The Cascadia Subduction Zone lies 50 miles off the coast of southwest British Columbia, Washington, Oregon and Northern California. It formed as the ocean crust of the Juan de Fuca Plate, subducts beneath the North American Plate. The fault runs about 50 miles offshore for 1094 kilometers (680 miles). The plates are locked and strain is building in the rocks.
Tectonic plate movement in the Pacific Northwest, USGS
Great earthquake on January 26, 1700
The last great Cascadia earthquake happened over 300 years ago. Records of the event were not written down but researchers have discovered through evidence in peat bogs, tree rings and Japanese tide records of a tsunami when the event occured and the time based on the speed of tsunamis.
Today scientists believe a megathrust earthquake occurred on January 26, 1700 at 9:00 pm. The fault broke along 1000 kilometers (620 miles) and produced an earthquake with a magnitude between 8.7 and 9.2 on the moment magnitude scale. Scientists believe another megathrust earthquake could happen at anytime sending tsunamis onto coastal areas.
Formation of Cascade Range
Towering volcanoes have formed on the continental side of the fault zone. Mount Rainier, Mount Saint Helens, Mount Hood, Mount Mazama and Mount Lassen are some of the volcanoes that make up the Cascade Range. These volcanoes have erupted in the not too distant past.
Mount Saint Helens
Mount Saint Helens is one of the most active in the Cascade Volcanic Arc. It erupted in 1980 with a massive eruption that formed a caldera in the summit. Today a lava dome is growing in the caldera and the area around the volcano has been declared a national monument.
2010 Chilean Earthquake Another megathrust earthquake struck Chile in 2010. Find out why these earthquakes occur so frequently there.
Island Arcs Island arcs are a string of volcanic islands in the ocean. Find out more about these islands in the Pacific Ocean.
Strike Slip Fault Learn more about strike slip faults that are boundaries between crustal plates including the San Andreas Fault.
Subduction Zones Find out why the Pacific Ring of Fire has so many subduction zones.
Aleutian Trench Learn more about this long trench which parallels the Aleutian Islands.
Cascadia Subduction Zone Learn more about the Cascadia Subduction Zone in the Pacific Northwest where a great earthquake could occur at any time.
Pacific Ring of Fire Learn more about the Ring of Fire which is home to towering volcanoes and great earthquakes.
Kids Fun Science The links on our home page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more.