Possible Tsunami Risk as Geologists Discover 45-Mile-Long Hidden Fault

A brand new 45-mile fault line has been discovered stretching along Canada’s Vancouver Island, just north of the Washington state border, and may pose a tsunami risk to people nearby.

The fault line was suspected to be lurking in the region by geologists, mineralogists and Earth and ocean scientists, who had recently found evidence of an earthquake occurring on the Saanich Peninsula between 4,700 and 2,300 years ago, according to new research in the journal Tectonics.

Proving difficult to find due to the thick forest coverage in the area, the fault line was finally found after intensive research.

“In the northern Cascadia forearc on the west coast of North America, high-resolution topography and geologic mapping show a [approximately] 2.3-m-high scarp across a [approximately] 14,000 year-old land surface 10 km [6.2 miles] north of downtown Victoria, British Columbia, Canada,” a team of researchers from France, the U.S. and Canada wrote in the paper.

If the fault were to see an earthquake, it could trigger a tsunami that would be catastrophic to those living nearby in both Canada and on the U.S. West coast.

“This newly identified fault, the XEOLXELEK-Elk Lake fault (XELF), crosses Saanich Peninsula within Greater Victoria and poses a hazard to the region’s [approximately] 400,000 inhabitants,” they said.

The faultline was discovered after a detailed investigation, involving shallow geophysical surveys, analyzing historical imagers, and remote sensing. The researchers found minerals in the rocks that indicated changes to the magnetic field over time, which suggests that the rock formations have been pulled apart or broken. This strongly implies the presence of a faultline.

On further investigation, they found that the faultline runs northwest to southeast for around 45 miles, and may be a slip-dip fault, meaning that the rocks move vertically up and down against each other, rather than sliding side to side.

In the paper, the researchers suggest that an earthquake at this faultline would likely trigger a tsunami that could hit the Canadian cities of Victoria and Vancouver, as well as places as far away as Seattle, Bellingham, Olympia and Tacoma in the U.S.

“Local tsunami in the waters surrounding Greater Victoria could result from a reverse-slip earthquake on the XELF,” they wrote in the paper.

The last earthquake from this faultline, which occurred several thousand years ago, had a magnitude of between 6.1 and 7.6, and may have also triggered a tsunami.

“There is a high potential that a local tsunami was generated by the paleo-earthquake recorded on the XELF, either from vertical offset of the seafloor or during a shaking-induced landslide. Future analyses of the subaqueous structures, along with exploration for regional tsunami deposits, could further test this hypothesis,” the authors wrote.

The researchers note that it’s very hard to predict when the faultline may cause another earthquake, but further study of the fault’s past will help them to elucidate how much risk it poses to people nearby.

“Determining whether it produced recent large earthquakes is important for updating regional earthquake hazard models and increasing earthquake preparedness,” they said.

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