Glossary term
Tsunami
Hazards & geography · earthquake & volcano glossary
What is Tsunami?
A series of ocean waves generated when an undersea earthquake, landslide, or eruption displaces a large volume of water. Strong shaking near the coast is itself a natural warning to move to high ground.
Tsunami hazard →Related terms
LiquefactionWhen shaking turns water-saturated, loose soil into a fluid-like state, causing buildings to sink or tilt. It is a major hazard in coastal and reclaimed areas.Pacific Ring of FireThe horseshoe-shaped belt around the Pacific Ocean where most of the world's earthquakes and volcanoes occur, driven by subducting tectonic plates. The Philippines, Japan, Indonesia, and Chile all sit on it.Subduction zoneA boundary where one tectonic plate dives beneath another. These zones produce the planet's largest earthquakes and most explosive volcanoes.Moment magnitude (Mw)The modern measure of an earthquake's size, based on the area of the fault that slipped and how far it moved. It replaced the original Richter scale for medium and large events because Richter saturates (stops increasing) for the biggest quakes. The scale is logarithmic: each whole number is about 10× more shaking amplitude and ~31× more energy.Richter scale (ML)The original 1935 local-magnitude scale. Still widely cited in the media, but agencies now report moment magnitude for most events because it stays accurate for large earthquakes.Intensity (MMI)How strongly shaking is felt at a given place, on the Modified Mercalli Intensity scale (I–XII). Unlike magnitude — one number per earthquake — intensity varies with distance, depth, and local soil. A single quake produces many intensity values.
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