- Magnitude is a measure of the amount of energy released during an earthquake. It is frequently described using the Richter scale. To calculate magnitude, the amplitude of waves on a seismogram is measured, correcting for the distance between the recording instrument and the earthquake epicentre. Since magnitude is representative of the earthquake itself, there is only one magnitude per earthquake.
- The magnitude scale is logarithmic. This means that, at the same distance, an earthquake of magnitude 6 produces vibrations with amplitudes 10 times greater than those from a magnitude 5 earthquake and 100 times greater than those from a magnitude 4 earthquake. In terms of energy, an earthquake of magnitude 6 releases about 30 times more energy than an earthquake of magnitude 5 and about 1,000 times more energy than an earthquake of magnitude 4.
- It is not likely that an earthquake of magnitude less than 5 could cause any damage.
- Though theoretically there is no mathematical limit with the magnitude calculation, physically there is a limit. The magnitude is related to the surface area of the tectonic plates which rub together and in doing so give rise to seismic waves. Since the tectonic plates have finite dimensions, the magnitude must therefore also reach a maximum. It is believed that the greatest earthquakes can reach magnitude 9.5.
- “Magnitude” is different than “intensity.” The intensity scale is designed to describe the effects of an earthquake, at a given place, on natural features, on industrial installations and on human beings. The intensity differs from the magnitude which is related to the energy released by an earthquake.
- The Modified Mercalli Intensity (MMI) Scale (http://www.earthquakescanada.nrcan.gc.ca/info-gen/scales-echelles/mercalli-eng.php) is designed to describe the effects of an earthquake, at a given place, on natural features, on industrial installations and on human beings. The intensity differs from the magnitude which is related to the energy released by an earthquake. There are multiple versions of the MMI scale, the one listed here being the 1931 version.
- The ranges on the Mercalli scale go from MMI I (1), where it is generally not felt at all, to MMI XII (12), where the impact extends to practically all works of construction being greatly damage or destroyed.
B.C. Earthquake and Tsunami Exercise
Exercise Coastal Response is Western Canada’s first, full-scale earthquake and tsunami response is a test of the BC Immediate Response Plan (IRP) that outlines the steps that the Province and its partners will undertake in the immediate aftermath of a massive earthquake. The goal is to exercise elements of the IRP and strengthen relationships among and across partners and stakeholders to enhance operational co-ordination. Learn more about Exercise Coastal Response