There’s an article in last Friday’s issue of Nature describing some changes in the rocks near the San Andreas Fault that occurred in the hours before two small earthquakes. Here’s the BBC’s writeup; for those of you who can sneak behind the Nature paywall, the original article is here.
A similar study was published sixteen years ago, not in Nature but in Science. The first author on the 1992 Science paper, Paul Silver, was also the second author on this week’s Nature paper. While the recent study measured stress changes along a fault using precise instrumentation installed in a pair of very fancypants boreholes, in 1992, Silver and his coauthor Nathalie Valette-Silver exploited a natural system that is also very sensitive to changes in the squeezing of surrounding rocks: California’s Old Faithful, in the wine country town of Calistoga.
So before considering the evidence presented in Nature this week, I’d like to bring you all up to speed on the latest developments in geyser-based earthquake prediction. It’ll be a short post.
The geyser in Calistoga is a commercial tourist attraction. At least part of its plumbing was man-made; it erupts through a well bore drilled in the late 1800s. Today, visitors pay $8 to see it erupt, and to spook the fainting goats and pet the llamas while they wait for the main event.
The geyser owners have been tracking the length of time between eruptions at Old Faithful for many years. Silver and Valette-Silver looked at this data, and found that while the eruption interval is usually regular enough to justify the nickname “Old Faithful”, every now and then it does something weird. “Weird” is loosely defined – sometimes the geyser starts picking randomly between two possible wait times instead of one, and other times visitors get consistently more quality time with the fainting goats – but in any case, Silver and Valette-Silver found about 190 instances of weird behavior in the 28-year period of record, and 3 of them occurred shortly before moderate regional earthquakes. After each of those earthquakes the geyser went super ginormously haywire, dwarfing the irregularities observed in the one or two days prior. While there were 5 other biggish earthquakes during those 28 years, there was no signal at the geyser either before or after them.
That’s pretty much where things stand today. The Calistoga geyser data set is still one of the longest records available for any proposed precursory signal; while weird behavior precedes earthquakes at a slightly higher rate than you’d expect purely by chance, it’s not so much higher that you can’t sniff at it, if you happen to be the sort of person who sniffs skeptically or disdainfully at things. The paper’s accumulated citations are mostly from people thinking about geyser eruption dynamics. We still can’t predict earthquakes.
I haven’t read this new paper yet, but I’m willing to bet a case of good beer that in 12 years, it’ll have made a non-splash, just like the Calistoga geyser.
- Silver, P.G., Valette-Silver, N.J. (1992). Detection of Hydrothermal Precursors to Large Northern California Earthquakes. Science, 257(5075), 1363-1368. DOI: 10.1126/science.257.5075.1363
- Niu, F., Silver, P.G., Daley, T.M., Cheng, X., Majer, E.L. (2008). Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site. Nature, 454(7201), 204-208. DOI: 10.1038/nature07111