How seismologists look at our chances of the next ‘Big One’

Second- and third-graders in Shellie Dungan's class at Skyblue Mesa Elementary School practice hiding under their desks during the "Great ShakeOut" statewide earthquake drill Thursday morning. October 17, 2019. Bobby Block / The Signal.
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Though she was only 6 years old at the time, Jan. 17, 1994, is a day longtime Newhall resident Colleen Oliver will never forget.

Startled awake at 4:31 a.m., Oliver remembers thinking, “The world is going to shake us right off of it.” 

Indeed, thousands of Santa Clarita Valley had felt the violent jolts, as numerous buildings collapsed and fires erupted in the night, as underground utility lines ruptured. 

“I remember my mom coming in and swooping me out of bed, telling me it’d be alright,” Oliver said. “I had heard of earthquakes, but I was still too young to really understand what they did — that day, I understood.” 

The 6.7 magnitude quake, whose epicenter was reported to have been in Reseda, a San Fernando Valley neighborhood just south of the SCV, left SCV residents cut off from Los Angeles after the Newhall Pass freeway connector collapsed, causing billions in damages across Southern California. 

Being in the southern part of the SCV, Oliver’s family home in Newhall was damaged in the quake, though not destroyed. 

“For months, we had this 3-inch crack going through our living room and out the front door,” she added.

Now 33, Oliver dreads every little shake, wondering if this could be “The Big One.” 

Today, SCV residents have a number of tools readily available to them that Oliver and her family did not in 1994, with technological advancements, like the cellphone, making notifications much easier. 

The MyShake app, created by the University of California, Berkeley, and released publicly in October, is available on iOS and Android systems.

File photo: On Jan. 17, 1994, a 6.7 earthquake rattled Southern California from the epicenter in Northridge.

Just a couple of weeks ago, the app’s technology was linked into the existing statewide alert system in a deal between Google and the state, allowing Californians and even tourists traveling in the area to automatically receive early quake warnings to their Android devices. 

Though only a magnitude-4.2, the July 30 quake that shook the SCV left many remembering the dangers, including Oliver, who was awoken by the app notification about a minute before the shaking began, she said.

“You best believe I went through my emergency supply bag that day and made sure I had everything I needed — you can never be too sure,” Oliver added.

The July quake was followed by a recent swarm of small earthquakes in the Salton Sea near the Mexico border on Aug. 10, leading seismologists with the U.S. Geological Survey to worry they might raise the chances of a much larger quake along the nearby San Andreas fault, which at times runs parallel to the SCV.

Though only the fourth time in 88 years that such a swarm occurred in this area, USGS seismologist Don Blakeman said swarms actually happen all the time. 

“We see them in various places. Yellowstone is very famous for this type of behavior,” Blakeman said. “It worries everyone because it can’t predict whether or not a big earthquake will happen, but oftentimes we just have swarms and there isn’t a mainshock (or larger quake).”  

By Aug. 14, USGS officials reported that the earthquake activity in the region had returned to typical pre-swarm levels, meaning there’s an approximately 1-in-10,000 chance of a magnitude 7+ on the southernmost section of the San Andreas fault. 

“The further in time we go away from a big event, the less likely something is going to happen,” Jennifer Andrews, a CalTech seismologist, said in a previous Signal interview. “But we are overdue for ‘The Big One.’”

Geologists who’ve studied fault lines believe this section of the San Andreas is capable of having a large magnitude quake every 150 to 200 years, the last of which occurred more than 300 years ago.

“That’s really quite a long time for us to not have had a San Andreas, big earthquake,” Andrews said. “But it’s not like clockwork.”

While back to normal levels, the swarm did not decrease the potential for a larger earthquake in the future, as Southern California continues to be one of the most seismically active areas in the nation.

On Jan. 17, 1994, a 6.7 earthquake rattled Southern California from the epicenter in Northridge.

So what’s really at fault?

To best understand the dangers, one must first know what an earthquake is, Blakeman said.

“An earthquake is the release of accumulated energy or stress in the crust,” he added. “And in general, the crust is broken up into about 12 big tectonic plates.”

Blakeman compares the Earth’s crust to a hard-boiled egg with a cracked shell.  

“The shell would still be stuck to the egg, but they’d be in pieces, and that’s kind of what the Earth’s crust is like, except there’s heat escaping from the interior of the earth and that drives those plates to move a little bit,” Blakeman said. 

While the plates generally do so slowly, only moving a few centimeters each year, rocks that are bound tightly across each fault line create pressure. 

“The pressure builds up, builds up, and eventually there’s so much stress and strain there that the rocks break the fault slips and that energy is released — the release of energy is an earthquake,” he added.

Though a trained geophysicist, Blakeman said he truly didn’t realize how active the Earth is until he began working at the USGS, finding that they’d publish approximately 30,000 earthquakes each year.

“They happen constantly, and I think that’s something most people don’t know,” he said. 

How to be prepared for one

“Living in California, the threat of an earthquake is ever-present,” the city of Santa Clarita’s Management Analyst Rebecca Widdison said via email. “By being prepared, you can help minimize the risk and ensure your family will have all the necessary supplies and know what action to take when an earthquake strikes.”

That being said, Widdison suggests SCV residents begin preparing now, rather than waiting until an earthquake strikes.

Before:

  • Secure items in your home that might fall and cause injuries, including bookshelves, mirrors and light fixtures.
  • Practice how to drop, cover and hold on, and participate in the next Great Shakeout Earthquake Drill set for Oct. 15.
  • Store critical supplies, such as food, water, sanitation and essentials, along with important documents. The city has an emergency supplies checklist available on its website.
  • Plan how you will communicate with family members.

During:

  • Drop down onto your hands and knees so the earthquake doesn’t knock you down.
  • Cover your head and neck with your arms to protect yourself from falling debris. If you are in danger from falling objects, and you can move safely, crawl to a safer place or seek cover under a desk or table, for example.
  • Hold on to any sturdy covering so you can move with it until the shaking stops.

After:

  • When the shaking stops, before you move, look around for things that might fall or for dangerous debris on the ground.
  • If you are in a damaged building and there is a safe way out through the debris, leave and go to an open space outside, away from damaged areas.
  • If you are trapped, do not move about or kick up dust.
  • If you have a cell phone with you, use it to call or text for help.
  • Tap on a pipe or wall or use a whistle, if you have one, so that rescuers can locate you.
  • Once safe, monitor local news reports for emergency information and instructions. 

SCV residents can sign up for the city’s Nixle alerts by texting “SCEMERGENCY” to 888777.

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