Note:This page contains AI-generated content for informational and entertainment purposes only. It may contain inaccuracies. Raw event data is from USGS and EMSC. All statistics, lists, and derived information are generated by this site. Full disclaimerFound an error?
Location:
13 km SW of Saiki, Japan
Period:
15 Apr 2016 16:25:06 - 16 Apr 2016 07:02:01 (14 hours 36 minutes)
Volcanoes in 100km radius:
Asosan(24km), Kujusan(47km), Unzendake(50km), Yufu-Tsurumi(71km)
Earthquakes:
11
M 7.0+:
M 7.0; 6 km ESE of Kumamoto, Japan; (15 Apr 2016) (9km from the swarm center)
No swarms nearby.
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm PS20160415.2 Near Saiki, Japan

Seismic swarm PS20160415.2 occurred 13 km southwest of Saiki in Oita Prefecture, Kyushu, Japan. The sequence began at 16:25 on 15 April 2016 and concluded at 07:02 on 16 April 2016, spanning 14 hours and 36 minutes. During this interval, 11 earthquakes were recorded, with the initial event registering magnitude 7.0 at a depth of 10 km.

The swarm unfolded rapidly in its early phase. Following the magnitude 7.0 mainshock, five events between magnitude 5.1 and 5.7 occurred within the first 21 minutes, all at 10 km depth. Subsequent activity included a magnitude 5.4 event at 4 km depth at 18:03 and a magnitude 5.5 event at 13 km depth at 18:55. Later shocks on 16 April comprised magnitudes 5.1–5.2 at depths of 9–10 km.

This activity aligns with the broader 2016 Kumamoto earthquake sequence. The magnitude 7.0 event matches the foreshock recorded 6 km east-southeast of Kumamoto, approximately 9 km from the swarm centroid. The region lies within the Beppu-Shimabara graben, an extensional feature transecting central Kyushu and influenced by the Median Tectonic Line. Active faulting along the Futagawa and Hinagu segments drives regional seismicity, with the 2016 sequence resulting from dextral strike-slip motion and associated normal faulting.

Historical data indicate limited swarm-type clustering in the area since 2000, with this event representing the sole recorded instance. The swarm highlights episodic energy release along pre-existing structures rather than isolated mainshock-aftershock patterns typical of the zone.

Geological context underscores Kyushu’s position at the junction of the Philippine Sea Plate and Eurasian Plate. Subduction-related stresses, combined with volcanic influences from nearby Aso and other calderas, contribute to elevated seismic hazard. Depths predominantly near 10 km reflect brittle failure within the upper crust.

Earthquake Sequence Summary

  • 15 Apr 2016 16:25:06 – M7.0 at 10 km
  • 15 Apr 2016 16:30:46 – M5.1 at 10 km
  • 15 Apr 2016 16:33:20 – M5.3 at 10 km
  • 15 Apr 2016 16:43:07 – M5.2 at 10 km
  • 15 Apr 2016 16:44:06 – M5.3 at 10 km
  • 15 Apr 2016 16:45:56 – M5.7 at 10 km
  • 15 Apr 2016 18:03:10 – M5.4 at 4 km
  • 15 Apr 2016 18:55:53 – M5.5 at 13 km
  • 15 Apr 2016 22:11:40 – M5.1 at 10 km
  • 16 Apr 2016 00:48:32 – M5.2 at 9 km
  • 16 Apr 2016 07:02:01 – M5.1 at 9 km

References

Japan Meteorological Agency earthquake catalog
Geological Survey of Japan, Active Fault Database of Japan
Headquarters for Earthquake Research Promotion, Long-term Evaluation of the Futagawa-Hinagu Fault Zone