Download Earthquakes

Questions of the Day 2/28/2017
• What is the difference between the epicenter
of an earthquake and the focus of an
earthquake?
List processes involved in plate
tectonics
◻ Convection currents in the mantle (temperature and
density differences)
◻ Different densities of crustal plates – oceanic and
continental
◻ Composition and chemical properties of types of rocks –
magnetic, formation differences, % elements/ type
◻ Time- how fast the plates move: different plates rate of
speed, and different times rate of speed
◻ Magnetic fields – inside and outside of the earth structure
Types of plate boundaries
Plate tectonics is currently the most unifying
geophysical theory of the planet dynamics, based on the
interactions between the earth’s interior and its outer
shell.
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Lithosphere plates move, break up, collide, slide past one another to
form new continents and oceans.
Plate movement is a direct result of convection currents in the mantle
Plates interact in one of three ways: divergence, convergence, and
lateral sliding
Materials from plates are recycled at subduction zones/ mid ocean ridges
Global Distribution of
Earthquakes…why here?
Earthquakes and plate movement
What is the deepest recorded
earthquake on the border of
SA?
Explain how we know where the
mantle ends and the core
begins?
How do we know the elemental
make up in each layer?
Earthquake terms:
Earthquake - movement of the ground caused
by the release of energy from a sudden shift of
rocks in Earth's crust.
Fault - a break in Earth's
crust where movement
of rock (and quakes)
occur
Elastic rebound theory:
Earthquakes are produced by the rapid release
of energy stored in rock that has been
subjected to great forces. When the strength
of the rock is
exceeded, it
suddenly breaks,
releasing energy
as seismic waves.
More quake terms:
Focus - the point below Earth's surface where
movement of rock produces an earthquake;
where an earthquake starts
Epicenter - the point
on Earth's surface
directly above the
focus of an earthquake
Earthquake energy:
When tectonic plates move they sometimes
generate energy at their boundaries and that
shock wave is known as a seismic wave.
Seismometers (a.k.a. seismographs) are used to
measure seismic waves, but those waves are
not always detectable.
Seismographs
Seismogram = ?
The graph output by a seismograph. It is a
record of the ground motion at a measuring
station as a function of time.
Body Seismic wave types:
P waves: primary (first)
waves which are pushpull in nature
(compressional)
S waves: secondary
waves which shake
particles at right
angles to their
direction of travel
(transverse)
Two types
of waves
are
measured
How do each of the
waves travel
differently?
Explain why some
stations do not
receive S waves.
What are S and P waves?
•Seismographs – record movement and waves
❏ Surface waves – travel along the outer layers of the earth
❏ Body waves – travel through the earth’s interior
•P waves ( push pull waves) ( like a spring): can move through
solid rock or fluids. Fastest seismic wave.
P-wave Animation
•S waves travel at right angles ( like a rope): can only move
through solid rock. Slower than p-wave.
S-wave Animation
Earthquakes were 1st studied by the Chinese over 2000 yrs ago,
Hmm why would they be interested?
Surface seismic waves:
Travel along Earth’s outer layer, causing ground
movement similar to how ocean waves toss a ship.
x
How do scientists locate earthquakes? By measuring
the arrival time of P and S waves (whose velocities
are known) earthquakes can be triangulated.
Reading a Seismograph
Which are the P
waves and which
are the S waves?
Which type of wave
would arrive at a
location 1st?
What causes them to
arrive at different
times?
Which station did
was closer to
the Epicenter?
Which was
farthest away?
How do you know? (use
evidence to explain)
Seismographs
---- record S and P wave arrival at a specific station
how is this information useful to
determine the origin of the earthquake??
Consider the seismicity maps and the data we reviewed - if each
station has it’s own set of data, that means we could do what?
Rate of wave travel
-Why do S and P waves travel at different rates?
- How did the the ability to measure S and P
waves help us understand what is in the
center of the earth?
One of the other ways to report and measure
Earthquake information is the Mercalli scale.
Two different scales to measure
Mercalli scale - perception based
- 1884 became “modified” and again later
- quantifies effects of the earthquake and
damage caused using roman numerals
- Numbering from 1 - 12
- Human perspective/ reports of damage
Hogwallow to Rattlesburg
Use the reports from residents to identify the
strength of earthquake waves at each
location.
Where does the epicenter seem to be?
What was the highest rating reported?
What is your overall impression of use of this
scale? (pros and cons)