Download Earthquakes

1989 Loma Prieta Earthquake
Investigating Earthquakes--San Francisco
What is an Earthquake?
o
Earthquakes: Vibrations (seismic waves) within Earth materials are
produced by the rapid release of energy
 Earth’s crust is in constant motion because of tectonic forces
 Earth’s crust can store elastic energy
 When forces exceed the elastic limits and structural strength of the rocks, the
rocks will break and/or move producing vibrations that travel outward in all
directions
Catastrophic Forces—Components & Causes of an Earthquake
Earthquakes
o
The actual place underground where the rocks break
producing vibrations is called the focus
o The place on the surface directly above the focus is
called the epicenter
What types of forces are created?
Tension Force:
 stretching or pulling force
 Makes a normal fault
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
What types of forces are created?
Compression Force:
 force pushing something together
 Makes a reverse fault
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
What types of forces are created?
Shear Force:
 a system of forces that operates against a
body from different sides
 Makes a strike-slip fault
http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
What causes Earthquakes?
 Movement along faults: occurs when the energy exceeds the
friction holding the sides of the fault together and is suddenly
released.
 Movement of magma (volcanic)
 Volcanic eruptions
Fault lines & EArthquakes
Seismic Waves
Originate at the focus and travel outward in all directions

Foreshocks: small earthquakes that come before a major
earthquake
Aftershocks: Are adjustments in the crust after in earthquake

o
Smaller than main earthquake, but can cause as much or more damage.
They can continue for weeks to months. Not every earthquake produces
aftershocks
Seismic Waves
3 Types of seismic Waves

P waves (primary waves) Compressional wave




Particles move back and forth in the same direction as the wave
Travels the fastest
Can pass through solids and liquids (gases also)
Does not cause damage
Types of Waves
 S wave (secondary wave, shear wave)




Particles move at right angles to the direction of the wave
Travels slower than P waves
Can pass through solids only
Does not cause damage
Types of Waves

L wave (long wave, surface wave, ground wave)




Particles move in elliptical orbit
Originates on the surface after the P and S waves
go straight up from the focus and reach the
surface
The L wave causes the damage and will be the
strongest at the epicenter
Travels the slowest
How do we Measure Earthquakes?
Earthquake waves are recorded by a seismograph and the
recording of waves on paper is called seismogram
How do we Measure Earthquakes?

Intensity – a measure of the effects on an earthquake at a
particular location

Magnitude: a measure of the strength or amount of energy
released during an earthquake
How do we Measure Earthquakes?

Richter Scale: Measures the amplitude of earthquake waves on seismograms

Scale from 1-10

Each number is 30
times the amplitude of the number below
Measuring Earthquakes

Locating the epicenter
1.
2.
3.

Lag time between the arrival of the P wave and the S wave to the seismograph station is
converted to a distance
A circle with a radius that equals the distance is drawn around the station.
Two stations can narrow down the location to two places where the two circles intersect
Locating the focus: the lag-time of the L wave will determine the
depth of the focus
Earthquake Dangers
o
Most injuries and deaths are caused by falling objects and
most property damage results from fires that start

Tsunami: seismic sea wave sometimes generated when an
earthquake originates on the ocean floor
Tsunami—December 2004
http://www.bedford.k12.ny.us:16080/flhs/science/images/tsunami2004/
Earthquake Dangers

Seiche: rhythmic sloshing of small bodies of water
A seiche is the sloshing of a closed body
of water from earthquake shaking.
Swimming pools often have seiches
during earthquakes.
Tsunami Clip—Discovery School
Tsunami by Brainpop
Earthquake Dangers

Liquefaction: unconsolidated materials that are water
saturated may turn to a fluid causing some underground
objects such as storage tanks to float to the surface
Ground fissures caused by liquefaction near the mouth of
the Pajaro River in California during the 1989 Loma Prieta
earthquake. When the surface of the ground oscillates,
wet, sandy, and muddy soils can flow like a liquid. This is
liquefaction. You can liquefy wet sand at the beach by
pumping it up and down with your feet. Photo courtesy of
the Loma Prieta Collection, Earthquake Engineering
Research Center, UC Berkeley.
Earthquake Dangers
How Does Plate Movement Generate Earthquakes?
Earthquake Dangers

Landslides
Earthquake Safety




Protect yourself from falling objects (GET UNDER SOMETHING) or
stand in a hallway or doorway (watch out for a swinging door)
Do not try to go outside during the earthquake
After the earthquake and before the aftershocks, go outside
Do not return to the building until it has been inspected
Protecting Structures
How structures react to earthquakes
Seismology: The Science of Predicting Earthquakes
Alaska Earthquake
Great Quakes
Earthquakes & Sky scrapers
Earthquakes by Brainpop