UVic-led team discovers active fault line beneath Greater Victoria

A fault line that runs underneath Greater Victoria, which geologists previously believed was inactive, has in fact caused past earthquakes in the region, according to a new study by a University of Victoria-led team.

The fault — called the Leech River fault — is between 30 and 60 kilometres long and extends across the southern portion of Vancouver Island through downtown Victoria. The new study says it may link up with another fault in northwestern Washington.

UVic geologist Kristen Morell said the fault could cause damage. "There is the potential that this could pose a hazard," Morell said.

The team also discovered that the fault  — described as crustal — has caused at least two major earthquakes in the last 15,000 years.

Scientists previously believed the fault was last active 50 million years ago.

The main quake threat on the West Coast comes from the better-known Cascadia megathrust fault, which scientists predict will cause the earthquake referred to as the "Big One." That quake is active every 300 to 500 years.

Cracks in the earth

Crustal faults can display no detectable seismic activity for thousands of years, making them difficult to study. Morell and her team examined topographical clues in the region that revealed previous tremors.

The next step, said Morell, is to determine exactly when those previous quakes struck Vancouver Island. That information could be used for emergency response planning in the region.

The study was featured this month in Geological Society of Amercia's publication, GSA Today.

A quake caused by a crustal fault would cause buildings to shake as well as "intense movement of the earth's surface," Morell said.

These kinds of earthquakes, including the one that struck New Zealand last November, can also cause metres-high steps to form on the earth's surface, she said.

The earthquake that struck New Zealand last November was caused by a crustal fault.

Contributors to the study included researchers from UVic's School of Earth and Ocean Sciences, as well as researchers from Boston University and Western Washington University.