M3.5 earthquake 20 km NNE of Choshi, Chiba, Japan
A magnitude 3.5 earthquake struck 20 km NNE of Choshi, Chiba, Japan at 03:40 local time (18:40 UTC) on 17 Sept 2026, at a depth of 30 km, according to JMA. The solution is preliminary and may be revised.
Data: JMA · updated 2026-09-16 18:42 UTC · automatic solution
- Magnitude
- 3.5minor
JMA magnitude (Mj) - Depth
- 30 km
- Status
- Automatic
- Origin time
- 2026-09-16 18:40:00 UTC
- Local: 17 Sept 2026, 03:40:00 (Asia/Tokyo)
- Epicentre
- 35.900° N, 140.900° E
Circles show this event and others within 30 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 |
|---|---|---|
| ChoshiChiba, Japan · pop. 58,431 | 20 km | IIWeak |
| HasakiChiba, Japan · pop. 39,209 | 20 km | IIWeak |
| KamisuIbaraki, Japan · pop. 95,454 | 21 km | IIWeak |
| Kashima-shiIbaraki, Japan · pop. 66,950 | 25 km | IIWeak |
| MitoIbaraki, Japan · pop. 270,685 | 64 km | INot felt |
| ChibaJapan · pop. 979,768 | 78 km | INot felt |
| KashiwaChiba, Japan · pop. 433,436 | 83 km | INot felt |
| IchiharaChiba, Japan · pop. 283,531 | 85 km | INot felt |
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.
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 JMA.
| Agency | Magnitude | Depth | Epicentre | Time offset | Status |
|---|---|---|---|---|---|
| JMAheadlineJMA via Japan Meteorological Agency | 3.5 Mj | 30 km | 35.90° N, 140.90° E | – | Automatic |
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How big was it?
Often felt by people at rest close to the epicentre, rarely causes damage.
It released roughly the energy of 2.7 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 30 km this was a shallow earthquake, which is felt more strongly at the surface than a deeper one of the same size.
M3.5 releases about 32× the energy of M2.5, and its waves are about 10× taller on a seismogram. Energy: 2.7 t of TNT vs 85 kg of TNT.
Each square is the energy of one M2.5. Energy from log₁₀E = 1.5M + 4.8.
Aftershocks and nearby activity
1 later earthquake within 30 km; the largest was M3.8 1 day ago. Aftershock rates usually fall off roughly in proportion to 1/time.
Mainshock M3.5
1 later earthquake nearby. Aftershock rates typically fall off roughly as 1/time (Omori's law).
| Time after mainshock (hours) | Magnitude | Depth (km) |
|---|---|---|
| 246.08 | 3.8 | 50 |
Did you feel it?
Reports from people help show where shaking was strong. They are anonymous and shown here in aggregate.
Reports on SeismoAtlas
No reports yet.
Event id jma20260917034007. First recorded here 28 Sept 2026, 17:32:06 UTC. Solutions: JMA (jma:20260917034007). Cite as: SeismoAtlas, “M3.5 earthquake 20 km NNE of Choshi, Chiba, Japan”, https://seismoatlas.com/earthquake/jma20260917034007-m3-5-earthquake-20-km-nne-of-choshi-chiba-japan, data from JMA.
JSON: /api/v1/events/jma20260917034007. SeismoAtlas is not an official warning service.