A century ago today, residents of San Francisco were roused from their sleep by a disturbing natural alarm clock.
A powerful earthquake, measuring 7.8 on the Richter scale, shook the city for an entire minute in the early morning of April 18, 1906. The violent jolt touched off fires, which reduced many of its neighborhoods to flattened, smoking rubble in just a few hours.
The scale of devastation in San Francisco was due partly to a lack of earthquake building knowledge at the time — a discipline that has since developed largely because of that event, scientists say.
"In 1906 there was no seismic building code, no clear understanding of plate tectonics or where the major faults were located," explained Jack Moehle, director of the Pacific Earthquake Engineering Research Center at the University of California, Berkeley .
Looking at what remained of the cityscape in San Francisco, as well as observing what other earthquakes knocked down in the following years, allowed California's structural engineers to build upon their knowledge.
"The shortcomings have been gradually worked out, to the point where today we have a fairly good understanding of seismic design requirements," Moehle said.
The same can't be said of other earthquake-prone regions across the county, including several big cities whose residents might not even realize they're at risk.
Fire, smoke and mirrors
The 1906 quake would become one of the most damaging in California's history, according to the U.S. Geological Survey .
An estimated 3,000 people died in the disaster, which also caused at least $524 million in property damage. City officials in the greater San Francisco area commemorated the somber anniversary Tuesday morning with exhibits and memorial dedications.
Meanwhile, earthquake experts are planning for what could happen when — not if — a quake of similar proportions tests the country again.
West Coast cities like San Francisco and Los Angeles should come through with better results, engineers say, even though it took several decades for the lessons learned in 1906 to be put into effect.
The first step toward enlightenment was admitting the truth.
"For a long time, the 1906 earthquake was referred to as the ‘Great Fire' because officials didn't want to give the impression that San Francisco was dangerous," said Andy Thompson, senior risk consultant with the engineering firm Arup . "As a result, building codes until the 1960s protected mainly against fire."
The watershed moment came in 1971, when a magnitude 6.7 quake shook the city of San Fernando, Calif., near Los Angeles. That earthquake proved enormously costly, leading builders to search for methods that would limit financial loss to their structures in the future.
Thompson calls this "performance-based" design, and it happens to complement the kind of designs that aim to keep the people inside buildings safe.
"The key is to put the damage in places that do not compromise the vertical-support system for the structure. This way the structure can absorb energy without falling down," he said. "This is similar to the crumple-zone at the front of cars. You want the car to absorb energy, but leave the passenger compartment undamaged."
How do you stand?
Employing this kind of technology in all of its new structures today, California now leads the way in earthquake building codes. Engineers believe that the rest of the country is still at risk for structural devastation, however.
Codes in some regions just don't match up with the danger of an earthquake happening there, Thompson explained.
"Certain places: Seattle, Vancouver and New Madrid [Missouri], to name a few, are places that have the potential (albeit low probability) of a high-consequence event," he said.
"A low probability will reduce risk and will reduce force requirements in the code. But this does not reduce the consequence of the event," Thompson added. "The upshot is that some of these areas are simply not designed for the levels of earthquakes to which they could be exposed."
Moehle agreed with Thompson's assessment.
"Much of the Midwest is filled with older unreinforced masonry construction, which poses the greatest risk," he said.
Several other geologists have warned of the risk near a stretch of land between southeastern Missouri and Memphis, Tenn., called the New Madrid Seismic Zone. The region was rocked by three great earthquakes — all near or over magnitude 8 — over a three-month period of 1811 and 1812.
It's not just the relatively sparse population of the Midwest that's in danger either, say scientists. Few residents of the densely populated Northeast corridor realize that they too live in an earthquake zone, though one much less active than what's found on the West Coast.
With historical records going back only a few hundred years in this region, the faults there are largely unstudied and it isn't known when the last "big one" hit. It is possible that even smaller faults could wreak serious havoc on a large, unprepared city in the Northeast.
Watch out, New York
How would New York fare in a serious earthquake?
"Potentially very, very badly," said Susan Hough, a seismologist with the USGS in Pasadena, Calif. "Without question, I would rather be in San Francisco during a [magnitude] 7.8 earthquake than in New York City during a [magnitude] 6.8 — and the latter is entirely possible."
And it isn't the hundred-story skyscrapers that people need to worry about, Hough told LiveScience.
"The very tall buildings in New York City should be okay: they are anchored in bedrock and designed with enough wind resistance that they are generally strong enough for earthquakes as well," she said. "It's all of the smaller masonry buildings that are scary to think about. And the infrastructure could be a total shambles: they have roads and bridges that are threatening to collapse under their own weight."
Shifting focus back to the Pacific coast, Hough also worries that residents of Oregon and Washington, where the Juan de Fuca subduction zone could create even stronger quakes than the San Andreas Fault, haven't kept up with their neighbors to the south, with potentially disastrous consequences.
"Their Big One will be closer to [magnitude] 9 than [magnitude] 8, and preparedness efforts have lagged far behind those here in California," Hough said. "They will also be facing an enormous tsunami when the Big One hits — and we've all seen what that can entail."
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