noun
leading wave; advancing wave
Specifically the initial wave of a tsunami that arrives as a crest before the trough, causing water to rush inland. Often contrasted with 引き波 (the receding wave).
See also: 引き波
津波の押し波で海岸線が一気に浸水した。
The leading wave of the tsunami flooded the coastline all at once.
押し波と引き波のメカニズムを理解することが防災に役立つ。
Understanding the mechanism of advancing and receding waves helps with disaster prevention.
引き波 is the receding wave of a tsunami, when water pulls back from the shore. 押し波 is the opposite: the incoming, advancing wave.
Compound of 押し (oshi, 'pushing') + 波 (nami, 'wave'). The term is used in tsunami science to describe the initial surge of water.