1. Chapter 19 Earth Science Riddle
Earthquakes
Chapter 19
Earth Science
Riddle

2. Stress and Strain Stress and Strain
earthquakes result of movement in Earth’s crust
Plate tectonics
Along plate boundaries plate resist movement
Build up stress
Stress the total force acting on crustal rocks per unit of area
When stress overcomes the strength of rocks, movement occurs along fractures in the rocks.
The vibrations are earthquakes

3. Stress Three types of stress
Compression: stress decreases the volume of material
Tension: pulls material apart
shear: causes material to twist

4. Deformation Elastic Material is bent for stretched. Low stress
Like pulling the ends of a rubber band
When stress released, it goes back to original size
Plastic
Stress builds to a certain point- elastic limit.
Strain the causes permanent deformation.
Does not go back to original size when stress is reduced to zero

5. Faults
Reverse
Movement partly horizontal and partly vertical compression
Squeezes rock
Shortens crust
One side of fault is pushed up relative to the other.

6. Normal Fault Partly horizontal and partly vertical
Pulls rocks apart and stretches the crust
Vertical movement when stretching causes rock to move down relative to the other side of the fault.

7. Strike-Slip Fault Caused by horizontal shear.
Movement is horizontal in opposite directions.
San Andreas is an example of a Strike-Slip fault

8. Earth Quake Waves Seismic Waves
The vibrations of the ground produced during an earthquake
Three types of seismic waves
Primary Waves
Secondary Waves
Surface Waves

9. Primary Waves
P-Waves
Squeeze and push rocks in the direction the waves are moving.
The first wave
Passes through Earth’s interior

10. Secondary Waves S Waves Second to arrive Slower than P waves
Motion causes rocks to move at right angles in relation to the wave
Passes through the Earth’s interior

11. Surface Waves Slowest type of wave Travel only Earth’s surface
Causes ground to move sideways and up and down
Most destructive
Take the longest to pass

12. Generation of Seismic Waves
The point at which the waves generate is the focus.
Epicenter is the point on Earth’s surface directly above the focus.

13. Seismic Waves and Earth’s Interior
Chapter 19
Section 2
Earth Science

14. Seismometer An instrument that can detect movement in Earth’s crust.
Rotating drum with a suspended pen and mass.
Records the movement on the paper on the drum.

15. Seismogram
The record produced by seismometer

16. Travel Time Curves
Using seismogram data, scientists have been able to construct a global travel time curves for the arrival for P and S waves.
Curves provide average travel time of each wave.

17. Distance from Epicenter
P waves arrive first
S waves arrive second
Distance between P and S waves increases as distance form the epicenter increase
This data is used to determine the distance from the epicenter

18. Clues to Earth’s Interior
Internal Structure
Seismic waves change speed and direction at boundaries between different materials.
P and S waves initially travel through mantle on fairly direct paths.
P waves are refracted when they hit the core and other boundaries of Earth’s layers
Travel times between refractions give information about Earth’s interior
Data about paths and travel times gave evidence that Earth’s core was at least partially liquid
Outer core mostly liquid
Inner core mostly solid

19. Earth’s Composition

20. Measuring and Locating Earthquakes
Chapter 19
Section 3
Earth Science

21. Earthquake Magnitude and Intensity
Richter scale
Numerical rating system measures the height largest seismic waves
Magnitude: energy of the largest seismic waves
Amplitude: height of the largest seismic wave
Each successive number represents an increase in the amplitude of a seismic wave by a factor of 10
Example: Magnitude of 8 is 10x larger than a magnitude of 7.

22. Moment Magnitude Scale
Measures the energy released by an earthquake
Used by seismologists
Takes into account the size of the fault and the rocks’ stiffness

23. Modified Mercalli Scale
Describes the earthquake with respect to the damage they cause.
Listed in Roman numerals to designate degree of intensity
The larger the numeral, the more damage.

24. Earthquake Intensity Depends on amplitude of surface waves
Surface waves decrease as they move away from the focus
Intensity decreases with distance
Maximum intensity at epicenter

25. Depth of Focus Earthquakes classified as
Shallow
Intermediate
Deep
Catastrophic earthquakes are almost always shallow-focus events
Deeper focus event produce smaller vibrations at the epicenter.
Mercalli scale affected by depth of focus- based on damage.
Richter scale is not affected by depth of focus.

26. Distance to an Earthquake
Scientists look at the difference between the arrival times of the P and S waves.
The longer the time between the two- the farther they are from the epicenter
Use Travel Time curves to calculate distances based on the arrival times of the P and S waves.

27. Seismic Belts Earthquake epicenters reveal a pattern
Majority of earthquakes occur on narrow seismic belts
Example Ring of Fire
Correspond closely with tectonic plates boundaries

28. Earthquakes and Society
Chapter 19
Section 4
Earth Science

29. Earthquake Hazards
Factors that determine the severity of damage are called Earthquake Hazards
Identifying the hazards in an area can prevent damage

30. Structural Failure Ground beneath structures shake
Supporting walls fail and cause upper levels to fall and collapse
Tall structures collapse or sway violently before falling

31. Land and Soil Failure Landslides are triggered on sloped areas.
Soil liquefaction:
vibrations cause ground to behave like liquid
Can cause trees and houses to sink

32. Tsunami
Large ocean wave generated by vertical motions on the ocean floor
Displace entire column of water overlying the fault

33. Tsunami