Focal depth information added to the Observatory’s earthquake reports

29 March 2023

The Hong Kong Observatory has enhanced its earthquake information service by adding information on focal depth of the earthquake in the earthquake reports including strong earthquake reports and locally felt earth tremor reports. The report first contained this earthquake parameter can be found from the locally felt earth tremor report issued today (29 March).

Focal depth indicates the distance between the hypocentre/focus of an earthquake where energy is released within the Earth’s crust and the ground level. Shallow earthquakes with a focal depth of less than 70 km are generally more destructive than deep earthquakes with a focal depth of more than 300 km for the same magnitude (i.e. energy released from the hypocentre/focus). Focal depth is an important earthquake parameter for earthquake monitoring and assessment of potential hazards associated with the earthquake including the possibility of triggering tsunami.

A schematic diagram showing the focal depth of an earthquake and some other earthquake parameters.