The sequence
Newest first.
- 4.8Bonin Islands, Japan region24 km SW of the mainshock3 hours ago· 482.2 km deep
- 5.3Bonin Islands, Japan region29 km SW of the mainshock3 hours ago· 485.1 km deep
- 4.2Bonin Islands, Japan region22 km SW of the mainshock22 hours ago· 499.8 km deep
- 4.8Bonin Islands, Japan region38 km SSW of the mainshock23 hours ago· 498.9 km deep
- 6.5Bonin Islands, Japan region36 km SW of the mainshock23 hours ago· 492.4 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 91 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.