Seismic data suggests slow slip events may presage larger earthquakes

January 29, 2016 by Bob Yirka, report
Seismogram being recorded by a seismograph at the Weston Observatory in Massachusetts, USA. Credit: Wikipedia

(—A team of researchers, two from Tohoku University in Japan and two from the University of California in the U.S., has found evidence that suggests that a speedup in small underground deformations may occur prior to larger earthquakes, possibly providing a means for sounding a warning. In their paper published in the journal Science, the team describes how they pored over seismic data that spanned 28 years and which included approximately 6,000 seismic events, and what they found as a result—they also suggest that their findings might one day lead to a true earthquake early warning system.

Scientists the world over have for years been searching for a way to predict when an earthquake will strike, with enough certainty to warn people in the area. To date such efforts have come up empty, though much has been learned in the process. In this new effort, the researchers report that they believe they may have found a possible indicator of an impending quake, and it is based on what are known as slips, small underground movement similar to earthquakes, but which happen so slowly that they don't cause damage or even register on seismic monitors—the only way to detect them is to use GPS equipment.

To come to these conclusions, the researchers analyzed for Japan's two largest islands, going back to 1984. Doing so led to the identification of 1,500 instances where there appeared to be a pattern of repetition—that allowed them to estimate the speed at which the tectonic plates below were moving. They then used statistics to correlate slippages with non-repeating measurable quakes with a magnitude of 5 or higher. Doing so revealed that there appeared to be a speedup in slippage just prior to . The team also looked at GPS data, which can actually be used to measure tectonic shifting, and report that it matched the rates they had calculated earlier.

The team acknowledges that much more work needs to be done before it can be confirmed that GPS monitoring devices could one day offer an early warning system, but suggest their research shows that there is the potential for such an outcome.

Explore further: Study results suggest slower seismic waves due to quakes may signal weak spots in crust

More information: N. Uchida et al. Periodic slow slip triggers megathrust zone earthquakes in northeastern Japan, Science (2016). DOI: 10.1126/science.aad3108

Both aseismic and seismic slip accommodate relative motion across partially coupled plate-boundary faults. In northeastern Japan, aseismic slip occurs in the form of decelerating afterslip after large interplate earthquakes and as relatively steady slip on uncoupled areas of the subduction thrust. Here we report on a previously unrecognized quasi-periodic slow-slip behavior that is widespread in the megathrust zone. The repeat intervals of the slow slip range from 1 to 6 years and often coincide with or precede clusters of large [magnitude (M) ≥ 5] earthquakes, including the 2011 M 9 Tohoku-oki earthquake. These results suggest that inherently periodic slow-slip events result in periodic stress perturbations and modulate the occurrence time of larger earthquakes. The periodicity in the slow-slip rate has the potential to help refine time-dependent earthquake forecasts.

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1 / 5 (2) Jan 29, 2016
We have had hundreds of little quakes on a fault which goes by my house, and is in parallel roughly with the Calaveras and Hayward Faults. My PV panels went up yesterday, and in a year I will have battery storage for a few days, charged by the PV panels and a dual fuel generator. With the EV, that can give me power, light, heat, and transportation when the power grid goes down.

Meanwhile, I have paid most of my power in advance for the next few decades.
4 / 5 (2) Jan 29, 2016
IMO, prediction is only useful if you can pinpoint it to within a few days or less... I don't think it really helps anyone if all you can say is, "we're due to have one any day now..."

Notice this study focused on slow movement, not small earthquakes... We already know frequent small earthquakes are a predictor of larger ones... Out of curiosity, how many of those 'hundreds' would you estimate that you've felt? How many of them have woken you up at night? (p.s. I didn't down-vote you, someone else did)

1 / 5 (2) Jan 29, 2016
"I don't think it really helps anyone if all you can say is, "we're due to have one any day now...""

Yes, it does, it gets us moving toward preparedness, as I have done.

I have only felt a few if them, being about 15-20 miles away. They were very small, and even those living in them did not feel them all. But they were very significant to the Seismologists. By relieving pressure on the smaller faults, they think it loads it on the major faults.
1 / 5 (2) Jan 29, 2016
" (p.s. I didn't down-vote you, someone else did)"

Yeah, a couple of chronic malcontents with grudges follow me around to "get even" with me for being a real person.
4 / 5 (4) Jan 29, 2016
"To say it very clearly: Earthquake swarms are not at all an indicator that something bigger is about to come. Too many times such swarms have happened without culminating in a big, destructive quake. This is especially true for the I-680 corridor. In May a swarm under Concord came and went. And since 1970 the northern segment of the Calaveras Fault in the region of Alamo, Danville and San Ramon has seen at least four swarms, most recently in 2003. Each lasted for weeks or months, but so far none was closely followed by a significant quake."

1 / 5 (3) Jan 29, 2016
". . but so far, . . . "
Oh, gosh, then obviously none will come.
Jan 30, 2016
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