The Most Powerful Earthquake to Ever Rumble Through Oregon

States in the western United States have a fairly high risk for earthquakes. Although Washington State receives more earthquakes than Oregon, the latter has still experienced some strong quakes in its history. Today, we’re going to look at the most powerful earthquake to ever rumble through Oregon. Learn how powerful this earthquake was, why experts don’t know much about it, and more!

What Was the Most Powerful Earthquake to Ever Rumble Through Oregon?

The most powerful earthquake to ever rumble through Oregon was an 8.7 to 9.2 M_w quake that struck the area on January 26, 1700. The earthquake occurred at the Cascadia subduction zone, a convergent plate boundary that runs from Vancouver Island in Canada to the northern part of California in the United States.

The interesting thing about this earthquake is the lack of information about it. Nobody made official records about the quake, and no tools existed to measure the earthquake by today’s standards, hence the estimate of the earthquake’s power.

Instead, scientists have relied on other evidence to get insights into the event. Some of the evidence includes changes in the coastal landscape, seawater advances, the widespread death of certain trees in the area during that time, and records of a tsunami hitting Japan early the following day. Scientists continue to study this quake and the impacts it had on the coastal areas.

What Caused the 1700 Cascadia Earthquake?

The most powerful earthquake to ever rumble through Oregon was caused by a megathrust event. Megathrusts occur in subduction zones where one tectonic plate is pushed under another. In this case, the Juna de Faca Plate is being pushed below the North American Plate. Every so often, the strain of these two plates moving against each other becomes too much, and the resulting shift causes powerful earthquakes.

Megathrust events often cause the most powerful earthquakes, generating more 8.5 M_w or stronger quakes than any other type of seismic event. Fortunately, the Cascadia subduction zone lies off the coast of Canada and the United States. Even though the quakes are very powerful, the fact that they occur far from inhabited areas limits the impact they have on human settlements.

Where Was the Epicenter on a Map?

Scientists believe that the earthquake’s epicenter was off the west coast of Oregon at 45°N 125°W. The epicenter would have been about 120 miles from Portland, Oregon today. So, the epicenter was far enough away from land that its impact was somewhat limited. Still, the earthquake caused a fair amount of destruction in the region.

The Damage Caused by the Earthquake and Its Subsequent Events

The 1700 Cascadia earthquake caused a great deal of damage to the coastal areas stretching from Vancouver Island to the northern parts of California. The coastline in the area dropped several feet, and a tsunami struck the area. Landslides caused widespread devastation in the area, endangering humans and animals alike. The quake’s shaking could have lasted as long as 7 minutes, destroying structures in the area and even making it hard to stand.

Oral traditions from this era say that villages along the coast were outright destroyed. However, a lack of written records from this time and place limits our collective understanding of the most powerful earthquake to ever rumble through Oregon.

However, written records from people in Japan mention the quake’s impacts on the island nation. High waves and minor flooding struck parts of Japan. However, no records of earthquakes exist in Asia or South America at this time. Scientists now believe that the 1700 Cascadia earthquake spawned the so-called “orphan tsunami” that led to minor damage in Japan.  

Did Any Casualties Occur from the Most Powerful Earthquake to Ever Rumble Through Oregon?

Unfortunately, the indigenous peoples living in the area did not write records about the impacts of the earthquake at the time. However, stories passed down by various indigenous peoples living in this area could be the key to understanding the events.

The Cowichan people living on Vancouver Island described violent shaking that collapsed homes. The tsunami completely wiped out a group of people living in a winter village at Pachena Bay. Other stories speak of a terrible nighttime earthquake that made their homes collapse, caused powerful floods, and spawned destructive landslides. The chances are good that some of these stories are connected to the 1700 Cascadia earthquake. However, some of them may not be.

The most powerful earthquake to ever rumble through Oregon was not directly measured using the tools and technology we have today. However, scientists believe that the quake had a magnitude of 8.7 to 9.2 M_w. No other quake has come close to the power and size of the 1700 Cascadia earthquake. However, given the nature of the subduction zone, another powerful earthquake is probably going to strike this area at some point in the future.

The photo featured at the top of this post is © MuhsinRina/Shutterstock.com