Mapping

Mapping seismic activity in Metro Vancouver

A new mapping project shows how earthquakes may travel through Metro Vancouver — and the hazards to prepare for

Vancouver's iconic Lions Gate Bridge. (Photo: Lee Robinson/Unsplash)
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In a yellowing field in Maple Ridge, Vancouver, a Western University-led team sets off tiny “earthquakes.” PhD student Benjamin Osei Fordjour lifts a sledge-hammer and strikes the ground, sending seismic wavelengths skipping through the ground and down a tape measure lined with geophones. He is Thor, but wielder of earthquakes. In the centre of the field are a series of shallow holes where red seismometers, the size of small bricks, record the Earth’s vibrations.

These field tests are part of the second phase of a 10-year study led by associate professor Sheri Molnar that is mapping how seismic hazards vary on a neighbourhood scale based on underlying ground conditions in Metro Vancouver. While pursuing postdoctoral work nearly a decade ago, Molnar was surprised to learn Metro Vancouver, one of Canada’s most seismically active regions, lacked a comprehensive seismic microzonation map.

Vancouver is built on a deep basin of sedimentary, or layered, rock, patches of which may dampen, prolong or intensify seismic waves. For example, softer sediments tend to amplify earthquake motions. If an earth- quake occurs, certain regions may be more susceptible to stronger shaking, which could contribute to landslides or liquefaction (when solid ground acts like a liquid).

So, Molnar set out to create a map that could “predict the amplitude and frequency of earthquake shaking.” Since then, Molnar and the team have completed Phase I, measuring seismic vibrations at more than 2,300 locations and collecting geological data for 15,000 sites in Vancouver as far east as Surrey. They found that Vancouver’s uplands feature complex geology, where seismic waves unexpectedly slow down before speeding up again as they move deeper into the stiffer Earth. This geology makes it hard to accurately predict earthquake ground motions (the Earth’s movement in response to an earthquake).

The team has released 29 region-specific maps and made them accessible to the general public so emergency managers, city planners, architects and homeowners can consider hazards and how to mitigate them. Molnar’s team plans to complete Phase II by 2026, creating a three-dimensional velocity model — the first of its kind.

“For the public […] it’s not about not buying a home,” Molnar says, “but being informed about what kind of earthquake insurance conversations you might want to have, and whether or not you might also experience land-slides or liquefaction.”

For many Vancouverites who worry about Vancouver’s dreaded “big one,” predicted to strike Vancouver within the next 200 years, better understanding seismic hazards can help with planning to reduce their impact — and perhaps allay a worry or two.

Elevation model: Japan Aerospace Exploration Agency (JAXA), 2024. Building footprint data: Openstreetmap Contributors, 2024. MYSMMP Maps Available at borealisdata.ca/dataverse/mvsmmp.mvsmmp Maps in this article: 13 (doi.org/10.5683/SP3/X23A5D); Map 15 (doi.ord/10.5683/SP3/WA6MER); 22 (doi.org/10.5683/SP3/ZIPEZX); 26 (doi.org/10.5683/SP3/ULMSX9)
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This story is from the January/February 2025 Issue

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