M 7.4 earthquake – 100 km ENE of Miyako, Japan

Earthquake magnitude and impact

• Initial magnitude 7.4 revised to 7.7; offshore epicenter.
• Tsunami: initial waves around 40 cm; forecasts up to 3 m, but no major tsunami reported.
• Several commenters characterize it as a “medium deal”: disruptive but not catastrophic, especially compared to the 9.1 quake that caused Fukushima.
• Noted that large quakes (M7+) are relatively common in Japan, often without major damage.

Felt effects and duration

• Reports from Tokyo, Kawasaki, Chiba, Aomori, and elsewhere: shaking ranged from “barely noticed” to the strongest/longest in years.
• Higher floors reported prolonged swaying, sometimes several minutes, described as “being on a boat” rather than violent jolts.
• Some regions (e.g., south of Nagoya) reported feeling nothing despite distance similar to Tokyo.
• One quoted rule-of-thumb: longer shaking generally correlates with higher magnitude (e.g., ~15 seconds ≈ M6.9, minutes-long for high-7s to 9.0).

Early warning systems and apps

• Many phones in Japan received alerts before shaking, with lead times ranging from ~10–20 seconds near Aomori to ~45 seconds in Tokyo; some got ~2 minutes for a different event.
• Uses of warning time: move away from windows/heavy objects, get under desks, stop trains/elevators/surgeries, halt hazardous work; for milder quakes, some treat it casually.
• Doorframe advice is called outdated; modern guidance favors quickly taking nearby cover.
• NERV app praised for detailed visualizations and countdown; compared favorably to default Android/iOS alerts and apps like MyShake in California.
• Some see early warning as a major human achievement; others note that useful lead time shrinks near the epicenter.

Infrastructure, policy, and privatization debate

• Japan uses built-in cell broadcast alerts but not for every quake; thresholds depend on expected intensity (Shindo scale mentioned).
• Some criticize relying on private apps for critical alerts; others argue that government/bureaucratic constraints make fast, automated alerts difficult, and private systems fill that gap.
• Discussion notes similar systems in other regions (California, Taiwan), with variable effectiveness and timing.

Seismology and regional context

• Clarification that the reported magnitude is on the moment magnitude scale, not the obsolete Richter scale.
• Emphasis that magnitude is exponential; M9+ is vastly more energetic than M7+.
• A commenter observes Japan’s seemingly higher quake frequency compared to the North American West Coast, referencing ring-of-fire maps, while acknowledging population-density and media effects.

Cultural and humorous tangents

• NERV app name/logo licensed from the anime “Evangelion,” prompting debate over its cultural status versus other franchises (e.g., Gundam, Ghibli, Star Wars comparisons).
• Light jokes about “M 7.4” sounding like a hardware/model number and “benchmarks” for earthquakes.