Earthquake scientists are learning warning signs of the 'big one.' When should they tell the public?

For U.S. earthquake scientists, Japan's 'megaquake' warning renewed worries about when and how to warn the public if they find clues that the 'big one' might be coming for the West COast.

COPALIS BEACH, WASH. — When Japan issued its first-ever “megaquake” warning last week, Harold Tobin, Washington state’s seismologist, was watching carefully.

The advisory came after a 7.1-magnitude earthquake struck the southern island of Kyushu. Although that shaking caused little major damage — the biggest tsunami wave it produced would have risen up to your knee — it wasn’t the main worry.

Rather, seismologists were concerned that the quake would create stress that could trigger a bomb ticking offshore: Japan’s Nankai trough, likely the country’s most dangerous fault. The subduction zone has the potential to generate 100-foot-tall tsunami waves and kill nearly a third of a million people, according to Japanese government estimates.

Did the smaller quake mean that the “big one” was on the doorstep? No one could say for sure, but the odds were suddenly higher — if only by a few percentage points.“Exactly what might keep me up at night,” Tobin said, if it were happening on the U.S. West Coast.

In Japan, the advisory prompted officials to close beaches, cancel fireworks celebrations and slow trains. People rushed to stock up on emergency supplies.

https://www.nbcnews.com/science/environment/earthquake-scientists-warning-signs-big-one-rcna161467

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