Module 3 Kavli Institute for Theoretical Physics by Nick
Nicastro
Slide 2
This module is intended for use by teachers of physics and
related sciences. It is based on the findings and compilations of
the 2014 Teacher-In- Residence Program at the Kavli Institute for
Theoretical Physics at the University of California, Santa Barbara.
Some parts of this presentation were based on the 2014 CIDER
CONFERENCE (Cooperative Institute for Deep Earth Reseach) at the
KITP.
Slide 3
MODULE 3 GENERAL OBJECTIVES: 1. To review basic concepts of
wave theory with a special emphasis on important terminology.
Slide 4
MODULE 3 GENERAL OBJECTIVES: 1. To review basic concepts of
wave theory with a special emphasis on important terminology. 2. To
review the basic internal structure of the Earth.
Slide 5
MODULE 3 GENERAL OBJECTIVES: 1. To review basic concepts of
wave theory with a special emphasis on important terminology. 2. To
review the basic internal structure of the Earth. 3. To explain why
and how waves are produced inside the Earth.
Slide 6
MODULE 3 GENERAL OBJECTIVES: 1. To review basic concepts of
wave theory with a special emphasis on important terminology. 2. To
review the basic internal structure of the Earth. 3. To explain why
and how waves are produced inside the Earth. 4. To understand the
varieties of geodynamic waves and their differences.
Slide 7
MODULE 3 GENERAL OBJECTIVES: 1. To review basic concepts of
wave theory with a special emphasis on important terminology. 2. To
review the basic internal structure of the Earth. 3. To explain why
and how waves are produced inside the Earth. 4. To understand the
varieties of geodynamic waves and their differences. 5. To show how
geodynamic waves propogate through the Earth.
Slide 8
MODULE 3 GENERAL OBJECTIVES: 1. To review basic concepts of
wave theory with a special emphasis on important terminology. 2. To
review the basic internal structure of the Earth. 3. To explain why
and how waves are produced inside the Earth. 4. To understand the
varieties of geodynamic waves and their differences. 5. To show how
geodynamic waves propogate through the Earth. 6. To demonstrate the
potential effects geodynamic waves can have on the surface of the
Earth.
Slide 9
MODULE 3 GENERAL OBJECTIVES: 1. To review basic concepts of
wave theory with a special emphasis on important terminology. 2. To
review the basic internal structure of the Earth. 3. To explain why
and how waves are produced inside the Earth. 4. To understand the
varieties of geodynamic waves and their differences. 5. To show how
geodynamic waves propogate through the Earth. 6. To demonstrate the
potential effects geodynamic waves can have on the surface of the
Earth. 7. To understand how these waves are measured.
Slide 10
MODULE 3 GENERAL OBJECTIVES: 1. To review basic concepts of
wave theory with a special emphasis on important terminology. 2. To
review the basic internal structure of the Earth. 3. To explain why
and how waves are produced inside the Earth. 4. To understand the
varieties of geodynamic waves and their differences. 5. To show how
geodynamic waves propogate through the Earth. 6. To demonstrate the
potential effects geodynamic waves can have on the surface of the
Earth. 7. To understand how these waves are measured. 8. To address
the question, Is there any way we can predict seismic occurrences
on the surface of the Earth before they happen?
Slide 11
PRE-MODULE QUESTIONS: 1.Waves are disturbances traveling
through a medium. (T/F) 2.Waves cannot pass through solid matter.
(T/F) 3.Waves transfer energy from point A to point B by moving a
mass from point A to point B. (T/F) 4.The greater the energy
carried in a wave, the greater the moving disturbance in the
medium. (T/F) 5.The speed of a wave has nothing to do with the
medium it is in. (T/F) 6.It is possible to predict the occurrence
of an earthquake hours in advance. (T/F) 7.Seismic waves travel at
different speeds inside the Earth. (T/F)
Slide 12
BASIC WAVE THEORY. Def. A WAVE is a disturbance traveling in a
medium. The medium can be a: *physical substance, such as a fluid
(e.g. air, water, any gas or liquid), or even a solid (wood,
crystal, metal, mineral, etc.), or a *force field (e.g. electric,
magnetic, a.k.a. electromagnetic, even gravitational) WAVES CARRY
ENERGY FROM ONE POINT TO ANOTHER THROUGH THE DISTURBANCE (a.k.a.,
pulse, vibration, etc). Waves that require a physical medium are
called MECHANICAL WAVES (since a mechanical force must be applied
to move the medium). These waves travel at sublight speeds. Waves
that do not require a physical medium are called NON-MECHANICAL
WAVES (electromagnetic, gravity). These waves travel at the speed
of light in a vacuum. Their speed in a transparent non-vacuum
depends on the nature of the medium.
Slide 13
BASIC WAVE THEORY There are two major types of waves: *
LONGITUDINAL WAVES: a wave in which the disturbance travels in the
same line as the direction of the wave: These are sometimes called
COMPRESSION, or PRESSURE waves, since the disturbance is a
traveling compression of part of the medium, leaving a partial
vacuum (rarefaction) in its place. line of wave; direction of
disturbance
Slide 14
BASIC WAVE THEORY There are two major types of waves: *
LONGITUDINAL WAVES: a wave in which the disturbance travels in the
same line as the direction of the wave: These are sometimes called
COMPRESSION, or PRESSURE waves, since the disturbance is a
traveling compression of part of the medium, leaving a partial
vacuum (rarefaction) in its place. A longitudinal wave can consist
of a single disturbance traveling through the medium. A train of
compressions represents a series of continuous compressions. line
of wave; direction of disturbance
Slide 15
BASIC WAVE THEORY WAVE TYPES There are two major types of
waves: * LONGITUDINAL WAVES: a wave in which the disturbance
travels in the same line as the direction of the wave: These are
sometimes called COMPRESSION, or PRESSURE waves, since the
disturbance is a traveling compression of part of the medium,
leaving a partial vacuum (rarefaction) in its place. A longitudinal
wave can consist of a single disturbance traveling through the
medium. A train of compressions represents a series of continuous
compressions. The number of compressions (or rarefactions) passing
a stationary point in a given amount of time (usually one second),
is known as the waves FREQUENCY (measured in cycles/sec). line of
wave; direction of disturbance
Slide 16
BASIC WAVE THEORY WAVE TYPES There are two major types of
waves: * LONGITUDINAL WAVES: a wave in which the disturbance
travels in the same line as the direction of the wave: For example,
if one compression (or pulse, or cycle, or vibration, etc.) passes
a given point per second, it said to have a frequency of one cycle
per second, otherwise known as one HERTZ (Hz). line of wave;
direction of disturbance
Slide 17
BASIC WAVE THEORY WAVE SPEED Just like a car traveling at 20
miles/hr, waves also have a speed as they travel through the
medium. line of wave; direction of disturbance
Slide 18
BASIC WAVE THEORY WAVE SPEED Just like a car traveling at 20
miles/hr, waves also have a speed as they travel through the
medium. line of wave; direction of disturbance IMPORTANT NOTE:
Unlike a car, which travels from point A to point B, it is the
disturbance (not the physical material) that travels from point A
to point B! (Its speed can be measured in any proper speed
unit.)
Slide 19
BASIC WAVE THEORY WAVE SPEED The speed of a longitudinal
(pressure) wave depends on the medium. line of wave; direction of
disturbance For example, a sound wave is a longitudinal wave, and
its speed depends on the density and elasticity of the medium; In
air (or most gases), sound travels at 360 m/sec; in water, it
travels at 1500 m/sec; In granite (at 20C), it travels at 6000
m/sec.
Slide 20
BASIC WAVE THEORY WAVE SPEED The speed of a longitudinal
(pressure) wave depends on the medium. line of wave; direction of
disturbance One way to calculate the speed of a longitudinal wave
is to determine how far one compression travels in a given time.
Another way...
Slide 21
BASIC WAVE THEORY WAVELENGTH () The WAVELENGTH of a
longitudinal (pressure) wave is the distance between successive
compressions. (It can be measured in any proper distance unit.)
line of wave; direction of disturbance Another way to calculate the
speed of a longitudinal wave is to multiply its frequency by its
wavelength. v = f
Slide 22
BASIC WAVE THEORY WAVE ENERGY The ENERGY carried in a wave
depends on the magnitude of the disturbance (e.g. a loud sound
produces a larger compression than a soft sound.) line of wave;
direction of disturbance IMPORTANT NOTE: The size of the
disturbance is not directly related to its speed. (e.g. A loud
sound doesnt travel faster than a soft sound.)
Slide 23
BASIC WAVE THEORY WAVE ENERGY The ENERGY carried in a wave
depends on the magnitude of the disturbance (e.g. a loud sound
produces a larger compression than a soft sound.) line of wave;
direction of disturbance REMEMBER: Since energy is the ability to
do work, the more energy a wave carries, the more work it is able
to do!
Slide 24
BASIC WAVE THEORY TRANSVERSE WAVE A TRANSVERSE WAVE is one in
which the disturbance is perpendicular to its direction. line of
wave; direction of disturbance axis
Slide 25
BASIC WAVE THEORY WAVELENGTH The WAVELENGTH of a transverse
wave is the distance between two successive peaks (or troughs, or
any two successive corresponding parts). line of wave; direction of
disturbance axis
Slide 26
BASIC WAVE THEORY FREQUENCY The FREQUENCY of a transverse wave
is the number of crests (or troughs) that pass a given point per
second. line of wave; direction of disturbance axis The same wave
equation can be used to determine a transverse waves speed, v = f
.
Slide 27
BASIC WAVE THEORY FREQUENCY The FREQUENCY of a transverse wave
is the number of crests (or troughs) that pass a given point per
second. line of wave; direction of disturbance axis The same wave
equation can be used to determine a transverse waves speed, v = f .
(All electromagnetic waves are transverse. e.g., light, radio,
infrared, ultraviolet, etc.)
Slide 28
BASIC WAVE THEORY WAVE ENERGY The ENERGY carried by a
transverse wave depends upon its AMPLITUDE, NOT its wavelength or
frequency! line of wave; direction of disturbance axis e.g., Since
a light wave has a higher frequency (10 14 Hz) than a microwave (10
6 Hz) it carries more energy, and can do more work.
Slide 29
BASIC WAVE THEORY WATER WAVES WATER WAVES are a bit more
complicated: Water waves are really a superposition of circular
moving water molecules traveling along a long transverse wave. The
water appears to be moving, but in actuality, it is the wave (the
disturbance) that is doing the moving. Thats why, when youre on a
boat and a wave comes along, you simply go up and down as the wave
passes.
Slide 30
BASIC WAVE THEORY WAVE PROPERTIES I.REFLECTION II.REFRACTION
III.DIFFRACTION IV.INTERFERENCE V.POLARIZATION WE WILL INVESTIGATE
TWO OF THESE PROPERTIES TO UNDERSTAND HOW THEY APPLY TO SEISMIC
WAVES.
Slide 31
BASIC WAVE THEORY WAVE PROPERTIES I.REFLECTION Reflection is
the change in direction of a wavefront at an interface between two
different media so that the wavefront returns into the medium from
which it originated.
Slide 32
BASIC WAVE THEORY WAVE PROPERTIES I.REFLECTION Reflection is
the change in direction of a wavefront at an interface between two
different media so that the wavefront returns into the medium from
which it originated. Common examples include the reflection of
light, sound and water waves.
Slide 33
BASIC WAVE THEORY WAVE PROPERTIES I.REFLECTION Reflection is
the change in direction of a wavefront at an interface between two
different media so that the wavefront returns into the medium from
which it originated. Common examples include the reflection of
light, sound and water waves. The law of reflection says that for
specular reflection, the angle at which the wave is incident on the
surface equals the angle at which it is reflected.
Slide 34
BASIC WAVE THEORY WAVE PROPERTIES I.REFLECTION In geology, it
is important in the study of seismic waves.
Slide 35
BASIC WAVE THEORY WAVE PROPERTIES II. REFRACTION Refraction is
the bending of the path of a light wave as it passes across the
boundary separating two media. Refraction is caused by the change
in speed experienced by a wave when it changes from one medium to
another.
Slide 36
BASIC WAVE THEORY WAVE PROPERTIES II. REFRACTION Refraction is
the bending of the path of a light wave as it passes across the
boundary separating two media. Refraction is caused by the change
in speed experienced by a wave when it changes from one medium to
another. The speed of a wave depends on the medium in which it is
in. The property of a medium that relates to a waves speed is
called the INDEX OF REFRACTION.
Slide 37
BASIC WAVE THEORY WAVE PROPERTIES II. REFRACTION
Slide 38
BASIC WAVE THEORY WAVE PROPERTIES II.REFRACTION SNELLS LAW
Slide 39
BASIC WAVE THEORY SNELLS LAW APPLIED TO SEISMOLOGY
Slide 40
Now, lets look at waves inside the Earth.
Slide 41
First, recall that the interior of the Earth consists of
layers, the major layers being the crust, the mantle (upper and
lower), and the core (inner and outer).
Slide 42
The center of the Earth (the inner core) is solid, while the
outer core is molten (liquid).
Slide 43
First, recall that the interior of the Earth consists of
layers, the major layers being the crust, the mantle (upper and
lower), and the core (inner and outer). The center of the Earth
(the inner core) is solid, while the outer core is molten (liquid).
Also recall that the crust (the surface to a hundred or so
kilometers down), consist of rigid plates that are subject to
motions in the upper mantlle.
Slide 44
Seismologists get information about the Earths interior from
EARTHQUAKES. Earthquakes occur when (tectonic) plates on the
surface slide over one another. From this, we can study the motions
beneath the crust. click on the image
Slide 45
There are three certain types of waves that are involved in an
earthquake. Lets look at two of them. P and S waves. LOOK FAMILIAR?
Pressure aka, Primary Shear aka, Secondary
Slide 46
P and S waves are also classified as BODY WAVES, since they
travel through the interior of the earth. LOOK FAMILIAR? Pressure
aka, Primary Shear aka, Secondary
Slide 47
The first one is called the Primary* wave, or for short, P
wave. In P or compressional waves, the vibration of the rock is in
the direction of propagation. The P wave is the smallest and
fastest wave of the three, it always happens when an earthquake
occurs. The P wave will probably only rattle some dishes on a
shelf, it is a warning that the earthquake is coming. This wave can
go through solids, liquids and gases. *or Pressure AS YOU CAN SEE,
THIS IS A LONGITUDINAL WAVE.
Slide 48
The first one is called the Primary* wave, or for short, P
wave. In P or compressional waves, the vibration of the rock is in
the direction of propagation. The P wave is the smallest and
fastest wave of the three, it always happens when an earthquake
occurs. The P wave will probably only rattle some dishes on a
shelf, it is a warning that the earthquake is coming. This wave can
go through solids, liquids and gases. *or Pressure AS YOU CAN SEE,
THIS IS A LONGITUDINAL WAVE.
Slide 49
The first one is called the Primary* wave, or for short, P
wave. In P or compressional waves, the vibration of the rock is in
the direction of propagation. The P wave is the smallest and
fastest wave of the three, it always happens when an earthquake
occurs. The P wave will probably only rattle some dishes on a
shelf, it is a warning that the earthquake is coming. This wave can
go through solids, liquids and gases. *or Pressure P waves travel
at an average 6 km/sec in the Earths crust, and its speed jumps to
13 km/sec through the core.
Slide 50
The second type of wave is called the secondary wave* or S
wave. This wave is slower than the P wave but stronger. In S or
shear* waves, rock oscillates perpendicular to the direction of
wave propagation. S waves generally travel about 60% the speed of P
waves, and the S wave always arrives after the P wave. For example,
sound waves are P waves at a high enough frequency to hear with
your ear. Unlike the P wave, this wave can only go through solids.
AS YOU CAN SEE, THIS IS A TRANSVERSE WAVE.
Slide 51
The second type of wave is called the secondary wave* or S
wave. This wave is slower than the P wave but stronger. In S or
shear* waves, rock oscillates perpendicular to the direction of
wave propagation. S waves generally travel about 60% the speed of P
waves, and the S wave always arrives after the P wave. For example,
sound waves are P waves at a high enough frequency to hear with
your ear. Unlike the P wave, this wave can only go through solids.
S waves travel at about 60% of the speed of P waves.
Slide 52
Both waves are produced at the moment an earthquake occurs, but
they have several different characteristics. It is important to
understand the differences between these two waves. LIQUID OUTER
CORE (NO S WAVES) REFRACTION DUE TO CHANGE OF MEDIUM (SNELLS
LAW)
Slide 53
Both waves are produced at the moment an earthquake occurs, but
they have several different characteristics. It is important to
understand the differences between these two waves. REFRACTION DUE
TO CHANGE OF MEDIUM (SNELLS LAW)
Slide 54
REFRACTION DUE TO CHANGE OF MEDIUM (SNELLS LAW) Reflection and
refraction (transmission) of seismic waves (P or S waves) at an
interface separating two different materials. Some energy is
reflected and some is transmitted. The effect can be illustrated
with two slinkys one metal and one plastic taped together Waves
traveling along one slinky are partially reflected at the boundary
between the two types of slinkys. For seismic waves in the Earth,
an incident P or S wave also results in converted S and P energy in
both the upper material (reflected) and the lower material
(transmitted). If the angle of approach of the wave (measured by
the angle of incidence, i, or the associated raypath) is not zero,
the resulting transmitted P and S raypaths will be bent or
refracted at the boundary. A similar change in angle is also
evident for the reflected, converted waves
Slide 55
Both waves are produced at the moment an earthquake occurs, but
they have several different characteristics. It is important to
understand the differences between these two waves. REFRACTION DUE
TO CHANGE OF MEDIUM (SNELLS LAW)
Slide 56
Locating the Epicenter Since P and S waves travel at different
rates, we can use them to calculate our distance to the epicenter.
P waves travel faster than S waves, and will always arrive at a
seismic station first. How far ahead of the S waves they arrive
depends on how far away the earthquake is. The further away the
epicenter is, the wider the gap will be between the P and S waves.
This is similar to the effect during a thunderstorm, when you can
estimate how far away the lightning is by timing how long you have
to wait for the thunder.
Slide 57
Locating the Epicenter P waves are like the lightning, and S
waves are like the thunder. The P waves travel faster and shake the
ground where you are first. Then the S waves follow and shake the
ground also. If you are close to the earthquake, the P and S wave
will come one right after the other, but if you are far away, there
will be more time between the two. By looking at the amount of time
between the P and S wave on a seismogram recorded on a seismograph,
scientists can tell how far away the earthquake was from that
location. However, they cant tell in what direction from the
seismograph the earthquake was, only how far away it was. If they
draw a circle on a map around the station where the radius of the
circle is the determined distance to the earthquake, they know the
earthquake lies somewhere on the circle.
Slide 58
Locating the Epicenter Scientists then use a method called
triangulation to determine exactly where the earthquake was. It is
called triangulation because a triangle has three sides, and it
takes three seismographs to locate an earthquake. If you draw a
circle on a map around three different seismographs where the
radius of each is the distance from that station to the earthquake,
the intersection of those three circles is the epicenter!
Slide 59
The last wave type is called the surface wave. This wave is the
slowest yet most destructive of the three, but this wave doesn't
always happen. The focus is where the earthquake starts and an
epicenter is the place on the surface above the focus so depending
on how deep the epicenter is the surface wave won't always happen.
There are two types of surface waves:
Slide 60
1 LOVE (L) WAVES. It's the fastest surface wave and moves the
ground from side-to-side. Confined to the surface of the crust,
Love waves produce entirely horizontal motion. (click on the
picture) Love waves travel at about 90% of the S wave velocity, and
have the largest amplitude, therefore porducing usually the most
damage.
Slide 61
2. RAYLEIGH WAVES A Rayleigh wave rolls along the ground just
like a wave rolls across a lake or an ocean. Because it rolls, it
moves the ground up and down, and side-to-side in the same
direction that the wave is moving. (click on the picture) Most of
the shaking felt from an earthquake is due to the Rayleigh wave,
which can be much larger than the other waves. They are slower than
body waves, roughly 90% of the velocity of S waves for typical
homogeneous elastic media. In the layered medium (like the crust
and upper mantle) the velocity of the Rayleigh waves depends on
their frequency and wavelength.
Slide 62
HOW DO WE MEASURE THESE WAVES?
Slide 63
SEISMOMETER: an instrument used to measure motions of the
ground (seismic waves generated by earthquakes, volcanic eruptions,
and other seismic sources).
Slide 64
These instruments measure the magnitude of the shock (and
after-shocks), as a function of the time they occurred.
Slide 65
Slide 66
CAN SCIENTISTS PREDICT EARTHQUAKES?
Slide 67
NO,
Slide 68
and it is unlikely they will ever be able to predict them.
Scientists have tried many different ways of predicting
earthquakes, but none have been successful. On any particular
fault, scientists know there will be another earthquake sometime in
the future, but they have no way of telling when it will
happen.
Slide 69
FOR MORE INFORMATION ABOUT EARTHQUAKES, INCLUDING EARTHQUAKE
FACTS AND FANTASIES, GO TO THE FOLLOWING:
http://earthquake.usgs.gov/learn/topics/megaqk_facts_fantasy.php
Slide 70
POST-MODULE QUESTIONS:
Slide 71
1.The interior of the Earth is completely solid. (T/F)
Slide 72
POST-MODULE QUESTIONS: 1.The interior of the Earth is
completely solid. (T/F) 2.Earthquakes are triggered by wave motion
passing between layers deep within the Earth. (T/F)
Slide 73
POST-MODULE QUESTIONS: 1.The interior of the Earth is
completely solid. (T/F) 2.Earthquakes are triggered by wave motion
passing between layers deep within the Earth. (T/F) 3.Seismic waves
cannot pass through the molten outer core of the Earth. (T/F).
Slide 74
POST-MODULE QUESTIONS: 1.The interior of the Earth is
completely solid. (T/F) 2.Earthquakes are triggered by wave motion
passing between layers deep within the Earth. (T/F) 3.Seismic waves
cannot pass through the molten outer core of the Earth. (T/F). 4.P
waves always arrive before S waves from the epicenter of an
earthquake. (T/F)
Slide 75
POST-MODULE QUESTIONS: 1.The interior of the Earth is
completely solid. (T/F) 2.Earthquakes are triggered by wave motion
passing between layers deep within the Earth. (T/F) 3.Seismic waves
cannot pass through the molten outer core of the Earth. (T/F). 4.P
waves always arrive before S waves from the epicenter of an
earthquake. (T/F) 5.Surface waves are the least destructive of
seismic waves. (T/F)
Slide 76
POST-MODULE QUESTIONS: 6.All seismic waves are longitudinal.
(T/F)
Slide 77
POST-MODULE QUESTIONS: 6.All seismic waves are longitudinal.
(T/F) 7.The inner core (at the center of the Earth) is the primary
source of waves inside the Earth. (T/F)
Slide 78
POST-MODULE QUESTIONS: 6.All seismic waves are longitudinal.
(T/F) 7.The inner core (at the center of the Earth) is the primary
source of waves inside the Earth. (T/F) 8.S waves can go through
solids, liquids and gases. (T/F)
Slide 79
POST-MODULE QUESTIONS: 6.All seismic waves are longitudinal.
(T/F) 7.The inner core (at the center of the Earth) is the primary
source of waves inside the Earth. (T/F) 8.S waves can go through
solids, liquids and gases. (T/F) 9.Since P and S waves travel at
different speeds, the location of the epicenter can be determined
by triangulation. (T/F)
Slide 80
POST-MODULE QUESTIONS: 6.All seismic waves are longitudinal.
(T/F) 7.The inner core (at the center of the Earth) is the primary
source of waves inside the Earth. (T/F) 8.S waves can go through
solids, liquids and gases. (T/F) 9.Since P and S waves travel at
different speeds, the location of the epicenter can be determined
by triangulation. (T/F) 10. P and S waves are also known as Body
Waves. (T/F)