China is setting out to chart an exquisitely detailed subterranean atlas across the country’s vast expanse. The $1 billion, 6-year survey, which will involve thousands of researchers from scores of institutions, is motivated not only by the nation’s hunger for natural resources, but also by fundamental science questions, including long-standing puzzles about India’s slow-motion collision with Eurasia and the rise of the Tibetan Plateau.
The initiative, SinoProbe II, was previewed last month at the DEEP-24 symposium in Beijing. Beginning in early 2025, researchers plan to deploy thousands of instruments and drill holes to record-setting depths, all with the goal of creating a 3D map of the rock layers kilometers below the surface. The scope of SinoProbe II—successor to SinoProbe I, a coarser survey that ran from 2008–16—“is mind-boggling,” says Larry Brown, a geophysicist at Cornell University. “I can’t think of any kind of geoscience it doesn’t cover, except atmospheric sciences.” Mian Liu, a geophysicist at the University of Missouri, says, “Sinoprobe II will give us a much better understanding of planet Earth.”
Priority No. 1 for the project, which is managed by the China Geological Survey, is to help the country wean itself off imported fossil fuels and ores such as iron and aluminum. “We need to firmly grasp resource security,” says Dong Shuwen, a geologist at Nanjing University who conceived SinoProbe. He notes that China’s shallower natural resources, within 500 meters of the surface, “are almost depleted.” Echoing an ongoing U.S. mineral survey called the Earth Mapping Resources Initiative, SinoProbe II aims to chart ore formations and fossil fuel basins as deep as 3 kilometers and develop extraction technologies. “That’s where China’s investment in SinoProbe II can see some immediate returns,” Liu says.
The prospecting could also benefit green technologies. It will hunt for critical minerals needed for solar panels, wind turbines, and electric vehicle batteries; traps of naturally occurring hydrogen gas that could be tapped for the carbon-free fuel; and strata of porous rocks in which carbon dioxide could be sequestered for the long term. A further societal benefit will be a refined map of earthquake-prone faults. “The data should provide plenty of grist for earthquake prediction,” says Jeffrey Park, a seismologist at Yale University.
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. The campaigns led to the discovery, for example, of uranium reserves in the lower Yangtze River Basin and a major molybdenum-tungsten deposit in the Nanling Mountains in southern China.
In SinoProbe II, researchers will conduct active seismic studies on a grand scale, collecting 20,000 kilometers of seismic profiles. By comparison, SinoProbe I was an incomplete sketch, Brown says. “Suppose all we knew about the western United States was what Lewis and Clark jotted in their journals.”
To plumb deeper structure all the way down to Earth’s core, SinoProbe II will rely on several thousand “passive” seismometers across China, listening for earthquakes near and far. 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. A comparable U.S. venture called EarthScope, a $200 million, 20-year-long effort to map the North American underworld that wrapped up field studies a few months ago, spaced seismometers 70 kilometers apart. SinoProbe II’s network will be twice as dense, with sensors placed 35 kilometers apart for higher resolution.
The network will be moved around the country over time, and first up is the Tibetan Plateau. “The plans to instrument all of Tibet are particularly ambitious and exciting, as this is one of the most tectonically active regions on Earth,” says James Hammond, a seismologist at Birkbeck, University of London. “It will be an epic challenge,” he says, to deploy such a dense network across the high-altitude terrain with scant infrastructure.
Another prong of SinoProbe II is a pair of magnetotelluric (MT) arrays, in which sensors measure surface electric and magnetic fields to gauge conductivity in the crust and mantle. “It’ll be like gold to have another set of continental data,” says Adam Schultz, a geophysicist at Oregon State University who led EarthScope’s MT campaign. The U.S. MT data had an unexpected payoff: a deeper understanding of the risks of space weather events, which induce geoelectric currents that can fry electrical grid infrastructure. The risk was thought to increase toward the poles, where Earth’s magnetic field funnels solar storms. EarthScope instead pointed to surprising vulnerabilities in hard, conductive rocks at lower latitudes, Schultz says, including along the Eastern Seaboard. Similar surprises could come out of SinoProbe II, Dong says.
Dong is especially excited about SinoProbe II’s third prong: ultradeep drilling. In 2018, Chinese geoscientists reached a depth of 7018 meters with their SK-2 drill site in Heilongjiang province in northeastern China. Starting in 2027, SinoProbe II will set out to drill more than 10 kilometers deep. It will also hone the technology to reach 13 to 15 kilometers, where it can be nearly hot enough to melt lead and pressures are higher than those in the deepest ocean trenches. Such stygian depths would beat the reigning drilling champion: the 12.2-kilometer Kola Superdeep Borehole drilled by the Soviet Union. One candidate site is in Tibet, Dong says, where sediment cores “could offer a record of the whole process of formation of the Tibetan Plateau.”
