1 Chapter 10: Earthquakes 10.1: How and Where Earthquakes Occur 10.2: Locating and Measuring Earthquakes 10.3: Earthquake Hazards 10.4: Studying Earth’s Interior

2 10.1: How and Where Earthquakes Occur A. Causes of Earthquakes 1. Earthquake-The shaking of Earth's crust caused by a release of energy. 2. The cause of most major earthquakes is strain that builds up along faults.

3 10.1: How and Where Earthquakes Occur 3. Fault-A break in the lithosphere along which plate movement occurs. 4. Focus-The point at which first movement occurs during an earthquake. 5. Epicenter-The point on the earth's surface directly above the focus.

4 10.1: How and Where Earthquakes Occur B. Body Waves 1. The energy from an earthquake is released in the form of waves. 2. Body Waves- Waves that travel from the focus to through the body of the earth.

5 10.1: How and Where Earthquakes Occur 3. P waves-Compression waves that squeeze and stretch rock material. They can travel through any material (water, magma, rock and air). 4. S waves- Shear waves that cause material to move at right angles to the direction of wave travel. They can travel through solids but not liquids or gases.

6 10.1: How and Where Earthquakes Occur C. Surface Waves 1. Earthquake waves that travel on the surface. 2. Appear when P and S waves reach the surface. 3. Cause the most damage. Why? 4. Two Types: Love and Rayleigh. Love waves move side to side. Rayleigh move in elliptical patterns. Animations of earthquake waves Animations of earthquake waves Examine P and S waves Examine P and S waves Savage Earth: Restless Planet Savage Earth: Restless Planet Because they are on the surface

7 10.2: Locating & Measuring Earthquakes A. Seismograph 1. Detects and records waves produced by earthquakes. 2. Seismogram-A record sheet placed on a drum. The drum turns slowly and any movement is recorded on the paper. See page 217.

8 10.2: Locating & Measuring Earthquakes B. Interpreting a Seismogram 1. P waves arrive first, then S waves. 2. The farther the station is from the earthquake, the larger the separation between P & S waves lines. Why? More time to get ahead. It is like a race between two people at different speeds.

9 10.2: Locating & Measuring Earthquakes C. Locating the Epicenter 1. We can triangulate the epicenter by using three different seismic stations. See page 219.

: Locating & Measuring Earthquakes D. Measuring an Earthquakes Magnitude 1. Magnitude-A measure of the amount of energy released in an earthquake. 2. The Richter Scale was developed in It measures the amount of energy released by an earthquake.

: Locating & Measuring Earthquakes 3. An increase of one whole number is equal to a 31- fold increase in energy. Ex. Mag. 6 earthquake is 31 times more powerful than a Mag. 5 earthquake. Build Your Own Seismograph Build Your Own Seismograph Build Your Own Seismograph Build Your Own Seismograph

: Earthquake Hazards A. Damage from Earthquakes 1. Damage is not only caused by the shaking from the earthquake, but also by foundation failure, fire and tsunamis. 2. Liquefaction-Occurs when loose soil temporarily takes on some of the properties of a liquid. This causes buildings and roads to collapse.

: Earthquake Hazards 3. Aftershocks-Series of small earthquakes that follow the initial quake. 4. Fire can cause substantial damage. It is usually triggered by ruptured gas lines. 5. Tsunamis-A huge ocean wave triggered by an earthquake. Can travel long distances at speeds up to 750 kph.

: Earthquake Hazards B. Preventing Earthquake Damage 1. Earthquake prone cities have special building codes to help prevent building collapse. 2. Monitoring equipment helps to continue learning what structures hold up the best during an earthquake.

: Earthquake Hazards C. Earthquake Risk 1. Areas near plate boundaries are not the only areas at risk. 2. New Madrid, MO is located near several faults buried under large amounts of sediments.

: Earthquake Hazards D. Predicting Earthquakes 1. Seismic Gaps- Areas where stress may be building up along a fault. 2. Scientists can predict at risk areas, but not specific locations or times.

: Studying Earth’s Interior A. The Shadow Zone 1. Changes in the speed and direction of P and S waves indicate changes in the composition and state of the earth's interior. 2. A shadow zone is created by these changes. Remember that S waves cannot travel through liquids. See page 228.

: Studying Earth’s Interior B. The Moho 1. Boundary between the crust and the mantle. 2. Where the dense rock of the mantle meets the less dense rock of the crust. 3. Located about 32 km under continents and km under the oceans. Why? The crust is thinner in the ocean.

: Studying Earth’s Interior C. Transition Zone 1. Region in the middle of the mantle where the densities of the upper and lower mantle vary. 2. This change is due to changes in pressure as depth increases.