1. earthquakes
sturdivant

2. Earthquake natgeo

3. What is an earthquake
Each year there are about 30,000 earthquakes strong enough to be felt by people
About 100 of these are “major”
An earthquake is a vibration of Earth caused by rapid release of energy in the lithosphere

4. Terms associated with earthquakes
Fault – fractures in Earth where movement has occurred
Focus – where an earthquake occurs (deep underground)
Epicenter – surface location above the focus of an earthquake

5. Surface evidence of fault lines

6. Causes of earthquakes
Elastic Rebound Hypothesis – most earthquakes are caused by a rapid release of energy stored in rock. When the rock strength fails, there is a break, releasing energy as seismic waves

7. Measuring earthquakes
Seismic Waves – waves traveling outwards carrying energy released from elastic rebound
Seismic Waves have two types – body and surface
Body Waves – travel through Earth’s interior as either P or S waves

8. P-Waves, S-waves, and surface waves
P-Waves – waves form in the direction of travel (slinky). Fastest. Travel through solids and liquids
S-Waves – waves form perpendicular to travel (rope). Medium speed. Only solids.
Surface Waves – Occurs when body waves reach surface. Slowest, most destructive

9. Measuring/recording earthquakes
Seismograph – Instrument used to record seismic waves
The seismograph has a weight balanced in place. As the Earth shakes, the weight remains stationary
Underneath the weight, the motion is recorded, relative to the stable weight

10. Seismogram – seismic plots
Each wave travels at a different speed, by looking at the time of arrival of each wave, we can determine how far away the earthquake occurred

11. Using seismograms to locate earthquakes

12. Earthquake magnitudes and the richter scale
Magnitude is a measure of the size of seismic waves
The Richter Scale measures the size of the largest seismic wave. Increasing by 1 on the Richter Scale means 10x more magnitude
Scientists no longer use the Richter Scale, but rather, the moment magnitude

13. High magnitude earthquake risks
Several hazards are associated with Earthquakes – seismic shaking, liquefaction, landslides, mudflows, and worst of all, tsunamis
Liquefaction – shaking of saturated soils causes the soil to behave as a liquid, which can be anywhere from – fun to play with – to destructive to building

14. More liquefaction

15. Tsunamis
Tsunami – wave that forms when the ocean floor shifts (by earthquakes, volcanic eruptions, underwater landslides, etc)
The waves in the middle of the ocean usually are less than a meter high
As the waves approach the coast at a few hundred km/hr, the waves stack – up to 30 METERS

16. Seismology and earth’s layers
If Earth were composed of all the same material, seismic waves would follow straight line paths across the planet
However, we noticed seismic waves change their speeds as they travel deeper, and S waves do not make it across the planet

17. Layers of earth – by composition
Earth has three layers defined by CHEMICAL COMPOSITION.
Crust – 7km thick at ocean. 8-75km thick over continents. Mostly granitic rock, denser at ocean
Mantle – 82% of Earth’s volume, extends to 2890km below surface.
Core – iron-nickel alloy with 4x density of crust

18. Layers of earth – by physical properties
As depth increases, pressure AND temperature increase. We can layer Earth by how it behaves physically due to pressure and temperature
Lithosphere – Relatively cool, rigid shell. Includes crust and some mantle. 100km thick
Asthenosphere – Warm rock layer that deforms easily. Part of mantle. Extends to 660km.
Lower Mantle – Warmer than asthenosphere, but high pressures make rocks stronger.
Outer Core – 2260km thick liquid layer. Flow of iron through this layer generates Earth’s magnetic field
Inner Core – 1220km thick bottom-most layer. It’s the hottest layer, but due to intense pressure, it is a solid, not a liquid