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84 <br /> <br />Tsunamis can result from off-shore earthquakes within the Bay Area or from distant <br />events. It is most common for tsunamis to be generated by offshore subduction faults <br />such as those in Washington, Alaska, Japan, and South America. Tsunami waves <br />generated at those far-off sites can travel across the ocean and can reach the <br />California coast with several hours of warning time. Local tsunamis can also be <br />generated from offshore strike-slip faults. Because of their close proximity, we would <br />have little warning time. However, the Bay Area faults that pass through portions of <br />the Pacific coastline or under portions of the Bay are not likely to produce significant <br />tsunamis because they move side to side, rather than up and down, which is the <br />displacement needed to create significant tsunamis. They may have slight vertical <br />displacements, or could cause small underwater landslides, but overall there is a <br />minimal risk of any significant tsunami occurring in the Bay Area from a local fault. <br />The greatest risk to the Bay Area is from tsunamis generated by earthquakes <br />elsewhere in the Pacific. But, a tsunami or seiche originating in the Pacific Ocean <br />would lose much of its energy passing through San Francisco Bay. <br /> <br />Though the Bay Area has experienced tsunamis, it has not experienced significant <br />tsunami damage. In 1859, a tsunami generated by an earthquake in Northern <br />California generated 4.6-meter wave heights near Half Moon Bay. <br /> <br />The M6.8 1868 earthquake on the Hayward fault is reported to have created a local <br />tsunami in the San Francisco Bay. In 1960, California experienced high water <br />resulting from a magnitude 9.5 earthquake off the coast of Chile. The tsunami <br />generated by the 1964 Alaskan earthquake caused wave heights of up to 1.1 meters <br />along the coasts of San Francisco, Marin and Sonoma Counties. <br /> <br />Although the 2011 tsunami created by the M9.0 Tohoku earthquake did not cause <br />damage inside the San Leandro marina, the marina did experience a 4 inch run-up. <br />California has been fortunate in past distant-source tsunamis (1960, 1964, and 2011) <br />that the events occurred during low tides. 18 In 2013, the USGS, in partnership with <br />the US Department of the Interior, published a tsunami scenario as part of the Science <br />Application for Risk Reduction (SAFRR) series.20 In the scenario, the multi- <br />disciplinary team modeled a M9.1 offshore Alaskan earthquake to study impacts to <br />California. Assuming that the tsunami reaches the central coast at high tide, the Bay <br />Area can expect heights ranging from two to seven meters near the shore. The study <br />suggests that this scenario inundation is only likely to occur once in a 100-year <br />period. <br /> <br /> <br /> <br /> <br /> <br /> <br />______________________________________________________________________________________________________ <br />________________________________________________________________________________________________ <br />20 Ibid <br />123