-
Marine geophysicists have just published the most comprehensive survey of the Cascadia Subduction Zone to date.
-
The Cascadia Subduction Zone is a fault located on the Pacific coast from northern California to British Columbia.
-
Is it possible to produce “giant” earthquakesand researchers have identified the most dangerous part of it.
Hidden off the west coast of the USA, beneath the Pacific Ocean, is the Cascadia Subduction Zone. This fault is capable of generating earthquakes greater than magnitude 8 that can be felt hundreds of kilometers away, and a recent study has identified the most dangerous segment along its 700-kilometer long stretch.
The results will help scientists evaluate earthquake and tsunami risk for this region, including a particularly vulnerable state: Washington.
“This has been a subduction zone this has been understudied with the types of tools we have available now,” geophysicist Suzanne Carbotte, Bruce Heezen Lamont Research Professor at Columbia University, told Business Insider.
Armed with cutting-edge technology that can probe in the depths of the ocean floor and create images, Carbotte and his team produced the first comprehensive survey of Cascadia’s complex underground composition. They published their work today in the scientific journal Science Advances.
The researchers found that Cascadia is divided into at least four segments, which has been suggested by previous studies but never confirmed, Carbotte said.
The image “before our study was a smooth surface with no obvious relationship to this segmentation,” Carbotte said. “But that smooth surface was based on very, very sparse data. And in some places, no data at all.”
This new image provides a much more accurate view of the complexity of Cascadia and the risk it poses to the US West Coast.
How the Cascadia Subduction Zone Causes Earthquakes
Cascadia is essentially the border between two tectonic plates: the huge North American continent and the smaller Juan de Fuca dish.
The Juan de Fuca plate is gradually sliding (or subducting) eastward beneath the North American platewhich creates a megathrust fault: a place where tectonic plates move against each other in dangerous ways.
The tension driving the Juan de Fuca plate beneath North America is continuous, Carbotte explained, but the plate’s motion is not. Sometimes it gets stuck.
When braking like this, the plates can only absorb the tension for so long before finally breaking, causing an earthquakeshe said.
This is what scientists think happened about 300 years ago when the zone broke into the sea and the resulting earthquake formed a huge tsunami that hit the coast of Japan.
Although Cascadia hasn’t produced a major earthquake since the 1700s, it’s only a matter of time.
Scientists can’t predict earthquakes, but they can get a better idea of the risk by understanding the complex structure of the fault deep below the ground.
Carbotte and his team have significantly changed course on that front.
Focusing on risk
Carbotte and his team found a lot of variability in the megathrust’s structure, which likely means that the danger varies at different locations along the fault, said Janet Watt, a research geophysicist at the U.S. Geological Survey Santa Cruz who was not involved in the study.
“It’s not a single answer, but it gives us an idea of this complexity,” Watt, speaking about Carbotte’s results, told BI.
Additionally, understanding that Cascadia is divided into segments is key to assessing earthquake risk, Watt said. This is because this segmentation means that the mega boost it could break into pieces rather than all at once. This could impact the size of future earthquakes, because shorter ruptures trigger smaller earthquakes.
Furthermore, the unique characteristics of each of these segments mean that each one represents a different level of risk. Another important finding from Carbotte’s study is that one of Cascadia’s segments is likely more likely to produce a large earthquake than the others.
This particularly dangerous segment essentially covers the Washington coast, running from the northern border of Oregon to southern British Columbia. It is flatter and smoother than the other segments, which means it can trigger the largest earthquakes, Carbotte told BI in an email.
Additionally, this segment probably extends further into the US than the others, which is bad news for the state of Washington. If this segment ruptures, Washington’s coastal communities could face the most extreme shaking, although the earthquake would extend far beyond the state’s borders, Carbotte wrote.
Knowing it could help this state prepare for the worst case scenario. “I think this is an example of a study that will lead to actions in the future in terms of building resilience along the coast. And it will be exciting to see where science takes us,” Watt said.
Carbotte’s research comes in the context of many other studies that are currently working to bring our picture of Cascadia into sharper focus.
“This is a specific study of a broader community effort that is underway to [understand] the system and then communicate what this means for communities on the coast and inland, and how we can actually turn science into action“Watt said.
Read the original article at Business Insider
