A late-night Boxing Day rumble was felt across Greater Victoria when a 3.3 magnitude earthquake struck between Vancouver Island and the mainland.
The quake, which took place at 10:36 p.m. just west of Stuart Island, was felt for no more than a few seconds and caused no damage, said Gary Rogers, earthquake scientist with Natural Resources Canada’s monitoring station in Sidney.
“This earthquake is in the subducted Juan de Fuca plate, that’s the plate that slides underneath Vancouver Island, Washington and Oregon,” he said. “It’s quite deep, about 60 kilometres down. … That’s a constant source of earthquakes around here.”
About half a dozen earthquakes are felt each year on southern Vancouver Island, he added.
Two waves are generated during any earthquake: the compressional, or P wave, and the shear, or S wave. In smaller quakes, only the slower and larger S wave is typically felt.
“People likely felt the S wave here, just a few seconds and a few shakes,” Rogers said.
Anyone who felt the quake is urged to fill out a questionnaire on the Earthquakes Canada website. The reports help seismographers more accurately track the impact of tectonic shifts, he said.
“Because it’s not felt by everybody, it makes reporting important,” he said. “It often tells us how far away things are felt and how widely it was felt.”
The U.S. Geological Survey pegged Wednesday’s earthquake at 3.9 magnitude, a discrepancy that can be attributed to a difference in measurement, Rogers said.
“We’re using the amplitude, the height of the wave. … The (USGS), they don’t have as high a dynamic range in their seismograph, so they use the duration of the shaking. And usually these give about the same answer, but sometimes they’re slightly different.”
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