Another major source of tsunamis in the western United States is the 

 Aleutian Trench. Only relatively recent records exist for the area. 

 Analysis of these records by Houston and Garcia (1974) , as revised in 

 Houston, et al. (1975b) and Houston and Garcia (1978), gives 



n(m) = 0.113" - 71 m 



(7) 



which is similar to the previous equation for the Peru-Chile Trench. The 

 probability of tsunami occurrence is assumed to be uniform along the 

 trench. The distribution of recent earthquakes along the Aleutian Trench 

 is shown in Figure 3, and the mean annual number of earthquakes of any 

 given magnitude in Figure 4. The straight lines in Figure 4 are not 

 accurate above an earthquake magnitude, M, of about 8.5 because of the 

 physical limits on allowable stresses in the rock forming the Earth's 

 crust. Also, the straight lines in Figure 4 representing the occurrence 

 of earthquakes in Alaska and the world would intersect at an earthquake 

 magnitude of about 2.5, so the plotted lines should not be extrapolated 

 to values of earthquake magnitude less than those shown. 



_70W I70E 



Figure 3. Principal fault systems and distribution of epicenters of major 

 Alaskan earthquakes, 1898-1961 (from Wilson, 1969; adapted from 

 Davis and Echols, 1962). 



25 



