Location:

Period:

28 Jun 2000 09:25:47 - 29 Jun 2000 09:53:28 (1 day 27 minutes)

Volcanoes in 100km radius:

Miyakejima(27km), Mikurajima(40km), Niijima(53km), Kozushima(59km), Toshima(59km), Izu-Oshima(68km), Kurose Hole(89km)

Earthquakes:

15 swarms found nearby.

2000

PS20000703.1(39.5km)

2 Jul

7 hours

5 earthquakes

S20000706.1(56.1km)

5 Jul

1 day 6 hours

27 earthquakes

PS20000712.1(54.2km)

11 Jul

2 days 5 hours

10 earthquakes

PS20000720.1(61.4km)

19 Jul

16 hours

6 earthquakes

PS20000723.1(50.6km)

23 Jul

1 day 5 hours

6 earthquakes

PS20000730.1(48.6km)

30 Jul

12 hours

5 earthquakes

PS20000803.1(62.0km)

2 Aug

21 hours

7 earthquakes

S20000803.1(52.1km)

3 Aug

1 day 20 hours

45 earthquakes

PS20000815.1(54.5km)

15 Aug

10 hours

7 earthquakes

2005

PS20050119.1(149.4km)

19 Jan

10 hours

6 earthquakes

PS20050121.1(162.0km)

20 Jan

1 day 3 hours

8 earthquakes

2011

PS20110311.2(193.0km)

11 Mar

21 hours

21 earthquakes

PS20110313.1(184.8km)

13 Mar

3 days 13 hours

14 earthquakes

2016

PS20160923.1(156.7km)

22 Sep

18 hours

8 earthquakes

2023

PS20230514.1(101.2km)

14 May

8 hours

8 earthquakes

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Seismic Swarm PS20000629.1 Near Shimoda, Japan: Event Analysis and Regional Context

A seismic swarm designated PS20000629.1 was recorded 61 km south-southeast of Shimoda on Japan’s Izu Peninsula. Activity began at 09:25 on 28 June 2000 and concluded at 09:53 on 29 June 2000, spanning 24 hours and 27 minutes. Ten earthquakes occurred during this interval, all with focal depths of 10 km.

The sequence included the following events: a magnitude 5.3 shock at 09:25:47 on 28 June; magnitude 5.2 at 16:15:17 the same day; magnitude 5.3 at 02:56:20 on 29 June; magnitude 5.3 at 03:11:51; magnitude 5.1 at 03:34:26; magnitude 5.5 at 04:02:36; magnitude 5.3 at 04:53:26; magnitude 5.1 at 05:54:55; magnitude 5.6 at 06:30:22; and magnitude 5.0 at 09:53:28 on 29 June. No single dominant mainshock is evident, consistent with swarm behavior in which events occur in close temporal and spatial proximity without a clear initiating rupture.

The Izu Peninsula lies at the northern terminus of the Izu-Bonin volcanic arc, where the Philippine Sea Plate subducts beneath the Eurasian Plate along the Sagami Trough. This tectonic setting produces frequent moderate-magnitude seismicity and occasional swarms, often linked to fluid migration or stress transfer along shallow crustal faults. Historical records document similar swarm episodes in the region during the twentieth century, reflecting the ongoing convergence rate of approximately 4–5 cm per year.

All events in the 2000 swarm share a uniform 10 km depth, suggesting activation of a discrete fault segment within the upper crust. Magnitudes ranged from 5.0 to 5.6, sufficient to produce felt shaking across the peninsula yet below the threshold for widespread damage. Such clusters contribute to long-term strain release along the plate boundary without generating large destructive earthquakes.

Seismic monitoring in the Izu region has improved since 2000 through expanded networks and real-time processing, yet the fundamental tectonic drivers remain unchanged. Continued observation of swarm characteristics aids in distinguishing tectonic from volcanic signals in this arc setting.

References

SeismoSight internal swarm classification PS20000629.1
USGS Earthquake Catalog (historical regional data)
Geological Survey of Japan, AIST (Izu Peninsula tectonics)