Transcript Earthquakes

Earthquakes
What they are
Where they occur
How fast they travel
How to locate their centers
Their strength
The Dynamic Crust – Earthquakes
• Definition- a shaking of the Earth’s crust caused by a
release of energy
• Question: What might happen to Hauppauge if a
major EQ hit?
• Effects of an earthquake on your neighborhood:
• buildings could collapse
• fires and explosions from broken electric and gas
lines
• contaminated water supplies from sewer lines
• emergency services overwhelmed or damaged
• roads and rails for outside help and supply
damaged
Causes of Earthquakes
• Can be small in strength
• An explosion
• Some manmade action – train tracks!
• Or large in strength
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• Volcano eruption
• Movement of plates
Elastic Rebound Theory
plates move along the plate boundary (a fault line)
friction may stop or deform the plate’s shape
pressure builds up as plates try to move
plate finally snaps back to normal shape and moves
to new location
Depth and Location of Earthquakes
• Depth of Earthquakes
• dependent on type of plate boundary
• most boundaries produce shallow quakes
- 30 km deep
• Many subduction zone quakes are deep
– up to 700 km deep
• This point below the surface where the plate
actually slips or snaps is called the FOCUS
• Epicenter – the point at the surface directly above
the focus
Detecting Earthquakes
• Seismometer
• a device used to detect earthquake waves
• horizontal form and vertical form
• seismograph – the recording of the earthquake’s
motions
• P-waves or primary waves
• compressional waves – like a slinky’s motion
• pass through every phase of matter
(solid/liquid/gas)
• FAST waves
• S-waves or secondary waves
• shear waves – move side to side like a snake
• only pass through solids like the inner core
• SLOW waves
Size of Earthquakes
• Charles Richter (1940’s)
• developed the Richter scale
• measures the total amount of energy released
• each magnitude from 1-7 is 32 times stronger
than previous magnitude
• A magnitude 6 earthquake is:
• 32x more powerful than a magnitude 5
• 1000x more powerful than a magnitude 4
• strongest recorded EQ
• Chile, 1960 – 8.3 on Richter scale
Highway Damage
Highway Damage
South America
Why you should not build on a
fault line
Alaskan Earthquake of 1964
Alaskan Earthquake of 1964
San Francisco Earthquake of
1908
Determining Distance to an Epicenter
• EARTHQUAKE RELATIONSHIP # 1
• P and S waves travel at specific speeds
• P – waves = faster
• S – waves = slower
• EARTHQUAKE RELATIONSHIP # 2
• the closer to the epicenter a seismograph is
• the shorter the time lag between P and S waves
• Look at ESRT on page 11
• The distance can be determined for any given EQ
• Example #1
• An earthquake’s P wave reaches Hauppauge at
8:00:00 am. Its S wave hits Hauppauge at 8:05:40
am. How far away was the earthquake in km?
Note 103 km = 1000 km
• Example #2
• Use the seismograph below. How far away is the
earthquake represented by the P and S waves?
9:00:00
9:03:00
9:01:00
9:02:00
• An earthquake occurs, and the P and S
waves are recorded at three seismometers
across the US
• Lets determine where the epicenter is
located….
Use the data from the recording stations:
• Station A: San Francisco, California
P-Wave arrival 3:02:20
S-Wave arrival 3:06:30
What is the time
difference
between P and
S wave arrivals?
Use the data from the recording stations:
• Station B: Denver, Colorado
P-Wave arrival 3:01:40
S-Wave arrival 3:05:00
What is the time
difference
between P and
S wave arrivals?
Use the data from the recording stations:
• Station C: Missoula, Montana
P-Wave arrival 3:01:00
S-Wave arrival 3:03:00
What is the time
difference
between P and
S wave arrivals?
TAKE A PIECE OF PAPER, AND MARK
OFF THE DIFFERENCE IN ARRIVAL TIME
4:10
2800Km
MOVE THE PAPER UNTIL THE TWO
TICK MARKS LINE UP WITH THE P
AND S CURVES
WHEN TICK MARKS LINE UP, GO
STRAIGHT DOWN AND READ THE
EPICENTER DISTANCE
EPICENTER DISTANCE
OF 2800 KM
EPICENTER DISTANCES
San Francisco: 4:10
2,800km
Denver, Colorado: 3:20
2,000km
Missoula, Montana 2:00
1100km
Recording Board
Difference in arrival times:
San Francisco: 41:0
2,800km
5,000
4,000
3,000
2,000
1,000
Open your compass to
the EXACT distance on
the scale.
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Determining Location
• Triangulation – a process of finding location
• Requires three seismic stations
• distance from three different stations used to find
the epicenter
Earthquake
Epicenter