Pacific Northwest Earthquake History
The Pacific Northwest has experienced several types of earthquake events over the years. The table below lists these historical events and the predicted magnitudes (M) of future events.
| Crustal Earthquakes | Deep or Intraplate Earthquakes | (Cascadia) Subduction Zone Earthquakes (CSZ) |
|
1872 North Cascades 1993 Scott Mills 1993 Klamath Falls 1999 Woodburn Evidence of 7 meters of uplift suggests a M 7.0 event occurred on the Seattle fault in the shallow crust below Seattle about 1100 years ago. |
1949 near Olympia, Washington 1965 between Seattle and Tacoma, Washington |
There have been no major earthquakes associated with this zone since historical records began in the 1790s. Earthquakes have occurred, however, at the southern end of the Cascadia Subduction Zone near the California-Oregon border, including a M 6.8 in 1873 and a M 7.1 in 1992.
There is evidence of a Pacific Northwest pre-European Habitation major earthquake event: January 26, 1700 |
| Future Events (maximum estimated magnitude) | ||
| M 6.5-7.0 | M 7.5 | M 8.0 to 9.0 |
Locations of Historical Earthquakes
Historical Evidence of Cascadia Subduction Zone (CSZ) Earthquakes
While there have not been any recent events in the Cascadia Subduction Zone (CSZ), there is a great deal of evidence that suggests the region experienced an extremely large earthquake event, M 9.0, on the evening of January 26, 1700, (Yeats et al. 1997) including the following:
· Native American Folklore: Stories exist within Pacific Northwest Native American tribes of coastal communities destroyed by great waves in the middle of the night many generations ago (Satake et al. 1996).· Japanese Historical Documents: Historical tsunami records from numerous coastal communities in Japan suggest an earthquake in the Pacific Northwest along the CSZ occurred at 9 p.m., January 26, 1700.
· Sudden Subsidence: Buried marsh soils and killed trees from tidal immersion show sudden subsidence of at least 0.5 meters at more than a dozen estuaries between Clayoquout Sound, British Columbia, and the Eel River, California. The timing of these events, approximately 1700 A.D., coincides with the Japanese documents.
· Tsunami Sedimentation: Some of the buried soils indicative of sudden subsidence are also covered by sand layers, suggesting tsunamis. In some cases, sand surrounds growth-position stems and leaves of plants. Again, the dating of these features places them near the proposed 1700 event.
· Liquefaction Features: Features along the lower Columbia River provide strong evidence that onshore shaking accompanied sudden land-level changes along the Pacific Coast. The features, identified 30 to 60 kilometers inland, include sand that erupted onto tidal swamps about 300 years ago.
For more information on earthquake history of the Pacific Northwest, visit the University of Washington Web site.