Waiting for “The Big One”

The chances of “The Big One” hitting California in the next few decades is near 100%. The only questions are—how big, and when?
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TRANSCRIPT

Question: Will “The Big One” ever hit California, and if so, when?

Arthur Lerner-Lam:  Yeah.  You know, we do talk about things like The Big One, when it will occur, how big it will be, what the impact will be.  You know a curious thing by the way, is that we are getting better at predicting the impact of an earthquake than we are at actually predicting an earthquake.  Once we know… Once we have a scenario earthquake, for example, of a certain size, a certain location, our computer modeling really is very good, so we can actually with a computer generate the possible ground motion from a scenario earthquake.  We know how buildings interact with the ground and what will cause a building to fall down.  We even have reasonable estimates of the casualties that might arise and the economic damage as well, so we’re getting very good at predicting the damage and we’ve constructed such a scenario for California, and the reason for that is that over the next few decades, 30 to 50 years, the chance of having a major earthquake in California is pretty close to 1, pretty close to unity.  In some sense it’s really safe for a seismologist to say that because earthquakes happen.  Almost certainly a large earthquake is going to happen in California, so you know I’m not sticking my neck out by saying there is a good chance of an earthquake happening, but the question is how… where it will be and how big it will be and that we base on trenching.  We base it on very fine measurements of the crust moving.  We have better calibrated models of the faults and the frictions on the faults and so we’re coming up with sort of a community understanding of what the big one might be. 

The US Geological Survey, an academic consortium called the Southern California Earthquake Center, which actually involves seismologists from all over the US, if not the globe, have come together with a consensus statement, the California Rupture Forecast as it were; and the two areas that are potentially very dangerous are a repeat of a major earthquake along the southern San Andreas, east of Los Angeles, but still close enough to do considerable damage to Los Angeles, and of course in the Inland Empire east, basically along I-10 and going down toward Palm Springs there is a good chance of significant damage and significant casualties there.  The second area is up in the East Bay, not a repeat of the 1906 earthquake, which is on the… which was on the San Francisco Peninsula, but in the East Bay along something called the Hayward fault, really part of the San Andreas system, but a separate fault.  That’s the fault that locally you may remember sort of runs right through the Berkeley football stadium, the hills above Berkeley and so on.  So you know Cal might have difficulty fielding a football team if that earthquake occurs, but our predictions of damage there are pretty severe as well, but again, you know knowledge of what might happen and particularly the damage that might happen goes a great way to providing the political will and in fact, the funding to do something about it.  You can’t stop it.  You can’t stop an earthquake, but you can build strong buildings.  You can prepare the population.  You can make people aware of what they might do when they feel an earthquake and there are other steps we can take as well.  You know we can’t predict. 

We’re getting better at forecasting, but there is also something interesting called the Earthquake Early Warning Systems and this is something that has taken awhile to develop, but when you think about it is kind of obvious and when we you start with the following analogy earthquake waves, an earthquake occurs.  It generates ground motion.  That ground motion leaves the earthquake zone, the rupture zone in a series of waves and there are several types of waves and they all move at different speeds.  We’ve you know some of our students that these are primary, secondary surface waves and so on and the primary waves are fast. The secondary waves are slower and the surface waves are slower still.  What is interesting about that progression is that the primary waves though fast aren’t very large.  The secondary waves are slower, but larger and the surface waves slower still are larger still and so it’s the large waves that do most of the damage, so the theory is that if you could detect that little bit of a P-wave coming along.  It’s not going to do a lot of damage, but it might give you enough time ranging from a few seconds, few tens of seconds to maybe even close to a minute or so or more.  It might give you enough time to do the sort of things that would save people, save structures.  You could stop trains.  You could shut off gas.  You could get people to find safe haven inside the buildings for example.  If you could do that that would constitute a pretty decent early warning system and so there are experiments on trying to do that.  It’s been implemented in Japan.  It’s been implemented in Taiwan and there are other countries around trying to investigate these systems.