Name: ______________________________________________ Date: _________________ Period: _______
Due Date: Wednesday, March 11th
Test Date: Friday, March 13th
Plate Tectonics Study Guide
Earthquakes:
Vocabulary:
 The focus of an earthquake is the point inside the earth where the earthquake
begins.
 The epicenter of an earthquake is the imaginary point on the earth’s surface above
the focus.
 Primary waves (P-waves) are seismic waves that arrive first. They compress and
expand the ground.
 Secondary waves (S-waves) are seismic waves that arrive second. They move the
ground up and down or side to side.
 Surface waves are seismic waves that move along the earth’s surface and are the
most destructive.
How to Read a Seismograph:
1. The smaller wave on the seismograph is a P-wave. The larger wave
on the seismograph is a S-wave.
2. The difference in time between the P and S waves is known as lag
time.
3. The city with the smallest amount of lag time is the one that is closest
to the epicenter.
4. The times that the waves arrive at each city are different because the
cities are different distances away from the epicenter.

The scale used to measure earthquake magnitude is the Richter Scale.
How do mountains form?
o An oceanic plate sinks beneath another plate and forms volcanic mountains or
islands.
o Hot rock/hot spots from within the earth rise through the ocean floor, forming
volcanic mountains.
o Two continental plates collide forming a mountain.
Earthquakes occur before volcanic eruptions because…
o The force of magma causes rock to fracture (or break)
o Pressure from escaping gases causes nearby rocks to fracture (or break)
o Pressure on rocks from magma causes rocks to break (or break)
Volcanoes
 Volcanoes can be both constructive (good/helpful) and destructive (bad/damaging.
o Constructive: creating new landforms like islands and mountains
o Destructive: hot lava can destroy towns and ash from a violent eruption can
cause breathing problems in humans, cover cops, and block sunlight.

The difference between magma and lava:
o Magma is molten rock beneath the earth’s surface. Lava is molten rock on the
earth’s surface.

Types of Volcanoes:
o Composite: A volcano that forms from alternating eruptions of viscous lava
and broken rock. It is steep near the summit and flat toward the base. It has
the most explosive eruptions. Mt. Pinatubo is an example of a composite
volcano.
o Shield: A wide, broadly sloping volcano that forms from runny lava. It is the
largest of volcanoes. See also cinder cone; composite volcano. Mt. Kilauea
and Mauna Loa in Hawaii are examples.
o Cinder Cone: A small (less than 400 meters high), cone-shaped volcano made
of broken rocks or blobs of hardened lava, called “cinders,” that accumulate
around the volcanic vent.
 Instruments scientists use to study and predict volcanic activity:
o Tiltmeter – instrument used to measure slight changes in the inclination of
the earth’s surface.
o Seismograph – an instrument that detects, records, and measures the
vibrations produced by an earthquake.
o Gas sensor – detects the presence of gases in an area
 Regions of volcanic activity:
o The Ring of Fire
o The Mid-Atlantic Ridge
o Hawaii and other hot spots
 Volcanic Ash:
o Hot ash clouds rise to the sky because of the upward force of the volcanic
eruption, pressure release, density differences between ash and air, and
convection.
o The direction of the wind can affect the placement of ash.
o Geologists can tell if ancient deposits of sediment are from a volcanic ash if
there are tiny fragments of volcanic remains/glass in the sediment.
Review Sheet
Part 1: Reading a Seismograph
A
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B
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Directions: Three different seismograph stations (A, B, and C) recorded an earthquake.
Complete the table below and answer the following questions. Station A is from Olympia,
Washington, Station B is from Honolulu, Hawaii, and Station C is from Columbia, South
Carolina
Time of Arrival at Station
.
Seismograph
S-wave minus PPrimary Wave
Secondary Wave wave
Station
(P-wave)
(S-wave)
A. Olympia,
Washington
B. Honolulu,
Hawaii
C. Columbia,
South Carolina
1. Which station is closest to the epicenter? Explain.
2. Why are the times that each earthquake wave arrived at each city different?
Part 2: Earthquakes – “Recognizing Differences”
3. What is the difference between the focus and the epicenter of an earthquake?
4. What is the difference between primary waves and secondary waves?
5. What is the difference between a seismograph and a seismogram?
6. What is the difference between a body wave and a surface wave?
Part 3: Earthquakes – “Three Reasons”
7. What are the three ways that mountains form?
8. What are the three reasons why earthquakes occur before volcanic eruptions?
Part 4: Volcanoes – Vocabulary
9. Composite ________
10. Cinder Cone ________
A. A wide, broadly sloping volcano that
forms from runny lava.
B. Molten rock on the earth’s surface.
11. Shield ________
C. A small cone-shaped volcano made of
broken rocks or blobs of hardened
lava.
12. Magma ________
D.
13. Lava ________
E. Molten rock below the earth’s
surface.
A volcano that forms from
alternating eruptions of viscous lava
and broken rock. It has the most
explosive eruptions.
Part 4: Volcanoes – Questions
14. Why do hot ash clouds rise to the sky?
15. What are the three regions of intense volcanic activity?
16. What are the three instruments that scientists use to study and predict volcanic
activity?
17. Can volcanoes be constructive and destructive?