Transcript Slide 1 - Blue Valley Schools

EARTHQUAKES
Due Dates:
Test: Friday Nov. 18
Assgn. Packet: Friday Nov. 18
Did You Know?
Over 30,000 earthquakes occur around the
world every year that can be felt.
About 75 major earthquake occur each year.
Earthquakes
sudden movements in Earth’s crust
caused by releases of energy
Anatomy of an Earthquake
Fault – crack in
surface where
movement can occur.
Site of most EQ’s
Focus – where EQ
originates within the
crust. Depth 0-400 miles
Epicenter – surface
location of EQ.
Directly above focus.
Seismic Waves –
energy waves produced
by failure along a fault.
Anatomy of an Earthquake
Shallower the focus,
greater its felt at the
surface
Where do you think
the damage from an
EQ is usually the
greatest?
Cause of Earthquakes
Elastic Rebound Hypothesis - the latest hypothesis for the cause of earthquakes.
A fault exists
Rocks layers deform
under slow steady stress.
Rock layers bend storing elastic
energy.
Stress exceeds strength of rock,
rupture occurs in rock.
Movement occurs along fault.
Energy released.
Forces start again to put
strain on rock layers.
Elastic Rebound
Hypothesis
Explains
Foreshocks Small releases of energy
(Smaller EQ’s) may
precede major failure.
AND
Aftershocks Follow the major failure.
Deadliest EQ’s
Haiti
Nova PBS video series
MEASURING EARTHQUAKES
EQ’s produce energy (seismic waves)
Travel in all directions from their source
Travel throughout Earth’s interior & surface
The instrument that receives
the signal of an EQ is called a
seismograph.
The strip of paper that records
the motion is called a seismogram
Map of World Seismograph Stations
Seismogram for Dec. 26, 2004 9.0 EQ off coast of Indonesia
Types of Seismic Waves
2 Categories: Surface Waves & Body Waves
Surface Waves




Travel along ground surface
Originate at epicenter
Most destructive type of wave
Complex motion (vertical,
lateral, circular)
Body Waves
 Travel thru Earth’s interior
 Originate at Focus
 2 Main Types: P-waves & S-Waves
1. P-waves (Primary Wave)
• Fastest kind of wave
• Travels through all types of earth material rock, liquids, etc)
• Travels in a forward-backward motion in the direction of travel
2. Shear (S)-waves
• Slower than P-waves
• Cannot travel through liquids (such as Earth’s outer core )
• Travels in an wave-like (up and down) motion perpendicular to the direction
of travel.
ASSIGNMENT
WORK IN ASSIGNMENT PACKET
 1-3 on p. 2
 1-5 on p. 3&4
 Turn in Plate Tectonics Assgn. Packet & any
Opt. HW for Plate Tectonics.
Locating The Epicenter of An Earthquake
 EQ location is by a process
called triangulation. At least 3
stations required.
 Based on difference in speed of
p-wave and s-wave.
 Arrive separately at
seismograph
 Greater the difference in
recorded arrival times, further
the epicenter location
Example 1
EQ occurs at 1:00 pm.
Your seismograph location is 1500
miles away from the epicenter.
At what time will you receive the
p-wave?
At what time will you receive the
s-wave?
How many minutes apart?
Example 2 (This is what
really occurs)
The p-wave and s-wave arrive at
your seismograph 1.5 min apart.
How far away is the epicenter?
Why Does It Take 3 Seismograph Stations?
1 seismogram can only state how far away the epicenter is from
that seismograph location.
The distance represents the
radius of a circle.
1500
It does not give direction.
However, the combined distances from at least 3 distant seismograph stations
will give exact location.
EARTH SPACE TODAY
 Finish EQ Notes
 Work in Assgn. Packet
Tomorrow
 Finish EQ Location Lab
 Begin Volcanoes
 TEST ON EQ & VOLCANOES NEXT
WEEK. PROBABLY THUR.
Where Do Most EQ’s Occur?
Data from seismographs indicate EQ’s are not random.
95% of major EQ’s occur within a few regions. (See map on front page of packet)
1. Pacific Rim
Outer edges of Pacific Ocean. Includes 80% of EQ’s
2. Mediterannean-Asian Belt
Other Moderate earthquake hazards in the
U.S.
Yellowstone Area
New England Area
New Madrid Area
Charleston, SC Area
Measuring the strength of an Earthquake
2 Different Methods: Magnitude & Intensity
Magnitude
Measure the amount of energy released at the source of the earthquake
Determined from amount of displacement that occurred along the fault.
Currently called the Moment Magnitude
Replaces older Richter Scale
Does not express building damage
Unitless number. No upper limit
Each unit increase = 10 1.5 (or 32) X more energy released
Example:
5.0 magnitude EQ releases 32 (10 1.5 ) X more energy
than 4.0
6.0 magnitude EQ releases 32 X 32 (10 3.0 ) more
energy than 4.0
7.0 magnitude EQ releases 32X32 X 32 (10 4.5 ) more
energy than 4.0
2 Major EQ’s:
Haiti, January 12, 2010, M7.0 Fatalities: over 300,000
Japan, March 11, M9.0 Fatalities: over 20,000
How much stronger was the Japan EQ?
DESTRUCTION FROM EARTHQUAKES
1. Building Damage . Factors that affect building damage
• Building design – were they designed to withstand EQ’s?
• Building materials – How were buildings constructed
• Reinforced concrete – best
• Unreinforced cinderblock, brick, stone – worst
• Wood frame – good. Wood will flex
• Geology of the surface - was the structure built on loose sediment or
solid rock?
• Loose sediment – liquefaction – ground turns to “quicksand” due to
shaking
•
Distance from epicentercloser to the epicenter, the greater the damage that often occurs.
Turkey Earthquake: Aug. 8, 1999
Surface Wave Magnitude: 7.8
Reasons for Building
Body Wave Magnitude: 6.3
Collapse
Duration Magnitude: 6.7
Poor concrete quality
Poor detailing of the
reinforcement
Weak/soft story
Structural alterations
(added floor)
Long cantilevers with
heavy load
Improper construction
site
2. Fire
How does this happen?
Breakage of Natural Gas lines, Power lines, Fuel pipelines, Fuel storage
tanks
Water lines break – can’t fight fires if they do get started
1906 San Francisco Earthquake
Aftermath due to fire.
3. Tsunami - sea wave generated by a major disturbance of the seafloor
and overlying water.
The most common cause of major tsunamis is the vertical displacement of
the seafloor along faults.
Major Tsunamis
December 26, 2004
9.0 EQ in Indonesia
Fatalities: over 280,000
1883 Krakatoa
Volcanic eruption
Fatalities: over 10,000
March 12, 2011
9.0 EQ in Japan
Fatalities: over 20,000
One of the most severely affected areas was that closest to the epicenter, the province of Aceh on
Sumatra, Indonesia. More than 130,000 people died and 36, 786 were still missing
4. Landslides
Boater fleeing a
landslide due to a
earthquake in
China
7.6-magnitude earthquake rocked El Salvador in
January 2001, this hillside above a suburban
neighborhood gave way. The landslide buried
hundreds of homes and accounted for over half of
the nearly 700 earthquake victims.
5. Liquefaction– the process by which sediment is converted to a
flowing sediment & water mass due to the movement of water
upward through the sediment.
EARTHQUAKES AND EARTH’S LAYERED STRUCTURE
Earth’s layered structure was developed from seismic records from earthquakes.
Seismic waves change speed and direction when encountering material of
different density and chemical composition
Layers Defined by Composition: Crust, Mantle, Core
Crust: Continental Crust & Oceanic Crust
Continental crust
5-50 miles thick
Many rock types. Avg. rock type is granitic
Density: 2.7 g/cm3
Older rocks. Up to 3.5 billion yrs old
Oceanic crust
~ 4 miles thick
Composed of denser basalt & gabbro
Avg. density: 3.0 g/cm3
Younger (less than 200 million yrs)
Layers Defined by Composition
Mantle
Almost 2900 km (1800 miles) thick
Rock type: periodotite
(like gabbro but more dense)
Density: 3.4 g/cm3
Core
Thickness: ~ 3500 km (2200 miles)
Iron-Nickel
Density: 13 g/cm3
Layers Defined by Physical Properties
Lithosphere, Asthenosphere, Lower Mantle, Outer Core, Inner Core
Lithosphere
Crust & Upper Mantle
Rigid Layer
~ 60 miles thick
Asthenosphere
Soft, weak layer
At or Near melting pt.
Easily deformed
Layers Defined by Physical Properties
Lithosphere, Asthenosphere, Lower Mantle, Outer Core, Inner Core
Lower Mantle
Depth: ~350 miles
More rigid than Asthenosphere
Very hot
Outer Core
1500 miles thick
Liquid
Generates magnetic field
Inner Core
750 miles thick
Greater pressure keeps it solid
Hotter than outer core