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Aftershock sequence

Aftershocks after the M 5.5 5 km ESE of Asahi, Japan earthquake

4 aftershocks recorded inside the 50 km rupture zone, the largest M 4.7, most recently 13 hours ago.

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Back to the M 5.5 5 km ESE of Asahi, Japan earthquake
Aftershocks4
StrongestM 4.7
Rupture zone50 km

The sequence

Newest first.

  1. 3.5Near east coast of Honshu, Japan17 km ESE of the mainshock13 hours ago· 26.0 km deep
  2. 4.310 km SSE of Hasaki, Japan17 km ESE of the mainshock13 hours ago· 26.0 km deep
  3. 4.7Near east coast of Honshu, Japan10 km NNW of the mainshock15 hours ago· 41.5 km deep
  4. 4.76 km N of Asahi, Japan10 km NNW of the mainshock15 hours ago· 41.5 km deep

How the rupture zone is measured

An aftershock is a smaller earthquake triggered as the crust settles around the fault that ruptured. They cluster along that rupture, so the area worth searching scales with the size of the mainshock rather than being a fixed radius.

The 50 km zone above comes from the Wells & Coppersmith (1994) rupture-length relation, doubled because aftershocks routinely extend about one rupture length beyond each end of the fault, then floored at 50 km and capped at 400 km. Anything outside it is counted as separate regional seismicity, not part of this sequence.

Aftershocks are most frequent in the hours right after the mainshock and taper off over days to months. A quiet day does not mean the sequence has ended.

Data from USGS, EMSC and partner agencies. Magnitudes and locations are preliminary and may be revised.