KABOOM! Dynamite explosions have given us a detailed glimpse of a geological "lubricant" that aids the movement of Earth's tectonic plates. These plates interlock like a massive jigsaw to make up the planet's outer layer, or lithosphere, which is around 70–100 kilometres deep. Their movement can trigger earthquakes, so gaining a better idea of how they move may aid our understanding of tremors, according to Tim Stern of Victoria University in Wellington, New Zealand.
The plates sit atop a lubricating channel that separates them from the asthenosphere underneath. "Tectonic lubrication is a valid description of what we think happens in this 10-kilometre-thick channel," says Stern. The lubricating layer contains viscous melted rock that allows the plates to move independently of the layers below (see diagram).
Stern and his colleagues directed explosions from Earth's surface down into a zone beneath New Zealand, then captured reflections of the resulting seismic waves to build up images of the base of the tectonic plate (Nature, DOI: 10.1038/nature14146). Previous studies relied on distant, low-frequency seismic waves from real earthquakes, which dramatically limited the resolution. By setting off 12 of their own "mini earthquakes" with dynamite buried in 50-metre-deep shafts, Stern's team got much sharper images with a resolution of less than a kilometre.
"What's so cool is that they've really identified the base of the plate, showing it's shallower and sharper than previous observations," says Catherine Rychert of the University of Southampton in the UK. "No one has been able to image the channel before."
This article appeared in print under the headline "Mini quakes reveal base of tectonic plates"
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