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What is a tsunami?

A Tsunami is a series of sea waves commonly generated by under-the-sea earthquakes and whose heights could be greater than 5 meters. It is erroneously called tidal waves and sometimes mistakenly associated with storm surges. Tsunamis can occur when the earthquake is shallow-seated and strong enough to displace parts of the seabed and disturb the mass of water over it.

How are tsunamis generated?

 The diagrams below show how tsunamis are generated when an earthquake occurs under the sea.

how tsunamis are generated

Two Kinds of Tsunami Threat in the Philippines

There are two types of tsunami generation: (1) local tsunami (2) and far field or distant tsunami. The coastal areas in the Philippines especially those facing the Pacific Ocean, South China Sea, Sulu Sea and Celebes Sea can be affected by tsunamis that may be generated by local earthquakes. Local tsunamis are confined to coasts within a hundred kilometers of the source usually earthquakes and a landslide or a pyroclastics flow. It can reach the shoreline within 2 to 5 minutes. Far field or distant tsunamis can travel from 1 to 24 hours before reaching the coast of the nearby countries. These tsunamis mainly coming from the countries bordering Pacific Ocean like Chile, Alaska in USA and Japan. The Pacific Tsunami Warning Center (PTWC) and Northwest Pacific Tsunami Advisory Center (NWPTAC) are the responsible agencies that closely monitor Pacific-wide tsunami event and send tsunami warning to the countries around the Pacific Ocean.

The Philippines is frequently visited by tsunamis. On 17 August 1976, a magnitude 7.9 earthquake in Moro Gulf produced up to 9-meter high tsunamis which devastated the southwest coast of Mindanao and left more than 3,000 people dead, with at least 1,000 people missing. Also on 15 November 1994 Mindoro Earthquake also generated tsunamis that left 49 casualties.

Tsunami Advisory

Natural Signs of an Approaching Local Tsunami

A Felt Earthquake
A Felt Earthquake

Unusual Sea Level Change

Unusual Sea Level Change

Rumbling Sound of Approaching Waves

Rumbling Sound of Approaching Waves

Tsunami Safety and Preparedness Measures

Each one of us in the community should learn some important Tsunami Safety and Preparedness Measures such as the following:

  1. Do not stay in low-lying coastal areas after a felt earthquake. Move to higher grounds immediately.
  2. If unusual sea conditions like rapid lowering of sea level are observed, immediately move towards high grounds.
  3. Never go down the beach to watch for a tsunami. When you see the wave, you are too close to escape it.
  4. During the retreat of sea level, interesting sights are often revealed. Fishes may be stranded on dry land thereby attracting people to collect them. Also sandbars and coral flats may be exposed. These scenes tempt people to flock to the shoreline thereby increasing the number of people at risk.