1. Chapter 15
Earthquakes

2. Earthquakes and Plate Tectonics
Objectives
Explain how earthquakes result from the buildup of stress in earth’s crust
Control normal, reverse, and strike-slip faults

3. Cause of Earthquakes Rocks similar to rubber band
Rocks move and break along surfaces called faults.
On each side of the fault rocks move in different directions
What causes rocks to move?
Plate tectonics

4. When plate move, stress builds up on rocks
To relieve stress rocks tend to
Bend
Compress
and stretch
If force is to great the rock breaks
Causes vibrations (earthquake)

6. Types Of Faults Most earthquakes occur along tectonic plate boundaries
80% of all occur along pacific Plate

8. Normal Faults – Rocks are subject to the force of tension
Occurs at divergent boundaries
Rocks above Fault surface move down
Rocks below move up
Theses types of faults occurred during the formation of the Sierra Nevada's

11. 2. Reverse Fault
- Compression forces are applied
- Rocks above fault surface are forced up
- Rocks below are forced down
-Generated at a convergent boundary
- Himalaya Mountains contain many reverse faults

14. 3. Strike-Slip Fault
- Transform Fault
-Each plate sliding past one another
-Subject to shearing forces
- Rocks moving in different but not opposite directions
- Most famous San Andreas Fault
- North American Plate and Pacific Plate

20. Seismic waves Generated by an earthquakes focus
Moves outward from the focus
Three types of waves

21. Primary Cause rock particles to move back and fourth Move the fastest
Slow down when they reach asthenosphere
Slowed but can travel through the liquid outer core

23. 2. Secondary
- rock particles move at right angles
- slower then primary waves
- Cannot travel through liquid
- cannot move through the outer core

27. 3. Surface Waves
- originates at the epicenter
- gives particles circular motion
- cause most of the destruction
- similar to waves in a pool or in the ocean
- are the slowest of the three waves

29. Locating an Epicenter
Seismic Waves are measured at seismograph stations
Primary waves arrive first
Secondary – second
Surface – last
The farther apart the waves the farther the epicenter is

30. 3 seismographs stations are needed to determine an epicenter
Distance btw. The station and the epicenter is determined
Scientist draw circles around each station
Where the three circles intersect is the epicenter

34. Mapping the Interior of Earth
Moho’s discontinuity
Seismic waves speed up in the denser lithosphere
Slow down in asthenosphere
Sped up in the solid lower mantle
Primary waves slowed down and deflected in the liquid outer core
Secondary waves is not transmitted through the outer core (Shadow Zone btw degrees)

35. Earthquake Damage

40. Tsunami
Large giant Sea Wave that is caused by an under water earthquake

41. Worst ever tragedy in Sri Lanka History
 The most powerful earthquake in 40 years erupted under the Indian Ocean near Sumatra on Dec. 26, It caused giant, deadly waves to crash ashore in nearly a dozen countries, killing tens of thousands. A long stretch of Sri Lanka's coast was devastated by these killer waves, with more than 40,000 dead and staggering 2.5 million people displaced. Although 1,600km from the epicentre, the waves struck with huge force and swept inland as far as 5 kilometers. Waves as high as six meters had crashed into coastal villages, sweeping away people, cars and even a train with 1700 passengers.  It was the worst human disaster in Sri Lanka history.