Focal Depth Information Added to Earthquake Reports

Focal Depth Information Added to Earthquake Reports

Wong Cheuk-yiu

Since 29 March, the Observatory has enhanced its earthquake information service by including focal depth in earthquake reports. Focal depth indicates the distance between the hypocentre/focus of an earthquake – where energy is released within the Earth’s crust – and ground level. Shallow earthquakes with a focal depth of less than 70km are generally more destructive than deep earthquakes with a focal depth of more than 300km if they are of the same magnitude (i.e., with the same energy released from the hypocentre/focus). Hence, focal depth is an important parameter for earthquake monitoring, and assessment of potential hazards associated with an earthquake.

For more information on earthquake parameters, please refer to this article in the Observatory’s online Educational Resources.

A schematic diagram showing the hypocentre/focus, epicentre, and focal depth of an earthquake