Here's why the tremor that shook Windsor-Essex was a 'good earthquake'

What did you do when the earth started shaking Thursday night?

Chances are you ran out into the street to ask friends and neighbours if they felt it too.

• Amherstburg earthquakefelt across Windsor-Essex

While that reaction is understandable, CBC meteorologistJohanna Wagstaffesays the safest thing to do when the windows start rattling is to follow three simple instructions: drop, cover and hold on.

Environment Canada initially said the earthquake had a magnitude of 3.9, but upgraded the measurement to 4.1 Friday. The U.S. Geological Survey (USGS) categorized the quake as a magnitude 3.6. The Canada and U.S. counterpart use different scales to measure earthquakes, and CBC News reported the USGS numbers primarily, because Canadian data was not yet available.

Wagstaffe said the quakeis a great reminder to make sure your family has an emergency safety kit and knows what to do in a disaster, she added.

"These are what I call good earthquakes," she explained. "People are talking about them and there are no injuries or damages, but it's a reminder that even though most of the earthquake action happens in B.C., we do get earthquakes right across the country, and it's a reminder you should know what to do when an earthquake happens."

Earthquakes are rare for southwestern Ontario because the area sits over averystable section of the tectonic plate.

Wagstaffesaid seismologists will use data from previous quakes to try to figure out whatcausedit old faults running through the region ormovement caused by parts of the continent slowly rebounding after the last ice age are two possibilities.

"It looks like it struck fairly shallow, just five kilometres below Amherstburg," she explained."It was pretty widely felt. I mean, it was shallow enough, even though it was a fairly weak earthquake, that a few million people felt weak to light shaking."

So what should you do when the next quake hits?

"If you feel shaking, immediately try and get under a desk or a sturdy object because most deaths and injuries that happen in cities similar to Canadian cities happen because of falling objects or because people are trying to run outside."