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

2. 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.

3. 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.

4. Primary Waves (P Waves)
A type of seismic wave that compresses and expands the ground
The first wave to arrive at an earthquake

5. 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.

6. Secondary Waves (S Waves)
A type of seismic wave that moves the ground up and down or side to side

7. 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.

9. Go to this site to see an animation of the path of p waves and s waves

10. Earthquake Waves & Earth’s Interior

11. Seismic Waves in the Earth

12. 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

13. Locating Earthquakes

14. Locating Earthquakes

15. Locating Earthquakes

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

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

18. Seismograph records energy waves of the earth

19. Typical Seismogram

20. 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.

21. How are Earthquakes Measured? Mercalli Intensity Scale
Click Link for Interactive Demo

22. How are Earthquakes Measured? Richter Scale

23. 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

24. 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.

25. Richter Magnitude
Number of Earthquakes per year
1.0 to 3.9
900,000 +
6200
800
226 18
Less than 2

26. San Francisco Earthquake 1906

27. Alaska Earthquake 1964

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

31. Earthquakes in the ocean cause
Tsunamis

32. Tsunamis
30’ Wall of Water
Destruction

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

34. 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

35. How do EQ cause tsunami?

36. 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

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

38. 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

39. 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)

40. 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

41. 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

42. 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

43. Possible tsunami
“run-up” zones

44. 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

45. 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

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

47. 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

48. Tsunami Warning System

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

50. 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

51. 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 years
Good page on seiches w/great animation earthguide/diagrams/waves /swf/wave_seiche.html