M4.9 earthquake 3 km W of Shibayama, Chiba, Japan
A magnitude 4.9 earthquake struck 3 km W of Shibayama, Chiba, Japan at 04:13 local time (19:13 UTC) on 8 Oct 2026, at a depth of 73 km, according to USGS and GFZ.
Reported by 2 agencies · revised from M5.0 · 3 reports to USGS “Did You Feel It?”
Data: USGS, GFZ · updated 2026-10-08 15:06 UTC · reviewed
- Magnitude
- 4.9light
moment magnitude (W phase) (mww)
revised from 5.0 - Depth
- 73 km
- Status
- Reviewed
- Origin time
- 2026-10-07 19:13:50 UTC
- Local: 8 Oct 2026, 04:13:50 (Asia/Tokyo)
- Epicentre
- 35.675° N, 140.396° E
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Circles show this event and others within 36 km from 7 days before to 30 days after. Lines: plate boundaries and GEM active faults. Open on the live map
Nearby places
| Place | Distance | Est. shaking |
|---|---|---|
| ShibayamaChiba, Japan · pop. 7,122 | 3 km | IIIWeak |
| SanmuChiba, Japan · pop. 48,444 | 5 km | IIIWeak |
| RyōgokuChiba, Japan · pop. 49,735 | 6 km | IIIWeak |
| YachimataChiba, Japan · pop. 68,769 | 7 km | IIIWeak |
| YokoshibaChiba, Japan · pop. 22,075 | 8 km | IIIWeak |
| ChibaJapan · pop. 979,768 | 26 km | IIIWeak |
| IchiharaChiba, Japan · pop. 283,531 | 33 km | IIIWeak |
| KashiwaChiba, Japan · pop. 433,436 | 43 km | IIIWeak |
Shaking is an estimate from the intensity prediction equation of Allen, Wald & Worden (2012), not an observation. Local ground and buildings can change it by a level or more. Likely felt out to about 88 km.
Every agency's solution
Agencies locate earthquakes with their own stations and methods, so their numbers differ. We match reports of the same event by time, distance and magnitude and show them side by side. The headline uses USGS, which has been reviewed by an analyst.
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How big was it?
Widely felt near the epicentre: rattling windows and objects. Significant damage is unlikely.
It released roughly the energy of 338 t of TNT. Magnitude is logarithmic: each whole step means about 32 times more energy and 10 times larger waves on a seismogram. Depth matters too: at 73 km this was a intermediate-depth earthquake, which spreads shaking over a wider area but less intensely.
M4.9 releases about 32× the energy of M3.9, and its waves are about 10× taller on a seismogram. Energy: 338 t of TNT vs 11 t of TNT.
Each square is the energy of one M3.9. Energy from log₁₀E = 1.5M + 4.8.
Aftershocks and nearby activity
1 later earthquake within 36 km; the largest was M3.9 20 h ago. 5 in the 7 days before. Aftershock rates usually fall off roughly in proportion to 1/time.
Mainshock M4.9
1 later earthquake nearby. Aftershock rates typically fall off roughly as 1/time (Omori's law).
| Time after mainshock (hours) | Magnitude | Depth (km) |
|---|---|---|
| 0.37 | 3.9 | 50 |
Did you feel it?
Reports from people help show where shaking was strong. They are anonymous and shown here in aggregate.
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Event id gfz2026trfk. First recorded here 7 Oct 2026, 19:26:16 UTC. Solutions: GFZ (geofon:gfz2026trfk); USGS (usgs:us6000u0u7). Cite as: SeismoAtlas, “M4.9 earthquake 3 km W of Shibayama, Chiba, Japan”, https://seismoatlas.com/earthquake/gfz2026trfk-m4-9-earthquake-3-km-w-of-shibayama-chiba-japan, data from USGS, GFZ.
JSON: /api/v1/events/gfz2026trfk. SeismoAtlas is not an official warning service.