Two tremors recorded northwest of Fort Good Hope

Data from Canadian and US geological services suggests two moderately sized earthquakes struck an area northwest of Fort Good Hope on Thursday.

Both the US Geological Survey and Earthquakes Canada reported back-to-back quakes of magnitude 4.0 to 4.6.

They occurred four hours apart on Thursday morning and early afternoon local time.

An Earthquakes Canada map of seismic activity also identifies a smaller, third shock of magnitude 3.2 between the two larger quakes, though the US Geological Survey carried no such report.

Earthquakes of magnitude 4.0 or above in the Northwest Territories are not uncommon, but equally are not an everyday occurrence.

These are the first reported NWT quakes of that size this year, though smaller, barely noticeable tremors have struck with regularity in the area of Fort McPherson.

According to the Earthquakes Canada registry, the territory’s last earthquake of this size occurred in early November 2017 – a 4.9-magnitude event south-east of Łutselk’e.

The territory had two in 2015 and six in 2014 of similar magnitude.

According to Earthquakes Canada, the NWT’s largest earthquake of the past half-century registered a magnitude of 5.7 west of Tulita in the Mackenzie mountains in 2006.

Though there are several variables affecting an earthquake’s impact – such as the depth at which it strikes – in general, only magnitudes of 5.5 or above cause damage of note.

As they ordinarily strike remote regions around the Mackenzies, rarely do NWT earthquakes cause injury or trigger reports of damage to property. There was no immediate suggestion of any injury or damage from Thursday’s quakes.

Earthquakes Canada said nobody had yet reported feeling the day’s tremors.

Measurements of the two quakes differed slightly between the US and Canadian reporting authorities.

Earthquakes Canada put the magnitude of the first earthquake at 4.5, and the second at 4.3.

The US Geological Survey recorded magnitudes of 4.6 and 4.0 respectively.

The quakes had epicentres on the south side of the Mackenzie River, around 90 km west-northwest of Fort Good Hope in the direction of Fort McPherson.