January 24, 2024

Team Profile:
Using natural seismic activity to map the subsurface

Bethany Hughes

photo credit:
Bethany Hughes

We're using natural seismic activity to gain insights into earthquake source mechanisms, faults, fluid pathways, and reservoir geometry and extent.

Seismic activity in geothermal fields is a natural occurrence influenced by fluid dynamics, magmatic processes, regional tectonics, as well as a result of harnessing steam and fluids for energy production. The characteristics of geothermal earthquakes can be utilised to understand the nature of the system and ultimately optimise production.

Late last year, we deployed a dense, temporary seismic network near Wairakei and Taupō. The Wairakei Earthquake and Tomography Array (WETA) is a collaboration between Te Herenga Waka – Victoria University of Wellington, The Australian National University, AuScope, Contact Energy, and Geothermal the Next Generation. Funding from Toka Tū Ake - EQC and Te Herenga Waka – Victoria University of Wellington enabled the team to bring the equipment to Aotearoa New Zealand.

The network consisted of 96 short-period nodes concentrated over the geothermal field, and 51 broadband nodes distributed over the wider region. The network continuously monitored seismicity from early-September to early-October 2023. Following a redeployment in mid-October, 25 short-period nodes and 50 broadband nodes continued to record seismicity until mid-November. 

Locations of WETA nodes operating between September-October 2023, and existing GeoNet stations.
Finn Illsley-Kemp installing a short-period node near Te Mihi Power Station (Photo: Bethany Hughes)

The data will be utilised for both seismic tomography and characterisation of seismicity in Wairakei and Taupō. The high density of the array allows for reliable detection of small magnitude events, which improves the precision of earthquake location and focal mechanism solutions. The wide distribution of nodes enhances depth resolution.

In this project, a catalogue of two months of seismicity at Wairakei will be constructed and characterised by precise earthquake locations, magnitudes, and focal mechanisms. Researchers at the Australian National University will use the nodal array to image the shallow (<5 km) seismic velocity structure of the geothermal system.

The outcomes of our research will be useful for refining conceptual models of the geothermal system, offering valuable insights for optimising production strategies.

Chengxin Jiang (ANU) demobilising a short-period node near Te Mihi Power Station (Photo: Bethany Hughes)
Liam Bramwell and Bethany Hughes installing a broadband node - with some helpers! (Photo: Finn Illsley-Kemp)

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field work
seismic tomography

Further Updates