Thousands of minor tremors have been recorded in recent weeks as part of the somewhat-annual ETS event. None are felt but they provide seismologists with valuable data. (John Cassidy/PNSN)

By NanaimoNewsNOW Staff

GROUNDBREAKING

Seismologists monitoring tremor and slip event ahead of province’s largest earthquake drill

Oct 14, 2020 | 1:19 PM

NANAIMO — It’s a busy time for seismologists on the B.C. coast.

The Great BC Shakeout earthquake drill is at 10:15 a.m. on Thursday, Oct. 15 with participants encouraged to drop, cover and hold on. The drill aims to create a muscle memory response in the event of a major earthquake.

This year, the drill will occur the same time as an episodic tremor and slip (ETS) event featuring thousands of small tremors along the Pacific Coast over the period of a couple of weeks.

“It helps us to actually understand how the tectonic plates are interacting…where they’re locked, how they’re storing energy for future earthquakes,” John Cassidy, seismologist, told NanaimoNewsNOW.

The tremors are typically not felt by people but can be detected by the 50-60 seismometers situated across Vancouver Island. They occur at a depth anywhere between 20 and 50 kilometres below the surface roughly every 14 months.

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“The tremors have been helping us map out the Juan de Fuca plate, where’s locked and not locked. Knowing where the fault is locked we can do calculations of ground shaking and what we might expect during one of these subduction earthquakes.”

ETS events were only discovered roughly 20 years ago but have likely been ongoing for hundreds of years. The tremor and slip events are not considered earthquakes and appear very differently on measuring tools.

Cassidy likened it to a train going by with gradual buildup and easing, instead of an instant, violent shaking.

Constant monitoring of the ground through seismometers and GPS equipment also discovered Vancouver Island moves throughout the year.

“We’re slowly moving towards the mainland about a centimetre each year. At the time of tremor and slip, we actually change direction and move backwards towards the ocean four to five millimetres,” Cassidy said.

For more information on the Great BC Shakout, visit their website.

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