Northwest has seen some big quakes
Last month, a series of four earthquakes was recorded in North Idaho, the largest of which was a 3.9 on April 23.
Land masses that we live on are constantly moving, which is referred to as plate tectonics. Large earthquakes in the Northwest are the result of the Juan de Fuca plate subducting, or moving under, the large North American plate, creating stress. Over time, the stress becomes too great and the rocks snap, resulting in large earthquakes that can sometimes generate massive tsunamis.
Based on historical evidence, there was a huge megathrust earthquake on Jan. 26, 1700, known as the Cascadia earthquake. It happened across a 620-mile area along the Cascadia subduction zone, from the middle of Vancouver Island in British Columbia, Canada, south along the Pacific Northwest coast down into Northern California. The magnitude was estimated between 8.7 and 9.2. The devastating Alaska earthquake in 1964, the second largest recorded in history, was a 9.2.
The big quake in 1700 was believed to have generated a large tsunami that hit the coast of Japan. It may also have been linked to the Bonneville Slide, a major landslide that dammed the Columbia River near Cascade Locks in Oregon. The Native Americans referred to this as the “bridge of the gods.” However, other investigations date the landslide to around 1450, based on radiocarbon dating and dendrochronology (tree rings).
Geologic evidence shows that major earthquakes that would likely cause heavy damage to Seattle, Portland, Vancouver and other cities along the Pacific Northwest coast, occur approximately every 400 to 500 years. So, the chances of a major event in the near future are relatively small.
A recent geophysical survey confirms the presence of earthquake faults beneath the Spokane area. In 2001, the Latah Creek Fault was believed to be responsible for a swarm of 105 small earthquakes in the Spokane area. Most were less than a 4.0 magnitude, but there is the potential for small tremors in this area. Just ask the residents in North Idaho.