A tsunami is a series of long water waves produced by a large, rapid displacement of water. Some undersea earthquakes create that displacement, especially when shallow fault motion moves the seafloor vertically. Magnitude alone cannot determine whether a tsunami occurred or how high waves will be at a coastline.
Quick answer
- The earthquake must couple enough displacement into the water.
- Shallow undersea thrust earthquakes are important generators, but not every one produces a tsunami.
- Strike-slip motion is usually less efficient at vertical displacement, though complex sources and secondary effects matter.
- Deep-ocean tsunami height can be small while wavelength and speed are large.
- A catalog
tsunamiflag is not the complete text of an official warning or observation.
How a tsunami is generated
When the seafloor rises or falls over a broad area, it displaces the water column. Gravity then propagates the disturbance across the ocean. Near shore, decreasing depth slows the waves and can increase their height through shoaling and local coastal geometry.
The source depends on fault mechanism, rupture area, slip, depth and bathymetry. Earthquakes can also trigger submarine landslides, another possible displacement source. Volcanic activity and landslides can generate tsunamis without a tectonic earthquake.
What monitoring systems observe
Seismic networks rapidly estimate earthquake location, depth, magnitude and mechanism. Tide gauges measure coastal water levels, while deep-ocean instruments can detect pressure changes from passing waves. Forecast models combine source estimates with ocean depth and coastal geometry.
Early products carry uncertainty because the full rupture and water response are not instantly known. Observations can confirm, revise or cancel initial assessments.
How to read a tsunami field
USGS sets the tsunami flag to 1 for large events in oceanic regions and 0 otherwise. A value of 1 adds a link to tsunami information; neither value confirms whether a tsunami occurred or will occur. It is not a coastal observation or warning.
Earthquake24 displays that source field as metadata and does not turn it into an independent warning. The USGS report guide explains how flags, products and source links differ.
Limits and common mistakes
Not every M7 offshore earthquake creates a tsunami, and a single magnitude threshold is not a coastline forecast. Epicentral distance is also insufficient because wave propagation depends on the whole source and ocean basin.
The first wave is not necessarily the largest, and a tsunami is not one isolated crest. Earthquake24 is a data explorer, not an official tsunami message service.
Common questions
Can a deep earthquake cause a tsunami?
Deep sources generally couple less direct vertical displacement to the seafloor, but magnitude, mechanism and secondary processes must be evaluated rather than depth alone.
Is a tsunami a tidal wave?
No. Tides are driven mainly by astronomical forces. Tsunamis are generated by rapid water displacement.
Does tsunami: 1 prove coastal damage?
No. It is a source catalog field, not a measured damage or universal wave-height statement.