1. Earthquakes
Poseidon
1964 Anchorage earthquake and Mt. St. Helens erupting in 1980.

2. Earthquakes Worldwide

3. Earthquakes Since 1900

4. Loss of Life and Economic Costs
Why should we care?
Loss of Life and Economic Costs
Has anyone felt an earthquake in the past?
What did you experience?
Northridge, California 1994

5. Where are Earthquakes found?
A map showing the locations of earthquakes on the Earth reveals a definite pattern, which geologists have linked to boundaries between tectonic plates.
Earth’s tectonic plates (left) and locations of earthquakes and volcanoes (right).

6. Montana Earthquakes

7. What is an Earthquake?
An earthquake is energy released in the form of seismic waves. Earthquakes occur when built up stress and pressure give-way resulting in shaking of earth’s crust.

8. Seismic Waves
P-wave
S- wave
Surface Wave

9. What happens to seismic waves in Earth’s interior?-

10. Shadow Zones -

11. Locating & Measuring Earthquakes
Seismograms
Seismograph in Mt. Rainier National Park. An instrument called a seismograph detects and records waves produced by earthquakes that may have originated hundreds, even thousands, of kilometers away.
Scientists use data from seismographs to locate earthquakes’ epicenters and to measure their magnitude.
There are more than 10,000 seismograph stations around the world.

12. - Seismographs Seismograph station at Cornell University
A modern seismograph station usually has three seismographs. The first one records up-and-down motions, the second one records side-to-side motions in a north/south direction, and the third one records side-to-side motions in an east/west direction.

13. Locating an Earthquake Epicenter - - Step 1- Analyzing 3 Seismograms

14. - Step 2- Read Travel-Time Graph

15. - Step 3 – Triangulate to find Epicenter.

16. Depth of Focus.
Yellow = shallow,
Red = intermediate,
Black = deep

17. Depth of Earthquakes
The depth at which an earthquake originates depends upon the type of plate boundary involved.
Divergent boundaries earthquakes occur at shallow depths about 30 Km.
Transform boundaries earthquakes occur at shallow depths.
Subduction boundaries, the focus of the earthquake can be very deep up to 700 kilometers.
Divergent boundaries: 30 km = about 18.6 miles. Subduction boundaries: 700 km = about 435 miles.

18. Measuring Earthquakes
Magnitude is a quantitative measurement that estimates the energy released.
Richter Scale
Moment Magnitude
Intensity is a qualitative measurement that evaluates the degree of earthquake shaking perceived by individuals
Modified Mercalli Scale
Intensity is a qualitative measurement that evaluates the degree of earthquake shaking perceived by individuals
Magnitude is a quantitative measurement that estimates the energy released.

19. Richter Scale (Magnitude)
Developed by Charles F. Richter in 1935.
Measurement of energy.
Each increase of one whole number in Richter magnitude is a 10 x increase in amplitude of wave and a 32 x increase in energy release.
For example, a magnitude 6 earthquake has 32 times the energy than a magnitude 5 earthquake. A magnitude 7 earthquake is more than 1024 times (32x32) more energy than magnitude 5 earthquake.

20. Magnitude

21. Reading a Nomogram

22. Richter Scale (Magnitude)
Description
Less than 3.5
Not generally felt by humans
Slight damage to structures
7.0 – 7.9
Serious damage
8.0 and greater
Total destruction of nearby communities

23. Moment Magnitude (Magnitude)
Moment Magnitude is the current method used for measuring earthquakes (especially large ones) and uses three measurements:
1. Average area of slip along the fault;
2. Distance traveled; and
3. Considers the strength of the rock.

24. Example Magnitudes Location Date Richter Magnitude Moment Magnitude
San Francisco
1906
8.3
7.9
Alaska
1964
8.5
9.2
Alaska released at least twice as much energy because it involved greater movements along a much larger fault plane.

25. Mercalli Scale (Intensity)
Mercalli Scale (Giuseppi Mercalli 1902) measures the intensity of a quake by using observed affects of ground movement.

27. Earthquake Risk
Where in the United States is the risk for earthquakes the greatest? Alaska and California are high risks since they are found near plate boundaries.
The middle of the country by Missouri is also at a higher risk, because many faults are buried deep beneath sediments deposited by the Mississippi, Missouri, and Ohio rivers.

28. Damage from Earthquakes
Ground shaking
Liquefaction
Aftershocks
Fire
Tsunamis

29. Ground Shaking
Ground shaking is produced by the waves set in motion by an earthquake’s sudden release of energy. Some of the ground vibrations are up-and-down, but the largest are side-to-side motions.
Most buildings can withstand fairly violent up-and-down shaking; however, few buildings can survive violent side-to-side shaking, and as a result many buildings collapse.

30. Liquefaction
-occurs when loose soil temporarily takes on some of the properties of a liquid.
- A building located on soil that settles is no longer safely supported and may collapse. For example, buildings located on bog muds or soil landfill can suffer severe damage or can collapse because of foundation failure.

31. Liquefaction caused the building in the front to tip nearly 22°
Liquefaction caused the building in the front to tip nearly 22°. The arrow points to a building that is tipped almost 70°.

32. Aftershocks
- are a series of smaller earthquakes originating close to the focus of the large earthquake.

33. Fire
- One of the most damaging effects of an earthquake may be the fires caused by the rupturing of gas lines by ground movement.

34. Tsunami
- Underwater earthquakes and landslides sometimes cause huge ocean waves.

35. Tsunami
When a tsunami reaches shallower water near a shoreline, it will slow down and increase dramatically in height.
A tsunami warning system is now in place for regions in the Pacific Ocean. Scientists monitor wave activity at various stations throughout the Pacific.

36. Tsunami Animation

37. Elastic Rebound Theory
- Stress is released and crust is cracked called the elastic-rebound theory normally occurring at faults.
-Stresses:
Plate Tectonics
Thermal expansion and contraction.
Gravitational attraction
Mineral phases

38. Tensional stress pulls rock away from adjacent rock thinning crust.
Normal faults occur when rock along one side of the fault slide down relative to the other.
Divergent Boundary

40. Compressional stress pushes rock together causing.
Reverse faults occur when rocks are pushed together and one side of the fault moves up.
Convergent Boundary

42. Rocky Mountain Front

43. Shearing stress pushes rock in two different directions adjacent to one another.
Strike-slip faults occur when blocks of rock on each side of the fault move in opposite directions.
TRANSFORM PLATE BOUNDARY