Japan earthquakes

M5.9 earthquake 2 km NE of Shiroi, Japan

A magnitude 5.9 earthquake struck 2 km NE of Shiroi, Japan on Fri, Oct 4, 1985, 9:25 PM JST (12:25 UTC), 85 km (53 mi) below the surface.

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Map

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The earthquake

Magnitude: 5.9 (Mw, moment), moderate
Magnitude from: USGS National Earthquake Information Center
Local time: Fri, Oct 4, 1985, 9:25 PM JST
UTC: 1985-10-04 12:25:51 UTC
Depth: 84.5 km (52.5 mi), intermediate-depth
Epicenter: 35.816° N, 140.093° E
Region: Japan
Strongest shaking: V, moderate shaking
Tsunami flag: No
Status: Reviewed by a seismologist

Magnitude estimates

Different scales measure different things and differ by a few tenths. The USGS marks one as preferred, and it is the one this page uses.

Mag.	Scale	Computed by	Notes
5.9	Mw, moment	USGS National Earthquake Information Center	Preferred · Reviewed
5.9	Mw, moment	ISC-GEM global catalog	Final · ±0.1
5.9	Mwc, centroid moment	Global CMT project	Preliminary

What happened

The USGS’s account of the effects of this earthquake.

Eighteen people injured. Felt (V JMA) at Tokyo, (IV JMA) at Nikko, Tateyama and Kumagaya, (III JMA) at Mito, Kofu and Maebashi. Felt (I JMA) as far north as Obihiro, Hokkaido, south to Hachijo-jima and west to Toyooka. FAULT PLANE SOLUTION: P-Waves NP1:Strike=343 Dip=85 Slip=-25 NP2:Strike=75 Dip=65 Slip=-174 Principal Axes: (T) Plg=14 Azm=32 (P) Plg=21 Azm=296 Comment: The focal mechanism is moderately well controlled and corresponds to strike-slip faulting with a moderate normal component. The preferred fault plane is not determined. MOMENT TENSOR SOLUTION Dep 90 No. of sta: 14 Moment Tensor; Scale 10**24 d-cm Mrr=-1.97 Mtt=5.78 Mff=-3.82 Mrt=-0.24 Mrf=-4.18 Mtf=-5.79 Principal axes: (T) Val=8.75 Plg=9 Azm=28 (N) Val=0.05 Plg=58 Azm=133 (P) Val=-8.80 Plg=30 Azm=292 Best Double Couple:Mo=8.8*10**24 NP1:Strike=74 Dip=62 Slip=-164 NP2:Strike=336 Dip=76 Slip=-29 CENTROID, MOMENT TENSOR (HRV) Data Used: GDSN L.P.B.: 14S, 29C Centroid Location: Origin Time 12:25:54.1 0.2 Lat 35.52N 0.02 Lon 139.74E 0.03 Dep 113.7 1.7 Half-duration 3.4 Moment Tensor; Scale 10**24 D-CM Mrr=-0.95 0.18 Mtt=1.35 0.26 Mff=-0.40 0.27 Mrt=1.47 0.15 Mrf=-7.75 0.19 Mtf=-3.38 0.30 Principal Axes: (T) Val=8.72 Plg=37 Azm=57 (N) Val=-0.11 Plg=23 Azm=167 (P) Val=-8.60 Plg=44 Azm=281 Best Double Couple:Mo=8.7*10**24 NP1:Strike=86 Dip=24 Slip=-171 NP2:Strike=348 Dip=86 Slip=-67

From the USGS event page for usp0002kf6. U.S. Geological Survey text and figures are in the public domain.

Shaking

The USGS ShakeMap: shaking estimated from seismic stations and the quake’s size, on the Modified Mercalli intensity scale.

Strongest estimated: V, moderate shaking
Peak ground acceleration: 5.5% of gravity
Peak ground velocity: 1.1 cm/s
Map: Automatic

USGS ShakeMap: estimated shaking intensity around the epicenter — Estimated shaking intensity. Map: USGS ShakeMap.

Did you feel it?

No one has reported feeling this quake to the USGS.

Nearest places

Distance and direction from each place to the epicenter, with its forecast.

Nearby

Within 100 km, magnitude 2.9 and up: 10 in the 60 days after this one and 2 in the 30 days before it.

After

Before

Earthquakes today Japan earthquakes Live radar here

Sources

From the USGS Earthquake Hazards Program and its partner networks, event usp0002kf6 (also filed as gcmtb100485b, gcmt19851004122551, atlas19851004122551, iscgem512471). Read Fri, Oct 2, 2026, 3:18 PM UTC.