Earthquakes and Tsunamis: Fundamental Concepts

In Earthquakes and Tsunamis: Fundamental Concepts , you'll learn ...

• How the scientific knowledge about earthquakes was developed
• How the severity and size of earthquakes are determined using: The Rossi-Forel Intensity Scale, The Modified Mercalli Intensity Scale, The Richter Magnitude Scale
• Faults and the geometrical relationship between the fault plane, the hypocenter (or focus) and the epicenter of an earthquake
• The seismograph (an instrument used to capture and record the ground vibrations that accompany an earthquake)

Overview

Credit: 3 PDH

Length: 25 pages

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 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.