Tsunami Early Warning of the Hunga Volcanic Eruption Using an Ocean Floor Observation Network Off the Japanese Islands

Abstract On 15 January 2022, an eruption of Hunga volcano generated an air-coupled tsunami that propagated across the Pacific Ocean. The tsunami reached Japan approximately 7 hr after the eruption and was recorded by coastal and offshore stations. We conducted a retroactive study of tsunami early warning using a data assimilation approach. We assimilated water pressure records of 44 offshore bottom pressure gauges (OBPGs) off the Japanese Islands after the volcanic eruption and forecasted tsunamis on the Shikoku Island and the Kii peninsula. The tsunami waveforms at 12 points of interest (i.e., coastal and near-coast stations) were predicted using a data assimilation approach at 15:00 (UTC) with forecast accuracy of 97%. Moreover, we discussed the effects of air-pressure variations generated by the volcanic eruption. The results showed that air-pressure variations had negligible effect on the assimilation results. This is the first time that data assimilation approach was applied to a nonseismic tsunami event for early warning. Our study indicates that data assimilation approach plays an important role in tsunami hazard mitigation. Early warnings of nonseismogenic tsunamis can be successfully achieved by assimilating offshore water pressure records of OBPGs.