Transform boundaries develop where one plate simply slides past the other along a transform fault, with the most famous example being the San Andreas fault along the western North America transform boundary. Historical accounts of many earthquakes along transform boundaries have shown that the amount of death and destruction is closely related to the population density and quality of buildings in an area. If a huge earthquake hits an unpopulated area, it is of little consequence. However, even moderate-sized earthquakes have killed tens and even hundreds of thousands of people in areas with homes made of unreinforced concrete, piles of stones, or loose earth. Southern California is the most vulnerable area in the United States for future large earthquakes along a transform boundary in a densely populated area, and residents in that area need to be diligent in application of strict building codes, in development of earthquake warning systems, and in preparation of sophisticated emergency response plans.
Southern California is most likely to suffer a major earthquake in the next 50 years, although it is currently impossible to tell exactly when this earthquake might strike. Government disaster planners in potentially affected regions are devising emergency response plans, and building codes have been improved to make the people and infrastructure in these areas less prone to injury and damage. Continued studies and monitoring can continue to improve the science of earthquake prediction, perhaps one day saving thousands of lives.
See also convergent plate margin processes; divergent plate margin processes; ophiolites; plate tectonics; structural geology.
Kious, W. Jacquelyne, and Robert I. Tilling. This Dynamic Earth: The Story of Plate Tectonics. Online edition. URL: http://pubs.usgs.gov/gip/dynamic/dynamic.html. Last modified March 27, 2007. Skinner, B. J., and B. J. Porter. The Dynamic Earth: An Introduction to Physical Geology, 5th ed. New York: John Wiley & Sons, 2004. Wallace, R. E., ed. "The San Andreas Fault System." Professional Paper 1515. Calif.: U.S. Geological Survey, 1990.
tsunami, generation mechanisms A tsunami is a long-wavelength seismic sea wave generated by the sudden displacement of the seafloor. The name is of Japanese origin, meaning harbor wave. Tsunamis are also commonly called tidal waves, although this is improper because they have nothing to do with tides. Every few years, these giant sea waves rise unexpectedly out of the ocean and sweep over coastal communities, killing hundreds or thousands of people and causing millions of dollars in damage. Major tsunamis hit coastal areas in 1946, 1960, 1964, 1992, 1993, and 1998 in coastal Pacific regions, and in 2004 the Indian ocean was swept by a tsunami that killed 283,000 people. in 1998 a catastrophic 50-foot- (15.2-m-) high wave unexpectedly struck Papua New Guinea, killing more than 2,000 people and leaving more than 10,000 homeless.
Tsunamis may be generated by any event that suddenly displaces the seafloor, which in turn causes the seawater to move suddenly to compensate for the displacement. Most tsunamis are caused by earthquakes on the seafloor or are induced by volcanic eruptions that suddenly boil or displace large amounts of water. Giant submarine landslides have initiated other tsunami, and it is even possible that gases dissolved on the seafloor may suddenly be released, forming a huge bubble that erupts upward to the surface, generating a tsunami. The most catastrophic tsunami in the geological record may have been thousands of feet (hundreds of meters) tall, generated when asteroids or meteorites impacted with Earth in the oceans, displacing huge amounts of water in a geological instant.
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