noun, used as a suffix
offshore earthquake
Used as a suffix attached to a place name to indicate an earthquake whose epicenter is offshore near that location, e.g. 三陸沖地震 (Sanriku-oki earthquake).
三陸沖地震は2011年に大きな津波を引き起こした。
The Sanriku-oki earthquake caused a massive tsunami in 2011.
Compound of 沖 (oki, 'offshore') and 地震 (jishin, 'earthquake').