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Northridge Earthquake 20 Years Later

Posted by on Jan 16th, 2014 and filed under News. You can follow any responses to this entry through the RSS 2.0. Both comments and pings are currently closed.

By Charly SHELTON and  Mary O’KEEFE

Monday, Jan. 17, 1994. At 4:31 a.m., a 6.7 magnitude earthquake rocked Southern California. Despite being known as the Northridge earthquake, the epicenter was actually Reseda. The shaking lasted only 10 to 20 seconds, yet the force exerted on the ground was so intense that movement was felt as far away as Las Vegas, Nev. More force was exerted on the ground, in fact, than has ever been recorded by instruments, with a ground acceleration speed of 16.7 m/s², or 1.8g (for reference, the Seismological Society of America estimates that the peak ground acceleration in the 2010 Haiti earthquake to be approximately 0.5g in certain parts of Canape Vert). In addition, the highest peak ground velocity ever recorded came from this earthquake as well, with ground movement clocked at 4.09 mph.

Two powerful aftershocks of a 6.0 magnitude rocked the plate again, with the first aftershock being just one minute after the initial quake and the second coming 11 hours later. These were the two most powerful of several thousand aftershocks. All in all, 57 people died, over 5,000 were injured and the property damage was estimated as more than $20 billion.

“We sit on the boundary between the Pacific plate and the North American plate, which are traveling past each other,” said Kate Hutton, seismologist at CalTech, “but there is a bend in the main plate boundary. So there’s actually compression along the San Gabriel Mountain and Santa Monica Mountain areas. That compression caused one side of the minor faults to slide up and over the other side, and that sudden motion produced vibrations in the ground that people felt as an earthquake. “

Earthquakes are all about pressure. As the plates of rock float on a magma surface, much like a puck on an air hockey table, they slide around very slowly. These plates, knocking into each other and grinding alongside each other, cause pressure to build up between them at the plate boundaries – the faults. Every so often, the pressure builds up enough and the plates slip causing an earthquake.

Think about it this way: put your hands together, palm-to-palm. Now push them together really hard. Now slowly pull one hand up and one hand down, keeping the pressure hard together. When your hands move, it’s not a gentle slide, it is a fast jerking motion as the pressure releases, moving your hands. That is the same as an earthquake.

“There was [a quake] in 1971 in the same area, but it was on a different fault,” said Hutton. “It was a very similar quake, sort of like a mirror image of the fault. The crust in California is very complicated; it’s full of faults. Both of these were faults that were known about before [the quake happened] but it wasn’t realized that it was a big threat.”

The Northridge earthquake began 15 miles below the surface, said Robert Graves, USGS geologist. The thing that made this earthquake different was that it was on a blind fault, meaning the fault line didn’t come to the surface and it was not actively monitored as a major threat.

“The Northridge quake provided the opportunity for instituting improvements in monitoring,” Graves said.

“It allowed us to get funding to expand our seismic network,” added Hutton, “and use a lot of modern technologies as they came along to have a faster response, to get the information out. And that would allow responders [to react] sooner, to know where the damage was, for example. It also caused an update in the building codes, at least one. It was an impetus to get funding and collaboration between a lot of different universities to map more faults and determine, statistically speaking, how often they break and come up with a risk map of California.”

Over the last 20 years, technology has improved including geological monitoring equipment.

“If Northridge would occur today, within a minute [USGS] could provide information on the location and magnitude. A couple of minutes later we could produce maps of ground shaking.  At the time of [the Northridge quake] it took us months to [get that information],” Graves said.

Insurance companies hit the ground running immediately after the Northridge earthquake.

“Earthquake insurance has evolved significantly since Northridge,” said Rick Dinger, owner of Crescenta Valley Insurance. Before, the prices for earthquake insurance were extremely high and difficult to get, but now, Dinger said, prices have come down.

“However everyone has a high deductible, from 15% to 25% of the cost to rebuild your home,” he said.

Commercial buildings are even tougher to get insured and fewer policies are being written, he added. So a home that is 1800 square feet on average would have a deductible of $54,000.

The cost is high, but Dinger said he feels it is still important to purchase insurance.

“We do suggest to [buy it]. I had toured New Orleans a year after [Hurricane] Katrina. You could see who had insurance and who did not,” Dinger said. “So it’s expensive, but that is better than taking a total loss.”

Emergency responders have also learned lessons from Northridge and other disasters worldwide that have taken place over the last two decades.

Capt. Shawn Grizzard from Los Angeles County Fire Dept. Station 63 is a member of International Search and Rescue. He has responded to disasters, many of them earthquakes, all over the world. Grizzard said what the teams have learned from those rescues, including those during the Northridge earthquake, have been included in present day training.

“In L.A. County, we have the highest trained firefighters for an earthquake situation and the most experienced,” he said.

Through the multiple rescues, Grizzard said, he has learned that the state’s building codes have made a big difference. When he went to Haiti, where codes were less strict, many of the buildings collapsed, but in New Zealand, where codes are closer to California standards, the buildings remained standing after a major earthquake.

They have also learned other, smaller lessons that have changed the way they train.

“When a building collapses, it can take us eight to 12 hours to get through the rubble,” Grizzard said. “We found that mattresses were a real problem. They have steel coils that are wrapped around everything.”

So now, the LACoFD has added mattresses to the debris they use during drills.

It is still important for residents to realize that being prepared for the next disaster is imperative. Organizations like CERT (Community Emergency Response Team), the American Red Cross and local law enforcement agencies join with the USGS for the annual shake out drill. This program prepares communities and official agencies to know what to do when the next large earthquake occurs.

For more information on CERT contact the CV Sheriff’s Station at (818) 248-3464. The next shake out drill is scheduled in October.

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