1984 Otaki earthquake
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| Date | September 14, 1984, local time (September 13, 1984 UTC) |
|---|---|
| Magnitude | Ms 6.3 (Mj 6.8) |
| Depth | 2 km (1 mi) |
| Epicenter | 35°47′N 137°29′E / 35.79°N 137.49°ECoordinates: 35°47′N 137°29′E / 35.79°N 137.49°E |
| Type | Intraplate |
| Areas affected | Japan |
| Max. intensity | Shindo 6 (estimate) |
| Peak acceleration | 0.3~ g |
| Tsunami | No |
| Landslides | Yes |
| Casualties | 14 dead 10 injured 15 missing |
The 1984 Otaki earthquake hit Nagano Prefecture, Japan on September 14, 1984, at 08:48 local time (September 13, 1984, at 23:48 UTC). Registering a magnitude of Ms 6.3, the earthquake destroyed Otaki (Japanese: 王滝(おうたき)), and elicited landslides. The earthquake left at least 29 people dead or missing, making it the deadliest earthquake in 1984.
Although the epicenter was only 2 km (1 mi) deep, no visible fault appeared. The Japan Meteorological Agency estimated that two faults, one 15 km (9 mi) long and one 5 km (3 mi) long, had ruptured simultaneously.
Seismologists including Akeo Yoshida state that the 1948 Fukui earthquake, a 7.0 Mj earthquake in Gifu Prefecture in 1961, a 6.6 Mj earthquake in Gifu Prefecture in 1969, and this earthquake were earthquakes that occurred in a cycle for a little while in the same area.
Since there was no seismometer in the area, the Japan Meteorological Agency made an estimate intensity, Shindo 6. Some unofficial estimates put it to Shindo 7. There are reports that rocks and pieces of wood flew in the air in areas near the epicenter, due to ground accelerations faster than gravitational acceleration in the 5 Hz~10 Hz shaking range. A seismometer at Makio Dam, 4 km (2 mi) away from the epicenter, observed very strong shaking but couldn't record more than 0.3 g which was the limit.
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