Earthquakes Flashcards
What causes earthquakes (2)
- Hypocenter
2. Epicenter
Hypocenter
the place where fault slip occurs
Epicenter
land surface right above the hypocenter
Displacement
the amount of movement across a fault
also called “offset”
cumulative over time
Fault trace
where the fault reaches the ground surface
not all faults reach the surface
Elastic strain
ability of rock to bend without breaking
Fault
built up elastic strain is released in a cracking event
Asperities
bumps across a surface leading to increased friction
Stick
friction prevents movement
Slip
friction is briefly overwhelmed by motion
InSAR
Interferometric Synthetic Aperture Radar
compares ground elevation changes over time.
display distortion as color bands
Major earthquakes may have the following (2)
- foreshocks
2. aftershocks
Body waves (2)
P and S waves
P-waves
Primary waves
Travel in earth interior
compress and extend material (slinky)
Travel in solid, liquid, gas
S-waves
Secondary waves
travel in earth interior
back and forth movement
travel in solid only
Types of seismic waves (2)
- L-waves
2. R-waves
L-waves
Love’s waves (surface waves)
most destructive
surface waves
back and forth movement (snake)
R-waves
Reilay waves (surface waves) move up and down die out with depth
Seismographs
instuments that detect ground motion
measure wave motion and magnitude
vertical motion
horizontal motion
Seismogram
data recoding on the piece of paper
P first, S second, surface last
Finding the epicenter (3)
- need 3 or more stations to triangulate
- P and S waves come in
- P waves come in first, S-second
- difference between the two show you epicenter distance
Earthquake size depends on (2)
- Magnitude
2. Intensity
Magnitude
maximum amplitude of seismograph motion
Ricter scale
good when close to epicenter
Moment scale
most accurate measure
M3 vs M7 earthquakes
earthquakes are logarithmic
M3: 100,000 per year
M7: 32 per year
intermediate and deep earthquakes
intermediate: 20-300km
Deep: 300-660 Km
San Andreas
Stike-slip Transform fault
hundreds of earthquakes per year
Order of wave arrival (4)
- P-waves
- S-waves
- L-waves - Snake
- R-waves - up/down
Wind waves:
influence upper 100m wavelength: 10s-100s (meters)* related to windspeed 10s Km per hour break in shallow water
Tsunami waves:
entire water depth wavelength: 10s - 100s Km* uneffected by wind speed 100s Km per hour arrived as raised plateau
