Scientists discover seismic hotspot in US that could trigger devastating magnitude 8 earthquakes

It was a groundbreaking discovery.

Scientists have found previously concealed fault lines along California’s north coast, sparking concerns that we could be drastically underestimating the earthquake risk in the region, per a seismic study published in the journal “Science.”

“If we don’t understand the underlying tectonic processes, it’s hard to predict the seismic hazard,” declared study co-author Amanda Thomas, professor of earth and planetary sciences at UC Davis, in a statement.

The area in question is the Mendocino Triple Junction, a seismic hot zone in the Pacific Ocean where three tectonic plates converge: the San Andreas Fault ending in the north, the Cascadia Subduction Zone in the south, and the Mendocino Fault in the east. 

San Andreas Fault, one of the components of the Mendocino Triple Junction. Mike – stock.adobe.com

As three fault systems collide here, this tectonic triple threat boasts some of the highest levels of seismic activity in the US. It was the source of the magnitude 7.2 earthquake that rocked Humboldt County in 1992.

However, the researchers discovered that the Triple Junction is comprised of a whopping five moving plates, not three — two of which are hidden from the surface.

In other words, we could be on shakier ground than previously thought, with frightening implications for the millions of people living in the region.

A map of the Mendocino Triple Junction, the meeting point of three tectonic plates. USGS

Lead author David Shelly of the USGS Geologic Hazards Center in Golden, Colorado analogized our understanding to glimpsing just the tip of the iceberg.

“You can see a bit at the surface, but you have to figure out what is the configuration underneath,” he declared.

Researchers happened across the quake-inducing quintet by employing a network of seismometers in the Pacific Northwest to track “low-frequency” earthquakes deep underground where tectonic plates grind against one another.

These tremors are reportedly too small to detect at the surface, per the research, which was confirmed using tidal-sensitivity models.

One of these tectonic threats is a chunk of the North American plate has broken off and is being pulled down along with the Gorda plate at the southern end of the Cascadia subduction zone.

The model also proved the theorized existence of the Pioneer fragment, a remnant of the ancient Farrallon plate that used to traverse the California coastline that has not all but disappeared. This straggler is now being dragged underneath the North American plate — a process called subduction.

However, the subducting surface of the quake-inducing quintet is not as deep as previously thought, which would explain why the 1992 earthquake’s origin point was so shallow.

“It had been assumed that faults follow the leading edge of the subducting slab, but this example deviates from that,” said tectonic geodesist Kathryn Materna, from the University of Colorado Boulder. “The plate boundary seems not to be where we thought it was.”