Chapter 4 - Earthquakes

Question 1

What are faults?

Answer 1

They are planar breaks in rock along which there is displacement of one side relative to the other.

Question 2

What is called creep?

Answer 2

When movement along faults occurs gradually and relatively smoothly. Also known aseismic slip.

Question 3

What is the focus?

Answer 3

The point on a fault at which the first movement or break occurs during an earthquake.

Question 4

What is the point on the earth’s surface directly above the focus called?

Answer 4

The epicenter

Question 5

What is the dip of a fault?

Answer 5

It is the angle the plane makes with the horizontal, a measure of the steepness of slope of the plane.

Question 6

What is a strike-slip fault?

Answer 6

It is a fault along which the displacement is parallel to the strike.

Question 7

What is a dip-slip fault?

Answer 7

It is a fault in which the displacement is vertical, up or down in the direction of dip.

Question 8

What are thrust faults?

Answer 8

They are reverse faults with relatively shallowly dipping fault planes.

Question 9

How does an earthquake release its stored up energy?

Answer 9

In seismic waves that travel away from the focus.

Question 10

What are body waves?

Answer 10

They are seismic waves that travel through the interior of the earth.

Question 11

What type of waves are P waves?

Answer 11

They are compressional, as they travel through matter they compress and expand it. They move through the earth similar to sound traveling through air.

Question 12

What kind of waves are S waves?

Answer 12

They are shear waves, involving a side-to-side motion of molecules.

Question 13

How are seismic surface waves similar to surface waves on water?

Answer 13

They cause rocks and soil to be displaced in such a way that the ground surface ripples or undulates.

Question 14

What is the major cause of structural damage during an earthquake?

Answer 14

Surface waves.

Question 15

What is the amount of ground motion related to?

Answer 15

The magnitude of the earthquake.

Question 16

How is the richter magnitude number assigned?

Answer 16

It is assigned to an earthquake on the basis of the amount of ground displacement or shaking that it produces near the epicenter.

Question 17

What are aftershocks?

Answer 17

They are earthquakes that are followed by, but weaker than, the original tremor.

Question 18

What is liquefaction?

Answer 18

When wet soil is shaken by an earthquake, the soil particles may be jarred apart, allowing water to seep between them, causing the ground to become somewhat like quicksand.

Question 19

How are tsunamis formed?

Answer 19

They form when an undersea or near-shore earthquake occurs, sudden movement of the sea floor sets up large waves traveling away from that spot.

Question 20

Why do fires occur during earthquakes?

Answer 20

Fires occur because fuel lines, tanks and power lines are broken, touching off flames and fueling them.

Question 21

What are seismic gaps?

Answer 21

Dormant sections of otherwise-active fault zones.

Question 22

What is the precursor phenomena?

Answer 22

A method of surveilling seismic activity, focuses on things that happen or rock properties that change prior to an earthquake.

Question 23

What are the 5 periods of the earthquake cycle?

Answer 23

Stress buildup, sudden fault rapture, brief intervals of aftershocks, minor lithospheric adjustments and another period of stress build up

Question 24

What is the term slow-slip earthquake used for?

Answer 24

When temperatures are high enough (50 km deep!) and rocks are plastic enough to where the fault generally slides smoothly.

Question 25

What is induced seismicity?

Answer 25

It is seismic activity caused by human activity.