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Except for the recent rumblings of a few moderate earthquakes and the eruption of Mt. St. Helen's, all has been relatively quiet on the Pacific Northwestern front. The Cascades region in the Pacific Northwest, a sporadically active earthquake and volcanic zone, still has great seismic potential [Atwater, 1987], as comparisons with other subduction zones around the world have shown [Heaton and Kanamori, 1984]. Recent tsunami propagation models [Satake, 1996] and tree ring studies suggest that the last great Cascadia earthquake occurred in the winter of 1700 A.D. and had a magnitude of −8.9. The North Cascades or Wenatchee earthquake followed in 1872. With an estimated magnitude greater than 7, it was the largest earthquake in the written history of Washington and Oregon.
Miller, M., Dragert, H., Endo, E., Freymueller, J., Goldfinger, C., Kelsey, H., Humphreys, E., & Johnson, D. (1998). Precise measurements help gauge pacific northwest’s earthquake potential. Eos, Transactions American Geophysical Union, 79(23), 269. https://doi.org/10.1029/98eo00202
Eos, Transactions American Geophysical Union
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