Slow Slip Event on Cascadia Subduction Zone: Vancouver Island hit by more than 4,200 quakes since March 20 – Cascadia about to blow?

Strange Sounds – April 5, 2022

You can’t feel it, but the ground far beneath our feet on south-central Vancouver Island has been moving.

Seismologists have been recording thousands of “episodic tremor and slip events” occurring at a rapid rate since March 20 moving in a southeasterly direction down the Island.

More than 4,200 tiny tremors have been recorded so far between 25 and 40 kilometres below the surface, said John Cassidy, an earthquake seismologist with Natural Resources Canada and a professor at the University of Victoria.

They’re not earthquakes. … On the instruments they look like series of a trains rolling by,” Cassidy said.

He said these bursts of small tremors and slips occur about every 15 months along faults that form the boundaries of tectonic plates — in our case, the Cascadia subduction zone from Brooks Peninsula on the Island to Northern California, where the Juan de Fuca plate system curves west beneath the North American plate.

The repeated episodes of slow fault slips — measuring about the size of five stacked dimes — usually occur over a period of several weeks, accompanied by tremors that appear on seismic records as prolonged, intermittent ground vibrations, Cassidy said.

The ETS activity has been going on for centuries, but has only recently been recorded using sophisticated GPS technology at more than 40 sites up and down the Island. They differ from earthquakes, which generate large, sharp shock waves that subside very quickly, but ETS can help in improving estimates on where and when the next earthquake might occur, Cassidy said.

By mapping out the areas on the subduction fault where stress is not accumulating over the long term, tremor events define the landward limit of the zone that could rupture during the next great earthquake.

That provides a more accurate estimate of how close the rupture could be to major West Coast cities such as Victoria, Vancouver and Seattle, and what shaking could occur, he said.

https://strangesounds.org

Earthquake warning as US and Canada ‘due for major event’: ‘It’s matter of when’

Joel Day – November 5, 2021

It has been centuries since the contiguous US, the entirety of the states, experienced a “Big One” — an earthquake with a magnitude greater than 9.0. The last on record was an earthquake in 1700 with an estimated magnitude of 9.0. This was along the Cascadia subduction zone where the Juan de Fuca plate is diving underneath the North American plate.

Huge earthquakes happen in this region because the plate that’s going down is usually oceanic crust, which is cold and dense, which means it can break in a sharp and sudden manner.

However, the cold dense crust that’s sinking can break for a much longer time and initially result in the seismic shifts and tremors.

The nature of the zone pairs any earthquake with another destructive event: a tsunami.

The earthquake that hit in 1700 sent a tsunami across the Pacific Ocean as far as Japan.

Researchers are now expecting another event at the Cascadia subduction zone, with the chances of it happening in the coming decades explored during NOVA PBS’ short documentary, ‘The Pacific Northwest is due for a Major Earthquake’.

Wendy Bohon, a geologist and senior science communication specialist at the Incorporated Research Institutions for Seismology, explained the process behind how a tsunami would result from an earthquake, and said: “You have one plate diving down beneath another, one section gets locked and it pushes another part up.

“When the fault ruptures, when the amount of stress overcomes the friction, it bounces back, which lifts up the water above it and causes that water to flow out in all directions.

“And that water flowing out in all directions in the tsunami.”

Oral histories of the earthquake and tsunami that hit in 1700 suggest many died from the event.

https://www.express.co.uk