Tsunami Warning System

Mr. YEUNG Kai-hing, Assistant Director of the Hong Kong Observatory said in a press conference today (28 December 2004) that the chance of a big tsunami affecting Hong Kong was very small because of its geographical location. He added that Hong Kong was part of the Pacific Tsunami Warning System, an international co-operation among countries around the Pacific, and the Hong Kong Observatory would issue a Tsunami Warning to advise members of the public if necessary.

Big tsunamis are caused by great submarine earthquakes that mainly occur along the circum-Pacific seismic belt, and along the active seismic belt between the Eurasian tectonic plate and the Indian-Australian tectonic plate. The disastrous earthquake that occurred west of northern Sumatra over the Indian Ocean on 26 December 2004 was located on the latter seismic belt. While Sumatra and the Malaysian Peninsula would block any tsunami generated over the Indian Ocean from reaching Hong Kong directly, the Philippines and Taiwan would similarly block most of the tsunamis originating from the Pacific Ocean. A tsunami that enters the South China Sea through the Luzon Strait would lose energy and weaken when passing over the shallow water over the continental shelf.

Since automatic tide gauges were installed in Hong Kong in the early 1950s, the Hong Kong Observatory has detected tsunamis on four occasions, caused respectively by an earthquake in Kamchatka in 1952, an earthquake in Chile in 1960, another earthquake in Chile in 1985 and an earthquake in Luzon Strait in 1988. The amplitude of the tsunami recorded in Hong Kong was less than 0.5 metre in all these events.

Under the framework of the Pacific Tsunami Warning System, after an earthquake is detected by the seismograph of the Hong Kong Observatory, the Observatory would transmit the arrival time of seismic waves to the Pacific Tsunami Warning Center (PTWC) in Hawaii. On receipt of this and similar information from other seismograph stations in different countries, PTWC would determine the location, depth and magnitude of the earthquake and assess the likelihood of a tsunami. It would send a message to participating countries and territories on details of any tsunami forecast including the expected arrival time and amplitude of the tsunami at different locations around the Pacific. On receiving the message from PTWC, the Hong Kong Observatory would issue a Tsunami Warning to warn the public if the tsunami expected in Hong Kong is significant.

Mr. YEUNG said that, with a very small chance for a big tsunami to affect Hong Kong and an effective warning system in place, the public need not worry unduly and should pay attention to any tsunami warning issued by the Observatory.

 

Assistant Director of the Hong Kong Observatory, Mr. YEUNG Kai-hing describing active seismic belts and tectonic plates

An illustration of tectonic plates