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New Zealand research features in international journal - 27/04/2007

Groundbreaking research by New Zealand scientists into earthquakes in the lower crust of the Earth has been published by the prestigious international scientific journal Nature.

The paper by Martin Reyners and Donna Eberhart-Phillips from GNS Science, and Graham Stuart from the University of Leeds, provides a novel explanation of why earthquakes are sometimes observed in the lower crust of the Earth where this crust is rifting apart. These earthquakes occur at a depth of 15 to 40 kilometres and have long puzzled seismologists, as the crust in this depth range has always been thought to be too hot to support the brittle failure which occurs during earthquakes.

Dr Reyners says the paper concentrates on a band of lower crustal earthquakes at the southern end of the Taupo Volcanic Zone, in the vicinity of Mt Ruapehu. These earthquakes range in magnitude from 1 to 5, and the vast majority are too small to have been felt. However, by installing a dense seismograph network above these small earthquakes, the authors have been able to construct three-dimensional images of the physical properties of the crust. The technique used is called seismic tomography, and has similarities to a medical CAT scan. This imaging has shown that fluids, including those released from the top of chilling magma bodies, are the most likely cause of the earthquakes. Such fluids weaken pre-existing faults in the lower crust, which then slip and produce earthquakes.

Dr Reyners says around 5000 earthquakes were recorded during field work at the site in 2001 and analysis of the data has been continuing since then.

“There is a lot of interest worldwide in our work and the very powerful images we have been able to produce. This will become a data set of choice for scientists for many years to come,” says Dr Reyners.

“We’re delighted with the coverage in Nature. It’s the scientific equivalent of being on the cover of Rolling Stone,” says Dr Reyners.

The GNS study is the first to relate lower crustal earthquakes to high-fidelity, three-dimensional images of physical properties within the crust. Insights from the study will also apply to other regions of the world where the crust is rifting apart.

The research was funded by the Foundation for Research, Science and Technology with contributions from the University of Leeds, and the Royal Society of London.

Philip Aldridge, Central and Southern Regional Manager for the Foundation says having the work published in Nature confirms the quality of scientific research carried out in New Zealand and will help raise the global profile of New Zealand’s science capability