Earthquakes Ch. 15 Lesson 1

What are Earthquakes? Earthquakes are the vibrations in the ground that result from the movement along breaks in Earth’s Lithosphere. Earthquakes are the vibrations in the ground that result from the movement along breaks in Earth’s Lithosphere.

What are Earthquakes? Why do rocks move along a fault? Why do rocks move along a fault? The forces that move tectonic plates also push and pull on rocks along faults The forces that move tectonic plates also push and pull on rocks along faults – movement of the plate due to convection currents

What are Earthquakes? These forces can move the rock side to side (horizontally) or up and down (vertically) These forces can move the rock side to side (horizontally) or up and down (vertically) The greater the force applied to a fault, the greater the chance of a large and destructive earthquake. The greater the force applied to a fault, the greater the chance of a large and destructive earthquake.

Quick Questions Why are earthquakes much more common in California? Why are earthquakes much more common in California? It is near (and in some places on top of) a plate boundary It is near (and in some places on top of) a plate boundary

Quick Questions What do you think scientists can learn by studying the damage caused by an earthquake? What do you think scientists can learn by studying the damage caused by an earthquake?

Quick Questions Are all earthquakes large and destructive? Are all earthquakes large and destructive? No! The destructiveness depends on the amount of force applied to a fault. The greater the force, the more energy builds up in a fault No! The destructiveness depends on the amount of force applied to a fault. The greater the force, the more energy builds up in a fault.

Where do Earthquakes Occur? The locations of major earthquakes that occurred between

Where do Earthquakes Occur? Notice, only a few earthquakes occurred in the middle of a continent. Notice, only a few earthquakes occurred in the middle of a continent. Most earthquakes occur where? Most earthquakes occur where?

Earthquakes and Plate Boundaries Some earthquakes occur more than 100 km below Earth’s surface. Some earthquakes occur more than 100 km below Earth’s surface. The deepest earthquakes occur where plates collide along a convergent plate boundary where subduction occurs The deepest earthquakes occur where plates collide along a convergent plate boundary where subduction occurs – Remember, oceanic meets continental crust !

Where do Earthquakes Occur? The locations of major earthquakes that occurred between

Shallow Earthquakes Shallow earthquakes are common where plates separate along a divergent plate boundary, like the mid-ocean ridge system. Shallow earthquakes are common where plates separate along a divergent plate boundary, like the mid-ocean ridge system.

Shallow Earthquakes Shallow earthquakes can also occur along transform plate boundaries like the San Andreas Fault in California. Shallow earthquakes can also occur along transform plate boundaries like the San Andreas Fault in California.

Continental Collisions Earthquakes of varying depths occur where continents collide. Earthquakes of varying depths occur where continents collide. Continental collisions result in the formation of large and deformed mountain ranges such as the Himalayas in Asia. Continental collisions result in the formation of large and deformed mountain ranges such as the Himalayas in Asia.

Rock Deformation When force is applied to a body of rock, depending on the properties of the rock and the force applied, the rock might bend or break. When force is applied to a body of rock, depending on the properties of the rock and the force applied, the rock might bend or break. When a force such as pressure is applied to rock along plate boundaries, the rock can change shape. When a force such as pressure is applied to rock along plate boundaries, the rock can change shape. – This is called rock deformation!

Rock Deformation Eventually the rocks can be deformed so much that they break and move. Eventually the rocks can be deformed so much that they break and move. The image shows how rock deformation has resulted in ground displacement The image shows how rock deformation has resulted in ground displacement

Faults When stress builds in places like a plate boundary rocks can form faults When stress builds in places like a plate boundary rocks can form faults A fault is a break in Earth’s lithosphere where one block of rock moves toward, away from, or past another. A fault is a break in Earth’s lithosphere where one block of rock moves toward, away from, or past another.

Faults When rocks move in any direction along a fault, an earthquake occurs. When rocks move in any direction along a fault, an earthquake occurs. The direction that rocks move depends on the forces applied. The direction that rocks move depends on the forces applied.

Faults

Quick Questions What is the relationship between earthquakes locations and plate boundaries? What is the relationship between earthquakes locations and plate boundaries? Most earthquakes result from the buildup and release of stress along active plate boundaries Most earthquakes result from the buildup and release of stress along active plate boundaries

Quick Questions Where do most earthquakes occur? Where do most earthquakes occur? Where stress builds up along active plate boundaries Where stress builds up along active plate boundaries

Quick Questions Why do earthquakes tend to be deeper and more disastrous along convergent plate boundaries compared to earthquakes along divergent boundaries? Why do earthquakes tend to be deeper and more disastrous along convergent plate boundaries compared to earthquakes along divergent boundaries? More energy is built up and released where plates move toward each other and where one plate is pushed below the other (subduction) at convergent boundaries More energy is built up and released where plates move toward each other and where one plate is pushed below the other (subduction) at convergent boundaries

Quick Questions What is rock deformation? What is rock deformation? Occurs when a rock changes shape Occurs when a rock changes shape

Quick Questions How can rock deformation result in ground displacement? How can rock deformation result in ground displacement? Eventually rocks can become so deformed that they break and move. When rocks move, ground displacement can occur Eventually rocks can become so deformed that they break and move. When rocks move, ground displacement can occur

Earthquake Focus When rocks move along a fault, they release energy that travels as vibrations on and in Earth called seismic waves. When rocks move along a fault, they release energy that travels as vibrations on and in Earth called seismic waves. These waves originate where rocks first move along the fault, at a location inside Earth called the focus. These waves originate where rocks first move along the fault, at a location inside Earth called the focus.

Earthquake Epicenter The epicenter is the location on Earth’s surface directly above the earthquake’s focus The epicenter is the location on Earth’s surface directly above the earthquake’s focus

Seismic Waves During an earthquake, a rapid release of energy along a fault produces seismic waves. During an earthquake, a rapid release of energy along a fault produces seismic waves. These waves travel outward in all directions through rock. These waves travel outward in all directions through rock. – these waves are a transfer of energy – create motion felt during earthquake – The energy is strongest near the epicenter and lessens as it moves outward

Types of Seismic Waves Scientists use wave motion, wave speed, and the type of material that the waves travel through to classify seismic waves. Scientists use wave motion, wave speed, and the type of material that the waves travel through to classify seismic waves. The 3 types of waves are The 3 types of waves are – Primary waves – Secondary waves – Surface Waves

Primary Waves Primary Waves (P- waves) cause particles in the ground to move in a push-pull motion similar to a coiled spring. Primary Waves (P- waves) cause particles in the ground to move in a push-pull motion similar to a coiled spring. They are the fastest moving seismic waves They are the fastest moving seismic waves The first waves you feel following an earthquake The first waves you feel following an earthquake

Secondary Waves Secondary Waves (S- waves) are slower than P- waves. Secondary Waves (S- waves) are slower than P- waves. Cause particles to move up and down at right angles relative to the direction the wave travels. Cause particles to move up and down at right angles relative to the direction the wave travels. – Like shaking a coiled spring side to side and up and down at the same time – Can’t move through liquid

Surface Waves Surface Waves cause particles in the ground to move up and down in a rolling motion Surface Waves cause particles in the ground to move up and down in a rolling motion – Similar to ocean waves Travel only on Earth’s surface closest to the epicenter Travel only on Earth’s surface closest to the epicenter – (only P and S waves can travel through Earth’s interior)

Seismic Waves

Quick Questions What are the 3 types of faults What are the 3 types of faults Strike-slip, normal, reverse Strike-slip, normal, reverse

Quick Questions Where do strike-slip faults occur? Where do strike-slip faults occur? Along transform plate boundaries Along transform plate boundaries

Quick Questions What are seismic waves? What are seismic waves? They are waves that travel as vibrations on and in Earth They are waves that travel as vibrations on and in Earth

Quick Questions Where do the seismic waves of an earthquake originate? Where do the seismic waves of an earthquake originate? Where rocks first move at an earthquake’s focus Where rocks first move at an earthquake’s focus

Quick Questions Why is locating the epicenter of an earthquake important to scientists? Why is locating the epicenter of an earthquake important to scientists? To observe patterns of movement along a fault and to predict the likelihood of future earthquakes nearby To observe patterns of movement along a fault and to predict the likelihood of future earthquakes nearby

Quick Questions What is the difference between surface waves and primary and secondary waves? What is the difference between surface waves and primary and secondary waves? Surface waves only travel on Earth’s surface. Primary and secondary waves also travel through Earth’s interior Surface waves only travel on Earth’s surface. Primary and secondary waves also travel through Earth’s interior

Mapping Earth’s Interior Scientists that study earthquakes are called seismologists Scientists that study earthquakes are called seismologists They use the properties of seismic waves to map Earth’s interior. They use the properties of seismic waves to map Earth’s interior.

Mapping Earth’s Interior P-waves and S-waves change speed and direction depending on the material they travel through. P-waves and S-waves change speed and direction depending on the material they travel through. By comparing these measurements to the densities of different Earth materials, scientists have determined the composition of Earth’s layers By comparing these measurements to the densities of different Earth materials, scientists have determined the composition of Earth’s layers

This figure shows the speed of P-waves and S-waves at different depths within Earth’s interior. This figure shows the speed of P-waves and S-waves at different depths within Earth’s interior.

Remember Me?

Inner and Outer Core S-waves cannot travel through the outer core! S-waves cannot travel through the outer core! Why would this be? Why would this be? Because the outer core is liquid unlike the solid inner core Because the outer core is liquid unlike the solid inner core By analyzing the speed of P-weaves traveling through the core, seismologists found that the inner and outer cores are composed of mostly iron and nickle By analyzing the speed of P-weaves traveling through the core, seismologists found that the inner and outer cores are composed of mostly iron and nickle

The Mantle Seismic wave studies determined convection currents in the mantle. Seismic wave studies determined convection currents in the mantle. The speeds of seismic waves depend on temperature, pressure, and chemistry of the rocks that the seismic waves travel through The speeds of seismic waves depend on temperature, pressure, and chemistry of the rocks that the seismic waves travel through They slow down through hot material They slow down through hot material Beneath mid-ocean ridges or hotspots Beneath mid-ocean ridges or hotspots Seismic waves are faster in cool areas Seismic waves are faster in cool areas Near subduction zones Near subduction zones

Locating an Earthquake’s Epicenter A seismometer measures and records ground motion and can be used to determine the distance seismic waves travel. A seismometer measures and records ground motion and can be used to determine the distance seismic waves travel. Ground motion is recorded as a seismogram – a graphical illustration of seismic waves Ground motion is recorded as a seismogram – a graphical illustration of seismic waves

Triangulation Seismologists use a method called triangulation to locate an earthquakes epicenter. Seismologists use a method called triangulation to locate an earthquakes epicenter. This method uses the speeds and travel times of seismic waves to determine the distance to the earthquake epicenter from at least 3 (like a triangle) different seismomenters This method uses the speeds and travel times of seismic waves to determine the distance to the earthquake epicenter from at least 3 (like a triangle) different seismomenters

Triangulation: Step 1 1)Find the arrival time difference determine the number of seconds between the arrival of the first P- wave and the first S- wave on the seismogram. determine the number of seconds between the arrival of the first P- wave and the first S- wave on the seismogram. This time difference is called lag time. This time difference is called lag time. Subtract the two times! Subtract the two times!

Triangulation: Step 2 2) Find the distance to the epicenter Use a graph showing the P-wave and S-wave lag time plotted against distance. Use a graph showing the P-wave and S-wave lag time plotted against distance. Look at the y-axis and locate line that intersects with lag time you calculated. Look at the y-axis and locate line that intersects with lag time you calculated. Red the corresponding distance from the epicenter on the x-axis Red the corresponding distance from the epicenter on the x-axis

Triangulation: Step 3 3)Plot the distance on a map

Quick Questions How do scientists learn about Earth’s interior How do scientists learn about Earth’s interior By using the properties of seismic waves to map Earth’s interior By using the properties of seismic waves to map Earth’s interior

Quick Questions How did scientists discover that Earth’s outer core is liquid? How did scientists discover that Earth’s outer core is liquid? Because S-waves cannot travel through the outer core Because S-waves cannot travel through the outer core

Quick Questions What happens to P- waves and S- waves at a depth of 2,500 km? What happens to P- waves and S- waves at a depth of 2,500 km? S-waveds stop because it is the liquid outer core. P- waves decrease in speed S-waveds stop because it is the liquid outer core. P- waves decrease in speed

Quick Questions What is the difference between a seismometer and a seismogram? What is the difference between a seismometer and a seismogram? A seismometer is an instrument that measures ground motion. A seismograph is a graphical illustration of earthquake waves A seismometer is an instrument that measures ground motion. A seismograph is a graphical illustration of earthquake waves

3 Scales Richter Scale Richter Scale Moment Magnitude Scale Moment Magnitude Scale Modified Mercalli Scale Modified Mercalli Scale

Determining Earthquake Magnitude The Richter Magnitude Scale uses the amount of ground motion at a given distance from an earthquake to determine the magnitude. The Richter Magnitude Scale uses the amount of ground motion at a given distance from an earthquake to determine the magnitude. – This is used when reporting to the public – It begins at zero, but there is no upper limit. – Each increase of 1 unit represents 10 times the amount of ground motion recorded

Richter Scale Example A magnitude 8 earthquake produces 10 times greater shaking than a magnitude 7 earthquake and 100 times greater than a magnitude 6. A magnitude 8 earthquake produces 10 times greater shaking than a magnitude 7 earthquake and 100 times greater than a magnitude 6.

Moment of Magnitude Scale A different scale used to measure the total amount of energy released by the earthquake. A different scale used to measure the total amount of energy released by the earthquake. – The units are exponential – For each increase of one unit on the scale, the earthquake releases 21.5 times more energy.

Moment of Magnitude Scale Example A magnitude 8 earthquake releases more than 992 times the amount of energy than that of a magnitude 6. A magnitude 8 earthquake releases more than 992 times the amount of energy than that of a magnitude 6.

The Modified Mercalli Scale Measures earthquake intensity based on descriptions of the earthquake’s effects on people and structures. Measures earthquake intensity based on descriptions of the earthquake’s effects on people and structures. – Ranges from I – XII (barely noticeable to everything is destroyed) (barely noticeable to everything is destroyed) – Places covered in loose sediment will experience a greater intensity of shaking than places on solid bedrock.

Earthquake Risk Most earthquakes occur near __________________ Most earthquakes occur near __________________ The ______________ plate boundary in California and ________________ plate boundaries in Oregon, Washington, and Alaska have the highest earthquake risks in the U.S. The ______________ plate boundary in California and ________________ plate boundaries in Oregon, Washington, and Alaska have the highest earthquake risks in the U.S.

Earthquake Risk U.S.

Tsunami OIfQ