Precursors

Sometimes we never see it coming. Kevin Flynn and Jim Dwyer of the New York Times listened to the last radio messages of firemen at the World Trade Center and noted the last transmission was ”Battalion 7 to Ladder 15”. “The voices, captured on a tape of Fire Department radio transmissions, betray no fear. The words are matter-of-fact. … There was no awareness of imminent doom.” Up until the last moment the firemen did not know the Towers were going to crumble under their feet. But can we see an earthquake coming? The most dreaded notion used in connection with the recent  5.1 magnitude quake in LA is ‘precursor’.  What can we make of this seeming prediction?

US Geological Survey seismologist Lucy Jones told Los Angeles Times that the 5.1 quake has a 5 percent chance of being a foreshock of an even larger quake. “There could be even a larger earthquake in the next few hours or the next few days,” Jones was quoted as saying.

Smithsonian Magazine calls Jones “the earthquake lady”.

Today Jones is among the world’s most influential seismologists—and perhaps the most recognizable. Her file cabinets bulge with fan letters, among them at least one marriage proposal. “The Earthquake Lady,” she’s called. A science adviser for the U.S. Geological Survey in Pasadena, Jones, 57, is an expert on foreshocks, having authored or co-authored 90 research papers, including the first to use statistical analysis to predict the likelihood that any given temblor will be followed by a bigger one.That research has been the basis for 11 earthquake advisories issued by the state of California since 1985.

But whether Jones can actually predict any earthquake meaningfully is open to dispute. When Jones predicts a quake she’s sure to eventually be right, in the way that one is always correct when pointing to someone and declaring “you will die”. Most everyone dies — eventually. And it’s easy to make a  statistical prediction.

With over 13,000 earthquakes around the world each year with a magnitude of 4.0 or greater, trivial success in earthquake prediction is easily obtained using sufficiently broad parameters of time, location, or magnitude. However, such trivial “successful predictions” are not useful.

But people don’t want to know about long-term odds. They want to know the day and the hour the Big One is coming so they can absent themselves from Los Angeles at that moment. As for overall risk, that has been priced into the real estate values already. Tokyo, for example, has extensive earthquake risk tables. The 2011 earthquake momentarily drove real estate investors away from Japan, but at least two major firms took that very time to buy up property. Given the overall location — such as Tokyo or Los Angeles — the next most important factors are also known: local soil conditions and building age and quality of construction.

Engineers have created a number “earthquake resistant” construction methods. They are like body armor. None of them are going to save people from a Chicxulub-class catastrophe any more than any vest is going to stop a 16-inch shell. But living in a good building founded on a good geologic foundation may successfully protect against lesser threats.  The relative frequency of earthquakes is shown by this USCGS table.

So we “know” something about earthquakes, we just don’t know our individual fates.

Just now, the Los Angeles area was rattled by another magnitude 4.1 earthquake, according to Reuters.  What we’d really like to know is whether this increases the probability of the Big One given the one just experienced. Or are they independent events?  Are we right back at concluding, as Jones did, that there is a 5% chance of a bigger earthquake given the one just experienced? Is it like a roll of the dice, where each throw is decoupled from the last?

The answer appears to be that foreshocks really do contain information about whether the Big One is night.  But the info is partly encoded in the location of the foreshocks and not in the frequency. It is written in data we have yet to capture. In other words, we need more than a frequency table to make a good prediction. What’s needed is a workable physical model which we do not have yet. Wikipedia notes:

the record of earthquake prediction has been disappointing. Even where earthquakes have unambiguously occurred within the parameters of a prediction, statistical analysis has generally shown these to be no better than lucky guesses. The optimism of the 1970s that routine prediction of earthquakes would be “soon”, perhaps within ten years, was coming up disappointingly short by the 1990s, and many scientists began wondering why. By 1997 it was being positively stated that earthquakes can not be predicted, which led to a notable debate in 1999 on whether prediction of individual earthquakes is a realistic scientific goal. For many the question is whether the prediction of individual earthquakes is merely hard, or intrinsically impossible.

Earthquake prediction may have failed only because it is “fiendishly difficult” and still beyond the current competency of science.

But the answer, is of course, “out there”.  Few of us would be so foolish as to imagine that the truth comes from press conferences or the utterances of politicians.  Earthquakes, storms and natural disasters are one of the few times when humankind acknowledges the intrusion of unalloyed reality into the modern world. Even O’Brien in 1984’s Room 101 would be hard put to deal with the roof caving in on his head.

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