Download S Ch 4 Earthquakes and Volcanoes NOTES

Name____________________________
NOTES CH 4 EARTHQUAKES AND VOLCANOES
Date__________
Earthquakes, ________________ and mountain ranges tend to happen in
similar areas.
The map above shows frequent earthquake activity as the bands of dots.
Most of the world's active volcanoes (triangles) are along the edges of tectonic plates (the lines).
Types of Plate Boundaries
A) Convergent- plates __________________ into each other.
1) Where an oceanic and a continental plate collide, the ____________
oceanic plate will be forced under (subduction) the other.
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B) Divergent- _______________ spread apart
1) Caused by _____________ upwelling from deep in the Earth
2) Usually found in the oceans along with ____________________
ridges
C) Transform- two _______________ slide past each other.
This picture (LEFT) shows the San Andreas Fault in California, which is a transform fault.
The aerial view (RIGHT) of the San Andreas Fault (transform) the trees in the orchard (dots)
have been offset by the slipping of the plates. The Pacific Plate is to the left and the North
American to the right.
D) Hot Spots - plumes of hot material in the ________________ of plates.
1) Spots stay __________________ while the plate moves above it.
2) Spot ________________ through the plate like a blowtorch and
produces a volcano above it.
3) As the plate moves, the spot melts through another spot producing a
____________________ of volcanic islands.
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4) Hawaii is an example of a hot spot island chain.
How Plates Move
A) Convection currents - causes ___________________ of the plates
deep within the Earth’s mantle.
1) Hotter Mantle material rises while _____________ material sinks.
2) The _________________ is split and diverges where the material
rises and spreads out.
3) The plates converge and __________ where the material is sinking.
B) The different types of plate boundaries are caused by a combination of the
direction of convection as well as they type of crust: continental or oceanic.
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Evidence of Continental Drift- Presented by scientist Alfred Wegner
A) Fossil Evidence- fossils of many land-living creatures have been found
on opposite shores.
1) The super-continent, _______________ formed 350 million
years ago during the Devonian and Carboniferous period, where
continents match up like puzzle pieces.
B) Coal in Antarctica- coal is formed in _________________ swamps,
from the remains of vegetation that grew as long as 400 million years ago.
1) Coal has been found in Antarctica, which means it used to be closer to
the _____________________.
B) Magnetic Strips- While lava is liquid, the bits of _______________
will tend to line up with a magnetic orientation pointing at the North Pole.
When the lava solidifies, the magnetic orientation is frozen into the rockessentially; it will have a “north end” and a “south end on the ocean floor.
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C) Mountain Chains appear at the __________________ of continents
where continents should have collided in the past.
That’s how the Himalayas were
Formed!!
D) Glacial Evidence- Ice sheets from a single glacier that effected southern
continents. When viewed on the current continents, it is inconsistent and
even highly improbable. For example, India, which is north or the
Equator, has glacial evidence coming from the south!
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Earthquakes
A) An event where two pieces of ______________ shift against each other.
1) The rumbling felt is from the ____________ slipping, sticking and
breaking.
2) The vibrations are called _______________ waves. There are
different types of seismic waves that vibrate in different ways.
a)
The ________________ is the spot within the earth
where the earthquake began.
b)
The ___________________ is the spot on Earth's
surface closest to the focus.
c)
A ___________ is a crack along which the rocks slide.
P-Waves
A) Primary wave- travels “phastest” so it arrives at _____________ stations
“phirst."
1) Push-pull wave: rock vibrates forward and backward in the same
direction that the wave travels ("parallel to propagation").
2) Pass through solids and liquids (magma).
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S-Waves
A) Secondary wave- arrives at a seismic station __________________.
1) Slow wave- not as fast as the P-wave.
2) Shake wave (shear wave)- vibrates side-to-side.
3) Solids wave- only travels through solids.
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Time Math
In order to do the calculations that help find the distance to epicenter and the
time of the earthquake, you’ll need to do math with time. It is difficult to do time
math in a calculator, and by hand it does not work exactly the same way as
regular math. Regular math is what they call “base 10” which means that
whenever you count past 9 you must move over one place to the tens column.
Time is base 60. You can count 59 seconds and then you go to the minute’s
column.
Time math works by taking over ten from the neighboring column you’ll take one
minute and convert it into 60 seconds.
3:13:25 (“3 hours, 13 minutes, and 25 seconds”)
-1:09:37
turns into:
3:12:85 (3 hrs,12 min, 85 secs is the same as 13:25)
-1:09:37
2:03:48
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How to Use the P-Wave and S-Wave Travel Time Chart
P-Wave & S-Wave Chart on pg 11 in the Handy Dandy ESRT
The P-line shows how much time it take a P-wave to travel a certain distance. So
if you need to know how much time it takes the p-wave to travel 2,000km, it is
just over 4 minutes (about 4:05). The S-wave works the same way: for 2,000km it
takes 7:20.
To find the distance to epicenter:
You are in charge of watching the seismic station tonight when the seismograph
detects an earthquake. The earthquake didn’t happen where you are- you can’t
even feel it. As a result, you don’t know what distance or direction the earthquake
happened. The P-wave and S-wave are separated by 4:05 (4 minutes, 5 seconds).
You need to find a spot on the graph where the P-line and the S-line are
separated by 4:05.
1) Take a scrap piece of paper; line it up along the left edge of the chart.
2) Put a small tick mark on your scrap paper at zero, and a small tick
mark at 4:05.
3) Slide the scrap paper up along the chart until it the two tick marks just
touch the P and S lines. BE SURE THAT YOUR SCRAP PAPER IS
PERFECTLY STRAIGHT UP AND DOWN (use the lines on the grid as
a guide).
4) Now that you have found the right spot on the graph, drop a line
straight down to the bottom of the graph to read the distance2,600km.
To Find The Time That The Earthquake Occurred
When a seismograph detects an earthquake that happened at some distance,
(2,600km for example) you know that the earthquake happened some time in the
past and it took time for the waves to reach your station. But how long ago? All
you need to do is answer the question “how long does it take a P-wave to travel
2,600km?
1) Find 2,600km on the bottom of the chart.
2) Go straight up until you reach the P-line and read the time from the left
of the chart: 5:00 (5 minutes).
3) Now compare times: if you detected the earthquake at 3:17:00 and it
took 5:00 then the earthquake happened 5 minutes before 3:17:00 or
3:12:00.
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Earthquake Strength
The intensity or strength of an earthquake is measured in two main ways:
The Richter Scale
A) Measures the amount of _____________ that an earthquake releases
1) Each number of magnitudes is __x stronger than the number below it.
The Mercalli Scale
A) Measures the amount of _______________ from an earthquake
1) Ranges from I to XII
2) Based on common earthquake occurrences such as "noticeable by
people" "damage to buildings" chimneys collapse" "fissures open in the
ground”.
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Seismic waves as “x-rays”
1) P-Waves travel through solid and liquid
2) S-Waves travel only through ________________
3) Seismic waves travel faster through ________________ material.
4) Because of this, the path traveled by a seismic wave is bent towards the
surface.
Properties of the material (such as density and pressure) that the waves pass
through can be inferred by the speed and angle that the waves travel.
The layers of the earth are determined by the jumps in velocity and “echoes” of
seismic waves.
The MOHO is a boundary between the crust and the upper mantle where the
velocity of waves jumps up sharply. This sharp increase in velocity is called a
discontinuity.
A shadow zone occurs on the opposite side of the earth from an earthquake
because of the liquid outer core. S-Waves are stopped all together while the PWaves are refracted (bent) to create a zone where no waves are picked up at all.
This zone is between 102° and 143°around the earth from the earthquake.
Lab research and studies of meteorites suggest that the core is made of Iron and
Nickel (FeNi).
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