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earthquakes which cause a sudden rise or fall of part of the ocean floor. Such movements may produce tsunami waves, which have nothing to do with the ordinary ocean tides. In the open ocean, far from land, in deep water, tsunami waves may be only a few inches high and thus be virtually undetectable, except by specia~ monitoring instruments. These waves travel across the ocean at speeds of several hundred mikes per hour. When such waves reach shallow water near the coastline, they slow down and can gain great heights. Tsunamis affecting the Oregon coast can be produced from very distant earthquakes off the coast of Alaska or elsewhere in the Pacific Ocean. For such tsunamis, the warning time for the Oregon coast would be at least several hours. However, interface earthquakes on the Cascadia Subduction Zone can also produce tsunamis. For such earthquakes the warning times would be very short, only a few minutes. Because of this extremely short warning time, emergency planning and public education are essential before such an event occurs. However, the Eugene/Springfield Metro Area, not being located on the coast, cannot be affected by such tsunamis on the Oregon Coast. Another earthquake related phenomenon is "seiches" which are waves from sloshing of inland bodies of waters such as lakes, reservoirs, or rivers. In some cases, seiches have caused damages to shorefront structures and to dams. However, for the Eugene/Springfield Metro Area vicinity the potential for seiches of sufficient magnitude to cause significant damage to upstream appears Iow. 10.4 Risk Assessment for Scenario Earthquakes As part of the Regional All Hazard Mitigation Plan (Phase Two), a seismic risk assessment for Benton, Lane and Linn Counties was conducted by estimating the extent of damage and casualties likely in each of the two scenario earthquakes on the Cascadia Subduction Zone discussed above: a M8.5 interface earthquake and a M7.5 intraplate earthquake. For Level One Loss modeling, earthquake ground motions were calculated at the center of each census tract and these values were used for the entire census tract. Further technical details of the loss estimation calculations are given in Chapter 4 of the Regional Mitigation Plan Phase Two Technical Appendix. The census data used for these loss estimates were from the 1990 census, as 2000 census results were not available at the time of this data compilation. Building inventory and thus damages and casualties are generally proportional to population. Thus, these 1990-based calculations can be adjusted to current population levels. Lane County's population rose about 14% between 1990 and 2000 and thus, the 2000 equivalents for the damage and casualty estimates would also be about 14% higher than the t990 values from the Regional Plan. For each of these scenario earthquakes, building damage estimates for Lane County are approximately $1.6 to $1.7 billion. Injuries were estimated to be about 2,600 to 2,700 for daytime earthquakes and about 700 for nighttime earthquakes. Deaths were estimated to be about 45 for daytime earthquakes and about 4 for nighttime earthquakes. Casualties are much lower for nighttime earthquakes, because most of 10-10