San Andreas Fault Linked to Cascadia Subduction Zone: Earthquakes Along Cascadia Trigger Similar Shakers on San Andreas Making For a Giant Seismic Event That Would Span the Entire West Coast of the U.S.

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Two of the west coast’s biggest earthquake faults may have far more interaction than previously thought.

According to geologists, an earthquake on the Cascadia Subduction Zone could trigger a similar shaker on the San Andreas fault to the south and thus create a giant seismic event along the U.S. West Coast.

Research Shows Cascadia Quakes Sometimes Trigger San Andreas Fault
Research shows Cascadia quakes sometimes trigger San Andreas Fault earthquakes. Today four earthquakes hit near the Mendocino Triple Junction where Cascadia and San Andreas meet. Map via USGS

Today, at least 4 earthquakes hit at on near the Mendocino Triple Junction, an area where the Cascadia and the San Andreas Fault meet.

And now a new earthquake research to be presented by Oregon-based geologists next week sounds like a B movie plot.

A great earthquake along the Pacific Northwest’s offshore Cascadia fault triggers another great earthquake on the northern San Andreas Fault.

In what may be a case where science catches up to the fertile imaginations of Hollywood script writers, attendees at a major earth science meeting in San Francisco will hear evidence that this cascade of disaster happened many times over the past couple of millennia.

I mean, Cascadia is big enough by itself,” said Goldfinger, a professor of geology and geophysics at the university. “But if you add in San Francisco and the North Coast, it is literally almost a grade B movie scenario that people don’t want to think about that much.

Yes, a major quake from the offshore Cascadia subduction zone could trigger California’s famous San Andreas Fault. And those are two of the most dangerous seismic regions in the U.S.

Link Between Cascadia and San Andreas

Goldfinger has been studying the Cascadia Subduction Zone for years. The fault runs roughly 600 miles off the west coast, from northern California to British Columbia, where several smaller tectonic plates are sliding under the much larger North American Plate. That subduction zone is capable of producing earthquakes with devastating destructive potential, up to magnitude 9.0.

The San Andreas fault, by contrast, runs about 750 miles under the northern California coast and parts of inland southern California. It is easily the world’s most infamous fault, responsible for the 1906 earthquake that leveled large parts of San Francisco and the Loma Prieta that shook the same region in 1989.

Unlike the Cascadia Subduction Zone, where plates are sliding under one another, the San Andreas Fault is known as a transform fault, the tectonic plates are moving laterally, sliding past each other.

The two faults meet in an area known as the Mendocino Triple Junction. Now, Goldfinger has found evidence that a quake on one could trigger a quake on the other, in essence making for one giant seismic event that would span the entire west coast of the U.S.

Research Shows Cascadia Quakes Sometimes Trigger San Andreas Fault, san andreas fault and cascadia subduction zone linked, The Cascadia Subduction Zone and the San Andreas Fault meet at the Mendocino Triple Junction
The Cascadia Subduction Zone and the San Andreas Fault meet at the Mendocino Triple Junction. Map via Oregon State University

The new results stem from the analysis of sediment cores from the Mendocino Triple Junction area. Those cores, pulled from canyons on the ocean floor, show evidence of earthquakes in the form of underwater landslides. Using carbon dating, Goldfinger found that nearly a dozen earthquakes occurred throughout history on both faults at the same time.

Moreover, the analysis found no evidence for the stress transfer working in reverse – from south to north.

Well, when you have two big faults that connect directly, there’s a pretty high probability they’re going to interact in some way. So one fault triggering another, or even becoming synchronized with the other for a period of time, is not a fantastical scenario. It is actually a fairly likely scenario. It just isn’t on the radar anywhere yet.

But it’s not so common to have linkage across two different kinds of faults, from a subduction zone onto a strike-slip fault. So this is new and interesting.

Hollywood Scenario Wasn’t That Far Actually

Well, back in 2004, an NBC miniseries titled “10.5” actually brought the catastrophic scenario to prime time.

The first rupture toppled Seattle’s Space Needle, and stronger aftershocks collapsed the Golden Gate Bridge too while, at the end, part of California fell into the ocean. At the time, West Coast earthquake experts dismissed the miniseries as an “impossible” mythical “fiction.”

Research Shows Cascadia Quakes Sometimes Trigger San Andreas Fault
Miniseries 10.5 – The Big One is only the beginning suspects a link between the Cascadia and the San Andreas Fault. Picture: 2004 NBC

As shown by the new scientific results, the miniseries was possibly prescient about one thing: a major quake from the offshore Cascadia fault zone could trigger California’s infamous San Andreas Fault.

Meanwhile, there is still a lot to be learned about the interaction between the Cascadia Subduction Zone and the San Andreas Fault. The Big One, but times 2! [AGU, OPB, OregonLive]

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3 COMMENTS

  1. my PREDICTIONS FOR QUAKES 5 TO 7. PLUS AND SO FAR WE HAD OVER 10 5 OR MORE QUAKES IN RING OF FIRE. 4.9
    197km SSE of Bristol Island, South Sandwich Islands
    2019-12-10 02:08:26 (UTC)
    10.0 km
    5.0
    27km S of Gisborne, New Zealand
    2019-12-09 23:58:01 (UTC)
    18.4 km

  2. We have Full Moon at 12.12am on 12-12-2019 I warn that s sign of many quakes rumbling beneath us and
    5-7.5 plus will be shaking planet in ring of fire. Western USA and Alaska Japan Philippine and Europe and Australia New Zealand and China , Russia and Middle east IRAN, Iraq, Afghanistan, Red alert for prepare
    cover and escape later. Jesus said there will be signs in the heavens

    Luke 21:25-28 ” And there shall be signs in the sun, and in the moon, and in the stars; and upon the earth distress of nations, with perplexity; the sea and the waves roaring; 26 Men’s hearts failing them for fear, and for looking after those things which are coming on the earth: for the powers of heaven shall be shaken. 27 And then shall they see the Son of man coming in a cloud with power and great glory. 28 And when these things begin to come to pass, then look up, and lift up your heads; for your redemption draweth nigh.”

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