Location:

Period:

24 Aug 2001 11:04:37 - 24 Aug 2001 21:40:44 (10 hours 36 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.1; 295 km NE of Gisborne, New Zealand; (21 Aug 2001) (20km from the swarm center)

7 swarms found nearby.

2001

PS20010822.1(1.5km)

21 Aug

1 day 13 hours

8 earthquakes

2011

PS20111118.1(117.3km)

18 Nov

5 hours

6 earthquakes

2016

PS20160901.1(118.2km)

31 Aug

1 day 4 hours

21 earthquakes

2020

PS20200126.2(134.5km)

25 Jan

14 hours

5 earthquakes

2021

PS20210304.1(115.5km)

4 Mar

3 days 9 hours

34 earthquakes

S20210304.1(74.6km)

4 Mar

6 days 0 hours

188 earthquakes

PS20210311.1(87.1km)

11 Mar

1 day 6 hours

6 earthquakes

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Seismic Swarm PS20010824.1 Northeast of Gisborne, New Zealand

On 24 August 2001, a seismic swarm designated PS20010824.1 occurred approximately 286 km northeast of Gisborne, New Zealand. The sequence began at 11:04 and concluded at 21:40, encompassing five earthquakes over a period of 10 hours and 36 minutes. All events were recorded at depths between 33 km and 36 km, with magnitudes ranging from 5.0 to 5.8.

The individual events unfolded as follows: a magnitude 5.2 earthquake at 11:04:37, followed later by two magnitude 5.4 events at 21:16:35 and 21:19:11. These were succeeded by a magnitude 5.8 shock at 21:34:00 and a final magnitude 5.0 event at 21:40:44. The swarm took place in a tectonically active offshore region associated with the Hikurangi subduction zone, where the Pacific Plate subducts beneath the Australian Plate.

This area has a well-documented history of seismic activity driven by plate convergence rates of approximately 4–5 cm per year. The 2001 swarm occurred shortly after a magnitude 7.1 earthquake on 21 August 2001, centered about 295 km northeast of Gisborne and roughly 20 km from the swarm's focal area. Such sequences can reflect stress adjustments along the subduction interface or within the overlying plate.

Geological records indicate that the Hikurangi Margin has produced numerous moderate to large earthquakes throughout the Holocene, including events capable of generating tsunami. The 2001 activity aligns with patterns of clustered seismicity observed in subduction settings worldwide, where swarms often occur without a single dominant mainshock.

Since 1 January 2000, only one swarm has been identified in this specific offshore sector according to internal classifications. No additional swarms have been recorded in the immediate vicinity through the present. The region continues to experience background seismicity consistent with ongoing subduction processes.

References
GNS Science. Hikurangi subduction zone overview. https://www.gns.cri.nz
USGS Earthquake Catalog. Search results for northeastern offshore New Zealand, 2000–2024. https://earthquake.usgs.gov
New Zealand National Seismic Hazard Model, 2022 update. GNS Science.