We attended the final session of Science on Tap last month, but I’m only now getting around to writing about it. A lot else has been happening. Following in the latest trend of this lecture series, this talk was about disasters. The previous occasion covered flooding and this last one was all about earthquakes. Dr. Michael Wysession of Washington University in Saint Louis was the night’s lecturer. He described some of the particulars of the big earthquakes of recent history, Nepal, Japan and Haiti and then went on to offer some predictions. He never offered any specifics about timing, but instead got a wee bit philosophical.
Predicting earthquakes is impossible and predicting the next big one is even more so. Predetermining the severity of an earthquake, even while it is occurring is difficult. Big quakes start off small, like ordinary ones, but just continue to grow. A thirty-second earthquake generally has a magnitude in the mid-sevens. A minute-long quake is in the high sevens, a two-minute quake has entered the eights, and a three-minute quake is in the high eights. By four minutes, an earthquake has hit magnitude 9 on the Richter scale.
While discussing the probability of the next big earthquake along the San Andreas, he offered up the analogy of the 8 o’clock bus. If you get to the bus stop at five of eight and wait a minute and no bus arrives, no one gets perturbed. With each passing minute the probability of the bus arriving is thought to increase. Such is the belief about earthquakes in areas of common seismic activity, but what if it is now five minutes after eight and the bus still has not arrived. Now, with each passing minute the likelihood of the bus ever showing up decreases. It might have had a breakdown or otherwise been detoured and might not come at all. The point that he was making was that just because a period of time as elapsed in an active seismic region, this is no indication that another earthquake is due soon.
Similarly, he offered up another analogy for earthquake predictions that of the NYC bear attack gap. Over the last century there have been many more bear attacks in Montana than there have been in NYC. Does this mean that NYC is due for a spate of bear attacks or is it intrinsically less susceptible to bear attacks? For bears the historical record is of sufficient duration to come to the correct conclusion, but that same record is woefully inadequate for judging events on the geological record.
All this being said, Wysession did offer up a few predictions. He gave LA a fifty-fifty chance of surviving its next big one. Big one in this context being on the order of a 9. If the energy from such a quake was directed west or out to sea, the city would remain relatively unscathed, but if the energy was directed east or inland, not so good. The last big earthquake in the Pacific Northwest occurred on September 26, 1700. This has been deduced from Japanese tsunami records. There was no Seattle back then. The next one will be devastating. Closer to home, he poo-pooed the risk of earthquakes here in Missouri, saying that he doesn’t even carry earthquake insurance, while in Oklahoma there have been over a thousand quakes recently and most of them in areas that have never record any seismic activity before. He blamed fracking for these events.