Chapter 4 - Earthquakes Flashcards
What are faults?
They are planar breaks in rock along which there is displacement of one side relative to the other.
What is called creep?
When movement along faults occurs gradually and relatively smoothly. Also known aseismic slip.
What is the focus?
The point on a fault at which the first movement or break occurs during an earthquake.
What is the point on the earth’s surface directly above the focus called?
The epicenter
What is the dip of a fault?
It is the angle the plane makes with the horizontal, a measure of the steepness of slope of the plane.
What is a strike-slip fault?
It is a fault along which the displacement is parallel to the strike.
What is a dip-slip fault?
It is a fault in which the displacement is vertical, up or down in the direction of dip.
What are thrust faults?
They are reverse faults with relatively shallowly dipping fault planes.
How does an earthquake release its stored up energy?
In seismic waves that travel away from the focus.
What are body waves?
They are seismic waves that travel through the interior of the earth.
What type of waves are P waves?
They are compressional, as they travel through matter they compress and expand it. They move through the earth similar to sound traveling through air.
What kind of waves are S waves?
They are shear waves, involving a side-to-side motion of molecules.
How are seismic surface waves similar to surface waves on water?
They cause rocks and soil to be displaced in such a way that the ground surface ripples or undulates.
What is the major cause of structural damage during an earthquake?
Surface waves.
What is the amount of ground motion related to?
The magnitude of the earthquake.
How is the richter magnitude number assigned?
It is assigned to an earthquake on the basis of the amount of ground displacement or shaking that it produces near the epicenter.
What are aftershocks?
They are earthquakes that are followed by, but weaker than, the original tremor.
What is liquefaction?
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.
How are tsunamis formed?
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.
Why do fires occur during earthquakes?
Fires occur because fuel lines, tanks and power lines are broken, touching off flames and fueling them.
What are seismic gaps?
Dormant sections of otherwise-active fault zones.
What is the precursor phenomena?
A method of surveilling seismic activity, focuses on things that happen or rock properties that change prior to an earthquake.
What are the 5 periods of the earthquake cycle?
Stress buildup, sudden fault rapture, brief intervals of aftershocks, minor lithospheric adjustments and another period of stress build up
What is the term slow-slip earthquake used for?
When temperatures are high enough (50 km deep!) and rocks are plastic enough to where the fault generally slides smoothly.
What is induced seismicity?
It is seismic activity caused by human activity.
