| Ken Hudnut: Cajon
Pass is the lowest point between Los Angeles and the rest of the
nation. So historically, going way back to the days of the pioneers
coming through in wagon trains through here, this was the low point.
And so over the years, old Route 66 came through here and one lifeline
after another got stacked in right through Cajon Pass. So now we have all of the telecom fiber-optic infrastructure, half a dozen high-tension power transmission lines, the I-15 freeway, 2 high-pressure gas lines, and 2 gasoline fuel lines all coming through Cajon Pass where it crosses the San Andreas Fault. The rupture propagation is one of the things that we're studying. That's what creates the big shockwave off the front of the rupture. |
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| 01:00 | So the ground motions through here would also be very large.
Things would get knocked down as well as broken. And then, a lot of that
energy gets channeled out into the Los Angeles Basin and then also out
to the northwest towards Bakersfield. Interviewer: So according to this scenario, what would happen to things like the freeway or the rail lines or maybe the gasoline and natural gas lines you mentioned? Ken Hudnut: First, the rupture would break one of the high-pressure gas lines that's just on the opposite side of the freeway from here. Then it would break through the freeway offsetting one lane of traffic on each side. It would then rupture through old Route 66 where all of the telecommunication fiber-optic lines are buried and then across through both of these straight lines that connect the ports of L.A. and Long Beach to the rest of the country. It would then keep breaking, go through the power lines and rupture another gas pipeline and then the two gasoline lines and where that happens, normally the ground current through that pipeline, that would be broken and you'd get an arc and so the gasoline would ignite and when actually having this scenario that you'd have an explosion forming a crater, right where it's co-incident with 2 of the really big power lines across the fault. |
| 02:09 | So that's just over here. This is not the place you want to
be when the big one actually hits. We created an earthquake scenario
that involves rupture of the part of the southern San Andreas Fault
that we are most concerned about. It has a recurrence interval of about
150 years and yet it's been more than 300 years since the last big
earthquake. So we know that that section of the fault is really locked and loaded, ready to go. And this scenario starts down there near the Salton Sea, ruptures pass Palm Springs and then passed us here Cajon Pass and keeps going up to Lake Hughes. It's a 180-mile section of the fault, 300 kilometers long. It's the part that we're almost concerned about rupturing in the next great earthquake on the San Andreas Fault. It's not to say that this exact earthquake would ever happen. We're just putting together as best we can a realistic scenario. |
| 03:00 | So in this case, we've said it would be a magnitude 7.8. We
based that on the fact that the 1857 Fort Tejon earthquake and also the
1906 San Francisco earthquake. Both of those San Andreas great
earthquakes were 7.8-7.9. So we wanted to go with that number because
we know that can happen. We also think it's possible that the San
Andreas Fault could even dish out a bigger earthquake than that. So
this is actually not a worst-case scenario. So, we based the ShakeOut Scenario Earthquake as a starting point on an earthquake that's actually one of the earthquakes that's thought to be quite plausible. It's within the National Seismic Hazard Maps. So that earthquake is one of thousands that form the basis for the National Seismic Hazard Maps. So it's generally considered that an earthquake of this size on this part of the fault is quite realistic. And a 7.8 earthquake is one that we think that this section in the San Andreas Fault is certainly capable of. |
| 04:00 | We are also trying to reach a level that was about like the level of
say Hurricane Katrina that we are asked to try to sort of tune it to
about that magnitude. And we came in pretty close when we tallied up
all the numbers in terms of total damages and so forth. To create this scenario, the ShakeOut Earthquake, we defined the source of the earthquake in a lot of detail. So the science that went into that basically involved decades of study, trenching to look at offset layers that have been disturbed in previous earthquakes and then dating those using radio carbon. So that was the effort of USGS and our colleagues to the Southern California Earthquake Center over a long period of time, a lot of studies. And also the USGS funded a special project of the Southern California Earthquake Center called SoSAFE which stands for Southern San Andreas Fault Evaluation. So the SoSAFE project, we really are trying to make Southern California safer for the residence here. |
| 05:00 |
So one way that we've had some
impact already with that project is in helping to define the earthquake
source. The endpoints were selected based on pre-historic earthquake
evidence. Also we ended at the northwest end because we had seen that
in the previous 3 earthquakes, there have been a large slit down to
Lake Hughes. But then from Lake Hughes to the southeast, there had been
a lot less slit. So our sense is that this is the section of the fault that we have rupturing in the ShakeOut Scenario that has the most strain loaded on it. So it was that accumulative evidence from the scientific literature that we put into this. And then we also had scientific workshops where we consider this and with our colleagues, developed this scenario and then we invented that through a process of interaction with our colleagues. State California Geological Survey also was vital and helping to form that image of the ShakeOut Earthquake. |