Transcript Earthquakes - staffordscience



What is it about earthquakes that make them so devastating?
Tell me what you already know about earthquakes.
 Each
year, more than 30,000 earthquakes
occur worldwide that are strong enough
to be felt.
 Only about 75 major earthquakes take
place each year and often occur in
remote regions
 Essential Question: How do we locate
an earthquake’s epicenter?
Unit 7
 Vibration
of Earth produced by a sudden
release of energy
 Associated with movements along faults
 Earthquakes
can be explained by this
theory
 The mechanism for an earthquake was
first explained in the early 1900’s by H.
Reid
 Rocks “spring
back” in a process called
elastic rebound
 Vibrations occur as rock elastically
returns to its original shape
 The earthquake itself is often preceded
by foreshocks and followed by
aftershocks
 What
do you think this is the study of?
• Earthquake waves
 The
instrument used to record the
movements of the earth is called a
seismograph
 The record that is produced is called a
seismogram
 1. Surface Waves: L
• Complex motion
• Slowest velocity
 2. Body
waves
• Two types:
 Primary & Secondary
waves
 Push-pull
motion: compressional wave
 Travel through solids, liquids, and gases
 Greatest velocity of all earthquakes
 Shake
motion
 Travels only through solids
 Slower than P waves
 Focus: the
place
within the Earth
where the
earthquake waves
originate
 Epicenter: the point
on the surface,
directly above the
focus
 Located
using the difference in the
arrival times b/w P and S wave
recordings, which are related to distance
 Do you know what it means to
triangulate a cell phone call?
 It’s the same idea
 In order to locate an earthquake 3 station
recordings are needed
A
circle equal to the epicenter distance is
drawn around each station.
 The point where the circles intersect is
the epicenter.
1.
2.
3.
How long would it take P waves moving
at 6.1 km/s to travel 100 km? How long
would it take P waves to travel 200 km?
S waves move at 4.1 km/s. 100 km? 200
km?
What is the time lag between the arrival
of P waves and S waves over a distance
of 100 km? 200?
1.
P waves:
• 100 km = 16.4 s
• 200 km = 32.8 s
2.
S waves:
• 100 km = 24.4 s
• 200 km = 48.8 s
3.
Lag time
• 100 km = 8 s
• 200 km = 16 s
 Mercalli
intensity scale
• Assesses damage at a specific location
• Depends on:
1. Strength of earthquake
2. Distance from epicenter
3. Nature of surface material
4. Building design
 Concept
introduced by Charles Richter
in 1935
 Measured on the Richter Scale
 Depends on the amplitude of the largest
wave recorded
 Each unit of magnitude increase
corresponds to a 10-fold increase in
amplitude and a 30-fold increase in
energy
 Largest
earthquakes are near a
magnitude of 8.6
 Magnitudes below 2.0 are usually not felt
 Factors that determine
• Magnitude of earthquake
• Proximity to population
destruction:
 Destruction is caused by:
• Ground shaking
• Liquefaction of the ground
• Tsunamis
• Landslides
• Fires
 There
is no reliable method for shortrange prediction
 Long-range: we can predict approximate
locations based upon previous tectonic
activity
 Research
major earthquake activity along
the San Andreas Fault over the past five
years. Write a report on your findings.
 Or
 Research a major a earthquake in Earth’s
history and write a report on your
findings.
1.
2.
3.
4.
What are some differences between
Primary (P) and Secondary (S) waves?
How do scientists pinpoint the location
of an epicenter?
Name 3 types of destruction either
caused or associated with earthquakes.
What is the focus of an earthquake?
 What
does an engineer or architect need
to think about when design a home in a
location prone to earthquakes?
 What are some ideas you have heard of
or researched that have been
implemented and successful?
 Simply
use the materials available to you
and construct a house.
 Groups of 4 or 5
• Teamwork is expected
 You
will have about 25 – 30 minutes to
build your house.
 Must be on cardboard.
 The
deepest well drilled is only 12 km
into Earth’s crust. With limited access,
how do we know what Earth’s interior is
like?
 Most
of what we know about the interior
of the Earth comes from the study of P
and S waves
 Thin
outer layer
 Varies in thickness: 5km – 70km
 Two types:
• Continental Crust: lighter granitic rock
• Oceanic Crust: basaltic composition
 Made
up of the crust and uppermost
mantle
 ~100km thick
 Cool, rigid, solid
 Thin
layer that separates the crust from
the mantle
 2885
km thick
 Composed mostly of igneous rock
 Asthenosphere
 Upper mantle
 Lower mantle
 Weak
layer below the
lithosphere in the upper
portion of the mantle
 Temperatures and
pressures reach near
melting point conditions
for rocks
 More
rigid than
asthenosphere
 Very hot
 Rocks still have the
ability to flow
 Below
mantle
 2270 km thick
 Mobile liquid
 Does not transmit S waves
 Mainly iron and nickel
 Related to Earth’s magnetic field
 1216
km radius
 Solid
 Iron
and nickel composition
 High density
 Describe
how the three different types of
seismic waves move and affect the
movement of the material they pass over
or through
 You will most likely see this on your
test…
 On
a white sheet of paper, you will draw
or construct a cross-section of Earth
exposing the different layers.
 You will need to label the layers and
include:
• How thick
• Composition
• 1 other fact
• Needs to be colored