EL SEGUNDO, Calif. — At 6 a.m. on February 9, 1971, a 6.6-magnitude earthquake struck the San Fernando Valley.
The Sylmar quake, as it’s known — which is one of the strongest earthquakes recorded in Southern California history — killed 65 people, injured 2,000 more, and caused north of $500 million in property damage, according to the California Institute of Technology (Caltech).
But the Sylmar quake steered the Southern California region into implementing new and safer building codes to enhance public safety, advanced earthquake technology, and, according to Caltech, led to a coalition of the United States Geological Survey (USGS) and the university in expanding seismic monitoring through the region.
We sat down with the Director of Caltech’s Earthquake Engineering Research Laboratory and Professor Emeritus of Engineering Seismology, Dr. Thomas Heaton, to better understand what happened 50 years ago, what we learned from it, and how we can better alert the public.
The statistics of earthquakes are very much like, believe it or not, epidemics and pandemics. You never know when the next one's going to come in. And you have no idea how big it's going to be. You just know they’ll happen. You can look at some statistics, and the statistics are something we call a Pareto distribution, which means that the biggest events, biggest earthquakes, biggest pandemics are the ones that really matter, and they don't happen very often. So the things that matter the most are very rare, and you have no idea when the next one's going to be.
The Van Norman Reservoir is up in the northern part of the San Fernando Valley, and it's where the Los Angeles Aqueduct comes in, and it was designed to be storage of water in case the aqueduct was broken by the San Andreas fault, believe it or not. And when they built that reservoir, they sluiced dirt into the end of the valley. It's called hydraulic fill, a kind of mining they used to do. They just take a fire hose on a Hillside and slurry the mud into someplace and let it settle, but it doesn't make a very stable slope. So they made the dam that way and in the ‘71 earthquake when it shook hard the mud like material re-liquefied and then the front of the dam just kind of slumped into the reservoir.
And it turns out that about 40 feet of the top of the dam slid in, and there was a six-foot leeway left to hold back the water. Fortunately, there was six feet. If it had slid another six feet it would have started to leak and it was just mud so it would have eroded immediately and they would have lost the dam very quickly. Estimates are that 10,000 people would have perished in that disaster ... And rather fortuitously, the Department of Water and Power, which owned that reservoir, had decided months earlier to decrease the capacity of the dam by 40 feet. So they lowered the water level 40 feet because they were thinking perhaps it was not very good in an earthquake, and if that decision hadn’t been made, it would have been a completely different event.
Probably the most important thing that happened in San Fernando was something we call in the business non-ductile concrete... There was a brand new hospital, the Olive View Hospital, that had just been completed, and they were just staffing it up, and it collapsed in the earthquake. And it was a reinforced concrete building with kind of an open first story. And of course it met all the codes at that time, it was a hospital. And people were kind of surprised to see how it collapsed.
So when they really started looking into what happened, they discovered that lots of assumptions they were making about reinforced concrete were incorrect. The fix had to do not so much with changing the concrete or the steel, but the way they connect all the steel together inside the concrete. So, for instance, if you have got a column and you’ve got a beam, and you've got steel running along those things to keep it from falling apart, if the steel just pulls out at the end of the beam, out from the column, you're going to lose the connection, you'll lose the building. Afterwards, they told people you have to put a hook in the rebar so that you positively connect the rebar from the column to the rebar from the beam.
The city of Los Angeles has tried to deal with this... They tried maybe half a dozen times until finally Eric Garcetti and Lucy Jones kind of put together the politics to actually get through a retrofit for these brittle concrete buildings. But I think it's got another couple of decades before the owners have to actually retrofit these things. And it's not going to be easy, it's expensive and the people who are in the buildings often have no idea they are in a dangerous building.
The most indestructible building of all, it’s amazing, are 7-Eleven stores... They're short. They’re one story tall, no windows, just solid concrete walls. The concrete’s made out of concrete block, and then you put rebar down the center cells, and then they pour concrete to turn it into a solid concrete wall. All the walls are tied together with steel, and then you tie it all together on the roof. You cannot touch those things with earthquakes... Wooden houses are extremely resilient in earthquakes ... When builders build houses, they put in all this additional bracing [in the floors] so that it's stiff enough that it doesn't flex much when you put a load in it. So when an earthquake comes along, it's going to give you a big enough load that you have to fix all your walls. But fixing your walls is nothing compared to losing the house.
This story actually starts in San Fernando. At the time of the San Fernando earthquake, the seismologists had seismographic stations around California... The seismologists would look at records that came in on telephone lines and in the [San Fernando] earthquake, the telephone lines were knocked out, and even more so, all of the records were off-scale anyway. Even if you recorded them, you couldn’t read them. So when the earthquake happened, the Caltech seismological laboratory was basically blind... People didn't realize that those hospitals had fallen down or what was going on with the reservoir. All they knew was that communications were out with that part of the world and it was a big problem for Los Angeles to respond to that.
So in the '80s, I was with the U.S. Geological Survey, and I was trying to push our office in Caltech towards having better systems to react during the earthquake itself. And by the time of the Northridge earthquake, we had made quite a bit of progress, but our budgets were pretty limited still and we weren't doing what we call real early warning... After the Northridge Earthquake, we got some important grants through FEMA and we were able to really beef up the seismic system, and when we beefed it up, we specifically planned that the hardware would be able to do what we call early warning, send the strong shaking in real time, and collect it so we could analyze it... Now we're at a point where we can tell you the shakiness is happening in California, and we can tell you the shaking is on its way, and that's the ShakeAlert project. It’s pretty exciting for me as a professional that at the end of my career, now I can say we built this system that can do the things that we really needed in San Fernando.