M 7.4 earthquake – 100 km ENE of Miyako, Japan
A magnitude 7.7 earthquake struck off the coast of northeastern Japan, producing only mild tsunamis and limited damage but being widely felt as long, rolling shaking as far as Tokyo. Commenters focus on how Japan’s earthquake early warning systems and apps like NERV provided alerts tens of seconds before the tremors arrived, allowing trains to stop, elevators to open, and people to take basic safety measures. The exchange also touches on how Japan’s seismic activity compares to other regions on the Pacific Ring of Fire and clarifies that modern quakes are measured on the moment magnitude scale rather than the old Richter scale.
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- Doorframe advice is called outdated; modern guidance favors quickly taking nearby cover.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.