Focus –. point inside the Earth where an Focus – point inside the Earth where an earthquake begins Epicenter – point on Earth’s surface above focus

Seismic Waves 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.

Body Waves Primary Waves Seismic 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.

Primary Waves (P Waves) 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

Body Waves Secondary Waves Seismic 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.

Secondary Waves (S Waves) A type of seismic wave that moves the ground up and down or side to side http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

Surface Waves 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

Go to this site to see an animation of the path of p waves and s waves http://www.pbs.org/wnet/savageearth/animations/earthquakes/

Earthquake Waves & Earth’s Interior

Seismic Waves in the Earth http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

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

Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

Earthquakes How do we measure the intensity of an earthquake? Mercalli, Richter, Magnitude, and Magnitude Scale

or the strength of an earthquake Seismograph measures Magnitude or the strength of an earthquake

Seismograph records energy waves of the earth

Typical Seismogram http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

Mercalli Scale I.People do not feel anything . 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.  

How are Earthquakes Measured? Mercalli Intensity Scale Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

How are Earthquakes Measured? Richter Scale

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? 10,000,000 Write 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

Liquification When the shaking from earthquakes turns soft soil into mud, causing landslides.

Earthquakes in the ocean cause Tsunamis

Tsunamis 30’ Wall of Water Destruction

The devastating impact of seismic sea waves Tsunami The devastating impact of seismic sea waves

Tsunami (harbor wave) Seismic sea waves (NOT tidal waves) earthquake Caused by processes that abruptly move large volumes of ocean water: earthquake submarine volcanic eruption coastal/submarine landslide or rockfall extraterrestrial impact

How do EQ cause tsunami? http://geology.com/articles/tsunami-geology.shtml

Tsunami causes Unless there is an underwater landslide, strike- slip EQ WILL NOT cause tsunami Most tsunami generated by subduction zones Chile, Alaska, Japan, Cascadia, Philippines, New Zealand

Tsunami wavelength Long wavelengths (over 100 km) Periods longer than 1 hour 316,800 ft = 60 miles

Tsunami wave speed Alaska to CA 4 to 7 hrs Alaska to Hawaii 4 to 6 hrs Travel at high speeds : 400 to 500 mph (~200 yards/sec) Alaska to CA 4 to 7 hrs Alaska to Hawaii 4 to 6 hrs Chile to Hawaii 14 to 15 hrs Chile to Japan 22 to 33 hrs

Tsunami wave speed v = 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)

What happens when tsunami gets near shore? Tsunami slows down (shallower water) Example: d = 100 m, v = 113 km/hr Wave gets taller λ gets shorter, T gets shorter

Tsunami nears shore 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

Tsunami run-up Run-up = measurement of height of water onshore observed above a reference sea level Generally don’t get big gigantic wave Water comes as a fast moving rise in tide that rapidly moves inland NOT JUST ONE WAVE…multiple waves coming in about ½ hour or so apart See tsunami wave simulator http://www.seed.slb.com/en/scictr/watch/living_planet/tsunami_wave/index.htm

Possible tsunami “run-up” zones

Energy in tsunami 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

Damage due to tsunami 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

Detecting a tsunami Pressure recorder on bottom of ocean Buoy to communicate readings via satellite Tsunami Warning Centers issue warning

Tsunami Warning Centers Hawaii and Alaska When EQ considered capable of generating tsunami, send warning with estimated arrival time Once tsunami hits somewhere, tsunami watch established to monitor tide gauges and ocean buoys

Tsunami Warning System http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

Tsunami How could you evaluate the level of risk due to tsunami?

Seiche Generated by wind or seismic activity standing wave Standing wave in an enclosed or partially enclosed body of water (similar to sloshing in a bath tub) Generated by wind or seismic activity Often swimming pools experience a seiche during EQ http://earthquake.usgs.gov/learning/glossary.php?term=seiche

Seiche potential in Lake Tahoe 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