A presentation at the 2021 Annual Meeting of the Seismic Society of America (SSA) has cast doubt on the traditional scientific narrative about one of
A presentation at the 2021 Annual Meeting of the Seismic Society of America (SSA) has cast doubt on the traditional scientific narrative about one of the most infamous earthquakes in modern history. The event in question was the Cascadia earthquake of January 26, 1700, an 8.7-9.2-magnitude seismic disaster that wreaked havoc along the western coast of North America and created a massive tsunami that traveled across the Pacific Ocean before hitting the shores of Japan. The immense and prolonged shaking of the earth of the Cascadia earthquake, plus associated flooding caused by the inrush of ocean water over the sinking land, physically transformed the coastal and near-coastal areas of what is now the Pacific Northwest in the United States and Canada.
The traditional explanation credits this catastrophe to a single, enormous mega-thrust earthquake, which was precipitated by a slippage of the entire tectonic plate boundary in the region. But there is another possibility , according to an analysis introduced by University of Oregon seismologist Diego Melgar at the recent SSA meeting.
Tsunami ≈ zone warning sign on the Pacific Ocean coast warns the public about possible danger after an earthquake, and many Native American tribes are preparing for the “next” Cascadia earthquake. ( MichaelVi / Adobe Stock)
The New View of the Cascadia Earthquake and It’s Not Good
Using sophisticated software that creates 3D models of tectonic geometry, Melgar performed thousands of simulations of potential earthquake ruptures in the Cascadia region , to chart their intensity levels, damage ranges, and other characteristics.
Following this methodology, he concluded that the destruction caused by the famous Cascadia earthquake could have actually been created by a series of earthquakes, which might have occurred over a period of several years or even a decade.
A slippage of just 40 percent along the tectonic boundary would have been enough to precipitate the initial large quake and the Japan tsunami, while four subsequent quakes in the 8.0 or less range would have caused the rest of the damage observed by re-examining the geological record.
Melgar’s simulations don’t negate the singular quake hypothesis. But they do establish the viability of alternative theories.
“The January 26, 1700 event, as part of a longer-lived sequence of earthquakes potentially spanning many decades, needs to be considered as a hypothesis that is at least equally likely,” Melgar said.
As Melgar noted, his results are far from inconsequential. Current earthquake hazard maps are based on the assumption that the Cascadia fault zone will fully rupture every 500 years or so, which is the average time that has elapsed between major earthquakes in this region.
If this new theory is incorrect, full ruptures might be less likely than previously presumed. But partial ruptures followed by subsequent plate movements that cause additional catastrophic damage may be more likely to occur, which changes the way risks must be evaluated.
“Whether there was a partial or full rupture fundamentally drives everything we put on the hazard maps,” Melgar acknowledged. “So we really need to work on that.”
Many Native American communities in the Pacific Northwest have stories about the 1700 Cascadia earthquake and they sense it will happen again. ( Daniel Avram / Adobe Stock)
The Cascadia Earthquake in Native American Traditions
At the time of this land and life-altering event, the west coast of North America was occupied by a diverse mixture of sedentary Native American peoples. Their lives were profoundly disrupted by the powerful earthquake and heavy flooding it caused, which irrevocably altered the land they depended on for security and sustenance.
These groups relied on oral storytelling to transmit their historical experiences to their descendants.
For example, the Yoruk people of northern California told a tale of a being they called Earthquake, who on that horrible night lumbered up and down the coast, his heavy feet pounding the land, causing the ground to sink and the ocean water to pour in over everything. The people of the villages escaped to the top of a nearby hill, and performed a ceremonial dance to drive Earthquake away. But their efforts failed, and once they saw water covering their entire village they realized their world would never be the same.
From the perspective of the Quileute and Hoh people, who lived what is now the state of Washington, the cause of the destruction was something quite different. In their oral tradition , they described how Thunderbird and Whale had engaged in an epic battle on that fateful evening, uprooting the trees and causing the mountains to shake and crumble. As the struggle ensued, the ocean rose and came rushing in to cover the entire land.
In the version of the story passed on among the Huu-ay-aht people, who lived on Vancouver Island, the shaking of the earth was followed quickly by an overwhelming flood, and it all happened so fast that most of the people didn’t have time to escape from their homes and reach their canoes. “Everything then drifted away, everything was lost and gone,” their tragic story concludes.
These are a just few examples of how different Native American groups experienced and interpreted the catastrophic occurrences of January 26, 1700. What is most notable is that all the indigenous peoples that lived in the region had their own version of the core story, and those stories were kept alive orally from generation to generation.
Such stories were designed to be both informative and unforgettable. They brought history alive, by presenting it in a partially fictive or mythological format, full of action and drama. A great story well-told could act as a warning to future descendants, Native American storytellers believed, alerting them to the dangers of being complacent or unprepared in the face of nature’s fierce unpredictability.
The Cascadia earthquake and its relation to the Juan de Fuca Plate and the North America Plate. (U.S. Geological Survey (USGS) / Public domain )
Ready or Not: The 1700 Cascadia event Will Repeat!
While most residents of cities like Seattle and Vancouver seem to prefer blissful ignorance, some local Native American peoples are already taking action to protect themselves against future earthquakes and tsunamis.
For example, the Huu-ay-aht people have already moved their administrative headquarters to the highest point in their Vancouver Island territory. They’ve developed evacuation plans that will move all residents to this building as quickly as possible, should an earthquake occur, or a tsunami warning be issued.
Meanwhile, the Shoalwater Bay Indian Tribe, which resides on Washington’s west coast halfway between Seattle and Portland, is currently in the process of moving their entire community to a higher location. They will be building a sturdy vertical evacuation tower near Willapa Harbor, which could protect them from mega-tsunami surges.
The Quileute people of coastal Washington are also relocating. They received a land grant from the U.S. government in 2012, to facilitate a move of their communities inland and out of the tsunami danger zone.
Whether most people are prepared or not, it is certain that another mega-earthquake, or mega-quake sequence, will be coming to the Pacific Northwest at some point in the future. A 500-year average gap between such quakes would put the ETA for the next one in the year 2200, but the most recent mega-quake before the 1700 event occurred in 1310, which was just 390 years earlier.
A similar gap the next time would have the super-quake or quake sequence arriving before the end of this century, which from an historical perspective is just a hiccup in time away.
Top image: The “next” Cascadia earthquake could flood the coastal cities of the Pacific Northwest. Source: Christophe Fouquin / Adobe Stock
By Nathan Falde