1. Earthquakes

2. Earthquakes A natural vibration of the ground caused when the stress built up between tectonic plates is suddenly released. There are three types of stress: ◦Compression – caused by two plates being push together. ◦Tension – Pulls plates apart. ◦Shear – causes plates to twist.

4. Types of faults There are three types of Faults 1.Normal fault  caused by tension. 2.Reverse fault  caused by compression. 3.Strike-slip fault  caused by shearing.

5. Three Types of Seismic Waves 1. Primary waves (p-waves) ◦Longitudinal waves – these vibrate by the compression of material in the direction of the wave’s motion. These can travel through the core. 2. Secondary waves (s-waves) ◦Transverse waves (Like in water) – these vibrate by moving the particles perpendicular to the direction of wave’s motion. These cannot travel through the core. 3. Surface waves ◦Vibrate in all directions.

8. Measuring Earthquakes Richter Scale ◦Based on size of the largest seismic waves generated by the Earthquake. ◦Each level increase represents an increase of energy by a factor of 32 and a wave size of 10 times.

10. Measuring Earthquakes Moment of Magnitude Scale ◦Based size of fault rupture, amount of movement, and rock characteristics. ◦More accurate than Richter scale. Modified Mercalli Scale ◦Measures the amount of damage caused by the Earthquake.

13. Strongest Earthquakes of 2010 1. Chile (Feb 27 th ) Mag. 8.8 2. Indonesia (April 6 th ) Mag. 7.7 3. Vanuatu (May 27 th ) Mag. 7.7 4. Indonesia (May 9 th ) Mag. 7.2 5. Mexcali Valley, California (April4th) Mag. 7.2 6. Solomon Islands (Jan 3 rd ) Mag. 7.1 7. Haiti (Jan 12 th ) Mag. 7.0 8. Ryukyu, Japan (Feb 27 th ) Mag. 7.0 There have been 7460 earthquakes so far this year. Most are below a magnitude of 4.9.

14. Chili 7 th Strongest in History 130 after shocks over the next week. The focus ground at epicenter moved 3.0 up and 10 m west. 500 times more powerful than Haiti Called a megathrust quake because it is in a subduction zone

15. Location of the Earthquake Focus ◦The location in the Earth’s crust where the earthquake occurs. ◦It can occur anywhere between the surface and a depth of 700 km. The closer to the surface it occurs, the more powerful the earthquake is. Epicenter ◦The location on the Earth’s surface above the focus.

16. Finding the Epicenter Epicenters are found using triangulation from three or more seismograph stations. P-waves travel a lot faster than s-waves. The difference between the arrival time of each type of wave tells you the distance to the epicenter. The speed of each wave is a constant factor.

17. Steps for finding the Epicenter 1. Determine the difference in time between the arrival of the s & p waves.

18. Steps for finding the Epicenter 1. Use the travel-time graph at which the p- curve and s- curve have the same separation. 2. Record this distance.

19. Steps for finding the Epicenter 1. Repeat the steps #1-3 for two other stations

20. Steps for finding the Epicenter 1. Use a compass to draw a circle around each station with the radius in step #3. 2. The epicenter is located where all three circles intersect.

21. Homework P. 499 #1-4 p. 504 #2, 4 P. 510 #1-4