens to seismic waves when they reach a fault | seismic waves bounce off a fault like a ball bouncing off a wall |
