Earthquakes Flashcards
earthquakes
Sudden release of energy
Mostly due to tectonic forces
The amount of energy determines the MAGNITUDE of the earthquake
Seismic waves
Waves through the layers of the earth
Carry the energy away from point of origin
San francisco, 1906 what happened
April 18, 1906
5:12 am
Massive shaking
Lasts 45 – 60 seconds
Felt from southern Oregon to south of LA
Felt in central Nevada
Fire
Ruptured fire mains and broken water mains
Within three days, most of the city was burned
Casualties
~700 – 800 people died (maybe as many as 3000)
Most in San Francisco
225,000 people homeless
(more than 50% of population)
28,000 buildings destroyed
From fire, mostly
san fran 1906 significance for earthquake history
Marked the start of modern study of San Andreas fault system
1st time we Really started worrying about modern earthquake science in the United States
Japan and Europe were way ahead of us—why? they get a lot more earthquakes especially because it takes us a while to get to the west coast to settle
Theory of Elastic Rebound
Geologist at Johns Hopkins University
comes to west coast to study earthquake Studied the displacement of the ground
Ruptures occur when elastic limit is exceeded
“Locked” faults eventually reach the elastic limit
BREAK
Movement occurs and elastic energy is released
faults
Planar breaks in the crust
Fractures where displacement has occurred(both sides have moved)
Most faults are sloping at an angle (vertical faults are rare)
fault geometry
Two blocks are defined
Footwall: bottom (could walk on)
Hanging wall: top (could hang from)
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Imagine a horizontal tunnel cutting through a fault in cross-section
3 types of faults: normal
Normal Faults
Hanging wall moves DOWN relative to foot wall
Extensional(wrists move apart)
Creates mountains and valleys known as “horsts and grabens”
graben: down into grave (valley)(hanging wall!)
horsts: up onto a horse (mountain)(footwall!)
Reverse Faults
Strike-slip Faults
3 types of faults: reverse
Reverse Faults
Hanging wall moves UP relative to the foot wall
high angle
Compressional (wrists move together)
Low angle reverse faults are called “thrust” faults
Older rocks are thrust over younger ones
Shortens the landscape
Strike-slip Faults
Keystone Thrust
outside Las Vegas, Nevada
Willard Thrust Davis County, Utah
3 types of faults: strike/slip faults
Strike-slip Faults
Principle movement is horizontal
Little or no vertical movement
Shear stress
Left or right lateral
evidences: Abrupt changes in drainage patterns (river shapes)
seismic waves
Three types:
-Primary waves
P-waves
-Secondary waves
S-waves
-Surface waves
L-waves
R-waves
p waves
Fastest waves
Alternating compression and dilation (expansion)
Passes through solids, liquids, and gases
Produces temporary changes in volume and density of material
s waves
Second fastest
“Shear” waves
Waves are perpendicular to the direction of travel
Elastically change the shape of materials
Liquids and gases do NOT behave elastically
Therefore:
Passes ONLY through solids
surface waves
Travel along the Earth’s exterior
Slowest & most destructive
L-waves
Love waves
S-waves intersecting the ground
R-waves
Rayleigh waves
P-waves intersecting the ground
