Chapter 05: Earthquakes (Ch 11) Flashcards
Earthquakes
Ground shaking caused by sudden movement of rock sliding past rock
Most occur near pre-existing faults
Faults
Fractures in the Earth’s crust; when active, slippage of the rocks located along faults causes earthquakes
Hypocenter/focus
Subsurface origin of earthquake
Epicenter
Surface location directly above hypocenter/focus
Causes of weak earthquakes (5)
Landslides
Meteorites
Dams
Deep well injection (waste injection, fracking)
Volcanic eruptions
Cause of strong earthquakes
Stress builds up from plate movement
Eventually, stress overcomes frictional resistance
Movement occurs as rocks break
Elastic rebound
The “snapping back” of the rock
Foreshocks and aftershocks
“Minor” earthquakes that occur before and after major earthquake
Rocks are either preparing to break or adjusting after breaking
Both can occur for years
San Andreas Fault System
North American & Pacific plate boundary (transform/strike-slip)
Big earthquake every ~100 years
P waves (primary waves)
Type of body wave
The first wave of vibrations felt
Travels faster than S waves
Travel through solids, liquids, and gases
Motion: slinky-like (lateral wave movement)
S waves (secondary waves)
Type of body wave
Felt after P waves (move slower than P waves)
Greater amplitude than P waves
Complex/slow motion (think: rope being shaken; up-down movement)
Surface waves
Last to arrive (after P and S waves)
These cause the most property damage
Liquefaction
Saturated or partially saturated soil substantially loses strength/stiffness in response to stress/vibrations, causing it to behave like a liquid
Tsunami
Caused by earthquake, submarine landslide, or other disturbance
New Madrid seismic zone
Middle of North American plate (Missouri, Arkansas, Kentucky, Tennessee)
Anomolous because in the middle of a plate
Two possibilities: plate getting ready to split apart, or aftershocks from Pangaea forming
