The 1971 Sylmar Earthquake. By Kenneth Lafler.

 

 

On February 9th at about 6 in the morning

the San Fernando Valley was rocked by one of the worst earthquakes in it's history. In fact this was one the worst earthquakes to hit an Urban area. The only thing keeping this from being far worse was the time of day it struck.

Had this quake been just three hours later the fatalities would have been far higher due to the traffic on the freeways with commuters on their way to work.

 

 

 

 

 

Also the fact that the Van Norman Dam did not  fail kept the death toll down. The Dam's water level had been lowered for repairs, so the dam did not completely fail but had a partial collapse. 

 

 

 

 

If this dam had  fully collapsed the number of fatalities could have been in the thousands.

Being over one hundred feet in height, the dam would have sent a huge wave into the homes directly below the dam, flooding the Granada Hills area and most of the housing on that side of the freeway. 

 

The strange irony of this was that Harvey Van Norman had been deputy engineer on the ill fated St. Francis dam which failed catastrophically on March 28th at 12 o'clock at night in 1928 killing hundreds of people while they slept.

 

 

 

The Quake was centered on the then unknown Placerita Fault, in Newhall. Geologists had no idea the fault existed, similar to the Northridge Quake. 

 

 

         
The Quake registered at 6.6  on the Richter Scale. There are two scales for measuring earthquakes, Richter and the Mercali Scale. The Mercali Scale goes higher than the Richter Scale so the Sylmar earthquake would have a much higher reading on Mercali.









  Liquefaction played an important part in the amount of damage from this quake. Some area's such as Panorama City which has a much higher ground water level were hit particularly hard. In this situation the ground actually turns to quick sand. Many homes simply slid off their foundation's.






   One of the hardest hit buildings was the Olive View Medical Center.  One section of the hospital grounds completely collapsed trapping hospital patients. The death toll at the hospital was about 66. Olive View has since been rebuilt.

A patrol officer on duty actually fell off of one of the collapsed freeway bridges to his death Near the Newhall Pass area. This area sustained extremely heavy damage to the freeway bridges and overpasses, due to Liquefaction , being next to the reservoir and dam area.

 

 

 

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For geologists these quakes are an unprecedented view into how major earthquakes function and  the effect on urban centers. The Sylmar Quake and the Northridge quake will probably be studied for as long as there are earthquakes. 

by

Kenneth Lafler

Lake Lee and Dam, Corona, Califiornia. By Ken Lafler

 A study of the Dam .

     Was this dam in such an advanced state of decomposition that it was on the brink of failure.





Lee Lake and Dam -
 The state of the dam today.

 This lake was completely filled just a few years ago in this same condition. Just how dangerous was this situation? Was the lake drained due to drought or due to fears of the dam collapsing. The water for our reservoir's comes from the Owens Valley and is not dependent on rain fall or run off. So why is the water level so low?

The spillway area and superstructure of the dam.

 This part appears to have been constructed at a later time than the rest of the structure - probably in the 1970's and is of a more sophisticated design.






   The spillway section.

   Notice the landslides to the right of the overflow dam on the water side. There was a larger landslide into the spillway which may be viewed in the next shots.

   The superstructure of the dam.

  Once again, notice the large cracks in the dam wall. Also It seems that there was a large amount of grouting used on the canyon walls. This  makes one wonder - why was so much support needed. The gray material on the canyon walls is the Grouting. In dam terminology this is called "Dental Work" where all openings are sealed.

 

 

The Landslide area

 

 This is the overflow section of the dam on the drainage side of the spillway.Once again notice the grouting in the left side of the shot. Once again these boulders are the size of a mid sized car. There appear to have been more that one landslide.

 

To see this, view the rubble on the left side of the spillway dam. The spillway is actually another dam in itself and much better built than the rest of the system.

   The spillway section.

  This area hase about a 60-70 foot drop off so care should be taken in this area of the dam. Most of the concrete structure is in this area. One must walk the lenght of the dam though to get to this part. Notice there's no grout next to the concrete area though.

  The damage to the side walls of the dam and support section.

 In this situation the disintegration of the concrete can cause a condition called hydraulic uplift. In this case water seepage causes the dam to be literally lifted off it's foundation.This was the case in the St. Francis failure of 1928, with the dam failing at 12 midnight and killing hundreds while they slept.

 

 

          The entire Dam, except the spillway.

 

By observing closely, the dam appears to have been constructed in four different stages. The first part was most likely built in the 1920's. 

This section is almost completely gone and is mostly rumble. You may see the second level towards the middle of the shot. This too is in terrible condition. 

The third part is concrete and earthen fill comprising the upper level of the dam.

 The spillway dam is of a much higher quality of construction and appears to be much newer. Also it is a much more sophisticated design than the rest of the dam. Were the dam to fail this section would most likely remain intact.

  This shot is of the landslide area in the spillway. Theses boulders are the size of a Mid sized Car. Notice the landslides around the spillway dam on the water side of the concrete also. In order for this to occur there must have been considerable ground movement and shifting.

  The Discharge pipe.

 This is for lowering the water level. This is  one of the most important sections of the system. Without this feature there would be no way of controlling the water levels and flow. Without this drainage system any dam is doomed to failure. It's not a question of how or when, but just how badly.

The side abutment of the dam.



 Notice the dam is not really anchored into the canyon wall but just runs into it. The Dam should go into the mountain side for more support. 

 This water system is what is called a Gravity Arch Dam, meaning that the shear dead weight of the structure is enough to contain the water.The arch configuration gives the dam added strenght with this design.

   By calculating the weight and strength of the concrete and the PSI of water, the structure should have the sufficient tensile strenght to contain the water...hopefully. This isn't always the case though as with the St. Francis, which was a Gravity Arch Dam,but completely different in design than this structure, being made entirely of concrete.

 

 

 

 

 

 

Severe damage to the original dam

   This would be part of the original dam. Notice the almost totally disintegration of the base. This is an extremely dangerous situation. Water seepage through the opening can cause "Hydraulic Uplift" and breach the dam sending a huge wall of water down the canyon.

In conclusion -

   While first visiting this site, I filmed a large amount of video footage and began viewing it. This was when I noticed all the damage to the concrete and the structure.

  I realized this dam was in an extremely dangerous state of decomposition. One doesn't have time to examine the dam to this degree while there the first time, but after watching hours of footage I came to the conclusion this lake was lowered deliberately with no doubt in my mind the dam  was ready to collapse in the next several years if not sooner. 

    By 
            Ken Lafler