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Earthquakes and Tsunamis: Fundamental
Concepts
Dr. Samir G. Khoury, Ph.D, P.G.
Overview
This
course introduces you to the fundamental concepts about earthquakes. Following a
brief narrative of the myths and mystery that surrounded the occurrence of
earthquakes throughout history, the course describes the precise effects of the
first major earthquake recorded in the mid-eighteenth century. This initial
advance led to the development of the new discipline of seismology in the
nineteenth century, and by the late nineteenth century sufficient progress had
been made to develop standardized scales to characterize the shaking severity of
earthquakes. With the advent of the twentieth century and the development of
instruments that capture and record the ground motion generated by earthquakes,
it became possible to eventually develop the Richter magnitude scale.
The
intensity of shaking as a measurement scale is presented: the Rossi-Forel and
the Modified Mercalli scales. An explanation is given as to why these scales are
not entirely satisfactory for measuring the absolute size of earthquakes. The
discussion about the modern magnitude scale covers its use as a measurement of
earthquake size and as an index of the energy released at the source of an
earthquake. The association between faults and earthquakes is explained and the
geometrical relationship between the fault plane, the hypocenter (or focus) and
the epicenter of an earthquake is illustrated.
The
major earthquakes that have affected North America, namely the 1811 New Madrid,
Missouri, the 1886 Charleston, South Carolina, and the 1906 San Francisco,
California, earthquakes are described. The intensity of the ground shaking
associated with these three earthquakes is presented in a figure that clearly
shows that at the same intensity level, the shaking effects extend over a much
larger area in the Eastern United States than in the Western United States.
The great 1964 Prince William
Sound, Alaska earthquake is described because of its very large magnitude and
because it disturbed the ocean floor generating immense sea waves called
“tsunamis”, a Japanese word for “huge wave”. These waves devastated coastal
towns around the Gulf of Alaska and along the western coast of North America.
The tsunami waves traveled across the Pacific Ocean at great speed reaching the
islands of Hawaii and Japan causing damage there too. Information about the
Great Southeast Asia Earthquake and Tsunami of 2004 is also presented and
discussed. This 2004 tsunami was one of the largest ever in terms of casualties
because it hit heavily populated low-lying coastal areas in many countries that
were completely unprepared.
Finally, the equations used to derive the Richter magnitude of an earthquake and
compute the energy released during that earthquake are presented in an Appendix.
Also, a glossary of terms and acronyms used is provided as a reference to assist
the student in following the concepts that are discussed throughout.
The information presented in this course is based on the professional experience
gained by the author over more than thirty-five years of dealing with various
aspects of seismic issues associated with the major engineering projects he
managed around the world. Subsequent courses will deal with additional aspects
of earthquake studies (such as detection, location, and the nature of ground
motion) and the advances that led to a fuller understanding of the structure of
the earth.
The
student must take a multiple-choice quiz consisting of seventeen questions at the end of this course
to earn PDH credits.
Specific Knowledge or Skill Attained
At
the end of this course, you should be able to understand how the scientific
knowledge about earthquakes was developed. You will also learn how the severity
and size of earthquakes are determined using:
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The Rossi-Forel Intensity Scale
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The Modified Mercalli Intensity Scale, and
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The Richter Magnitude Scale
You
will learn about faults and should be able to understand the geometrical
relationship between the fault plane, the hypocenter (or focus) and the
epicenter of an earthquake. You should also be able to follow the basic concepts
behind:
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The seismograph (an instrument used to capture and record the ground
vibrations that accompany an earthquake)
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The seismogram (the permanent record of an earthquake as recorded by a
seismograph), and
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The basic equations that are used to compute the Richter magnitude and the
total energy released during an earthquake
Finally you will learn about the major earthquakes that have affected North
America and their effects over large areas. You will also learn that large
earthquakes that affect the ocean floor are capable of generating immense sea
waves called “tsunamis”, a Japanese word for “huge wave”. These tsunami waves
can travel across oceans at great speed inflicting significant damage to distant
coastal towns.
Course
Click on the following PDF attachment to review
the course "Earthquakes: Fundamental Concepts" prior to taking a
quiz for credit.
"Earthquakes
Tsunamis
Fundamental Concepts" (544 KB)
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credit. Click on the link below.
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