The magnitude of an earthquake is usually expressed by the Richter Scale to indicate the energy released at the source, while the intensity is expressed by the Modified Mercalli Scale to indicate an earthquake’s degree of impact at a certain place. The intensity of an earthquake decreases with distance from the source.
Earthquakes of different magnitudes, depending on factors such as the depth of the source and its distance from Hong Kong may cause locally felt earth tremors. After such a felt earth tremor has occurred, the Observatory immediately analyses data from seismographic networks and reports from the public (including information on the extent and duration of the felt vibrations and spatial distribution of the reports) to determine the earthquake’s local intensity.
A “Locally Felt Earth Tremor Report” is then issued through various channels including the Observatory’s website, the “MyObservatory” app, social media pages and the Government News and Media Information System. Each report covers the origin time, magnitude, epicentre location, and local intensity of the earthquake, as well as the number of reports received from the public, etc.
“Cool Met Stuff” introduces the difference between an earthquake’s magnitude and intensity [in Cantonese]
