Warnings Space NASA's
GNSS-based Upper Atmospheric Realtime Disaster Information and Alert Network (GUARDIAN), comprising a portion of the
Global Navigation Satellite System, had an
AI component installed the day before the earthquake, which informed scientists in near real-time of the tsunami crossing open ocean. The vast column of water uplifted over a wide area pushed up the mass of air above it, sending ripples of low-frequency sound and gravity waves upwards into the
ionosphere, thus measurably perturbing the orbits of
GPS satellites.
Asia The
Pacific Tsunami Warning Center (PTWC) warned of "hazardous
tsunami waves" along the coasts of Russia and Japan. Authorities in Russia also issued tsunami warnings for the Kamchatka Peninsula and the
Kuril Islands, which were cancelled on the evening of 30 July. On 3 August, a magnitude 7.0 aftershock off the Kuril Islands prompted Russian authorities to issue a tsunami warning in parts of Kamchatka, with the
Ministry of Emergency Situations warning of waves of up to . The alert was lifted later that day. In the first tsunami alerts issued in Japan since the
2024 Hualien earthquake, and elsewhere; 900,000 people in 133 municipalities were also advised to evacuate. The agency said up to waves were expected to reach the coast and urged the evacuation of the areas expected to be impacted. The runways of
Sendai Airport were closed, while
JR East,
JR Central, and
JR Hokkaido suspended rail services. Workers at the
Fukushima Daiichi Nuclear Power Plant were ordered to evacuate, while a scheduled release of treated radioactive water from the facility into the Pacific Ocean was halted. The
Japanese Defense Ministry deployed its air assets to the Pacific coast to gather information. The JMA downgraded its warnings to advisories on the night of 30 July Indonesia's
Meteorology, Climatology, and Geophysical Agency issued a warning for parts of
Papua,
North Maluku,
North Sulawesi, and
Gorontalo. Authorities in Indonesia expected small tsunami waves of less than in coastal areas of the regions mentioned, advising residents to move away from beaches and low-lying shores. In
China, the
Ministry of Natural Resources issued a yellow alert, the second lowest of a four-tier tsunami alert level system, covering Taiwan,
Zhejiang Province, and
Shanghai. Taiwan's
Central Weather Administration issued a "tsunami watch" alert, saying that waves as high as could hit the island's southeastern and southwestern coasts. The tsunami marked the first time the
Central Emergency Operation Center was activated for such an event, causing 23 rescue aircraft and 14 naval vessels to be placed on standby. The
Philippine Institute of Volcanology and Seismology issued a tsunami advisory for the
Pacific coast of the Philippines with waves expected to be up to . The advisory covered 22 provinces from
Batanes to
Davao Occidental. The advisory was eventually cancelled as the seismological agency did not record significant sea level disturbances and destructive tsunami waves. The PTWC also warned of waves measuring less than hitting South Korea.
Oceania The PTWC warned that tsunami waves high were possible in Hawaii and the
Solomon Islands, and that waves up to were likely to affect
American Samoa,
Chuuk,
Kiribati,
Nauru,
New Caledonia,
Niue,
Papua New Guinea, the
Pitcairn Islands,
Tokelau,
Tuvalu,
Vanuatu, and
Wallis and Futuna. and alerts were also issued in
Palau and the
Northern Mariana Islands. An advisory was issued by the
National Emergency Management Agency (NEMA) for "strong currents and unpredictable surges" around the entire coast of New Zealand; the next day, NEMA extended the advisory for another 24 hours due to rebounding tsunami activity from South America. An alert was issued by
Tonga's Meteorological Services, advising people in tsunami threat areas to evacuate. In
Fiji, the Mineral Resources department similarly issued a tsunami watch for low-lying coastal areas. The
Cook Islands' Meteorological Services issued an advisory, saying there was no immediate threat to the islands but the situation was being monitored.
Samoa's Meteorological Office issued an advisory, cautioning the public around coastal areas, while the PTWC said a threat to American Samoa was still under investigation. In the
Marquesas Islands, French Polynesia, authorities warned that waves of up to could reach the islands of
Ua Huka,
Nuku Hiva, and
Hiva Oa. The entirety of the
U.S. West Coast (California, Oregon, and Washington state) was placed under alert, as were portions of coastal Alaska and the
Aleutian Islands. In California, the
Central Coast and
San Francisco Bay Area were placed under advisory by the
National Oceanic and Atmospheric Administration. A warning was also issued covering the coast from
Cape Mendocino, California, to the border with Oregon. The
Mexican Navy warned of strong currents at ports along the Pacific coast from
Baja California to
Chiapas. The government also urged residents to stay away from beaches. Alerts were also issued in
Chile,
Colombia,
Costa Rica,
Peru, and the
Galápagos Islands in
Ecuador. with a wave striking
Severo-Kurilsk in the nearby
Kuril Islands. Inundation in Severo-Kurilsk reached roughly 600 meters. The first wave was the largest in Severo-Kurilsk. On
Shumshu, the tsunami flooded as far as inland with waves and reached a maximum run-up height of in Baikovo. The
Shirshov Institute of Oceanology said waves of may have struck parts of the peninsula's coast. Waves of were found along Khalaktyrsky beach during a survey by the Kamchatka Hydrometeorological Center. An American tsunami scientist estimated that waves of up to may have struck lesser populated areas of
Kamchatka. In Japan, tsunamis were observed in 22 of the country's 47 prefectures. Tsunamis measuring were reported to have struck
Hachijō-jima and
Nemuro, Hokkaido, Wave heights reached up to in areas such as
Hamanaka, Hokkaido. A wave was observed in
Harumi, Tokyo. A tsunami was observed in the
Galapagos Islands. In the
Hawaiian Islands, a tsunami struck
Midway Atoll at 17:00
SST.
Kahului, Hawaii, was struck by a wave, while at
Hilo, the tsunami was high.
Haleʻiwa was struck by a surge at 19:48 HST. The town's gauge recorded an amplitude of relative to normal sea level in the tsunami's first impact in the area. In
Washington, waves of occurred at
La Push and waves were recorded in
Seattle. Along the Chilean coast, waves of over were recorded. At some beaches, wave heights reached . In
Boyeruca,
Maule Region, a rise in sea level was observed. At
Coquimbo and
Coliumo, these measurements were and , respectively. ==Damage and casualties==