Campus researchers conduct productive ‘CT scan’ beneath Earth’s surface

Berkeley Seismological Laboratory/Courtesy
Campus researchers gathered data from numerous earthquakes around the world to compile a model of Earth's interior structure.

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With a paper published Thursday, UC Berkeley researchers have conclusively mapped the inner workings of hot, rocky channels deep below ground, in the process unearthing a connection that has long eluded scientists.

Barbara Romanowicz, a professor in the campus department of earth and planetary science, and former UC Berkeley doctoral student Scott French — who is now an alumnus — used seismic data and supercomputers to produce the clearest image yet of the chutes through which hot rock travels.

Their results established a connection between massive plumes of hot rock below ground and volcanic hot spots — long hypothesized to form chains of volcanic islands such as Hawaii and Iceland — formalizing a conclusion debated by earth scientists for decades.

“Hot material rises, but there is a long standing question about whether material rises all the way from the base of the mantle,” said Bruce Buffett, campus professor in the earth and planetary science department, in an email. Buffett noted that some scientists have argued that hot spots draw their material from shallow pools beneath the earth’s surface, while others hypothesized that the plumes did not exist at all.

The chutes transport solid hot rock, as opposed to liquid magma, in a manner analogous to the flow of glaciers and at a rate of centimeters per year, French said in an email.

Seismologists working with the study’s process — akin to computer tomography, or CT imaging — had postulated that deep chutes of hot rock were linked to volcanic hot-spot islands, such as Hawaii or Samoa in the Pacific, but earlier renderings failed to prove the link conclusively.

“While a CAT scan uses X-rays and beams X-rays at you from many different directions … we used seismic waves,” French said.

French said their study examined seismic waves at a variety of speeds as they passed through different regions of the mantle, allowing them to make inferences about the materials’ temperature and plate tectonics. Included in the data French and Romanowicz analyzed were more than 200 powerful earthquakes over the past two decades.

Seismologists have used computer imaging to map Earth’s interior for several decades, but the supercomputer technology used in the study allowed for a precise, unambiguous image, overcoming shortcomings of earlier seismic tomography, according to French.

Romanowicz and French additionally discovered that plumes are “unusually broad,” leading to questions about their exact composition or the speed of convection in the mantle.

“We didn’t expect these things to be so thick,” Buffett said in an email. “Other (scientists) will now try (to) understand the dynamics that allows these features to form.”

French anticipates additional discoveries in seismology and earth sciences as more researchers use supercomputers to create higher-resolution images and models of the earth’s interior structure.

Contact Anna Sturla at [email protected].