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■天文台在寶珊道設置全港最先進的地震站，最遠可偵察到發生在數千公里以外的地震。圖為地震站內的監測儀器。資料圖片
香港天文台斥資在半山設立全港最先進的地震站，站內的寬頻地震儀可記錄較寬頻率的地震，遠至數千公里外的地震亦能探測得到。天文台高級科學主任黃永德表示，新地震站有助收集南海地震數據，準確計算海嘯抵港的時間及高度。天文台表示，若震央位處菲律賓附近，產生的海嘯或對港構成危險，監測系統起一定作用，但強調香港受海嘯威脅的風險低。
天文台在半山區寶珊道新建的地震站在2月18日啟用，設於300米排水隧道的末端，站內設有地震儀及強震儀。黃永德表示，地震站選址理想，遠離城市的干擾，而隧道內氣壓、濕度及溫度相當穩定，但為確保地震儀不會錯誤測度隧道震動，故測量設施置於岩層上的混凝土，可監測岩層的震動。
黃表示，新地震站可計算出地震時間、震央、震源深度及震級等，並推算地殼移動參數，有助利用電腦模式估計因地震引發的海嘯的抵港時間及高度。
黃表示，新地震站的構思源自南亞海嘯事件，當時發現南海的地震監測點不足，而新建地震站錄得的數據會透過地震學聯合研究會實時發布，有助全球地震及海嘯監測中心更快計算地震及海嘯情況。
New Seismograph Station Set to Detect Earthquakes from Thousands of Kilometers
The Hong Kong Observatory has set up the most advanced seismograph station in Hong Kong at a site in the Mid-levels. The station houses a broadband seismograph which is able to record a broader frequency of seismic waves and to detect earthquakes occurring several thousands of kilometers away. Dr Wong Wing-tak, senior scientific officer of the Hong Kong Observatory, said that the new station enables the gathering of seismic data from locations in the South China Sea and facilitates the calculation of the precise arrival time and height of tsunamis reaching Hong Kong. According to the Observatory, if the epicenter of an earthquake is located somewhere near the Philippines, the tsunami caused by the quake may pose a danger to Hong Kong, so the earthquake monitoring system performs a significant function in safeguarding. However, the Observatory stresses that the risk of Hong Kong being hit by a tsunami is low.
The new seismograph station in Po Shan Road was put into service on 18 February. Built at the end of a 300-meter drainage tunnel, the station has in it a seismograph and a strong motion accelerometer. Wong said that the site is a perfect location as it is far away from the interferences often seen in urban areas, and the air pressure, humidity and temperature inside the tunnel are relatively stable. The seismograph has been installed on a concrete plate above the rock layer so that it will only detect tremors of the rock layer without erroneously measuring the vibrations of the tunnel.
Wong said the new station can calculate the time of occurrence, location of the epicenter, focal depth and magnitude of the earthquake. It can also project the parameters of crust movements, which enhances computer-modeled predictions of arrival time and height of subsequent tsunamis that may hit Hong Kong.
Wong also said that the idea of building the new station was triggered by the tsunami that devastated South Asia. At that time, it was discovered that seismic monitoring in the South China Sea was insufficient. Real-time data recorded at the new station will be disseminated through the Incorporated Research Institutions of Seismology(IRIS)to help seismic and tsunami monitoring centers around the world to measure earthquake and tsunami conditions more accurately and timely. ■Translation by 開明
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