Date post: | 28-Dec-2015 |
Category: |
Documents |
Upload: | abel-price |
View: | 214 times |
Download: | 1 times |
What is an earthquake?
• Natural vibration of the ground
• Caused by movement along fractures or volcanic eruptions
Most earthquakes occur when…
• Rocks fracture or break deep within the Earth.
• Fractures form when STRESS, the forces per unit area acting on a material, exceeds the strength of the rocks involved.
Faults
• Many rocks that make up the crust fail when stress is applied to quickly.
• The result is a system of fractures called FAULTS.
Seismic Waves
• Vibrations of the ground during an earthquake are called Seismic Waves (there are 3 types).
1. Primary Waves (P Waves)
• Squeeze and pull rocks in the same direction along the wave direction.
• The first wave to arrive at an earthquake
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Secondary Waves (S Waves)
• Cause rocks to move at right angles in relation to the direction of the wave.
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Surface Waves
• Move in 2 directions as they pass through rock.
• Produces motion in the upper crust– Motion can be up and down– Motion can be around– Motion can be back and forth
• Travel more slowly than S and P waves• More destructive
Focus – point inside the Earth where an earthquake begins
Epicenter – point on Earth’s surface above focus
Typical Seismogram
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
How do scientists calculate how far a location is from the epicenter of an earthquake?
• Scientists calculate the difference between arrival times of the P waves and S waves
• The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves
Most earthquakes…. Are associated with tectonic plate
boundaries.
Almost 80% of all earthquakes occur in the Circum-Pacific Belt!
Destruction to buildings
“Pancaking”
• Where structural buildings fall and debris resembles a stack of pancakes.
Formation of a tsunami
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Tsunami Warning System
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt