Seismic Sensors Improve Earthquake Preparedness
Amid the excitement of last month’s Vancouver 2010 Olympic and Paralympic Winter Games, visitors may not have noticed earthquake detection devices — known as strong motion sensors — that were installed at a number of the Games’ venues.
Designed by scientists and researchers at Natural Resources Canada’s (NRCan’s) Geological Survey of Canada (GSC), these strong motion sensors provide immediate, accurate measurements of any seismic activity. This information is essential to determining whether a building is safe after an earthquake.
"The strong motion sensors tell us right away exactly how much motion has been experienced by a particular building," says Dr. David McCormack, program manager for GSC’s Canadian Hazards Information Systems. "If the motion is less than what the building was designed to handle, a decision can be made to put the building back into service without the delays needed for a formal inspection, which could take days or even weeks."
The GSC worked with the Vancouver Organizing Committee for the 2010 Winter Games (VANOC) to install the sensors at sites where unnecessary downtime would have had a serious impact on the Games.
Dr. John Cassidy, a GSC research scientist, is part of the international team that devised a way to predict how buildings and soil will respond to earth tremors — knowledge that can be used to update building codes so that future structures can better withstand earthquakes. By using background sound such as traffic noise, the international team was able to increase their understanding of how both soil and buildings respond to ground shaking.
“The soil has a fundamental frequency, like the sound that you get when you blow into a pop bottle,” explains John. “It might be 1 Hertz [Hz], where the ground moves up and down once per second. Somewhere else, the frequency of the soil might be 10 Hz, and the ground would be moving up and down 10 times per second. Buildings also have a fundamental frequency. For a tall 10-storey building, the frequency is about 1 Hz. For a small one-storey home, it’s about 10 Hz.”
There is a clear cause-and-effect relationship between the frequency of the ground’s motion and that of the building. Tall buildings are most affected by slow shaking (1 Hz or less), while low-rise buildings are most affected by rapid shaking (10 Hz). If the frequency of the soil matches that of the buildings in the area, then greater damage can be expected during and after an earthquake.
NRCan’s research is playing an important part in increasing national and international earthquake preparedness. By looking at soil, ground shaking and the type and size of a structure, building codes can be improved so that new structures are more resistant to earthquakes. And the same information can be used to guide the quakeproofing of existing buildings.
John says the team's findings are already being put to work. “The results of our research are being used, among other things, for the Seismic School Mitigation program in B.C., a 15-year, $1.5-billion project funded by the Government of British Columbia to upgrade hundreds of schools in the province.”
To learn more, visit NRCan’s EarthquakesCanada Web site.