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Study Guide: Earthquakes & Volcanoes
Key
1. What is a fault?
a fracture in the Earth where movement has occurred
2. Where on the Earth is an earthquake’s epicenter located?
the place on the surface of the earth directly above the focus
3. Define: Focus
When an earthquake occurs, energy radiates in all directions from its source (the place where the
rocks break to cause the earthquake to occur)
4. What is the name of the largest fault in California?
the San Andreas fault
5. Which type of seismic wave travels the fastest?
P waves
6. Describe the characteristics of S-waves.
They travel more slowly than P waves
They shake particles at right angles to the direction the waves travel. (side to side)
They cannot be transmitted through water or air. (solids only)
7. Which type of seismic waves are the most destructive?
surface waves
8. How many seismic stations are needed to locate the epicenter of an earthquake?
Three
9. Using the graph above, what is the distance between the seismic station and an earthquake epicenter, if the first S
wave arrives 4.0 minutes after the first P wave?
1500km
10. Using the graph above, when will the first P wave be received, if an earthquake epicenter is approximately 1800
kilometers from the seismic station?
5.5 minutes after the earthquake
11. Use the graph above to determine the difference in the travel-times between the first P wave and the first S wave,
if the seismic station is 2800 kilometers from the epicenter.
14min (s) – 8min (p) = 6min
12. What is the name of the most widely used scale used to measure earthquakes?
moment magnitude scale
13. Name the instrument that is used to record earthquakes.
Seismograph
14. The trace that records an earthquake from seismic instruments is called a _______________________.
Seismogram
15. List at least three factors that affect the amount of destruction that can be caused by earthquakes.
the design of structures
the intensity and duration of the vibrations
the nature of the material on which structures are built
16. What type of area would a very large earthquake cause the most damage? (Hint = think building material)
area with older brick structures
17. a. What is a Tsunami?
a large, often destructive, sea wave
b. What causes a tsunami?
generated by movements of the ocean floor, either by earthquakes or underwater landslides
18. Why do earthquakes often cause damaging fires?
Earthquake vibrations can break gas lines, water lines, and electrical lines
19. Name the two major plates that are involved in the movement of the San Andreas fault.
North American and Pacific
20. Most earthquakes around the world occur at _______________________________.
Plate boundaries
21. Why do Geologists study the path of P-waves and S-waves?
Helps scientists determine the depth of the mantle and the core, and their state of matter
22. List at least three destructive events that can be caused by an earthquake.
Fires Landslides
Tsunamis
23. Name the three major types of volcanoes.
Shield volcano
Composite volcano (aka. Stratovolcano)
Cinder Cone
24. In a volcano, the magma’s viscosity is directly related to its _____________________________.
Silica content
25. As the temperature of lava increases, the viscosity __________________________.
Decreases
26. Describe the magma that is associated with highly explosive volcanoes.
High silica content
High viscosity
Higher gas content
27. List the three factors of magma that determine the type of volcanic eruption that will occur.
amount of dissolved gases
temperature
composition
28. Define: Pyroclastic material
The rock and ash particles produced in volcanic eruptions
29. What type of volcano is the smallest type of volcano, built almost entirely from ejected lava fragments, and
usually occurs in groups ? (Ex. Paricutin in Mexico)
cinder cone
30. The broad, slightly dome-shaped volcanoes of Hawaii are an example of what type of volcano?
Shield volcanoes
31. Which type of volcano is the most violent/explosive and has eruptions of BOTH lava and pyroclastic material?
(Examples include Mt. St. Helens or Mt. Shasta in California.)
Composite volcano
32. The two most abundant gases associated with volcanic activity are ___________ and _____________.
Water vapor & carbon dioxide
33. The major factor in determining the form/type of a volcano is its _______________________________.
Magma composition
34. Mild volcanic eruptions are associated with what type of volcano?
Shield volcanoes
35. A large depression in a volcano is known as a _________________________.
Crater
36. The Hawaiian Islands were formed by what type of volcanism?
intraplate volcanism
37. The opening to the surface of a volcano is known as the ____________________________.
Vent
38. Name the mountain located in Southern California that has the greatest probability of eruption in the future.
Mammoth Mountain
39. What is the name given to the volcanoes that are located around the edges of the Pacific Plate?
Ring of Fire
40. True or False: All volcanic eruptions emit (release) large amounts of gas.
True
41. What is the term that describes a conduit that feeds magma to a volcano’s surface?
Pipe
42. What is significant about the mountains that surround Thousand Oaks?
They used to be located under water AND they used to be active volcanoes
45. What is the Geothermal Gradient?
rate at which temperature changes with depth below the Earth’s surface
46. List the type(s) of plate boundaries were volcanoes can be formed.
Both - convergent and divergent
47. The adjustments of materials that follow a major earthquake often generate smaller earthquakes called ___
aftershocks _____.
48. Major earthquakes are sometimes preceded by smaller earthquakes called __ Foreshocks ___.
49. How fast do the plates on the San Andreas fault move per year on average?
2 inches, 5 cm
50. What area of the west coast has the most active volcanoes?
Pacific Northwest (Washington/Oregon, N. California)