Module 3 Kavli Institute for Theoretical Physics by Nick Nicastro.

Module 3 Kavli Institute for Theoretical Physics by Nick Nicastro

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.

MODULE 3 GENERAL OBJECTIVES: 1. To review basic concepts of wave theory with a special emphasis on important terminology.

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.

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.

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.

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.

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.

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.

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?

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)

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.

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

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

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

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

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

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.)

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.

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...

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

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.)

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!

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

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

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 .

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.)

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.

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.

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.

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.

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.

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.

BASIC WAVE THEORY WAVE PROPERTIES I.REFLECTION In geology, it is important in the study of seismic waves.

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.

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.

BASIC WAVE THEORY WAVE PROPERTIES II. REFRACTION

BASIC WAVE THEORY WAVE PROPERTIES II.REFRACTION SNELLS LAW

BASIC WAVE THEORY SNELLS LAW APPLIED TO SEISMOLOGY

Now, lets look at waves inside the Earth.

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).

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.

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

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

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

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.

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.

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.

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.

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)

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)

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

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)

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.

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.

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!

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:

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.

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.

HOW DO WE MEASURE THESE WAVES?

SEISMOMETER: an instrument used to measure motions of the ground (seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources).

These instruments measure the magnitude of the shock (and after-shocks), as a function of the time they occurred.

CAN SCIENTISTS PREDICT EARTHQUAKES?

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.

FOR MORE INFORMATION ABOUT EARTHQUAKES, INCLUDING EARTHQUAKE FACTS AND FANTASIES, GO TO THE FOLLOWING: http://earthquake.usgs.gov/learn/topics/megaqk_facts_fantasy.php

POST-MODULE QUESTIONS:

1.The interior of the Earth is completely solid. (T/F)

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)

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).

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)

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)

POST-MODULE QUESTIONS: 6.All seismic waves are longitudinal. (T/F)

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)

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)

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)

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)

Module 3 Kavli Institute for Theoretical Physics by Nick Nicastro.

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Transcript of Module 3 Kavli Institute for Theoretical Physics by Nick Nicastro.