What term describes an earthquake that produces a much larger tsunami than its seismic waves suggest?

An earthquake that produces a much larger tsunami than its seismic waves suggest is called a tsunami earthquake.

The term describes an event whose tsunami magnitude is unusually large compared with its magnitude from shorter-period seismic waves. These earthquakes typically rupture slowly and release an unusually large share of their energy at long periods, while deforming the shallow seafloor efficiently enough to displace a great volume of water.

That combination makes tsunami earthquakes especially dangerous. People near the source may feel weak or oddly prolonged shaking, even though a destructive tsunami is forming offshore. Standard earthquake-based warning methods can therefore underestimate the hazard or fail to issue an immediate warning.

The concept was introduced by Japanese seismologist Hiroo Kanamori in 1972. The 1946 Aleutian earthquake is a notable example, although local submarine landsliding also contributed to its extreme run-up. Tsunami earthquakes are most associated with shallow parts of subduction zones, where weak sediments can slow fault rupture.