11-7 Seismometers are used to record seismic waves as well as locate and measure earthquakes Earthquake magnitude is expressed as a whole number and a decimal fraction Seismology is the study of seismic waves to learn about Earth’s interior, the Earth’s internal discontinuities, and to image the interior using seismic tomography Learning Objectives: You will understand how to use a seismogram to locate an earthquake, how earthquake size is measured, and how seismologists use data from earthquakes to learn about Earth’s internal structure. Earthquakes: Part 2 CHAPTER 11

First seismic instrument: Chang Heng’s Seismoscope 132 AD 11-7 Seismometers are used to record seismic waves as well as locate and measure earthquakes. More modern seismometers record the ground shaking. The recording is called a seismogram. Now, seismograms are recorded digitally with sophisticated electronics. 1970’s

A seismogram is made by a seismometer. Copyright © 2014 John Wiley & Sons, Inc. All rights reserved Seismometers are used to record seismic waves as well as locate and measure earthquakes.

With three seismograms, we can triangulate the earthquake’s location 11-7 Seismometers are used to record seismic waves as well as locate and measure earthquakes.

11-8 Earthquake magnitude is expressed as a whole number and a decimal fraction Seismology is the study of seismic waves to learn about Earth’s interior, the Earth’s internal discontinuities, and to image the interior using seismic tomography Learning Objectives: You will understand how to use a seismogram to locate an earthquake, how earthquake size is measured, and how seismologists use data from earthquakes to learn about Earth’s internal structure. Earthquakes: Part 2 CHAPTER 11

Richter scale is a magnitude system designed specifically for earthquakes in California Copyright © 2014 John Wiley & Sons, Inc. All rights reserved Earthquake magnitude is expressed as a whole number and a decimal fraction This “corrects” for the decay in amplitude with distance The amplitude reflects the intensity of the quake

Richter Scale  Magnitude ranges from 0 to 10  An increase in magnitude of 1.0 indicates an earthquake that 32 times larger!  There are many more small earthquakes than big ones 11-8 Earthquake magnitude is expressed as a whole number and a decimal fraction

The earthquake Intensity Scale (Modified Mercalli) measures the damage caused by earthquakes Earthquake magnitude is expressed as a whole number and a decimal fraction

Seismologists measure earthquake strength using Moment Magnitude. It measures the energy released based on the total area of the slip surface and the amount of slip. It is generally applicable to earthquakes every where in the world and gives higher precision for larger quakes Earthquake magnitude is expressed as a whole number and a decimal fraction

Earthquake Prediction? Not possible yet! Instead, we have Earthquake Forecasts.

11-7 Seismometers are used to record seismic waves as well as locate and measure earthquakes Earthquake magnitude is expressed as a whole number and a decimal fraction Seismology is the study of seismic waves to learn about Earth’s interior, the Earth’s internal discontinuities, and to image the interior using seismic tomography. Learning Objectives: You will understand how to use a seismogram to locate an earthquake, how earthquake size is measured, and how seismologists use data from earthquakes to learn about Earth’s internal structure. Earthquakes: Part 2 CHAPTER 11

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved. Wave reflection and refraction are used to identify a seismic discontinuity Seismology is the study of seismic waves to learn about Earth’s interior, the seismic discontinuities in the Earth, to image the interior using seismic tomography Slower seismic waves Faster seismic waves Slower seismic waves

P-wave and S-wave shadow zones confirm the presence of a liquid outer-core Copyright © 2014 John Wiley & Sons, Inc. All rights reserved Seismology is the study of seismic waves to learn about Earth’s interior, the discontinuities in the Earth, to image the interior using seismic tomography

P-wave and S-wave shadow zones confirm the presence of a liquid outer-core Copyright © 2014 John Wiley & Sons, Inc. All rights reserved Seismology is the study of seismic waves to learn about Earth’s interior, the discontinuities in the Earth, to image the interior using seismic tomography

Reflections and refractions confirm the presence of discontinuities in rock density inside the Earth Seismology is the study of seismic waves to learn about Earth’s interior, the seismic discontinuities in the Earth, to image the interior using seismic tomography Mohorovicic Discontinuity is the base of the crust: ~ 8 km beneath oceanic basins ~ 20 to ~70 km beneath continents

Seismic Tomography is used to image the Earth’s interior (see also Seismology is the study of seismic waves to learn about Earth’s interior, the seismic discontinuities in the Earth, to image the interior using seismic tomography Red = slow seismic waves, low density, hot Blue =fast seismic waves, high density, “cool”

Modeling with tomographic images Copyright © 2014 John Wiley & Sons, Inc. All rights reserved Seismology is the study of seismic waves to learn about Earth’s interior, the seismic discontinuities in the Earth, to image the interior using seismic tomography

Tomography images of the Hawaiian mantle plume NW SE NW SE Seismology is the study of seismic waves to learn about Earth’s interior, the seismic discontinuities in the Earth, to image the interior using seismic tomography Red = slow seismic waves, low density, hot Green= normal mantle Blue =fast seismic waves, high density, “cool”

Tomography studies of the Western US image subducting lithosphere and the Yellowstone mantle plume Seismology is the study of seismic waves to learn about Earth’s interior, the seismic discontinuities in the Earth, to image the interior using seismic tomography

11-7 Seismometers are used to record seismic waves as well as locate and measure earthquakes Earthquake magnitude is expressed as a whole number and a decimal fraction Seismology is the study of seismic waves to learn about Earth’s interior, the Earth’s internal discontinuities, and to image the interior using seismic tomography. Learning Objectives: You will understand how to use a seismogram to locate an earthquake, how earthquake size is measured, and how seismologists use data from earthquakes to learn about Earth’s internal structure. Earthquakes: Part 2 CHAPTER 11