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LCQ8: Earthquake risks and its impact on buildings

Following is a question by the Hon Raymond Ho and a written reply by the Secretary for Development, Mrs Carrie Lam, in the Legislative Council today (June 24):

Question:

It has been reported that a member of the Chinese Academy of Engineering who is an earthquake expert has said that earthquakes of Intensity V to VI on the Modified Mercalli Scale might occur in the coming 10 to 30 years in the Guangdong areas, which are situated in the "middle-to-low intensity" earthquake activity zone. In this connection, will the Government inform this Council:

(a) given that the Buildings Department had appointed a consultant to study and assess the earthquake risks in Hong Kong and its impact on local buildings, whether the relevant report has been completed and whether it will be made public; whether the report includes or will include the relevant comments and assessment results made by mainland earthquake experts regarding the chance of earthquakes occurring in the Guangdong areas adjacent to Hong Kong;

(b) as Hong Kong's schools and disaster emergency relief facilities (e.g. buildings such as fire stations, hospitals and police stations) are all wind-resistant, whether such buildings are at present capable of withstanding earthquakes as well; if so, of the intensity of earthquakes these buildings are able to withstand, and whether their seismic resisting capability is comparatively lower than that of the taller buildings in Hong Kong in general; and

(c) given that the earthquakes which occurred in Wenchuan, Sichuan last year demonstrated the importance for buildings to have seismic resisting capability, whether the Government will consider enhancing the seismic resisting capability of schools and the aforesaid disaster emergency relief facilities, so as to ensure that these buildings can be used as temporary shelters and emergency relief command centres in the event of earthquakes; and of the Government's major considerations, other than financial factors, when it considers whether or not to enhance the seismic resisting capability of these buildings?

Reply:

President,

Intense earthquakes in the world mostly occur along the boundaries of crustal plates. Hong Kong lies within the Eurasian plate but not on the boundary of the plate. The well-known Circum-Pacific seismic belt where major plates meet runs through Japan, Taiwan and the Philippines. Hong Kong is quite far away from this seismic belt, with about 600 kilometres from the nearest point. As such, the possibility of serious earthquakes in Hong Kong caused by collision of crustal plates is relatively low. On the other hand, according to geological structure analysis, the faults in Hong Kong are not active. The geological settings are not conducive to causing strong earthquakes. Earthquakes that occur in Hong Kong and its vicinity can cause tremor that can be felt by ordinary people, but the chance of causing serious damage is relatively low. In fact, since 1905 when the Hong Kong Observatory started recording locally felt earth tremors in the territory, Hong Kong has experienced 163 earth tremors of different intensities without causing any casualties. The strongest tremor ever recorded in Hong Kong was of Intensity VI to VII on the Modified Mercalli Scale (MMS). This locally felt tremor, which occurred in 1918, was caused by an earthquake near Shantou and was more than 300 km away from Hong Kong, and inflicted minor damage on the walls of a few buildings constructed under the prevailing building standards at that time. This has been the only earthquake that has caused damage in Hong Kong since 1905.

The reply to the three-part question is as follows:

(a) The Buildings Department (BD) has commissioned a consultancy study on issues concerning seismic effects with a major objective to assess the earthquake risks in Hong Kong and the effects of earthquakes on local buildings. The study was conducted in accordance with internationally recognised methodologies. It covered analysis of seismic data and records in Hong Kong and neighbouring regions, including a large amount of data on the seismic activities occurred in the Southeast China. It also made reference to the code for seismic design of buildings issued by the relevant departments of the Mainland regarding the need for seismic resistant designs for buildings based on the assessment of intensity of earthquakes in the Hong Kong region. The overall study has reached its final phase. The Administration is carefully consolidating and considering the findings of the study and will consult the stakeholders to map out the way forward.

(b) The consultancy study has found that in general the seismic resisting capability of buildings with fewer storeys is lower than that of buildings with more storeys. Schools and disaster emergency relief facilities (e.g. buildings such as fire stations, hospitals, police stations, etc) have been designed to be wind resistant since the 1930s. The standard of wind resistance has been regularly upgraded to meet the changing needs. Therefore, these buildings possess load-resistant and seismic-resistant capabilities. In case where a severe earthquake occurs in the neighbouring regions causing a tremor of MMS Intensity VII in Hong Kong, these buildings are still basically safe and will suffer no serious damage. This has also been confirmed by the consultancy study commissioned by the BD, that is, most of the buildings in Hong Kong are basically safe in the event of an earthquake that may take place in the territory.

(c) As mentioned in the first part of the reply, in exploring the way forward, the Government will take into account public safety and social needs as the primary considerations in examining whether there is a need to further enhance the seismic resisting capability of schools and disaster emergency relief facilities (e.g. buildings such as fire stations, hospitals, police stations, etc).

Ends/Wednesday, June 24, 2009
Issued at HKT 14:34

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