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“We can use the ambient seismic vibrations and analyze the speed of seismic waves to sense the aquifers,” he said.

Vidale said he was busy studying graphs that record ground vibrations caused by seismic waves when one data set “curiously stood out from the rest.”

To get a sharp picture of the crust near the surface, the project will build on active-source seismic profiling carried out during SinoProbe I. In more than a dozen provinces, researchers laid geophones and seismometers along a transect, set off explosions at the surface, and charted the seismic waves reflected back to the surface by buried rock layers.

By charting how rock layers slow or accelerate the seismic waves, the instrument network could reveal hot plumes of rock rising from the mantle, cool blobs dripping off the keels of buoyant continents, and dead slabs of ocean crust that plunged into the mantle long ago.

By measuring how fast seismic waves travel, scientists have worked out what material they are most likely to be moving through.