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Earthquake/Volcano Study Guide
For each of the diagrams describe the type of stress affecting them, the type of fault associated with
them, and the type of plate boundary associated with them.
Stress _Shear
Fault _Strike Slip
Boundary _Transform
Stress _Tension
Fault _Normal Fault
Boundary _Divergent
Stress _Compression
Fault _Reverse Fault
Boundary _Convergent
Stress _Compression
Fault _Reverse Fault
Boundary _Convergent
Stress _Tension
Fault _Normal Fault
Boundary _Divergent
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Stress _Shear
Fault _Strike Slip Fault
Boundary _Transform
What is an Earthquakes epicenter?
It is the location on the surface of the Earth directly above the first movement of a fault. It is where the
shaking from an Earthquake is normally the worst.
What are the 2 types of Earthquake waves needed to calculate the distance to an Earthquake’s
epicenter?
Primary (P) waves, and Secondary (S) waves
What are the differences between those 2 waves? Primary waves are the fastest, and arrive at
earthquake monitoring stations first. P waves are compression waves and vibrate parallel to the
direction of the wave. S waves are slower, and vibrate perpendicular to the direction of the wave.
Describe why 3 Earthquake monitoring stations are needed to find the epicenter of an Earthquake?
By measuring the time difference between the arrival of the “P” & “S” waves the distance to the
earthquake’s epicenter can be calculated, but the direction can not. Using the distance from 3 stations
the location can be determined by drawing 3 circles around the stations using the distance as the radius.
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What Earthquake scale is the best, and why is it the best? _Moment Magnitude
Why? The Moment magnitude scale calculates the total energy released from an earthquake, the others
use only damage to structures or just earthquake waves.
Where are most earthquakes located? _Plate Boundaries
Why do they happen there? That is where plates interact the most. They grind against each other, get
stuck, and slip.
Label the diagram:
8) _Pipe
9) _Crater
10) _Vent
11) _Lava Flow
12) _Magma Chamber
Why does magma rise through the crust? It is less dense than the solid rock above it.
How do Volcanoes form along convergent boundaries? Volcanoes at convergent boundaries form from
the subduction of oceanic crust. As the crust sinks into the mantle it brings water and other materials
down into the mantle with it. As it melts it works its way back up through the crust forming a volcano
on the continent, or an island arc in the ocean. Because the magma is cooler, has more gas and silca,
these volcanoes can be very violent.
Why do geologists monitor earthquake activity near volcanoes? Increasing earthquake activity and the
intensity of the earthquake waves tell scientists when a volcanic eruption will happen.
Describe how volcanoes form at a hot spot under oceanic crust: A hot spot is a place in the mantle that
is much hotter than the rest of the mantle. It is hot enough to melt through the thin oceanic crust and
erupt onto the ocean floor. Over many years the eruptions build up an island in the ocean. Eventually
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the crust moves due to plate tectonics off of the hot spot and the volcano becomes extinct. Which
means it will not erupt again.
Describe a Shield volcano, how it forms, and the type of magma it normally has: A shield volcano
normally forms from a hot spot in the mantle. The magma comes mainly from the mantle, and is low in
silica and trapped gases- but is very hot. This makes for low viscosity magma, and gentle eruptions of
fast moving lava that forms a flattened shape of a shield.
Describe a Cinder Cone volcano, how it forms, and the types of magma it normally has: A cinder cone
volcano forms mainly from eruptions of ash, and not much lava. They are usually the result of
subduction of an oceanic plate, but can also form on the flanks of bigger volcanoes. The magma is
typically cooler, has a lot of trapped gases, and is high in silica content. That combination often results
in violent eruptions and a very steep cone shaped volcano.
Describe a Composite volcano, how it forms, and the types of magma it normally has: A composite
volcano normally forms from subduction of an oceanic plate. The oceanic plate subduction produces
cooler magma that is high in silica and trapped gases. The magma works its way to the surface where it
erupts. It can have quiet eruptions of lava, and more violent eruptions of ash. It has the classic volcano
shape.