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Monday, 15th April 2013

The Earthquake Monitoring and Information Services of the Hong Kong Observatory

Earthquakes are natural phenomena that are capable of inflicting severe damage, and may induce destructive tsunamis thousands of miles away. The Indian Oceanic tsunami in 2004, the Wenchuan earthquake in 2008, the Haiti earthquake in 2010 as well as the Japanese tsunami in 2011 were all shocking calamities.

Earth tremors are felt in Hong Kong from time to time (twice a year on average), but it has been rather rare for them to bring some minor damages to buildings. Although the chance of destructive earthquakes to occur in Hong Kong is not high (See GEO Information Notes No. 2/2012), as a economic and cultural hub, many facets of Hong Kong would still be affected by overseas earthquakes as well as the associated tsunamis, which will attract the attention of Hong Kong people travelling, planning to travel, and staying abroad as well as that of government organisations and private enterprises. To meet the high demand for information on earthquakes worldwide, the Observatory closely monitors seismic activities and provides timely earthquake information for the public.

The magnitude 7.3 Nan'ao earthquake in 1918, which inflicted minor damage to a few buildings in Hong Kong, propelled the Observatory to start instrumental monitoring of seismic activities with a set of long-period seismographs in 1921. Following the Tangshan earthquake in 1976 which caused great public concern, the Observatory established a local seismograph network with four stations in 1979, thus enabling monitoring and analyses of earthquakes within the territory and around 200 km of Hong Kong. The network was subsequently expanded to 9 stations in 1997. In 2010, a broadband seismograph station near Po Shan Road, Mid-levels on Hong Kong Island was commissioned and became one of the 150+ members of the Global Seismographic Network (Figure 1 & 2). Not only has the Po Shan Seismograph Station significantly enhanced the capability to monitor earthquakes and tsunamis in the South China Sea, it has also become the tenth member of the Hong Kong Seismograph Network (Figure 3). In 2011, real-time accelerometers were installed at five stations in the network, with a view to facilitating the determination of intensities of locally felt earth tremors and more timely issuance of related earthquake reports and messages.

During the past few decades, advances in information technology have greatly expedited the exchange of data and led to more timely seismic analyses. Before the World War II, staff of the Observatory had to manually analyse the arrival time of seismic waves and mailed the results to the International Seismological Summary (ISS), which compiled global earthquake catalogues (Figure 4). The whole process took many days to complete. Since early 1960's, the Observatory started sending analysed seismic messages to the then Pacific Tidal Wave Warning Service and could be able to provide information on larger earthquakes worldwide to local press in several hours after occurrences (Figure 5). In late 1990's, the emergence of the Internet shortened the issuance of earthquake press releases to about one hour. In 2007, the Observatory developed a software package that automated a majority part of the analysis process, further speeding up the issuance to around half an hour. In 2010, the Observatory commissioned the automatic seismic information system, utilising real-time seismic waves collected from seismograph stations all over the world (Figure 6 & 7). In March 2011, the Observatory experimented with the issuance of quick earthquake messages to the public over Twitter (Figure 8), and subsequently extended the dissemination channels to Weibo and RSS for the public, as well as emails and SMS for the electronic media and other special users. The Quick Earthquake Message service became operational in August 2012. Nowadays, quick earthquake messages can typically be issued within 10 minutes after the occurrences of earthquakes of magnitude 6 or above, much shorter than those in the early years that were counted by days.

Woo Wang-chun, Mok Hing-yim

Related Websites:

1. HKO Quakes (Twitter):

2. HKO (Twitter):

3. HKO (Weibo):


[1.] GEO Information Notes No. 2/2012 - Seismicity of Hong Kong

[2.] Quick Earthquake Messages on Twitter Trial Version (23 March 2011)

[3.] Global Earthquake Information Services of the Hong Kong Observatory (The Fifth Guangdong - Hong Kong - Macao Seminar on Earthquake Science and Technology, Macao, 12 - 13 April 2012) (Chinese Only)

[4.] Quick Earthquake Messages Service of the Hong Kong Observatory becoming operational (22 August, 2012)

Figure 1

Figure 1      The Hong Kong Po Shan Seismograph Station near Po Shan Road, Mid-Levels, Hong Kong Island.

Figure 2

Figure 2      The Hong Kong Po Shan Seismograph Station is one of the 150+ stations of the Global Seismographic Network.

Figure 3

Figure 3      Distribution of the ten stations in the Hong Kong Seismograph Network.

Figure 4

Figure 4      Seismic record of the Hong Kong Observatory appearing on International Seismological Summary 1922.

Figure 5

Figure 5      The manuscript of the earthquake press release issued by the Hong Kong Observatory on 27 January 1979.

Figure 6

Figure 6      Observatory's staff conducting seismic re-analyses on computer.

Figure 7

Figure 7      Analyses of the Observatory's Automatic Seismic Information System. The orange circle near Indonesia indicates the
location of the epicentre, while the triangles represents those seismograph stations detecting the earthquake.

Figure 8

Figure 8      Quick Earthquake Messages issued by the Hong Kong Observatory through Twitter.

Last revision date: <05 Jun 2013>