The Hong Kong Observatory has monitored distant earthquakes since 1921 using long-period seismographs. In 1979, a short-period seismograph network of three stations was installed to detect also local tremors. The seismological network in Hong Kong was upgraded to an advanced digital network with eight stations in 1997.

Signals from the seismometers are digitized at field stations and transmitted to an acquisition computer at the Hong Kong Observatory Headquarters through telephone lines. The computer collects and archives these data which are time stamped from a GPS synchronized clock. When the amplitude of the signals for certain selected stations exceed specific thresholds, the seismic signals of all the stations would be analyzed to obtain the epicentral parameters and magnitude of the tremor.

In the event of a locally felt earthquake, the epicentral parameters would be computed and cross-checked with information received from mainland seismological authorities before dissemination to the public.

The long-period seismographs detect large earthquakes all over the world. Whenever a significant event is recorded, the first arrival time of the seismic waves is determined and passed to other national centres such as the National Earthquake Information Centre (NEIC) and the Pacific Tsunami Warning Centre (PTWC). With data collected from other stations, these centres compute the location and magnitude of the earthquakes and disseminate the results. The Hong Kong Observatory issues press releases to inform the public of any earthquakes greater than magnitude 6.5.