Seismological study provides insight into composition and thermal state of Earth's lower mantle https://phys.org/news/2023-07-seismolog ... state.html
by Ma Xuange, University of Science and Technology of China
China
A research team led by Professor Wu Zhongqing from the School of Earth and Space Sciences at the University of Science and Technology of China of the Chinese Academy of Sciences has made a significant breakthrough in constraining the material composition and thermal state of the Earth's lower mantle.
Their research findings, titled "Compositional and thermal state of the lower mantle from joint 3D inversion with seismic tomography and mineral elasticity," were published in the journal Proceedings of the National Academy of Sciences.
The Earth's interior can be roughly divided into the crust, upper mantle, lower mantle, and core. The lower mantle, located at depths ranging from 660 to 2,890 km below the surface, comprises a substantial portion of the Earth's volume and mass. It plays a critical role in the planet's structure and dynamics.
Previous seismological studies have revealed variations in seismic wave velocities within the lower mantle, including large-scale low shear wave velocity provinces (LLSVPs) beneath Africa and the Pacific. However, the nature, origin, and implications of these anomalies remain incompletely understood. Therefore, obtaining a comprehensive understanding of the spatial distribution of material composition and temperature within the lower mantle is crucial for unraveling the Earth's formation, evolution, and dynamics.
Carbon Dioxide – Not Water – Triggers Explosive Basaltic Volcanoes August 7, 2023
Introduction:
(Eurekalert) ITHACA, N.Y. – Geoscientists have long thought that water – along with shallow magma stored in Earth’s crust – drives volcanoes to erupt. Now, thanks to newly developed research tools at Cornell, scientists have learned that gaseous carbon dioxide can trigger explosive eruptions.
A new model suggests that basaltic volcanoes, typically located on the interior of tectonic plates, are fed by a deep magma within the mantle, stored about 20 to 30 kilometers below Earth’s surface.
The research, which offers a clearer picture of our planet’s deep internal dynamics and composition, with implications for improving volcanic-hazards planning, published August 7, 2023 at 3:00pm ET in the Proceedings of the National Academy of Sciences.
“We used to think all the action happened in the crust,” said senior author Esteban Gazel, the Charles N. Mellowes Professor in Engineering in the Department of Earth and Atmospheric Sciences, in Cornell Engineering. “Our data implies the magma comes directly from the mantle – passing fast through the crust ¬– driven by the exsolution (the process phase of separating gas from liquid) of carbon dioxide.
“This completely changes the paradigm of how these eruptions happen,” Gazel said. “All volcanic models had been dominated by water as the main eruption driver, but water has little to do with these volcanoes. It’s carbon dioxide that brings this magma from the deep Earth.”
Mountain ranges play a key role in global climate, altering weather and shaping the flora and fauna that inhabit their slopes and the valleys below. As warm air rises windward grades and cools, moisture condenses into rain and snow. On the leeward side, it's quite the opposite. Deserts prevail, a phenomenon known as rain shadow. Thus, the way mountain ranges form is a matter of intense interest among those who study and model climates of the past.
That debate will soon grow more heated with a new paper in the journal Nature Geoscience. A team of researchers at the Stanford Doerr School of Sustainability has adapted a technique used to study meteorites to measure historic altitudes in sedimentary rocks to show that one of the world's most familiar mountain ranges, the Himalayas, did not form as experts have long assumed.
"The controversy rests mainly in what existed 'before' the Himalayas were there," explains Page Chamberlain, professor of Earth and planetary sciences and of Earth system science at the Doerr School of Sustainability, and senior author of the study. "Our study shows for the first time that the edges of the two tectonic plates were already quite high prior to the collision that created the Himalayas—about 3.5 kilometers on average."
"That's more than 60% of their present height," added Daniel Ibarra, Ph.D., a postdoctoral researcher from Chamberlain's lab, first author of the paper, and now an assistant professor at Brown University. "That's a lot higher than many thought and this new understanding could reshape theories about past climate and biodiversity."
At the very least, the findings mean that ancient climate models will have to be recalibrated, and it will likely lead to new paleoclimatic assumptions about the Himalayan region of Southern Tibet, an area known as the Gangdese Arc. It could also beget closer scrutiny of other key mountain ranges, such as the Andes and the Sierra Nevada.
For more than 30 years, the models that researchers and government agencies use to forecast earthquake aftershocks have remained largely unchanged. While these older models work well with limited data, they struggle with the huge seismology datasets that are now available.
To address this limitation, a team of researchers at the University of California, Santa Cruz and the Technical University of Munich created a new model that uses deep learning to forecast aftershocks: the Recurrent Earthquake foreCAST (RECAST). In a paper published today in Geophysical Research Letters, the scientists show how the deep learning model is more flexible and scalable than the earthquake forecasting models currently used.
The new model outperformed the current model, known as the Epidemic Type Aftershock Sequence (ETAS) model, for earthquake catalogs of about 10,000 events and greater.
"The ETAS model approach was designed for the observations that we had in the 80s and 90s when we were trying to build reliable forecasts based on very few observations," said Kelian Dascher-Cousineau, the lead author of the paper who recently completed his Ph.D. at UC Santa Cruz. "It's a very different landscape today." Now, with more sensitive equipment and larger data storage capabilities, earthquake catalogs are much larger and more detailed
"We've started to have million-earthquake catalogs, and the old model simply couldn't handle that amount of data," said Emily Brodsky, a professor of earth and planetary sciences at UC Santa Cruz and co-author on the paper. In fact, one of the main challenges of the study was not designing the new RECAST model itself but getting the older ETAS model to work on huge data sets in order to compare the two.
