Tsunami Precursors
(1) Strong ground vibration. Because seismic waves reach the coast before tsunamis, they must leave the coast quickly and move to inland heights.
(2) Abnormal seawater retreat or rose suddenly. The seawater retreats first before the tsunami arrives at the coasts, which is a bit like ebb tide, but the sea water retreats further, many marine animals such as fish and shrimp are often left in the shallows when sea water recedes abnormally. At this time we must not go to pick up fish or watch the fun, must quickly leave the coast, move to the inland high places. Unlike normal high tides, tsunami waves are very regular, with high waves like a wall. Escape at the sight of such a wave.
(3) A low-frequency roar will occur before the tsunami arrives. Unlike normal waves, strange low-frequency waves (roars) heard at the seaside should be evacuated immediately to safe heights.
(4) Ships in shallow waters suddenly bumps violently up and down.
(5) In the shallow waters not far from the coast, the sea suddenly turns white and a long bright wall of water appears in front of it.
(6)The sea suddenly retreated far away from the beach, and the beach looks much larger than usual, with a large area of bare sand.
(7)Animals behave strangely: they may suddenly leave, gather in groups, or enter places where they usually don't go.
Tsunami Warning and Forecasting(1)
Tsunami is predictable.
The tsunami is so powerful that early warning is very important in order to win the time of early evacuation and reduce casualties and property losses. Seismic waves travel along the earth's crust much faster than tsunami wave, providing valuable time for tsunami prediction in advance. The Global Tsunami Warning System Coordination Group was established in 1964. Tsunami warning systems are well developed in the Pacific Ocean due to the frequent occurrence of tsunamis. In 1965, 26 countries and regions cooperated to establish the Pacific Tsunami Warning Center (PTWC) in Hawaii (Fig. 5-2). Once an earthquake occurs in the ocean from the seismograph, PTWC can calculate the time when the tsunami arrives in all parts of the Pacific Ocean and give an early warning, China joined the Pacific Tsunami Prediction Center in 1983. The Pacific Tsunami Warning Center has nearly 100 monitoring stations in the Pacific Ocean, which can monitor sea level fluctuations, the occurrence and intensity of tsunamis at any time. Monitoring stations are connected by satellites, cables and early warning systems, and early warning centers are connected to huge seismic monitoring networks that can observe the earthquakes may cause tsunamis in the first time, so as to send out warnings in time.
Figure 5-2 Pacific Tsunami Forecasting Center
Since there are few tsunamis in the history of the Indian Ocean and there has been no tsunami in the past 100 years, no country has participated in the tsunami warning system, the Indian Ocean tsunami in 2004 caused heavy casualties and had no early warning system. Fifteen minutes after the earthquake, the Pacific tsunami warning center issued early warning information to countries participating in the joint warning system. The Indian Ocean countries did not join the system, so they did not receive early warning information.
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