Dr Carolyn Boulton is a structural geologist at Victoria University of Wellington and she sees things in rocks that most of us would never notice. Including finding beauty in greywacke, which is a common, rather ordinary grey rock that most geologists would regard as somewhat dull.
Carolyn’s real passion, however, is earthquakes and the way faults – and greywacke faults in particular – behave.
The Hutt River follows the Wellington Fault, which is surrounded by a damage zone of grey crushed rocks. Photo: Alison Ballance
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Finding faults
A fault is a sliding zone, where two blocks of rock slip past one another during an earthquake. That slipping is often lubricated by fault gouge, a fine-grained clay-like substance that is created by the grinding pressure of the rocks on either side.
Carolyn has become an expert fault hunter, reading the landscape for clues about its past. Last winter she noticed that big floods in the Hutt River had washed away a thick layer of gravels to reveal a new exposure of the Wellington Fault. She has been returning to the site to study it and collect samples of the fault gouge. She will study these small samples in overseas labs under high temperature and pressure, like those experienced within the fault itself, and she hopes the data will shed new light on why faults sometimes slide and sometimes stick.
Eavesdropping on earthquakes
Geophysicists such as Professor Martha Savage, from Victoria University of Wellington, often use seismic noise to visualise what lies beneath the ground. Noise, after all, is just vibrations and seismic noise is the earth vibrating in response to all sorts of things – including earthquakes, as well as wind, people walking and passing traffic.
Geophysicists use seismographs or seismometers to detect this noise and there is a network of these positioned all around the country.
Martha and colleagues have been developing some sophisticated methods that use the background seismic noise collected by this nationwide network of seismic detectors in new ways. These methods can help determine the structure of the earth and they might also be useful in future for developing earthquake detection and early warning systems.
Martha has also been working on an EQC funded project that is installing seismic detectors around Wellington and the Wairarapa next to existing water monitoring stations, to measure how both the ground itself as well as groundwater levels respond during earthquakes.
Prof. Martha Savage installs a seismic noise detector Photo: Supplied / N. Little EQC 1
To learn more:
- If you would like to find out more about seismic noise then head to Claire’s recent story on ‘The hum of the Alpine Fault.’
- Or check out our extensive collection of earthquake-related stories.