A common assumption that surfaces after a strong earthquake is that a tsunami will inevitably follow. In reality, only a specific subset of earthquakes is capable of generating tsunami waves.
When Earthquakes Can Trigger Tsunamis
Tsunamis are driven not by shaking alone, but by the displacement of a large volume of water. This typically occurs when:
The earthquake originates beneath the ocean
The magnitude is sufficiently large (generally above 6.5 on the moment magnitude scale)
There is vertical movement of the seabed — where the seafloor is forced upward or downward, lifting or disturbing the water column above it
In such conditions, the uplift or subsidence of the ocean floor becomes the initial pulse that propagates as tsunami waves.
When Earthquakes Do Not Produce Tsunamis
Many earthquakes do not create tsunamis, even if they are strong. This is especially the case when:
The epicenter is located on land
The magnitude is relatively small
The fault movement is horizontal (strike-slip), which shifts tectonic plates laterally without significantly disturbing the water column
In these scenarios, the absence of vertical displacement and offshore rupture prevents the conditions needed for tsunami generation.
Historical Illustrations
Two well-documented events highlight this contrast clearly:
Cianjur, Indonesia (2022) — A strong inland earthquake caused significant ground damage but produced no tsunami, as it did not occur underwater.
Indian Ocean Earthquake (2004) — A massive megathrust rupture beneath the seafloor triggered one of the most devastating tsunamis in recorded history.
Key Takeaway
Earthquakes do not inherently produce tsunamis. Tsunamis arise only when underwater seismic activity displaces the seafloor in a way that transfers energy into the ocean. Distinguishing between these conditions is critical for interpreting seismic events accurately and responding with appropriate levels of alertness.