EOSC 114 Chapter Notes -Seismometer, Cascadia Subduction Zone, Love Wave

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31 Jan 2013
EOSC 114: Earthquakes Learning Goals
1. Describe the global distribution of
earthquakes and how often quakes of various
magnitudes occur
- globally, earthquakes located mostly on
tectonic plate boundaries
- higher frequency = lower magnitude; higher
magnitude = lower frequency
2. Understand the different types of faulting at
different plate boundaries, and which plate
boundaries produce the largest quakes
Plate boundaries+ Faults:
1. Divergent: Plates move apart at mid-ocean
ridges & spreading centressmall
earthquakes normal dip-slip faults
2. Transform: Plates slide beside each other
(shearing) many medium-large
earthquakes strike-slip faults
3. Convergent Type 1: Plates collide, causing
compression. One plate is more dense and
subducts under other small to largest
earthquakes (at subduction zone) reverse
dip-slip faults
4. Convergent Type 2: Plates collide, causing
compression. Neither subducts so crumple,
form mountains small to large
earthquakes reverse dip-slip faults
3. Describe how the Earth builds, stores, and
releases energy in earthquakes (elastic
Constant movement of tectonic plates over
many years builds pressure, storing PE.
Increased stress breaking, so too much
stress causes a slip, releasing energy in an
elastic form (reverting to original form)
4. Understand concepts of (1) stress causing
strain and (2) plastic versus brittle deformation
1. Stress is force/unit area, while strain is how
material changes shape from stress.
ie.strain is change in shape due to stress
2. Plastic deformation is permanent change,
ie. hammering gold sheets. Brittle is breakage,
does not hold plastic shape well, ie.
hammering glass plate
5. Describe how the rupture propagates from
the focus and why shaking and damage are
not necessarily greatest at the epicenter
6. Describe the different types of seismic
waves and how they move through the Earth
1. Body Waves: travel in earth (faster than
surface waves) in curved pathways (refracted
due to earth layers)
a) P-wave (primary) particles move back &
forth in direction wave is travelling (ex. slinky)
b) S-wave (secondary) particles move
vertically perpendicular to direction wave is
travelling (ex. up&down snake); can’t travel
through liquids/water
2. Surface Waves: travel on surface of earth
(slower, more damaging than body waves)
a) Rayleigh Waveslargest, most damaging;
particles rotate backwards, counter clockwise
(like ocean)
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