According to a new study reported in Scientific American, hundreds of earthquakes too subtle for humans to feel are shaking Southern California every day. Nearly two million earthquakes that took place over the past ten years and were previously hidden from scientists, have just been added to the log of the region’s seismic activity. Using powerful computer analysis, those two million new data points may now help us understand–and potentially even predict–future quakes.
While seismologists long suspected these subtle quakes were happening, they were unable to accurately record them. The temblors were gentle enough that things like jackhammering in a street could obscure the signatures. The breakthrough came 15 years ago, when they discovered a previously unknown pattern.
It turns out that any two earthquakes that start in the same place make the same waveform shape on a seismometer, even if one is very large and another very gentle. Once they knew that, they could plug in the waveform signatures of larger quakes and look for smaller versions–but one more hurdle remained. Computers of 15 years ago were only powerful enough to analyze small sets of waveforms at a time. Only recent advances in technology have make it possible to fully scour the Southern California Seismic Network archive.
They fed the complete archive of 2008 to 2017 into the system and let the computers crunch the numbers for 90 straight days. What came out was the confirmation of two million undetected earthquakes–about 495 per day.
The next step is to sift through the new information to see what can be learned about the concept of foreshocks–a truly exciting area of seismic research. Just as aftershocks follow a major quake, foreshocks precede one. While scientists agree foreshocks take place, it has previously been difficult to detect them, and there’s debate about what causes them. If more could be pinned down about how foreshocks work, it could be a game-changer in early warning systems for major quakes.
“If we could really predict when the next big earthquake will occur, we’re in business—that’s the Holy Grail in seismic hazard analysis,” the study’s co-author Daniel Trugman told Scientific American. “I definitely wouldn’t say we’re there yet, but it’s this type of work that’s going to hopefully push us forward.”
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