Download P waves

Earthquakes are the shaking, rolling or
sudden shock of the earth’s surface.
Earthquakes happen along fault lines in the
earth’s crust. Earthquakes can be felt over
large areas although they usually last less
than one minute.
Earthquakes cannot be
predicted -- although
scientists are working on it!
•  Most of the time, you will notice an earthquake by
the gentle shaking of the ground. You may notice
hanging plants swaying or objects wobbling on
shelves. Sometimes you may hear a low rumbling
noise or feel a sharp jolt. A survivor of the 1906
earthquake in San Francisco said the sensation
was like riding a bicycle down a long flight of
stairs.
•  The intensity of an earthquake can be measured.
One measurement is called the Richter scale.
Earthquakes below 4.0 on the Richter scale usually
do not cause damage, and earthquakes below 2.0
usually can’t be felt. Earthquakes
over 5.0 on the scale can cause
damage. A magnitude 6.0
earthquake is considered strong
and a magnitude 7.0 is a major
earthquake. The Northridge
Earthquake, which hit Southern
California in 1994, was magnitude 6.7.
Earthquakes often occur when tectonic plates collide
What happens when plates collide? It depends how the plates
are moving when they meet:
When two plates collide head-on, they push each other up and
form mountains. That's how the Himalayas and other great
mountain ranges (including the Rockies, long ago) were
created.
When one plate dives below another plate,
it creates a subduction zone as the diving
plate is crushed and melted. This process
often creates volcanoes as the magma
(molten rock)
rises up to the
surface.
When two
plates slide
past each
other, they
create a
transform
fault, like
the San
Andreas
fault.
Types of Faults
•  When a section of rock breaks, rocks on either side
of the break might move because of elastic
rebound. The surface of this break is called a fault
•  Elastic rebound is when the stress of the forces
within the rocks becomes so great that the rocks
separate and an earthquake results.
•  There are different kinds of faults
Normal Faults
•  Normal Faults
–  When tension forces pull rocks apart
Rock above the
fault moves down
compared to rock
below the fault
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
Reverse Faults
•  Reverse Faults
–  When compression forces squeeze rocks together
Rock above the
fault moves up
compared to rock
below the fault
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
Strike-Slip Faults
•  Strike-slip Faults
–  When shear forces cause rocks to move past one
another in opposite directions on Earth’s surface
Rocks do not move up
or down, but rather
move side by side
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
•  Earthquakes can happen in any of these situations.
Despite the powerful forces driving plate movement,
the plates themselves spend much of the time locked in
place by the friction of the plates rubbing against each
other. Eventually, however, they build up so much
pressure that the plates
abruptly snap forward.
Then the ground can shift
a few feet—or a few dozen!
Shock waves from that
sudden motion shoot out
in all directions, creating an earthquake.
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file
and location.
•  Two great plates, the Pacific and the North
American, meet in California. The Pacific Plate
is moving north, creating a transform fault
(the San Andreas and related faults) Over
the last 20 million years the
Pacific Plate has slid about
200 miles north. If it keeps
moving as predicted, San
Francisco will become
neighbors with Seattle in
20 million years!
Because the San Andreas
fault curves around Los
Angeles, and then again
into the Pacific in
northern California, the
two plates cannot slide
smoothly against each
other. Instead, the
complex stresses of plate
movement have fractured
the land and created
dozens of smaller fault
lines.
•  Earthquakes can also occur within
plates, although plate-boundary
earthquakes are much more common.
Less than 10 percent of all earthquakes
occur within plate interiors. The New
Madrid earthquakes of 1811-1812 and
the 1886 Charleston earthquake
occurred within the North American
plate.
•  Earthquakes: Facts and Fiction
•  Fiction: Earthquakes usually happen in the morning.
Fact: Earthquakes happen in both the day and the night.
There is no pattern.
•  Fiction: There is such a thing as "earthquake weather."
Fact: There is no connection between earthquakes and
weather. Remember, earthquakes happen deep in the earth,
far away from the weather!
•  Fiction: Earthquakes are on the increase.
Fact: It may seem like we’re having more earthquakes
because there are more reporting stations, but the truth is
we’re not.
•  Fiction: We can prevent earthquakes from happening.
Fact: No. You can protect yourself by doing things to
secure buildings, like your home, but earthquakes can’t be
prevented -- or predicted.
The point beneath the Earth's surface where the
rocks break and move is called the focus of the
earthquake. The focus is the underground
point of origin of an earthquake.
Directly above the
focus, on the
Earth's surface, is
the epicenter.
•  Earthquake waves are known as
seismic waves. There are three main types of
seismic waves.
•  Each type of wave
has a characteristic
speed and manner
of travel.
•  Primary Waves
•  Seismic waves that travel the fastest are called
primary waves, or P waves. P waves arrive at
a given point before any other type of seismic
wave. P waves travel through solids, liquids
and gases.
•  P waves are push-pull waves. As P waves travel,
they push rock particles into the particles ahead
of them, thus compressing the particles. The rock
particles then bounce back. They hit the particles
behind them that are being pushed forward. The
particles move back and forth in the direction the
waves are moving.
•  Secondary Waves
•  Seismic waves that do not travel through the Earth
as fast as P waves do are secondary waves, or
S waves. S waves arrive at a given point after P
waves do. S waves travel through solids but not
through liquids and gases.
Body
P waves
S waves
Primary (1st to arrive)
Secondary (2nd to arrive larger) Transverse, Shear
waves
AKA
Longitudinal, Compression
Moves
through
all states of matter
(solid, liquid, gas)
Movement
of rock
back and forth movement of rock
•  push/pull or compression/stretch out
•  Like slinky down stairs
Vibration is same as the direction of travel
Can go through solids
only
Move sideways
•  perpendicular to direction of wave
travel
•  Like snake
Lets test your understanding!!
Is this a P or an S wave?
S Wave
P wave!
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
•  This is an image of a seismograph, an instrument
used to record the energy released by an
earthquake. When the needle is moved by the
motion of the earth, it leaves a wavy line.
HOW TO READ SEISMOGRAMS
P & S (body waves) move through earth & arrive first
•  P & S waves used to calculate magnitude of earthquake
•  Amplitude = height of wave (how much the rock moves; size of vibration)
Ways to Predict Earthquakes
•  Scientists cannot predict earthquakes, but
they can study changes in the Earth that lead
up to them, such as:
-movement along fault lines
-changes in groundwater levels
-electrical properties of rocks under stress
-rock layers that have been affected by ancient
earthquakes
Tsunamis
•  Tsunamis
–  Seismic sea waves resulting from an
earthquake on the ocean floor
–  These waves can travel outward from the
earthquake thousands of kilometers in all
directions
More Tsunamis
Why are they so dangerous?
At sea their wave heights are less than a meter
in deep water, ships would ride right over
them
When they approach the shore, the waves
slow down and their heights increase as the
waves drag along the bottom of the seafloor
Even More Tsunamis
This can create waves 30 meters tall!
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
Chapter 15, section 2
Volcanoes!
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
•  Lava
magma that has come through to the surface
of the Earth
•  Crater
circular holes at the top of volcanoes where
lava and other matter is shot out
•  Tephra
bits of rock and solidified lava dropped from
the air during a volcanic eruption (can be
very small like ash and cinders to very large
rocks called bombs or blocks)
Convergent boundaries can result in volcanic
islands
When subduction occurs, the sinking plate
melts and forms a magma chamber
This magma is what caused the volcanic
eruptions that formed the Caribbean Islands
Pyroclastic Flows
Huge avalanches of hot, glowing rock flowing
on a cushion of extremely hot gases (it flows
very quickly, up to 200 km/hr)
https://www.youtube.com/watch?
feature=player_detailpage&v=95bYATFIO
xs
Volcanoes can destroy but they also add new
rock to Earth’s crust
Different types of eruptions form different
types of volcanoes
Why are some volcanoes violent and
others calmer?
Violent vs. Non-violent
Eruptions
The makeup of the magma/ lava!
Lava that contains more silicon is thicker and
flows more slowly
Lava that has more iron and magnesium and
less silicon flows more easily
The amount of water vapor and other gasses
trapped within the lava also plays a part in
how the volcano erupts
Steam builds pressure in magma
the pressure is released as the volcano erupts
The more gas/ water vapor is trapped within
the lava, the more violent the eruption will
be (lava with more silicon traps more water/
gas)
Shield Volcanoes
•  Made from basaltic lava (iron and magnesium-rich,
low in silicon)
•  Flows in broad, flat layers
•  Forms a broad volcano with gently sloping sides
•  These are the largest types of volcanoes
•  Formed where magma is forced up from very deep
within the Earth or at divergent boundaries
Shield Volcano
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
Cinder Cone Volcanoes
•  Rising magma accumulates gases on it’s
way to the surface
•  The gasses build up pressure that finally
causes an eruption
•  The eruptions are moderate to violent and
spew ash, cinders and lava high into the air
•  The tephra forms a small coned volcano
•  Eruptions are usually quick because once
the gas is released the force behind the
eruption is gone
Cinder Cone Volcano
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
Composite Volcanoes
• 
• 
• 
• 
• 
Steep-sided
Alternating layers of lava and tephra
Some violent eruptions (release tephra)
Some quieter eruptions (release lava)
Form because of subduction
Composite Volcano
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
Fissure Eruptions
•  Very fluid magma seeps through cracks in
Earth’s surface
•  Lava is not very viscous (not thick, flows
easily)
•  Lava flows freely across land and forms
flood basalts
•  Flood basalts erode and over millions of
years become lava plateaus (flat
landforms)
Fissure Eruptions
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
Chapter 15 section 3
Earthquakes, Volcanoes, and Plate
Tectonics
Where Volcanoes Form
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the
correct file and location.
Most volcanoes form along plate
boundaries!
Divergent plate boundaries:
•  When plates separate rifts form between them
•  The rifts have cracks that conduct magma from
the mantle
•  Fissure eruptions occur along rifts (form lava that
cools and solidifies into basalt
•  Most rocks in the Earth’s crust are basalt
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points
to the correct file and location.
Convergent Plate Boundaries:
•  when one plate subducts, basalt and sediment move
down into the mantle
•  Water that moves in lowers the melting point of the
surrounding rock
•  Heat in the mantle causes pat of the subducted plate
to melt
•  This molten material gets forced upward
Hot Spots:
Large rising bodies of magma
Hot spots can force their way up through the mantle
and crust creating volcanoes within plates rather
than at plate boundaries
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
There is a hot spot
under Hawaii
Volcanoes usually form along rift zones, subduction
zones, or over hot spots
Most (~80%) earthquakes occur in the Pacific
Ring of Fire, the same area where most of
Earth’s volcanoes occur
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
Movement of the plates produces forces that
generate the energy that cause earthquakes
How seismic waves pass through a material depends
on the properties of that material
Scientists can study seismic waves to determine what
kind of material is inside the Earth
Waves will travel differently through solids, liquids
and gases and through liquids with different
viscosity
Remember that p waves travel through solids, liquids,
and gases, while s waves only travel through solids
Convection Currents
Convection currents inside the Earth cause plate
movement which then creates conditions that cause
earthquakes and volcanoes
Hot, less dense magma is forced towards the surface
where it eventually cools and sinks back into the
mantle towards Earth’s core
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.