New fault line might explain overdue San Andreas earthquake

The San Andreas Fault in California is long overdue for a major earthquake — like, more than 100 years overdue. But scientists just made a discovery that might tell us why the fault has been so quiet.

It's called the Salton Trough Fault, and it lies along the northeastern edge of the Salton Sea in Southern California. The fault line is underwater, so scientists didn't find it until recently.

Scientist believe the Salton Trough could be absorbing strain from San Andreas. That might explain why a major earthquake hasn't occurred along the San Andreas in more than 300 years.

SEE MORE: Don't Freak Out About California's Swarm Of Earthquakes Just Yet

And Southern California has been waiting for the "big one." A series of small earthquakes earlier this year caused worry among residents and scientists.

See more on fault lines in the US:

Active fault lines/zones in the United States -- earthquakes
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Active fault lines/zones in the United States -- earthquakes

The Alaska-Aleutian Megathrust is located across 3,600 kilometers between Kamchatka, Russia to the Gulf of Alaska.

(Photo by Daniel A. Leifheit via Getty Images)

The Cascadia Megathrust stretches along the coasts of Washington and Oregon up into Canada

(Photo via Encyclopaedia Britannica/UIG via Getty Images)

The Eastern Tennessee Seismic Zone runs from Alabama to Virginia and is responsible for four earthquakes in the past century. 

(Photo by Harrison Shull via Getty Images)

The Elsinore Fault Zone lies along the Santa Ana Mountains in Southern California

(Photo handout via NASA)

The Hayward Fault Zone runs along San Francisco Bay for 119 miles.

(Photo by Dave and Les Jacobs via Getty Images)

The Humboldt Fault (red) and the Midcontinent Rift System (green) are both located in Kansas and Nebraska. 

(Photo via Public Domain)

The Laguna Salada Fault runs from the US to Mexico and caused the 2010 Mexicali quake.

(Photo credit should read Daniel CONEJO/AFP/Getty Images)

The Moab Fault is located in Utah.

(By Andrew Wilson (Own work) [CC BY-SA 4.0], via Wikimedia Commons)

The New Madrid Fault Zone is located in Missouri.

(Photo via Public Domain)

The San Andreas Fault System runs along 1,300 kilometers in California. 


USA-EARTHQUAKE HISTORIC - Map of California visualizing earthquake activity over the past 25 years. Includes fault lines

"Any time there is significant seismic activity in the vicinity of the San Andreas Fault, we seismologists get nervous," one specialist told The Los Angeles Times.

The "big one" is a hypothetical earthquake with a magnitude predicted to be greater than 7. Southern Californians have anticipated such a quake for a long time.

To put that in perspective, the 2010 earthquake in Haiti was a magnitude 7. The Haitian government's official death toll for that quake was more than 300,000 people. And the earthquake leveled the areas it struck.

But scientists say the Salton Trough still needs to be researched. When that series of small earthquakes hit San Andreas earlier this year, one seismologist noted the lack of records on the Salton Trough makes it difficult to see if the two faults affect each other at all.

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