A tsunami identified far from its source before the parent earthquake is known is called an orphan tsunami.
The term describes a wave whose origin is initially mysterious because the tsunami reaches a distant coastline without an obvious locally felt earthquake. Investigators can later work backward from historical records, coastal deposits, and computer models to identify the “parent” earthquake that generated it. The name captures the tsunami’s apparent lack of a known source at the time of observation.
The best-known example is the orphan tsunami that struck Japan in January 1700. Japanese records documented an unusual tsunami without a clearly felt local earthquake. Centuries later, scientists matched those observations with evidence of a great Cascadia earthquake on the Pacific Northwest coast of North America, establishing that the distant earthquake occurred on 26 January 1700.
An orphan tsunami is not simply any large or distant tsunami. “Teletsunami” describes a tsunami traveling more than about 1,000 kilometers or across an ocean, while “orphan” emphasizes that the generating earthquake was unknown when the wave was recognized. Terms such as ghost wave, seismic surge, and rogue tsunami are not the standard scientific label for this situation.