1. EarthReading11
Earthquakes

2. Earthquakes
An earthquake is a shaking of the Earth’s crust caused by a release of energy.
A fault is a break in the lithosphere along which movement has occurred.
The focus of an earthquake is the point at which movement first occurs.
The epicenter of an earthquake is the point on the surface of the Earth directly above the focus.
Earthquake animation

3. April 18th 1906 San Francisco Earthquake, Van Ness Street
Earthquake animation

4. Days after the earthquake residents watch the city burn.

5. Downtown Anchorage Alaska after the 1964 earthquake.

6. Tsunami from the 1964 earthquake destroyed the waterfront in Kodiak Alaska.

7. A 1976 earthquake near Guatemala City shattered this bridge in Agua Caliente, cutting off the city’s main supply route to the Atlantic. The 7.5-magnitude quake killed more than 23,000 people

8. An earthquake's destructive power varies depending on the composition of the ground in an area and the design and placement of manmade structures.

9. Downtown Crescent City, March 1964
The Tsunami caused by the 1964 Alaskan earthquake was responsible for 122 deaths.
The Tsunami moved at 400 mph reaching the Hawaiian Islands, Oregon, and California.
Ten people died in Crescent City California.
Downtown Crescent City, March 1964

10. 1952 Bakersfield Earthquake Magnitude 7.5 along the White Wolf Fault

13. Beale clock tower after the 1952 earthquake.

14. Locations of Earthquakes
Earthquakes occur predominantly at plate boundaries where neighboring plates move past each other.
Understanding the theory of plate tectonics helps geoscientists understand and predict earthquakes.
USGS Earthquake Location Website

15. Causes of Earthquakes
Magma rising towards the surface of a volcano. Yellowstone and the Long Valley Caldera (Mammoth)
Rock bursts/collapses in deep mines.
The majority of earthquakes are caused by two faces of rock slipping past each other along an approximately flat internal surface, called a fault.

16. What Governs the Timing of Earthquakes?
There is currently no agreed-upon method to predict the location, size, and probable time of an impending earthquake on a particular fault.
It is possible to forecast the likelihood of earthquakes of a given size in a fault region over time periods of decades to centuries.

17. Look what happens above and below the ground.

18. Types of Faults
Strike-slip faults are vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally.
Dip-slip faults are inclined fractures where the blocks have mostly shifted vertically.
If the rock mass above an inclined fault moves down, the fault is termed normal, whereas if the rock above the fault moves up, the fault is termed reverse. A thrust fault is a reverse fault with a dip of 45° or less.
Fault Animation

19. Earthquakes lift and turn mountains.

20. Types of Stress
Compression stress is the stress that squeezes something. Thrust Fault
Tensional stress is the stress that tends to pull something apart. Normal Fault
Shear stress is the stress component parallel to a given surface. Strike Slip Fault

21. Measuring an Earthquake
The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions and measured with a seismometer.

22. Type of Seismic Waves
P- Wave is a seismic body wave that shakes the ground back and forth in the same direction and the opposite direction as the direction the wave is moving.
S-Wave, or shear wave, is a seismic body wave that shakes the ground back and forth perpendicular (right angle) to the direction the wave is moving.
Surface Wave (2) a. Love, b. Raleigh- travel near the earth's surface.
Wave Animation

23. How do these seismic waves work?
Click here for a demonstration of the S and P waves.
Then, under Tutorials, click on SP Lag Time.

24. The Earthquake sets off a chain reaction.
Surface waves are responsible for most of the damage associated with earthquakes, because they cause the most intense vibrations.

26. S waves cannot travel through the liquid core
P waves are refracted by the liquid core

27. Here is an animation on how to visualize how seismic waves move
through the Earth. As you will see, differences in how these waves
travel have revealed the layers of our planet’s interior.
Further Questions
Do these layers exist on other planets?
How far have humans drilled into the Earth—all the way to the core or just how far?

29. Earthquake Scales
Richter Scale is calculated from the amplitude of the largest seismic wave.
The scale is logarithmic which means that each unit increases the level of ground shaking by a magnitude of ten.
Each unit increase release an amount of energy equal to 32. Therefore a magnitude 7 releases 32 times the energy of a magnitude 6 and shakes 10 times as much.

30. Richter Scale Intensity Scale Description Effects less than 2 Micro
not felt
2-3
Very Minor
not felt but recorded
3-4
Minor
often felt, no damage
4-5
Light
shaking observed
5-6
Moderate
Some damage
6-7
Strong
damaging over a 100 mile area
7-8
Major
serious damage over wider area
greater than 8
Great
Serious damage over several hundred miles
World's Biggest Earthquakes
California Earthquakes

31. The Mercalli scale measure the amount of damage an earthquake causes.
Intensity Scale
Classification
Effect description I
Instrumental
Detected only by seismographs II
Feeble
Noticed by sensitive people
III
Slight
Similar to a passing lorry IV
Moderate
Loose objects are rocked V
Rather strong
Felt generally VI
Strong
Trees sway, loose objects fall
VII
Very strong
Walls crack
VIII
Destructive
Chimneys fall; masonry cracks IX
Ruinous
Houses collapse where ground starts to crack X
Disastrous
Ground badly cracked; buildings destroyed XI
Very disastrous
Bridges and most buildings destroyed; landslides
XII
Catastrophic
Ground moves in waves; total destruction