Download Types of Seismic Waves

Deformation is the bending &
breaking of the crust!
 Balance
of Earth’s lithosphere (crust) as
though they were floating on the denser
underlying layer of the athensphere
(upper mantle composed of weak, plastic
rock that is about 110 km below the
surface.
 Isostasy controls the regional elevations
of continents and ocean floors because of
the density of their underlying rocks.
ISOSTATIC ADJUSTMENT CAUSE
EFFECT

Wind, Water, & Ice erode


River deposit sediment


Glaciers form from snow


Glaciers melt with temp.

Uplift occurs due to lighter
mountain from erosion.
The ocean floor becomes
heavier so goes down
(subsidence)
The glacier’s weight causes
sinking (subsidence)
The lessening of glacier’s
weight causes sinking
(subsidence) in ocean.
Most earthquakes occur when rocks
fracture, or break, deep within Earth.
Fractures form when stress exceeds the
strength of the rocks involved.
Stress is the forces per unit/area.
Strain is the deformation of materials in
response to stress. (Temperature,
pressure, & rock composition matter.)
•
not always permanent if slow
•
Permanent a) Brittle b) ductile
There are three kinds of stress
that act on Earth’s rocks:
– Compression (squeezing) is stress
that decreases the volume of a
material.
– Tension (stretching)is stress that
pulls a material apart.
– Shear (break or twist) is stress
that causes a material to twist.
There is a relationship between stress and strain
that can be plotted as a stress-strain curve.
– A stress-strain curve has two
segments: a straight segment
and a curved segment.
– Low stresses produce the
straight segment, which
represents the elastic strain
of a material.
– If the elastic strain is reduced
to zero, the deformation
disappears.
Ductile Deformation
– When stress exceeds the
strength of a material, the
material breaks, or fails, as
designated by the X on
the graph. It produces
permanent deformation,
which means that the material
stays deformed even if the
stress is reduced to zero.
– Most rocks, though brittle on
the surface, become ductile
at the higher temperatures
present at greater depths.
Folding
& Fault
Block
Mountains
 Folding
is a bending of the rock layer due
to compression.
 Rocks will folded symmetrically or
asymmetrically (most).
 Folds can very in shape & size (>1,000’s
km).
 Folds have sloping sides called limbs & the
bend is the hinge (meeting place).
 Anticline
- Oldest
rocks in the
middle of the fold.
 Syncline
– oldest
rocks on the
outside.
 Monocline
limbs are
horizontal.
–2
 Mountain
Ranges- groups of
mountains with similar sizes,
shapes, & ages.
Ex. Himalaya & Cascade Mtns.
http://www.youtube.com/watch?v=kSFur_X5moo
http://www.cascadeloop.com/index.php?page_id=473
 Mountain
System – made up of
mtn. ranges .
Ex. The Appalachian Mtns.
Consists of the Smoky, Blue Ridge,
Green, White, & Cumberland.
http://www.visitnc.com/journeys/highlights/outdoor-playground
http://www.visitnc.com/journeys/highlights/appalachiantrail http://www.visitnc.com/journeys/highlights/blue-ridge
 Mountain
Belts – largest
systems
located at
convergent
boundaries.
The circum –
Pacific & the
EurasianMelanesian
belts.
 Continental
– Continental produces thrust
faults. Ex. Himalaya Mtns.
 Oceanic-
Continental produce terranes
Ex. Andes Mtns.
 Oceanic-Oceanic
–produce island arc
(volcanic mtn. on the ocean floor).
Ex. Mariana Islands
These different types of mountain have distinguishing physical characteristics &also different formations.
Volcanic Mountain
Volcanoes form volcanic mountains and these mountains are then shaped by further eruptions, lava
flows, and collapses forever altering the view of this mountain. So explosive was this eruption, that it can
alter the height of the mountain by nearly 1,300 feet. other major Volcanic Mountains in North America
include Mt. Ranier, Washington, with an elevation of 14,410 feet, making it the highest peak of the Cascade
Mountain Range. Mount Shasta, California, with an elevation of 14, 162. Also in the USA is Mount Hood,
Oregon, with an elevation of 11, 235 feet, and Mount Spur, Alaska, with an elevation of 11, 067 feet.
Dome Mountain
As their name states, Dome Mountains have a characteristic ‘dome’ top. In the USA, the Black Hills of
South Dakota offer excellent examples of dome topped mountains. Erosion is believed to be a major
factor in the shaping of most dome formations.
Fold Mountain
Again, the name tells a lot. and through time with great force, pushed pieces of earth upward and folded
them over onto themselves. Example of Fold Mountains includes the Appalachian Mountains.
Fault-Block Mountain
As in ‘Fold’ mountains, great force is behind the Fault-Block Mountains. What differs is that instead of the
earth folding over, the earth fractures and blocks are stacked.
Plateau Mountain
To appreciate theses High levels of flat land one only has to look at the Catskills of New York.
More Mountain Facts
* The Himalayas are the world’s overall tallest mountains.
* The Andes, which runs more than 4,900 miles, is the longest mountain range in the world.
* Mauna Kea, with an elevation of 13,796 feet, is actually 32,000 feet tall from its start on the sea floor,
making it the world’s highest island peak from base to tip.
* Mount Everest, part of the Himalayas, is the highest point on earth, with a height of 29,023 feet. What
many don’t realize is that Mt. Everest is only one in this range of over 30 peaks that rise to over 24,000
feet. Also in this range is Kanchenjunga at 28,208 feet, Makalu at 27,766 feet, and Dhaulagiri at 26,810 feet.
* Mount Mitchell is the Appalachians highest peak at 6,684 feet.
* High Knob, in the Pocono Mountains is only 2,162 feet tall.
* Pikes Peak Mountain, part of the Great Rocky Mountains, is an astounding 14,110 feet high.
Various Mountain Chains - 4 different ways
•Volcanic
Ring of Fire: Pacific Rim
•Dome (Erosional)
Rocky Mountains : Western US
•Fault-Block
Sierra Nevada Mountains : Nevada
Basin and Range Province : Arizona
•Folded
Himalaya Range : China/Tibet/India/Nepal
Appalachian Mountains : Eastern US
Ural Mountains : Spain/France
Types of Faults
There are
3 types of faults:
Reverse faults are
fractures that form as
a result of horizontal compression.
Normal faults are fractures caused
by horizontal tension.
Strike-slip faults are fractures
caused by horizontal shear.
Earthquakes are natural vibrations of the ground
caused by movement along fractures in Earth’s
crust, or by volcanic eruptions.
In some instances a single earthquake have killed
more than 100,000 people and destroyed entire
cities.
More than 1million earthquakes occur each year.
More than 90 % of earthquakes are not felt and
cause little damage.
A fault is the fracture or
system of fractures along
which movement occurs
called the fault plane.
MOST EARTHQUAKES ARE
CAUSED BY MOVEMENTS
ALONG FAULTS.
•
Irregular surfaces in
rocks can snag and
lock, causing stress
to build in the rocks.
•
When the rocks
reach their elastic
limit they break, and
this produces an
earthquake.
HAITIAN EARTHQUAKE
Types of Seismic Waves
The vibrations of the ground
during an earthquake are
seismic waves.
Every earthquake generates
3 types of seismic waves.
Primary, Surface, &
Secondary Waves
Primary waves, or Pwaves, squeeze and pull
rocks in the same
direction along which the
waves are traveling.
Types of Seismic Waves
Secondary waves
or S-waves,
cause rocks to
move at right
angles to the
direction of
the waves.
Surface waves
travel along
Earth’s surface,
moving in two
directions.
Types of Seismic Waves
– P-waves and S-waves (body waves) pass through
Earth’s interior.
– The focus of an earthquake is the point of failure of
rocks at the depth where an earthquake originates.
– The epicenter of
an earthquake is
the point on Earth’s
surface directly
above the focus.
Seismology is the study of earthquake waves.
• The seismic waves that shake the ground
during a quake also penetrate Earth’s interior.
• This has provided information that has
enabled Earth scientists to construct models
of Earth’s internal structure.
Seismometers, or
seismographs, are sensitive
instruments that detect and
record the vibrations sent
out by earthquakes.
• All seismometers include a frame
that is anchored to the ground
and a mass that is suspended
from a spring or wire.
• The relative motion of the mass
in relation to the frame is
recorded during an earthquake.
A seismogram is the record produced by
a seismometer.
Travel-Time Curves
– The time separation between
the P-waves and S-waves
increases with travel distance.
– From this separation, the
distance from the epicenter of
a quake to the seismic facility
that recorded the seismogram
can be determined.
– The P-waves always arrive
first at a seismic facility.
Seismic waves change speed and direction
when they encounter different materials in Earth’s
interior.
http://science.howstuffworks.com/nature/naturaldisasters/earthquake4.htm
http://www.youtube.com/watch?v=yOGoKCK17a4
– P-waves and S-waves traveling through the mantle
follow fairly direct paths.
– P-waves that strike the core are refracted, or bent,
causing P-wave shadow zones .
P-waves appear on seismograms.
– S-waves do not enter Earth’s core because they
cannot travel through liquids and do not reappear
beyond the P-Wave shadow zone.
Seismic Waves and Earth’s Interior
Earth’s Internal
Structure
– This disappearance of Swaves has allowed
seismologists to reason
that Earth’s outer core
must be liquid
– Detailed studies of how
other seismic waves
reflect deep within Earth
show that Earth’s inner
core is solid
Seismic Waves and Earth’s Interior
Earth’s Internal Structure
– Lithosphere - Igneous rocks
granite, basalt, and peridotite.
– Asthenosphere - peridotite.
– Lower mantle -solid and
is probably composed of simple
oxides containing iron, silicon,
and magnesium.
– The core -a mixture of iron and
nickel supported by studies of
meteorites. Meteorites of iron,
nickel, and chunks of rock similar
to peridotite in the same
proportions as the rocks thought
to make up Earth’s core and
mantle.
Magnitude is the measurement of the amount
of energy released during an earthquake.
The Richter scale is a numerical scale based on
the size of the largest seismic waves generated
by a quake that is used to describe its magnitude.
– Each successive number in the scale represents
an increase in seismic-wave size, or amplitude, of
a factor of 10.
– Each increase in magnitude corresponds to about
a 32-fold increase in seismic energy.
Moment Magnitude Scale
– The moment magnitude scale, used by
seismologists to measure earthquake magnitude.
 Size of the fault rupture,
 The amount of movement along the fault
 Rocks’ stiffness.
– Moment magnitude values are estimated from the
size of several types of seismic waves produced by
an earthquake.
Modified Mercalli Scale
 Measures the amount of damage done to the
structures.
 This scale uses the I to XII to designate the degree of
intensity. The higher the # the worse the damage!
Modified Mercalli Scale
– Earthquake intensity
depends on the amplitude of
the surface waves
generated.
– Maximum intensity values near the epicenter; Mercalli
values decrease to I at
distances very far from the
epicenter.
– Modified Mercalli scale
intensity values can be
compiled to make a seismicintensity map.
–
Depth of Focus
Earthquake intensity is
related to earthquake
magnitude.
–
The depth of the quake’s
focus determines the
intensity of an
earthquake.
–
An earthquake’s focus is
classified as shallow,
intermediate, or deep.
–
A deep-focus
earthquake produces
smaller vibrations at the
epicenter.
Distance to an Earthquake
– All epicenter locations & times of
occurrence can be easily
determined using seismograms
and travel-time curves.
– The P-S separation determines the
epicentral distance (distance to a
quake’s epicenter from the seismic
station that recorded the waves).
– The travel time of either wave at
the epicentral distance of that
station can be read from the traveltime graph.
– The time of occurrence of the
earthquake is determined by
subtracting the travel time from
the arrival time.
Distance to an Earthquake
– The earthquake could have
occurred anywhere on a
circle around the seismic
station.
– The radius of the circle
is equal to the epicentral
distance.
– If 3 or more epicentral
distances known - the
exact location of the
epicenter can be determined.
The majority of the world’s earthquakes occur
in relatively narrow seismic belts that are
associated with tectonic plate boundaries.
– 80 % of all earthquakes in the Circum-Pacific Belt.
– 15 % take place across southern Europe and Asia.
– 4% in narrow bands that run along the crests of
ocean ridges.
– 1% happen far from tectonic plate boundaries and
are random.
– http://www.digitalgeology.net/page9.html
Structural Failure
 In many earthquake-prone areas, buildings are destroyed as
the ground beneath them shakes. The most severe damage stone, concrete, or other brittle building materials.
 Wooden structures & modern high-rise, steel-frame buildings
sustain little damage .
 “Pancaking” - the supporting walls of the ground floor fail,
causing the upper floors to fall and collapse as they hit lower
floors.
 When a quake has the same period of vibration as the natural
sway of a building, they will sway violently.
 The natural sway of a building is related to height; Longer
waves - taller buildings .
Fault Scarps
Fault movements associated
with earthquakes can
produce fault scarps.
Fault scarps are areas of
great vertical offset (slope)
where the fault intersects the
ground surface.
Tsunami
A tsunami is a large ocean wave
generated by vertical motions of the
seafloor during an earthquake.
– Displaces the entire column of water
overlying the fault, creating bulges
and depressions in the water.
– Spreads out from the epicenter in the
form of extremely long waves.
(Speeds 500 - 800 km/h)
– May form huge breakers (Heights
may > 30 m)
– Earthquakes may trigger massive
landslides in sloping areas.
– In fluid-saturated sand, seismic
vibrations may cause subsurface
materials to liquefy act like
quicksand.
– Wave size and earthquake intensity
are amplified in soft, unconsolidated
sediments and are slowed in hard,
resistant rocks such as granite.
The past
seismic
activity is a
reliable
indicator of
future
earthquakes
and can be
used to
generate
seismic-risk
maps.
Earthquake Prediction
2 factors:
http://www.youtube.com/watch?v=xQXDt4VdS0E
http://www.youtube.com/watch?v=o0tVbjrbkp8&feature=related
– The history of earthquakes in an area
– The rate at which strain builds up in the rocks
Probability (ratio) based on Seismic gaps
(active faults that haven’t experienced significant
earthquakes for a long period of time.)
To predict scientists make several measurements.
• Amount of strain
• Amount of time passed since an earthquake has struck
that section of the fault
Why might only buildings that are between
5 and 10 stories tall be seriously affected
during an earthquake?
If the shaking caused by the quake had the
same period of vibration as the natural sway
of buildings at that height, they would be
more violently affected than either taller or
shorter buildings.
What is a seismic gap, and how would it possibly
affect the prediction of earthquakes for the area?
A seismic gap is a section of an active fault that
hasn’t experienced a significant earthquake for a
log period of time. A seismic gap would generally
have a higher probability of a future earthquake.
Identify whether the following statements
are true or false.
______
false All high seismic risk areas in the United States
are located on the Pacific coast.
______
false Fault scarps are areas of horizontal offset.
______
true Wooden structures generally fair better in an
earthquake than do stone structures.
______
true San Francisco sits above a seismic gap.
Match the following terms with their
definitions.
A. deformation of materials in
E stress
___
A strain
___
D fault
___
___
C focus
___
B epicenter
response to forces acting
upon them
B. surface point directly above an
earthquake’s point of origination
C. actual point where an earthquake
originates
D. a fracture or system of fractures in
Earth’s crust along which
movement occurs
E. force per unit area acting on
a material
Which type of fault best describes the San
Andreas Fault? Why?
The San Andreas Fault is a strike-slip
fault. The movement in this fault is
primarily horizontal and is caused by two
plates that are sliding past each other
rather than by subduction.
Identify whether the following statements are
true or false.
______
true A P-wave causes rocks to move back
and forth.
______
true S-waves pass through Earth’s interior.
______
false A material that undergoes ductile deformation
will return to its original state if stress is
reduced to zero.
______
true The focus of an earthquake is usually several
kilometers below Earth’s surface.
What happens to P-waves when they enter
Earth’s core?
P-waves are refracted when they pass
through Earth’s core, which causes a shadow
zone where no direct P-waves can be
detected by seismometers.
How can the distance to an earthquake’s
epicenter be determined?
Seismologists have been able to construct
global time-travel curves for the initial P-waves
and S-waves of an earthquake. The difference in
time between the arrival of the initial P-waves
and S-waves indicates the distance from the
seismometer to the earthquake’s epicenter.
Identify whether the following statements
are true or false.
______
false Direct S-waves are present in a P-wave
shadow zone.
______
false Earth’s inner core is probably liquid.
______
true A 4-minute, 30-second separation between the
arrival of P-waves and S-waves would indicate
that the epicenter was about 3000 km away.
______
true Meteorites are believed to similar in composition
to Earth’s core.
Match the following terms with their
definitions.
A. rates intensity through the type
___
D magnitude
of damage and other effects of
an earthquake
___
Richter scale
C
___ moment magnitude
B. takes into account the fault
B scale
rupture, the amount of
___ modified Mercalli
movement along the fault, and
scale
A
the rock’s stiffness
C. describes a quake based on its
largest seismic waves
D. the amount of energy released
during an earthquake
How can a high magnitude earthquake rank
relatively low on the modified Mercalli scale?
The modified Mercalli scale measures the
intensity of an earthquake against specific
damage that it causes. A high magnitude, deepfocus quake would probably have a lower
Mercalli rating than a moderate, shallow-focus
quake. The Mercalli rating will generally go down
with distance from the epicenter, regardless of
the magnitude.
Identify whether the following statements are
true or false.
______
true A Mercalli rating of VI would indicate less
damage than a rating of VIII.
______
false A quake with a magnitude of 7 on the Richter
scale would have 10 times the amount of
seismic energy as magnitude 6 quake.
______
true Most earthquakes occur along plate boundaries.
______
false Less than 10 000 earthquakes occur in an
average year.