Seismic Swarm S20161113.1 Near Blenheim, New Zealand

A notable earthquake swarm designated S20161113.1 occurred southeast of Blenheim in New Zealand's South Island between 13 and 16 November 2016. The sequence began at 11:49 on 13 November and concluded at 04:47 on 16 November, spanning 64 hours and 58 minutes. During this period, 59 earthquakes were recorded at a location approximately 31 km southeast of Blenheim.

The swarm exhibited a range of magnitudes from 3.8 to 4.9, with the majority clustered between 4.0 and 4.9. Depths varied from 5 km to 22 km, indicating activity within the shallow to mid-crustal levels typical of the region's tectonic setting. Multiple events of magnitude 4.6 to 4.9 occurred in the initial hours, including several closely timed pairs, followed by a gradual decline in frequency and intensity over the subsequent days.

This swarm represents the third such episode documented in the area since 2000. Earlier swarms took place in 2013, with two separate sequences recorded that year. The 2016 event marks the sole swarm identified in its respective year within the historical record.

The Marlborough region, where the swarm was centered, lies within a zone of active deformation along the boundary between the Pacific and Australian tectonic plates. This area features the Marlborough Fault System, a network of strike-slip faults that accommodate oblique convergence. The Wairau Fault, in particular, traverses nearby terrain and contributes to the region's elevated seismicity. Historical geological records show that such fault interactions have produced recurrent seismic activity, shaping the landscape through uplift and lateral displacement over millennia.

Seismic swarms in this setting often reflect fluid migration or stress transfer along fault segments rather than a single mainshock-aftershock sequence. The November 2016 activity aligns with patterns observed in prior events, underscoring the ongoing tectonic adjustment in the northern South Island.

References

GeoNet New Zealand Earthquake Catalogue
USGS Earthquake Hazards Program
GNS Science Geological Maps of New Zealand