On January 26, 1700, Japan was hit by a tsunami. We know this from written records of coastal flooding. But what’s most remarkable about these records is what they don’t say: the tsunami was the result of water displaced by an earthquake. The 1700 Tsunami This tsunami was not associated with an earthquake felt in Japan and there were no precursor tremors. This “orphan tsunami” was the result of a large earthquake across the Pacific Ocean off the coast of what is now Oregon and Washington. The same event occurred in Oral tradition The records of the Native Americans of the Pacific Northwest include records of earthquakes and floods. A ghostly forest that has been submerged for a long timeIn 1700 it suddenly died before the growing season had even begun.
The earthquake, estimated at magnitude 9, was reportedly a devastating event for the Pacific Northwest, with stories of entire villages and tribes wiped out, The biggest earthquake It is the largest earthquake in human history. Modern geological analysis shows that the 1700 earthquake More than 40 major earthquakes The quake was the most powerful to shake the region in the past 10,000 years, joining about 20 other earthquakes of magnitude 9 or higher that occurred in the same period. All occurred in the Cascadia Subduction Zone, a fault line that runs for 600 miles from southern British Columbia to northern California. Along the fault line, the small oceanic Juan de Fuca plate is slipping downward and pushing up against the much larger North American plate, building friction and pressure that could lead to an inevitable rupture.
for is more than 10 yearsSeismologists warn A new earthquake is approachingOn average, a major earthquake (magnitude 8 or greater) occurs in this region about every 230 years, and an even larger earthquake (magnitude 9 or greater) occurs about every 500 years. It has been more than 324 years since the last earthquake. The sudden shifts or ruptures that cause earthquakes don’t happen with any regularity, but they do happen eventually.
A new study offers greater insight into the collision of the two plates than ever before. Published in the June 7th Journal Scientific advances, The data includes an image of the topography of the lower plate, confirming that the entire subduction zone has broken up into smaller chunks. This data and analysis will help improve predictions of future earthquakes and tsunamis, helping prepare for the seismic fate of the Pacific Northwest.
It offers “an unprecedented, detailed view of the Cascadia Mountains.” [fault]We know that there is the potential for a major earthquake.” Erin Worth“The study is a step forward for the science community,” said John F. Kennedy, a research geophysicist at the U.S. Geological Survey in Seattle who was not involved in the study. Popular Science“These results will be important inputs for models of future earthquakes and tsunamis,” she says.
For 41 days in 2021, members of the research team worked on a high-performance Research VesselThousands of underwater recording devices were dragged miles behind the ship, firing powerful pulses of sound toward the ocean floor and collecting the echoes with sensitive hydrophones. Based on the strength and timing of the returning signals, scientists say they were able to work out much of the fault’s topography and characteristics. Harold Tobin“It works in a similar way to radar,” says University of Washington geophysics professor and study co-author.
But while the gist of the method may have been simple, analyzing the sheer amount of information collected was not. “It takes supercomputer-level work to do all the processing,” says Dr. [only] “Now it’s being published,” Tobin added, saying he hopes the study will be the first of many as he, his colleagues and other scientists dig deeper into the dataset.
He agrees that the paper “only scratches the surface.” Chris GoldfingerGoldfinger, a professor of marine geology at Oregon State University who was not involved in the new study, is one of the world’s leading experts on the Cascadia subduction zone. “They’ve done a ton of work, but there’s a lot more depth to the data set, and there’s going to be new results coming out over the next few decades,” Goldfinger said.
In their first foray into this data pool, Tobin and his coauthors have already identified several key findings. First, their analysis Existing theory Smaller horizontal faults penetrate both the upper and lower plates, dividing the subduction zone into several segments. (The exact number of segments varies depending on how the division is defined, but is between 3 and 5.) When an earthquake occurs, it can involve any number of these segments. The more segments that slip at once, the greater the area affected, the magnitude of the earthquake, and the potential scale of the disaster.
Another key finding is that the Juan de Fuca Plate segment offshore Washington (which splits into multiple segments depending on how it’s cut) is very smooth and flat, Tobin says. “Counterintuitively, if the fault at the boundary between two plates is smooth, it can generate bigger earthquakes than a rougher fault,” he adds. Smoothness means more contact between the plates, more friction over a wider area, and fewer geological features to impede the spread of slip. It would be especially dramatic if the Washington segment were to disappear. “We can speculate that that’s what’s going to be the majority of the risk of future earthquake ruptures,” he says.
The study also provides more detailed information about the subduction zone, including the depth of the faults throughout the region. In many areas along the fault, the new data shows that the faults are shallower (i.e., closer to the ocean floor surface) than previously thought. “This could have implications for ground shaking and tsunami hazard,” says Worth. “The closer you are to the fault, or the closer the fault is to the surface, the stronger the ground shaking and potentially the greater the tsunami generation.” But she stresses that more analysis and quantification is needed to better understand this, and the exact impact of all the study’s observations. That’s where models come in.
“There’s no guarantee of exactly what the next event will bring,” Tobin says. Really big stuff) “It could happen tomorrow, or it could be literally centuries into the future… The more we know, the easier it is to construct a guide.”
Already, Worth and his USGS colleagues have begun incorporating this new information into their simulations, and the results of these computer tests will eventually be used by hazard researchers to make more accurate predictions. Shake MapThey are used by engineers to test building designs and responses, and by local and state governments to determine building codes.
Though unprecedented in its scale and depth, and able to help improve future models, the new geostationary data does have limitations. It lacks imagery of the portion of the fault closest to the coastline, which Liss said is “very important” in predicting the impact of earthquakes. And each data-collection track along the study area is spaced about 50 kilometers apart, depending on ship routes, Goldfinger said. Past studies suggest it’s possible to fill in those 50-kilometer gaps with some information, but nothing as detailed as the new data. “This is a really good dataset,” he says. “50 kilometers of line spacing is pretty big, and there’s a lot we still can’t see in between.”
But more data shows that the Pacific Northwest is still woefully unprepared for a potential major earthquake. “The scientific consensus is strong enough that the story isn’t going to fundamentally change,” Goldfinger said. “We’re in a situation where we’ve discovered a time bomb. [beneath] “Fragile Cities” Grassroots Initiative School renovation And build Tsunami evacuation tower Though they have been hit by earthquakes in recent years, Oregon and Washington lag far behind earthquake-prone areas like Japan and neighboring California, with building collapses limited to Turkey and Haiti. [no or poorly enforced] “But the Pacific Northwest is in the same situation as Turkey and Haiti, because until 1994 they didn’t have building codes that met standards,” Goldfinger said.
Seattle, Portland, Tacoma, and other major cities in earthquake zones are riddled with unreinforced masonry buildings that are prone to collapse. Tsunami inundation areas include schools along the coast. There is no evacuation routeEven the standard advice on how to protect yourself during an earthquake Probably not Goldfinger said many places and people in the Cascadia region are at risk: “Our infrastructure is very fragile, and we’re on the brink of a major earthquake. How do we tell people that?”
Correction June 7, 2024 7:17 pm: Updated quote attribution for Smooth Juan de Fucapreto. Details of Türkiye’s building code have been revealed.
