Crowdsourced seismic sensors might save your life someday.

But, ultimately, earthquakes are a physical process. The earthquake releases physical energy that has been stored in the earth. So, shouldn’t a series of small, frequent quakes reduce the chances for a large earthquake? Possibly — the town of Moodus, CT experiences very frequent micro-quakes, to the point of supposedly inducing native religious beliefs around the phenomenon. Perhaps as a result, the area is considered seismically stable, with large quakes rare in nearly 500 years of recorded history.

A similar unanswered question is whether there are physical limits on maximum quake size.

(A certain “non-fiction” cable channel frequently carries a “documentary” about a magnitude 11 quake that hit the St Louis area in the unpopulated 1700s, “but would destroy Chicago if it happened today.” Although St Louis is slightly seismically active, according to USGS quake maps Chicago is not. Moreover, even after reviewing historical accounts, seismologists think the physical limit for a quake might be 9-10. This same “non-fiction” cable channel also frequently carries a “documentary” asserting that Nostradamus died standing, which we assure you is impossible unless you are a pirate in a ride at Disneyland. Maintaining bipedal balance is computationally challenging for robots and even most animals. Consciousness (or physical supports) are required to remain standing. Cable channel buyer beware. If the media can get away with distortions on such well-understood topics, imagine how bad the reporting on earthquakes must be.)

As Nate Silver discusses in the aforementioned book chapter, the physical limit discussion actually turns out to be important. Apparently, Japanese seismologists (or at least the ones consulting in the design of Fukushima) believed the sea floor in Japan limited especially strong earthquakes. In this, they ignored the historical and oral records of powerful tsunamis  hitting the area over the centuries. This caused them to adopt a more complicated model that may have “overfit” the earthquake data, underestimating the odds of the magnitude-9 earthquake and resulting tsunami that ultimately caused a major nuclear accident.

Lack of Predictive Power in Existing Earthquake Models Due to Lack of the Right Data

Unfortunately, with current models that have any demonstrated predictive power, very little can be said. The 100-aftershocks might perhaps constitute an “earthquake swarm” like the one seen in Italy, but this only slightly increases the chances short term of a major quake. (It is not much of an “earthquake swarm” yet, either. If you look at USGS earthquakes 3.5 and above that have hit California recently, you see a typical pattern of 7-14 per month. March was different, with over 30 so far. But that’s only 2x the normal rate. Most of the 100-aftershocks quoted by the media have been below 3.5 in magnitude, barely perceptible and likely well in “the noise” given the failure of any predictive model to date to successfully use this information.)

The one valid predictive model observation is that, with the 5.1 quake, there is now a 5% chance of a stronger quake within the next three days. (Put another way, there is a 95% chance that there will not be a stronger quake within the next three days, or a 95% chance that the much-feared “Big One” will not happen within the next three days. After three days, we go back to the best predictive model we have, which is the old 1/12000 chance of a 6.5 quake on any given day in Los Angeles.)

5% (of a quake stronger than 5.1 magnitude) is certainly higher than the normal 1/12000 of a 6.5 quake (more than 10x stronger than a 5.1 magnitude), but it is still low odds. (And, based on USGS mortality statistics, a 6.5 earthquake in modern earthquake-resistant construction should be very survivable.) We won’t be temporarily relocating to rattlesnake country or increasing our life insurance coverage for this. We will double check our earthquake-preparedness kit, however.

So why are these predictive models so poor, and is there anything we can do about it? Well, the fundamental problem is that we don’t understand the underlying physical processes very well, because we can’t easily observe pressure in rock. This will change. As Arthur C. Clarke once said, any sufficiently advanced technology is indistinguishable from magic. Although seeing through rock with technologies such as ground-penetrating radar is currently limited, with time and computing power, these technologies will get better. Moreover, it will become increasingly more feasible to place pressure sensors and ground-penetrating radar in very deep wells, despite the costs and enormous heat. Although there are some experimental seismic monitoring deep wells, to build a vast arrays these is currently cost prohibitive. But technology is advancing exponentially, and the cost of placing deep sensors in seismically active areas won’t always stay prohibitive. (This is where we disagree with Nate Silver, who speculates we may never be able to predict earthquakes because we will never be able to see through rocks.)

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