This chapter will help you understand the nature and origin of earthquakes. We discuss the seismic waves created by earthquakes and how the quakes are measured and located by studying these waves. We also describe some effects of earthquakes, such as ground motion and displacement, damage to buildings, and quake-caused fires, landslides, and seismic sea waves (tsunamis).
Earthquakes commonly affect other parts of the Earth system. Intense shaking associated with an earthquake can not only cause tremendous damage and loss of life, but can also trigger landslides that may disperse pathogenic microbes into the atmosphere and cause additional human health concerns. Such was the case after the 1994 Northridge, California earthquake. Another effect on the biosphere may be the unusual behavior of animals just before an earthquake as reported by Chinese scientists. Ground breakage associated with earthquakes may affect the hydrosphere by creating new lakes (sag ponds), increasing groundwater flow from springs, and displacing stream channels. Tsunamis generated by submarine earthquakes may cause tremendous damage to the coastal environment.
Earthquakes are largely confined to a few narrow belts on Earth. This distribution was once puzzling to geologists, but here we show how the concept of plate tectonics neatly explains it.
As geologists learn more about earthquake behavior, there is the possibility that we will be able to forecast earthquakes. We conclude the chapter with a look at this developing branch of study.
