Tsunami Overview and Generation

Tsunami Overview

• Tsunami is a series of sea waves generated by geological processes, often undersea earthquakes
• Wave heights can exceed 5 meters
• Recent examples in the Philippines include the August 1976 Moro Gulf Earthquake and Tsunami, and the November 1994 Oriental Mindoro Earthquake and Tsunami.

Tsunami vs. Storm Surge

• Tsunami, meaning "harbor waves" in Japanese, is generated by earthquakes disrupting the ocean floor.
• Strong, shallow-seated earthquakes displace significant water volumes, creating tsunamis.
• Storm surge is a rise in sea level associated with strong winds or tropical cyclones.

How Tsunamis are Generated

• Tsunamis are commonly generated in subduction zones, where two tectonic plates collide, with one plate moving under the other.
• When plates get stuck, the overriding plate is distorted.
• The stuck area ruptures, triggering an earthquake that pushes the ocean floor and seawater upwards, initiating the tsunami.
• The tsunami then moves in opposite directions.

Two Types of Tsunami

• Local Tsunamis: Contained within 100 kilometers of the source, typically caused by earthquakes and landslides. They reach the shoreline within 2 to 5 minutes.
• Far-field/Distant Tsunamis: Can travel 1 to 24 hours before reaching the coast, originating from earthquakes in other countries (e.g., Chile, Alaska, Japan). Monitoring centers like Pacific Tsunami Warning Center (PTWC) and Northwest Pacific Tsunami Advisory Center (NWPTAC) track these and warn nearby countries.

Philippines Tsunami Information

• The Philippines is at risk of tsunamis, particularly coastal areas along the Pacific Ocean, West Philippine Sea, Sulu Sea, and Celebes Sea
• These are caused by undersea earthquakes or submarine landslides
• Tsunamis from other countries can also affect the Philippines

Natural Signs of an Impending Tsunami

• 1. Feel an Earthquake: A strong undersea earthquake, often felt in coastal areas, can precede a tsunami. However, if shaking occurs far from the shore, you might not feel it.
• 2. See Receding Water: Before a tsunami wave arrives, water may recede significantly from the shoreline.
• 3. Hear an Unusual Roaring Sound: A loud roar or sound like a jet or train suggests an approaching tsunami.

PHIVOLCS Tsunami Warnings

• PHIVOLCS issues tsunami warnings to alert the public of potential danger.
• GREEN Advisory: No tsunami threat; no evacuation needed. The advisory is for information purposes only.
• YELLOW Advisory: Sea level changes are being monitored.
• ORANGE Advisory: Minor sea level disturbance; people are warned to stay away from the coast.
• TSUNAMI WARNING: Destructive tsunami with potentially life-threatening waves, necessitating immediate evacuation. Evacuation of areas near the coast is advised. Ownership of boats near the coast should be secured away from the coast. People at sea should move away from the shore to deeper waters until further notice.