Geologists Solve Tectonic Mystery with Explosives

Local geologists may have finally explained how tectonic plates shift by blowing up hundreds of kilograms of dynamite in a 100km line from Glendhu Rocks in the Wairarapa to Queen Elizabeth Park on the Kapiti Coast.

The seismic waves produced by the subsequent explosion reached the base of the tectonic plate and rebounded to the surface, where they were recorded by 1200 portable seismographs, on loan from the United States and Japan.

Because seismic waves encode information about each of the layers they pass through, an international team of researchers was able to use them to produce detailed images of what lies beneath the earth’s surface.

The data enabled the scientists to deduce that the Pacific Plate is 73km thick beneath the lower North Island, thinner than some earlier predictions.

Detonating 500kg of dynamite – the equivalent of more than 2600 sticks – provided far sharper echoes than recording seismic waves produced by earthquakes, Victoria University researcher Tim Stern said.

Stern told the New Zealand Herald that this country was an ideal testing ground for the experiment.

“The eastern North Island presents a specially favourable location for this study because the oceanic Pacific plate comes and dips beneath the country at such a shallow angle – 12-15 degrees – and it’s very shallow at 15-30km deep,” Stern said.

“In comparison, for example, the Pacific plate beneath eastern Honshu in Japan is more like 60-80km deep and dipping at 40 degrees.”

The results are published in the latest issue of the renowned scientific journal, Nature.

Original article by Michael Safi, The Guardian, February 5, 2015.

Photo by Diana Plater/AAP.