About a year-and-a-half ago, University of Victoria geologist Kristin Morell made an alarming discovery — an active fault line that runs a few kilometres from downtown Victoria, just offshore from James Bay and Clover Point.
She had an inkling a long time ago the fault was active given there’s a fault zone called the Devil’s Mountain (mapped in western Washington State) that appears to link up with the Leech River fault across the Strait of Juan de Fuca.
Now researchers are trying to determine exactly when and how big the most recent earthquakes along the fault were. The good news is that Morell doesn’t think it’s too concerning.
“That’s the key piece of information that will determine how likely it is to happen in the near future,” said Morell.
The recently published international study, conducted by researchers at the University of Victoria, Boston University and Western Washington University, discovered that the Leech River fault, previously believed to be inactive, has caused at least two major earthquakes since the last glaciation more than 15,000 years ago.
Unlike the better-known Cascadia megathrust fault, which is active every 300 to 500 years and predicted to cause “the big one,” crustal faults can display no detectable seismic activity for thousands of years, making them difficult to study.
In an effort to learn more, Morell and her team read the trail of clues earthquakes leave behind long after they’ve ended. Topographic features show how past earthquakes shaped the area. Now that the Leech River fault has been identified as active, Morell said another question is whether it’s actively accumulating stress or any strain along it.
“Not all faults are capable of rupturing and that’s what we’re trying to do is determine which of the many faults are the ones that will rupture,” said Morell, noting that information can be used to help with hazard mitigation and emergency response planning. “When we understand the risks posed, there’s a lot we can do to keep our communities safe.”
Information on the discovery was incorporated into the recent seismic vulnerability assessment commissioned by the City of Victoria. The assessment found approximately 30 per cent of building stock within the city has a greater than five per cent probability of being completely damaged in the event of a massive earthquake in the next 50 years.
Should a massive earthquake hit, the most vulnerable buildings are those that were built before 1972, three to four-storey wood apartment buildings, single-family wood homes built before 1960 and unreinforced masonry buildings.
Approximately 80 per cent of the city’s building stock was built before 1972.