M8.7 earthquake in Western Pacific, tsunami warning issued

Tsunami alerts and public response

• Initial messaging: tsunami.gov showed a watch for the US West Coast, and warnings/advisories for Alaska, Hawaii, and much of the North Pacific; levels later downgraded (e.g., Hawaii from warning to advisory).
• People in Hawaii, New Zealand, Japan, Oregon, and elsewhere report loud phone alerts, sirens, and beach closures; some evacuations to higher ground (e.g., Mililani on Oahu, upland areas in Oregon, mass relocation near Shanghai).
• Several note clear, jargon-free alert wording (“stay away from the water”) as a positive; others describe confusion when forecasts are high but impacts are small, making it hard to know which information to trust.

Magnitude, measurement, and context

• The quake’s magnitude is repeatedly revised (8 → 8.7 → 8.8), with discussion of how USGS and tsunami.gov updates can differ in time.
• Commenters compare it to historic megathrust events (1952 Kamchatka, 1960 Valdivia, 2011 Tōhoku), noting this is among the strongest ever instrumentally recorded, and orders of magnitude more energetic than quakes like 1994 Northridge.
• There is explanation of different magnitude scales (Richter, moment magnitude) and why energy scaling is ~10^1.5 per unit.

Tsunami behavior and “is it a wave?” debate

• Substantial discussion clarifies that tsunamis in deep water are low-amplitude, long-wavelength waves, invisible from planes and often barely felt by ships, but dramatically amplify in shallow coastal water.
• Buoy data and early Japanese observations show relatively modest open-ocean height changes (~1.3 m or less), with later coastal waves in Japan mostly under ~1.5 m, far smaller than 2011.
• A long, heated subthread debates whether tsunamis should be thought of as “waves” vs “sudden sea-level rise,” emphasizing they behave unlike familiar surf waves and can inundate inland for many minutes.

Regional impacts reported so far

• Kamchatka/Petropavlovsk: reports of strong shaking, some building cracks, minor injuries, local flooding, port damage in Severo-Kurilsk, and several thousand precautionary evacuations; overall impact described as limited.
• Japan: coastal alerts up to ~3 m forecast, but observed waves mostly <1 m; heavy emphasis on Japan’s dense, data-rich televised coverage and evacuation culture.
• Pacific basin: small tsunamis reported at Midway, Guam, and parts of the Americas; some beach closures in Costa Rica; Oregon gas lines and traffic as people self-evacuate.

Tools, infrastructure, and prediction

• People share links to live tsunami and USGS maps, DART buoy data, AIS ship tracking, and mobile apps like MyShake; government mapping sites experience “hug of death.”
• Some question perceived “overprediction” of tsunami heights; replies stress the rarity of events, high uncertainty, and asymmetric cost of false negatives.
• A side thread contrasts science-based monitoring with superstition around a manga “megaquake prophecy,” with most commenters skeptical.