earthquakes
DESCRIPTION
EARTHQUAKES. Section 21.2. What is an earthquake?. WHAT IS AN EARTHQUAKE? An earthquake is a movement of Earth’s crust caused by a release of energy . WHAT CAUSES AN EARTHQUAKE? Eruption of a volcano Collapse of a cavern or building Major cause – stress between two plates. - PowerPoint PPT PresentationTRANSCRIPT
Section 21.2
WHAT IS AN EARTHQUAKE?
An earthquake is a movement of Earth’s crust caused by a release of energy
WHAT CAUSES AN EARTHQUAKE?
Eruption of a volcano
Collapse of a cavern or building
Major cause – stress between two plates
Friction builds up between two plates The stress causes the plates to deform or
‘stretch’ Eventually, the stress becomes great
enough that it overcomes friction and the plates move
The plates ‘snap’ back into their original shape and begin building up friction again
Point on the fault (or plates) where movement first occurs
Where an earthquake starts 3 types
Shallow (0-70km) Intermediate (71-300km) Deep (301km and higher)
Point on the Earth’s surface directly above the focus
What is reported as the location of an earthquake
P-waves: primary waves; travel through solids, liquids, and gases; back and forth motion
P waves are ______________ waves.
S-waves: secondary waves; travel through solids only; side to side motion (snake)
S waves are ___________ waves
L-waves: surface waves
Combination of up and down and back and forth motion
Cause the most damage due to their rolling action and long wavelengths
Seismograph: an instrument that detects and records earthquake waves
P-waves always arrive first, then S-waves, then L-waves
P and S Waves Graph – pg.767 – Under Graphing Skills
As distance increases, the travel time for seismic waves increases also.
To locate the exact location of an epicenter, you must have points from three separate seismograph locations around the world
Richter Scale Developed by Charles Richter in the 1940’s Measures the amount of energy released
by the earthquake itself Scale from 1-10 (weakest - strongest) Each number is 32 times stronger than the
next lower number (Ex: ‘6’ is 32 times stronger than a ‘5’ and 1024 times stronger than a ‘4’)
We cannot predict earthquakes other than giving periods of time in which we think they will occur.
Earthquakes are most common along sliding plate boundaries, but they can occur in other places.
http://earthquake.usgs.gov/learn/kids/