Puget Sound faults about 1100 years ago (AD 900—930) an earthquake of magnitude 7+ uplifted Restoration Point and Alki Point, dropped West Point (the three white triangles in the Seattle Basin on the map), caused rockslides in the Olympics, landslides into Lake Washington, and a tsunami on Puget Sound. It extends as far east as (and probably terminates at) the Rattlesnake Mountain Fault Zone (RMFZ; the southern extension of the SWIF) near Fall City. This seems geologically reasonable, as both the SWIF and RMFZ appear to be the contact between Tertiary Crescent Formation basement of Puget Sound on the west and the older
1965 Puget Sound earthquake about the installation of the Pacific Northwest Seismic Network in 1969. 1965 Puget Sound earthquake The 1965 Puget Sound earthquake occurred at 08:28 PDT (15:28 UTC) on April 29 within the Puget Sound region of Washington State. It had a magnitude of 6.7 on the moment magnitude scale and a maximum perceived intensity of VIII ("Severe") on the Mercalli intensity scale. It caused the deaths of seven people and about $12.5–28 million in damage. There were no recorded aftershocks. The western part of Washington State lies above the Cascadia subduction zone, where the Juan de Fuca Plate is being subducted