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Earthquakes: Basic Principles

Samir G. Khoury, Ph.D., P.G.

This course introduces you to the basic concepts about earthquakes. Following a brief narrative of the myths and mystery that surrounded the occurrence of earthquakes through 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 1811-1812 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. You will also learn that the 1906 San Francisco earthquake produced a wealth of recorded observations that allowed H. F. Reid to formulate the elastic rebound theory to explain the mechanism of earthquake generation.

Some of the largest magnitude earthquakes in the World since 1900 are the 1960 Chile earthquake, the 1964 Alaska earthquake and the 2004 South East Asia earthquake. These earthquakes are described because of their very large magnitude and because they disturbed the ocean floor generating immense sea waves called “tsunamis”, a Japanese word for “port wave”. These waves devastated the coastal towns they hit. Information about the Great Southeast Asia Earthquake and Tsunami of 2004 is 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 caught 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 long and varied experience of the author gained while dealing with the diverse seismic issues he encountered on the major engineering projects he managed in the United States and around the world.

This course includes a multiple choice quiz at the end, which is designed to enhance the understanding of the course materials.

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NY PE & PLS: You must choose courses that are technical in nature or related to matters of laws and ethics contributing to the health and welfare of the public. NY Board does not accept courses related to office management, risk management, leadership, marketing, accounting, financial planning, real estate, and basic CAD. Specific course topics that are on the borderline and are not acceptable by the NY Board have been noted under the course description on our website.