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Earthquake waves are known as seismic waves. There are two main types of seismic waves, which are then broken into subtypes.
Body Waves: A wave that travels in Earth’s interior
Surface Waves: A wave that travels on Earth’s surface.
Primary WavesSeismic waves that travel the fastest are called primary waves, or P waves. P waves arrive at a given point before any other type of seismic wave. P waves travel through solids, liquids and gases.
P waves are push-pull waves. As P waves travel, they push rock particles into the particles ahead of them, thus compressing the particles.
The rock particles then bounce back. They hit the particles behind them that are being pushed forward.
The particles move back and forth in the direction the waves are moving.
A type of seismic wave that compresses and expands the ground
The first wave to arrive at an earthquake
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Secondary WavesSeismic waves that do not travel through the Earth as fast as P waves do are secondary waves, or S waves. S waves arrive at a given point after P waves do. S waves travel through solids but not through liquids and gases.
A type of seismic wave that moves the ground up and down or side to side
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
The slowest-moving seismic waves are called surface waves, or L waves.
L waves arrive at a given point after primary and secondary waves do.
L waves originate at the epicenter.
Surface waves travel along the surface of the earth, rather than down into the earth.
Although they are the slowest of all the earthquake waves, L waves usually cause more damage than P or S waves.
http://uc.wisc.edu/news/features/quake/pwaves.html
http://www.pbs.org/wnet/savageearth/animations/earthquakes/
Go to this site to see an animation of the path of p waves and s waves
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
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
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
How do we measure the intensity of an earthquake?
Mercalli, Richter, Magnitude, and Magnitude Scale
or the strength of an earthquake
Seismograph records energy waves of the earth
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
V. •People feel movement. •Doors open •Pictures fall off wall.
VII. •Some buildings lose bricks. •Difficulty driving.IX.
Considerable damage to homes. Cracks in earth.
XII. •Almost everything is destroyed.• The ground moves in waves or ripples.
Mercalli ScaleI.People do not feel anything .
Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf
Each number is 10X stronger than the previous number.
How much stronger is the 3 than the 1? 100
Times
How much stronger is the 8 than the 1?
10,000,000Write the number in scientific notation. 106
Why is the Richter Scale more accurate than the Mercalli Scale?
•The Richter Scale is objective and based on mathematical measurements.
•The Mercalli scale is subjective and based on people’s perception and experience.
•On Mercalli scale if the area is unihabited there is no way to measure the magnitude of the earthquake.
Richter Magnitude Number of Earthquakes per year
1.0 to 3.9 900,000 +
4.0-4.9 6200
5.0-5.9 800
6.0-6.9 226
7.0-7.9 18
8.0-8.9 Less than 2
San Francisco Earthquake 1906
Alaska Earthquake 1964
When the shaking from earthquakes turns soft soil into mud, causing landslides.
Earthquakes in the ocean cause
Destruction
30’ Wall of Water
The devastating impact of seismic sea waves
Tsunami (harbor wave)Seismic sea waves (NOT tidal waves)
Caused by processes that abruptly move large volumes of ocean water:
earthquakesubmarine volcanic eruption
coastal/submarine landslide or rockfall
extraterrestrial impact
http://geology.com/articles/tsunami-geology.shtml
Unless there is an underwater landslide, strike-slip EQ WILL NOT cause tsunami
Most tsunami generated by subduction zones
Chile, Chile, Alaska, Alaska, Japan, Japan, Cascadia, Cascadia, Philippines, Philippines, New ZealandNew Zealand
Long wavelengths (over 100 km)Periods longer than 1 hour
316,800 ft = 60 miles
Travel at high speeds :400 to 500 mph (~200 yards/sec)
Alaska to CA 4 to 7 hrsAlaska to CA 4 to 7 hrs Alaska to Hawaii 4 to 6 hrsAlaska to Hawaii 4 to 6 hrs Chile to Hawaii 14 to 15 hrsChile to Hawaii 14 to 15 hrs Chile to Japan 22 to 33 hrsChile to Japan 22 to 33 hrs
v = speedv = speed ~~
g = acceleration of gravity (9.8 m/sec2)d = depth of ocean (m)
deeper water means higher speed
For d = 4,600 m, v = 763 km/hr (speed of jet plane)
gd
Tsunami slows down (shallower water)Example: d = 100 m, v = 113 km/hr
Wave gets taller λ gets shorter, T gets shorter
As wave gets into shallow water bottom of wave drags along ocean floor
Top of wave still moving fast: can cause cresting of wave, and breaking onto shore
Run-up = measurement of height of water onshore observed above a reference sea level
Generally don’t get big gigantic waveWater comes as a fast moving rise in tide that
rapidly moves inlandNOT JUST ONE WAVE…multiple waves coming in
about ½ hour or so apartSee tsunami wave simulator
http://www.seed.slb.com/en/scictr/watch/living_planet/tsunami_wave/index.htm
Possible tsunami“run-up” zones
Loss of energy in a wave is inversely proportional to λ
Since λ very long, little energy lost
Waves can travel great distances and still be very distructive
Waves often full of debris (trees, cars, pieces of wood etc.)
As the wave recedes, the debris drags more stuff with it
Can recede as much as a km out to see, leaving shoreline empty with flopping fish, boats, etc. on the bottom
Pressure recorder on bottom of ocean
Buoy to communicate readings via satellite
Tsunami Warning Centers issue warning
Hawaii and AlaskaWhen EQ considered capable of generating
tsunami, send warning with estimated arrival time
Once tsunami hits Once tsunami hits somewhere, tsunami somewhere, tsunami watch established to watch established to monitor tide gauges monitor tide gauges and ocean buoysand ocean buoys
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Tsunami
How could you evaluate the level of riskdue to tsunami?
Standing wave in an enclosed or partially enclosed body of water (similar to sloshing in a bath tub)
http://earthquake.usgs.gov/learning/glossary.php?term=seiche
Generated by wind Generated by wind or seismic activityor seismic activity
Often swimming Often swimming pools experience a pools experience a seiche during EQseiche during EQ
standing wave
Scientists at UNR have determinsed the seiches have occurred on Lake Tahoe in the past
Low probability – on average once every 2000 to 3000 years
Good page on seiches
w/great animation http://earthguide.ucsd.edu/earthguide/diagrams/waves/swf/wave_seiche.html