1984 Otaki earthquake

1984 Otaki earthquake
Date September 14, 1984 local time (September 13, 1984 UTC)
Magnitude Ms 6.3 (Mj 6.8)
Depth 2 km (1 mi)[1]
Epicenter 35°47′N 137°29′E / 35.79°N 137.49°E / 35.79; 137.49Coordinates: 35°47′N 137°29′E / 35.79°N 137.49°E / 35.79; 137.49
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[2]

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.[3][4] The earthquake left at least 29 people dead or missing, making it the deadliest earthquake in 1984.

Geology

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.[1]

Relation to other earthquakes

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.

Main Shock

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.[5] 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.

Damage

This lake was formed after a part of the Otaki river was blocked by a landslide

Due to torrential rains in the area before the earthquake, many landslides occurred.

Total Damage
Dead 14
Missing 15
Injured 10
Collapsed buildings 14
Half collapsed buildings 73
Damaged Buildings 517
Economic cost US$28 million

Incidents

Precursors

Response

9 check dams were built on Mount Ontake in 4 years after the earthquake.

See also

References

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