Earthquake waves are known as seismic waves. There are two main types of seismic waves, which are...

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