Earthquake

2. How Earthquakes work
Investigating Earthquakes--San Francisco

3. o EarthquakesEarthquakes: 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
What is an Earthquake?

5. o The actual place underground where
the rocks break producing vibrations is
called the focusfocus
o The place on the surface directly
above the focus is called the epicenterepicenter
Earthquakes

7. Tension ForceTension Force:
 stretching or pulling force
 Makes a normalnormal fault
What types ofWhat types of forcesforces are
created?

9. Compression ForceCompression Force:
 force pushingpushing something togethertogether
 Makes a reversereverse fault
What types ofWhat types of forcesforces are
created?

12. Shear ForceShear Force:
 a system of forces that
operates against a body from
different sides
 Makes a strike-slipstrike-slip fault
What types ofWhat types of forcesforces are
created?

14.  Movement along faults: occurs when the
energy exceeds the friction holding the sides of
the fault together and is suddenly releasedreleased.
 Movement of magma (volcanic)
 Volcanic eruptions
What causes Earthquakes?

16. Originate at the focus and travel outward in all
directions
 ForeshocksForeshocks: small earthquakes that come
before a major earthquake
 AftershocksAftershocks: 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
weeksweeks to monthsmonths. Not every earthquake
Seismic Waves

17. Seismic Waves

18.  P wavesP 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
3 Types of seismic
Waves

19.  S waveS 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

20.  L waveL 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
Types of Waves

22. How do we Measure
Earthquakes?
Earthquake waves are recorded by
a seismograph and the recording
of waves on paper is called
seismogram

23. How do we Measure
Earthquakes?
 IntensityIntensity – a measure of the
effects on an earthquake at a
particular location
 MagnitudeMagnitude: a measure of the
strength or amount of energy
released during an earthquake

24.  Richter ScaleRichter Scale: Measures the amplitude of
earthquake waves on seismograms
 Scale from 1-10
 Each number is 10 times the amplitude of
the number below
How do we Measure
Earthquakes?

27.  Locating the epicenterLocating the epicenter
1. Lag time between the arrival of the P waveP wave
and the S waveand the S wave to the seismograph station is
converted to a distance
2. A circle with a radius that equals the
distance is drawn around the station.
3. Two stations can narrow down the location to
two places where the two circles intersect.
 Locating the focusLocating the focus: the lag-time of
Measuring Earthquakes

29. Earthquake Dangers
o Most injuries and deaths are
caused by falling objects and
most property damage results
from fires that start.
 TsunamiTsunami: seismic sea wave
sometimes generated when an

31. Tsunami December 2004—

32. Earthquake Dangers
 SeicheSeiche: 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.

33.  LiquefactionLiquefaction: unconsolidated
materials that are water saturated
may turn to a fluid causing some
underground objects such as
storage tanks to float to the surface
Earthquake Dangers
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.

34.  LandslidesLandslides
Earthquake Dangers

35. 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