Microzonation facilitates earthquake assessment on a property-by-property basis

Advances in ‘seismic microzonation’ allow underwriters to assess earthquake risk on a property-by-property basis based on a soil analysis of the site, delegates heard at the Canadian Seismic Research Network’s Workshop on Seismic Hazard and Microzonation.
Professor Luc Chouinard of McGill University described efforts to analyze soil in and around the city of Montreal. Chouinard’s team identified thick clay deposits in parts of the city. A soft soil like clay, he explained, will amplify the ground motion associated with earthquakes, and raise the potential for damage.
He pointed to a moderate earthquake that occurred more than 300 kilometres from Montreal. The Old City Hall of East Montreal, in the eastern part of the city, sustained extensive damage to its masonry.
“Interesting enough, this building was located in the eastern part of Montreal at a site where we have a thick layer of clay, about 17 metres. This is the type of [damage] we would expect, [caused by] amplification of the soil movement where you have thick, soft soil deposits,” Chouinard told delegates.
By using microzonation to identify these types of soil deposits in earthquake-prone zones, experts can also evaluate the vulnerabilities of:
•zones where critical infrastructure exists, including hospitals, schools and fire stations;
•critical lifelines, in terms of bridges, tunnels and water supply; and
•industrial sites.
“Microzonation gives us a better idea of hazards, so it can guide us in building new construction and retrofitting existing structures in earthquake prone areas,” he added.