Earthquake Basics Presentation

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Earthquake Basics
Robert Butler
ANGLE Project
https://serc.carleton.edu/ANGLE

Stick-slip: Elastic Rebound Theory
Jerky motions on faults produce EQs
Three Fs of earthquakes: forces, faults, and fricti...

Three Basic Types of Plate Boundaries
Transform (e.g. San Andreas Fault)
Strike-slip faulting
Magnitudes generally < 7

Three Basic Types of Plate Boundaries
Divergent (e.g. spreading ocean ridge)
Normal faulting Magnitudes < 6

Three Basic Types of Plate Boundaries
Convergent (e.g. subduction zone)
Magnitudes up to 9 or larger
Depths to 700 km

Hypocenter or Focus: Point WITHIN
Earth where EQ occurred.
Epicenter: Location on Earth’s
surface directly ABOVE the EQ.

Body waves
(P and S) travel
inside Earth.
Surface waves
travel along
Earth’s surface.
Body Waves and Surface Waves
While P...

P Waves Are Pressure Waves
P waves are fastest seismic waves.

S Waves Are Shear Waves
S waves are slower than P waves
but faster than surface waves.

Amplitude greatest at surface,
decreasing with depth.
Slower than P or S waves.
Often are largest amplitude and
most damag...

Human Waves
Modeling P, S, and Surface Waves
Seismic Slinky
Human Waves

A seismograph detects
and records earthquakes.
A seismogram is the
earthquake record.
How do scientists detect earthquakes...

University of Portland AS-1 Seismometer
M7.7 Earthquake off Northern Chile Nov 14, 2007
P waves
~12 min
~720 sec
S waves
~...

Seismic Waves from Chile Earthquake
USArray
Animations
QuickTime
Animation

Seismic waves crossing the
US recorded by the USArray.

Seismic waves crossing the
US recorded by the USArray.

Distance of earthquake from seismometer?
Determined from S arrival time - P arrival time.
4 min 45 sec
3300 km

Locating an Earthquake
1) Determine distance of EQ from
three seismic stations by
calculating the S minus P arrival
times....

Moment Magnitude Pasta Quake
QuickTime Animation

Magnitudes and Energies of Earthquakes
MOST of the energy is released by ~20 magnitude-7
and larger earthquakes every year.

Earthquake Intensity
Violence and Effects of Ground Shaking.
QuickTime Animation

Effects of Near-Surface Geology
Amplitude of oscillation increasing

Ground-Shaking Amplification
Seismic waves are amplified as they pass from
bedrock into basins filled with sedimentary roc...

Liquefaction
What happens to a structure built on a weak
foundation when an earthquake strikes?
Liquefaction
Niigata, Japa...

Duration of Ground Shaking
• Long duration can drive oscillation of large structures.
• Long (bridges) and tall (high-rise...

Seismic Landslides in Anchorage, 1964
Government Hill Elementary SchoolFourth Avenue near C Street

Seismic Landslides in Anchorage, 1964
Block diagram of translational landslide.

Seismic Landslide Hazard Map
Earthquake Hazard Maps

“Earthquakes don’t kill people ……. buildings that
collapse during earthquake ground shaking kill people.”
Build a Better W...

Cripple wall failure
Cripple
Wall
Failure
A common problem
for older wood-
frame houses.

Nonstructural Damage
Objects falling are common ”nonstructural” risks.
Many are very easy to secure.

Nonstructural Damage
Wood stoves
Fuel tanks
Fire is very common result of ground shaking.

Building Resonance
Oscillating blocks experiment
BOSS Model

Great Alaska ShakeOut 10:18 AM October 18, 2018

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