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.
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.
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?
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. 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.
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.
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. 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 vetted 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.