The most common cause of tsunami is seismic activity. Over the past two millennia, earthquakes have produced 82.3% of all tsunami in the Pacific Ocean. Displacement of the Earth’s crust by several meters during underwater earthquakes may cover tens of thousands of square kilometers and impart tremendous potential energy to the overlying water. These types of events are common; however, tsunamigenic earthquakes are rare. Between 1861 and 1948, over 15,000 earthquakes produced only 124 tsunami. Along the west coast of South America, which is one of the most tsunamiprone coasts in the world, 1,098 offshore earthquakes have generated only 20 tsunami. This low frequency of occurrence may simply reflect the fact that most tsunami are small in amplitude and go unnoticed. Two-thirds of damaging tsunami in the Pacific Ocean region have been associated with earthquakes with a surface wave magnitude of 7.5 or more (Figure 5.1). The majority of these earthquakes have been teleseismic events affecting distant coastlines as well as local ones. One out of every three of these teleseismic events has been generated in the 20th century by earthquakes in Peru or Chile. This chapter discusses the mechanics of tsunamigenic earthquakes, and where possible, attempts to associate them with some of the signatures for tsunami presented in Chapter 3.
KeywordsSurface Wave Subduction Zone Inform ATION Surface Wave Magnitude Tsunami Earthquake
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