Ken Hudnut: Through the ShakeOut study, we’ve learned
that the large ground motions from a big one on the
San Andreas fault would be large enough to potentially
cause collapses of many tall buildings here in Los Angeles.
We then had a panel of the world’s leading experts,
structural engineers, who studied tall buildings and who
are very familiar with the seismically vulnerable types
of tall buildings assess what the damage would be.
And we actually put in the ShakeOut scenario a total of
10 building collapses, most of which occurred right
here in the Downtown Los Angeles area.
We set out in the ShakeOut study as one of our prime
objectives to get a much more sure answer about the ground
motions here in Los Angeles where we have tall buildings,
and we’ve concluded through a very thorough investigation
that the ground motions will be large enough to
potentially cause collapses of tall buildings.
We’ve seen around the world in other large earthquakes
tall buildings collapse, older seismically vulnerable types,
steel frames with brittle welds and also reinforced concrete
structures that just didn’t use as much as
rebar as if it were built today.
For ShakeOut, for the first time, we went through a process
of calculating the ground motions and then reviewing those
with structural engineers. That was really unique.
And prior to this study, we had had differences of opinion
about what the ground motions would be and whether tall buildings might collapse.
What we achieved here was a new level of understanding of the ground motions and also agreement with
structural
engineering experts that tall building collapses are quite
a realistic possibility and a big one on the San Andreas.
As the earthquake progresses along the fault, first,
the waves are going to hit Palm Springs and the Coachella
Valley within about 30 seconds. Damaging and shaking will
continue for about a minute there, and as that is occurring,
the rupture keeps going, it hits San Bernardino next, shakes
for about a minute there. After about a minute from the
beginning of the earthquake, Downtown L.A. is going to be
shaken by about six feet per second kind of ground motions
for a full minute. This damaging shaking is going to hit
all of Southern California; it will be felt all the way down
even as far away as San Diego very strongly.
So the pattern of shaking is concentrated along the fault but even
areas distant from the fault will receive damaging levels of shaking.
Our sensors out along the Southern San Andreas Fault can
pick up the waves as soon as they start to come off of the fault.
We can then speed that information back to L.A. and provide
over half a minute of early warning here in Los Angeles.
The main thing we know we could do with an early warning system
is trigger automated systems to shut off. We also know that
school children who are very well trained on “drop, cover and
hold on” drills will have time to react and get to a safe place
if they’re provided with an early warning alert.
So those are our biggest hopes and we think that the technology
is there and that this is something that could be done.
So although we can’t predict earthquakes, we can do early warning.
It has been, for me, really rewarding to make the connection
with not only the emergency managers but the utilities and lifeline
operators here in Southern California in a completely new way.
We’ve connected with them and we just feel that the earthquake
research that we’ve been all doing for decades has been made
societally relevant to the point where these connections are
just happening right now.
We’ve not only met people but worked with them.
We know that they’re taking action to make Southern California
safer as a result of the ShakeOut exercise.