1. Earth Science Ch. 8
Earthquakes

2. An earthquake is the vibrations of earth produced by rapid release of energy in the lithosphere.
Earthquakes are caused by movements along faults

3. Parts of an earthquake
Focus: point within the earth where an earthquake starts below the surface
Epicenter: location on the surface directly above the focus.
Seismic waves: energy produced by an earthquake that travels in all directions from the focus.

5. Elastic Rebound Hypothesis
Probable cause of earthquakes
Earthquakes are produced by release of energy stored in rock that has been subjected to great pressure.
When the strength of the rock is exceeded it suddenly breaks releasing energy as seismic waves.
The rock breaks at its weakest point. This is called the focus.
After an earthquake, the rocks along the fault spring back to their original position. This is called elastic rebound.

7. An aftershock is an earthquake that occurs after a major earthquake.
Foreshocks are small earthquakes that occur before a major earthquake.

8. Measuring Earthquakes
Earthquakes produce 2 main types of seismic waves: surface waves and body waves
Body waves
P waves
primary waves/compression waves
travel in the same direction the earthquake travels
can travel through solids, liquids, or gases
First waves to arrive at the surface

9. S waves secondary / transverse waves
particles move at right angles to the direction of the earthquake
Can only travel through solids
Second waves to arrive at the surface

10. Surface waves travel slower than body waves Most destructive
Last to arrive at the surface
2 types:
Love: side to side movement
Rayleigh: rolling waves

11. Body Waves
P and S waves
Surface Waves
Love and Rayleigh

12. Seismograph: instrument that records seismic waves
Seismogram: a time record of ground motion during an earthquake
All 3 types of seismic waves are shown

15. Intensity and Magnitude
Intensity is the measure of damage an earthquake causes
The Mercalli Scale is used to measure intensity.

17. Magnitude is the measure of the amount of energy released by an earthquake
Richter Scale
Each number on the scale represents a 10 fold increase in the wave height
Only useful for small shallow earthquakes
Moment Magnitude
Measures the amount of movement along a fault.
The most widely used
only scale that estimates energy released by any earthquake.

23. Locating an Earthquake
Calculate the difference in arrival times between P and S waves.
The greater the time interval the greater the distance to the epicenter.
A time travel graph is used to find the distance to the epicenter.
Data is collected from 3 seismograph stations to find the epicenter.

26. Tsunamis
Series of waves formed by an earthquake on the ocean floor or by underwater landslides.
The height of tsunami waves increases as the water becomes more shallow.
A tsunami warning system is used to alert people that live in coastal regions around the Pacific Ocean (Ring of Fire).

29. Earthquake Safety Drop, cover, and hold
If indoors crouch beneath a sturdy table or desk
Crouch against an inner wall or stand in a door frame.
Avoid furniture that might fall
If outside move to an open area and sit down
Avoid vehicles, power lines, trees, and buildings

30. Earth’s Layered Structure
Most of the knowledge about the earth’s interior comes from the study of seismic waves.
As the speed of seismic waves changes, the waves refract or bend
Scientists study the speed and paths of seismic waves to determine the chemical composition of rocks inside the earth

31. 3 Major Layers of Earth Crust Thin rocky outer layer of the earth
There are 2 types of crust: oceanic and continental
Oceanic crust is composed mostly of the igneous rock basalt
The most common rock in continental crust is granite
Rocks in oceanic crust are more dense and younger than those in continents
The continental crust is thicker

32. The 8 most abundant elements in the earth’s crust:
Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium

33. Mantle Largest layer of earth Solid
The boundary between the crust and mantle represents a change in the physical properties and a change in seismic waves
Has the same chemical composition as the crust.

34. Core Composed mostly of iron and nickel
Most dense area due to extreme pressure

35. Layers Defined by Physical Properties
Temperature, pressure, and density all increase with depth
The temperature and pressure determine the physical properties of the rock
Solid, putty, liquid

36. Lithosphere Earth’s outer most layer
Consists of the crust and the upper mantle
Cool rigid shell

37. Asthenosphere Lower Mantle Softer weaker rock
Rocks are close enough to the melting point that they are easily deformed
Found entirely in the mantle
Rocks in this layer are solid but able to flow like putty
Lower Mantle
More rigid but still very hot and capable of gradual flow

38. Outer Core Inner Core Liquid layer
Flow of liquid iron generates earth’s magnetic field
Inner Core
Extremely high temperatures
Exists in a solid state due to immense pressure
The heat of the core is caused by:
Radioactive decay
Friction
Formation of the Earth

40. Boundaries Between Layers
Mohorovicic Discontinuity (Moho)
Boundary between the crust and mantle
Speed of seismic waves decreases.
Gutenberg Discontinuity
Boundary between the mantle and core
Speed of seismic waves decreases

41. P waves of earthquakes bend when they reach the liquid outer core
P waves of earthquakes bend when they reach the liquid outer core. This causes a region called a shadow zone.
P waves bend when the material changes.
S waves cannot travel through the outer core which shows that this region is liquid.

43. There are 3 Types of Earthquakes that occur at convergent plate boundaries
Shallow focus
0 – 70 km deep
Most destructive
Intermediate focus
70 – 300 km deep
Deep Focus
Below 300 km