Opinion

Earthquake myths about the Pacific Rim

A tragic month along the tectonic subduction zones that surround the Pacific Rim has also been a spellbinding one for seismologists. A magnitude 6.2 quake on April 14 was followed a day later by a magnitude 7.0, together killing about 50 in the Kyushu region of Japan. Less than 24 hours later, a magnitude 7.8 in Ecuador killed more than 650. Major deep earthquakes in Myanmar and Afghanistan in April were also deadly, and a series of quakes this month struck Vanuatu, too.

Giant faults such as the San Andreas dominate the danger.

World-destroying films such as "San Andreas" and "Earthquake" feature magnitude 8s and 9s. NBC even produced a miniseries called "10.5: Apocalypse," about a quake that splits North America into two islands. "The Really Big One," the New Yorker story for which Kathryn Schulz won a Pulitzer Prize this year, explained the potential dangers of living near the large Cascadia fault in the Pacific Northwest. And the plate collision zones under South America and Alaska's Aleutian Islands are famous for the monster quakes they spawned in the 1960s: magnitude 9.5 in Chile and magnitude 9.2 in Alaska.

But the bigger threats come from smaller quakes. Christchurch, New Zealand, had to be essentially rebuilt after a direct hit from a mere 6.3 in 2011. Japan was shocked when a magnitude 6.9 decimated Kobe in 1995. And the costliest U.S. earthquake was the magnitude 6.7 Northridge quake that shook Southern California in 1994.

Huge tsunamis are the foremost consequence of giant quakes.

Two horrific tsunamis, in 2004 in Indonesia and 2011 in Japan, jointly killed some 300,000 people. No wonder floods consume so much of our imagination. As a quote in Schulz's New Yorker article put it, "Everything west of Interstate 5 will be toast" when a big quake triggers a mega-tsunami. Summarizing on Fox News, Shepard Smith predicted "Seattle, Tacoma, Portland and Olympia, Salem and Eugene, wiped out, altogether about 7 million people. That's not including tourists."

But in the United States and many other countries, the costliest and most deadly faults are inland. The scariest likely scenario is a temblor that hits the heart of Los Angeles, the San Francisco bay area, Seattle, Portland or Vancouver, not the nearby Pacific Rim oceanfront.

Earthquakes often trigger volcanic eruptions.

According to the laws of geology, where tectonic plates collide, volcanoes rise in the background. Volcanoes such as Mount St. Helens throw a long and deep shadow in the Pacific Northwest. And Charles Darwin said he observed volcanic eruptions triggered by the magnitude 8.5 Chile megaquake during the voyage of the HMS Beagle in 1835.

But the connection is hardly reliable, as this doesn't happen very often. Earthquakes result from shifting tectonic plates, not magma flows, and have only a weak effect on volcanoes.

The major American Pacific fault lines are "10 months pregnant," "locked and loaded" or "overdue."

In "The Really Big One," the Cascadia fault is on the verge of popping. "Counting from the earthquake of 1700, we are now three hundred and fifteen years into a two-hundred-and-forty-three-year cycle," Schulz wrote. It is easy to imagine a valve keeping more and more pressure contained until it finally bursts.

Yet earthquakes tend to unfold differently with each iteration on a given patch of fault. Quake recurrence is fairly sporadic because the strength of fault surfaces is highly irregular, and so the complex ruptures are unique each time. The current risk of a magnitude 9.0 earthquake for the Puget Sound, for instance, is 1 chance in 300 per year. Quakes are not like a pregnancy - after a certain amount of time, birth is not inevitable or immediate.

5. The entire Ring of Fire settles down or pipes up all at once.

There have been six earthquakes greater than magnitude 8.5 since 2004, after none between 1965 and 2004. Some scientists say we've entered a period of enhanced earthquake activity ("a sign of the times," as a recent article in Nature had it). One week in April saw five places near the Pacific Rim with greater than magnitude 6.5 quakes. Signs of the Times, a site dedicated to undercovered global trends, drew connections between 10 Pacific Rim volcanoes active at the same time in 2013. One well-circulated reading of scientific data says current conditions –– including a spike in carbon monoxide –– indicate that it's unsafe to visit the West Coast.

Truth is, tere really is almost nothing to foreshadow big quakes, although we continue to prospect for silver bullets. Relax, build a long-term shaking- and tsunami-resilient society, and play it as it lies.

Vidale, a professor at the University of Washington, directs the Pacific Northwest Seismic Network and is the Washington state seismologist.

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