“It’s almost impossible to make a sensible earthquake hazard map,” argues Northwestern University geophysicist Seth Stein (no relation to Ross). “The onus is on Ross to prove that his complicated maps work better than the old maps — and that they work better than random.”
Robert Geller, a University of Tokyo geophysicist, said the standard maps “are simply wrong” and are based on the false premise that earthquakes repeat themselves at more or less regular intervals.
“We call this the ‘whack-a-mole model’ of earthquake hazard mapping. The mole will come up the same hole that it went down,” Seth Stein said. And that’s rarely the case.
Geller and Seth Stein contend that the seismic hazard maps haven’t shown themselves to offer information about potential earthquake location and intensity that’s better than a random guess.
The U.S. government disagrees. David Applegate, associate director for natural hazards at the USGS, said the hazard maps in this country are incorporating data going back thousands of years in some cases. And Art Frankel, a USGS geophysicist who led the National Seismic Hazard maps program from 1993 to 2004, said the maps are useful for designing building codes.
“I don’t buy this idea that we don’t know anything and every place is the same hazard. We know a lot,” Frankel said.
Since the development of the theory of plate tectonics in the 1960s, scientists have a better understanding of why earthquakes occur along plate boundaries. The 1906 San Francisco earthquake, for example, released the strain that had built up as the North American plate and Pacific plate fitfully tried to slide past each other along a plate boundary, the San Andreas Fault. Scientists have tried to monitor the motion of tectonic plates and create maps showing where strain is building at a locked plate boundary.
But earthquakes remain fundamentally unpredictable and eccentric. Scientists were surprised by the location of the 9.1 magnitude earthquake in the Indian Ocean on Dec. 26, 2004, which generated a huge tsunami and took 230,000 lives. That portion of the subduction zone near Sumatra had been considered an unlikely source of a great earthquake.
Since then, more surprises. The 2008 earthquake in China’s Sichuan province, which killed 68,000 people, was in an area that “did not look like a very active region,” American geologist Peter Molnar said afterward. The 2010 earthquake in Haiti occurred along a fault generally considered less dangerous than another fault to the north. And New Zealand has had two significant earthquakes on unmapped faults in the past year and a half.
Surprises may be the norm for the seismic future, even in places considered hazard-free. The Virginia earthquake in August, which damaged the Washington Monument and the National Cathedral, is a reminder that the East Coast could be more vulnerable to tremors than most people realize.
“All of the region plausibly has within it faults and residual strains and stress accumulations from the history that has been experienced by the crusts,” Lay said Friday.
One area in the United States that is receiving increased attention is the Pacific Northwest. A number of popular beach towns, such as Seaside, Ore., are in the line of fire of the Cascadia subduction zone, said Patrick Lynett, a University of Southern California professor of civil engineering who is an expert on tsunami hazards.
The West Coast does not have evacuation towers, and residents facing an incoming tsunami would have to evacuate on foot to higher ground, he said, before the first waves arrived in 15 to 30 minutes. Lynett noted that Seaside has summer festivals in which thousands of people crowd the beach. “You could have a lot of really bad factors coming together,” he said.
The Cascadia subduction zone last ruptured in the year 1700. When is the next Big One? The answer, unfortunately, is somewhere off the coast, in ancient crust beneath the sea.