The recent magnitude-9.1 megaquake and the tsunami that followed it showed that Japan was not fully prepared for so violent a tremor. If even a country that suffers frequent earthquakes wasn't ready, what of the US, which itself contains several seismic hotspots?
Over the past two decades, the US has made considerable advances in fortifying its cities against quakes, but geologists and engineers agree that there is still much to be done. In a National Research Council (NRC) report published today, they have outlined just what that means.
The National Earthquake Resilience report is particularly concerned with the possibility of a "Katrina-like earthquake": not just a moderately damaging tremor, but a cataclysm rivalling the 1906 San Francisco quake, estimated at magnitude 7.9, which probably led to thousands of deaths.
Geologists fear that because of the US's relatively unshaken recent history, its citizens have been lulled into a false sense of security, believing that a devastating earthquake is unlikely to strike the country – although it's not even 50 years since Alaska felt the force of the second largest quake in recorded history. The magnitude-9.2 Prince William sound event led to 115 deaths in Alaska alone.
The NRC report recommends three major goals: raising understanding of earthquakes; developing cost-effective measures to reduce the effects of earthquakes on individuals, the built environment and society at large; and improving the earthquake resilience of communities nationwide. Over 20 years, reaching those goals is likely to cost $6.8 billion.
Crucial minute
Early-warning systems are of particular importance. Japan has the world's most sophisticated system, with 1000 seismometers scattered about the country: it gave some people nearly a minute's notice before the recent earthquake struck their towns, and probably saved many lives. Such systems work by detecting relatively harmless seismic P-waves, which ripple through the Earth at great speeds ahead of the slower – but far more damaging – S-waves.
The report also recommends involving the public in planning earthquake response measures, because this could help to provide people with information that could save their lives. In the November 2008 Great Southern California ShakeOut more than 5.5 million citizens, 5000 emergency responders and disaster recovery agents – and 300 scientists – participated in a drill that modelled what would happen during and after a magnitude 7.8-earthquake on the southernmost 300 kilometres of the San Andreas fault. The ShakeOut scenario estimated that an earthquake of that size would cause over 1800 deaths, 50,000 injuries and $200 billion in damage and other losses – and stands as a dramatic call to action to prepare for the real thing.
William Ellsworth of the Earthquake Science Center in Menlo Park, California, points out that most US cities are now much better prepared for a massive earthquake than San Francisco was in 1906 – but, crucially, preparedness is not uniform, even within each city. "The building codes we have in US today are pretty good, but lots of smaller structures are not covered by those codes and neither are older buildings."
Engineer Gregory Deierlein of Stanford University, California, explains that two-storey buildings with apartments on top of a relatively open structure like a restaurant or parking lot are particularly prone to collapse. These buildings could be adapted to be more earthquake resilient.
Bounce back
As important as protecting buildings is ensuring that a city's utilities and transportation systems are not crippled by a quake, says Deierlein. "If roadways and utilities are largely intact, society tends to back bounce back pretty well," he says. "But major disruptions to roads, power and water lines really delays recovery."
Ellsworth says thanks to an energetic programme of improvements and replacements, US roads and highways – especially on the west coast – should fare much better in any future earthquake than they did after big Californian quakes in 1989 and 1994. After both events some roads remained unusable for years.
"Earthquakes are going to happen, and we are going to take some hits, so we have to have procedures in place to recover from an earthquake in an effective way," Ellsworth says. "That's the whole idea of earthquake resilience."
Deierlein agrees. "Resilience means there will be a lot of damage and clean-up, but the city will not be paralysed."
in: newscientist.com
No comments:
Post a Comment