A tsunami (often misnamed a "tidal wave") is a series of ocean waves typically generated by a major undersea earthquake or landslide. Historically, in California, tsunamis have most often been caused by distant earthquakes along the Pacific Rim, such as in Japan, Russia, Alaska and Chile. For example, the catastrophic tsunami caused by the great 2011 Japan earthquake (magnitude 9), after destroying coastal cities along Japan’s Sendai coast, raced 5,000 miles across the Pacific Ocean and caused millions of dollars in damage to several California harbors. A potential nearby source of tsunamis is the Cascadia subduction zone, a great undersea earthquake fault off the coast of Washington and Oregon that extends southward along the northern California coast. Low-lying coastal communities are most at risk from tsunami inundation. Beyond the immediate coastal area, there is little or no tsunami risk.
Although potential tsunami inundation is not a required disclosure under California law, increasingly coastal municipalities regulate development to minimize the threat of tsunamis to life and property. For this reason, a prospective buyer is likely to consider it material to a transaction if the sale property is located in a tsunami zone that is designated by a city or county in its General Plan Safety Element.