Locating an Epicenter

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Locating an Epicenter

• Different waves, different speeds

Fastest
P-Waves - S-Waves - L-Waves - (surface waves)
Used to locate an earthquake
Slower
Slowest
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Measuring Seismic Waves

• 3 Instruments

1. Laser Geodimeter
2. Creep Meter
3. Seismograph
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1. Laser Geodimeter

• A measuring device using laser light to detect
  movement of the earths crust

1. Laser Geodimeter
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2. Creep meter

• - A device used to detect subtle movement through
  the use of a wire

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3. Seismograph-

• An instrument used to register earthquake waves
  and record the time that they arrive

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a. Seismogram-

• The lines traced on the recording tape during a
  quake

Height determines strength
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b. Seismologist-

• The person who studies earthquakes

BENO GUTENBERG was the foremost observational
seismologist of the twentieth century.
http//newton.nap.edu/html/biomems/bgutenberg.html
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Seismograph Stations

• -use wave speeds to locate epicenters

Quake Local lt100km Regional 100-1400km Teleseismic
gt 1400km
Triangulate to find epicenter
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Basic Structure of the Earth
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Basic Structure of the Earth
Crust outer layer -between 5km and 60km
thick -lots of Si Al little Fe Mg -less dense
than mantle
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Basic Structure of the Earth
Mantle Largest layer -lots of Si, O, Mg,
Fe -Upper and Lower mantle -Asthenosphere weak
rock that can flow slowly
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Basic Structure of the Earth
Outer Core Liquid Mostly Fe
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Basic Structure of the Earth
Inner Core Solid Mostly Fe
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Mapping Earths Internal Structure
The speeds and paths of seismic waves change as
they move through different materials
As DEPTH Increases, DENSITY Increases
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Shadow Zones-
Areas of the earth that DONT receive seismic
waves
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P-waves- slowed and bent by liquid outer
core -speed up in the inner core
S-waves- cannot travel through liquid -travel in
mantle only
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Layer Boundaries

• Mohorovicic Discontinuity (Moho)- Boundary
  between the crust and upper mantle

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People and Earthquakes

• Earthquake Activity

• Provide info. About the Earths interior
• -Cause BILLIONS of in damage
• (lost lives/destruction)

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Studying Earthquakes

• -Seismologists

• Use seismographs seismograms

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Measuring Earthquake Magnitude

• Magnitude-

Measure of the energy released during an
earthquake (shown on a seismogram)
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Richter Scale-
A measurement of the MAGNITUDE of an
earthquake by calculating the seismic ENERGY
released. (based on the height of the lines of
the seismogram)
-No upper limit (9.5) -Most quakes are too
low to be felt
55,000 3.0 - 4.9 1000s every day lt 3.0
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Describing Earthquake Intensity
Mercalli Scale-
A scale for measuring the seismic
intensity of an earthquake by rating THE EFFECTS
(amount of damage) at different sites
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Damage depends on

• Strength of quake
• Nature of surface material
• Design of structures
• Distance from epicenter

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Liquefaction-

• Occurs when wet soil acts more like a liquid
  during an earthquake
• May cause buildings to sink or collapse

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Tsunamis-
Seismic Seawave

• Begins over the earthquakes focus
• Can be highly destructive
• Can reach 30 meters high !!

(Pacific Tsunami Warning Center, Hilo Hawaii)
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Earthquake Safety
Cant predict but Knowing where quakes are
likely to happen helps us to prepare
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Quake Resistant Structures
Most loss of life is due to crumbling structures

• Reinforced walls with steal bars
• Flexible foundation supports
• (absorb shock)

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Before a Quake
-Move heavy objects to lower shelves -Learn how
to turn off gas/water/ electric - Secure hot
water heater and other major appliances
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During a Quake
Indoors-
Move away from glass and falling objects -get
under a sturdy door frame or table / desk
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During a Quake
Outdoors-
Stay away from power lines, buildings,
chimneys -get out in the open
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After a Quake
-Check gas/water/electricity for damage -shut
off valves -Leave building, call authorities -Be
careful, things could still fall