The American Geophysical Union meeting highlights student research

Welcome to Temblor’s coverage of the Fall 2020 meeting of the American Geophysical Union (AGU)! Today (Thursday, December 10, for those who follow the tracking), we focus on student-led research that our readers may find interesting. Read on to find out some of our favorites of the day.

Written by Alka Tripathi Lang, Ph.D., science writer (DrAlkaTrip)

Citation: Tripathy-Lang, A., 2020, American Geophysical Union Meeting Highlights Student Research, Temblor, http://doi.org/10.32858/temblor.144

Subduction zone tremors

A doctoral student at the Instituto de Globe de Paris Gaspar Varge studies earthquakes or low-frequency earthquakes in subduction zones. The tremors tell scientists about the movement of fluids, unlike high-frequency (normal-type) earthquakes that indicate the fracturing of rocks. In his poster, Farge and colleagues show a simple model designed to replicate tremor activity at the surface separating an inclined plate from the dominant plate tectonics.

In their model, the subduction interface is fed by a steady, deep water source. In real life, water comes from dehydration reactions, in which water-bearing minerals settle into surface conditions that cut through the rapid subduction path to the mantle, and release water when it undergoes high pressures and transforms into new molecules. This liberated water passes in the channel between the two tectonic plates. FARGE models water pressure accumulator as a valve between areas of low and high permeability. These valves open when the pressure difference between the zones is high enough. Once the primary valve releases its water to the next section of the subduction duct, pressure builds on the adjacent valves, causing the chain to release. Each opening valve acts as a seismic source.

Farge and colleagues compared their model to the distribution of tremors along the subduction zone façade in Guerrero, Mexico, and found that they could replicate tremors’ tendencies to migrate and congregate in time and space. “Our title might sound a little bit simple,” Farge told Temblor, pointing to the query above his poster: Tectonic tremor without slip? However, he and his colleagues are simply exploring the contribution of fluids to subduction processes, and differences in pore pressure appear to be just as important as slip.

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Indiana University doctoral student Elizabeth Sherrill has presented her work in the Nankai Basin, which caused two major earthquakes in the recent past – the 1944 earthquake measuring 8.1 tons and the 1946 Nankai earthquake of 8.4 magnitude. This part of the subduction zone off the coast of Japan is the most used in the world, and includes data dating back to the 1940s.

Sherrill modeled the slip during and after these events, and although this research is ongoing, they have made some interesting observations. Firstly, the slip budget, explained by Sherrill is the amount of movement that must occur on the interface between two moving panels, met in certain places and under what should be in other places. In particular, her model showed that 30 years of seismic slip, a movement without earthquakes that occurs after an earthquake, following massive earthquakes in the 1940s, helps fill in some of the lost slip between 12 to 25 miles (20 to 40 kilometers) down an island Shikoku. It also found that in western Shikoku, the slip is lost at shallow depths. “There might be an additional seismic slip that we couldn’t detect,” says Sherrill. “Or, this region … may explode in a larger, massive earthquake to make up for this lack of slip.”

East African volcano rift and rift modeling

PhD student Joshua Robert Jones of Virginia Tech, studies the rift zone in East Africa. In his poster, find out how changes in Ol Doinyo Lengai, an active carbon volcano, could affect pressure on the nearby Natron fault. “Natron crack, where the lingai crack and natron crack [are] Located, it is one of the smaller rift areas [in this part] Jones told Temblor. Since this is a very small part, he said, “Understanding how tension is transmitted … can help us investigate the initial processes of fracturing.” He said that exploring the stress transition between an active volcano and faults would help scientists better understand how “these risks are affected by changing stress.”

The first Doinyo Lengai. Credit: Clem23 (CC BY-SA 3.0)

In his poster, Jones designed volcano and faults using PyLith, an open-source program that allows users to simulate crust distortion and troubleshoot faults. In his model, he altered magma chamber size, topography and material properties, which acted as a proxy for lithology. Then compare the models and calculate the pressure difference between them. Based on these preliminary results, the presence of the terrain should result in the most significant change in pressure on the Natron fault, with the potential for magma chamber size also to play a role.

For now, Jones and colleagues are comparing a flat model to that of Ol Doinyo Lengai. “We are not able to have dynamic terrain that changes with inflation and deflation,” he said, “however [seeing how] Change in terrain during the impulse cycle will affect stress transmission [would be interesting]. “He said that the size and tube of magma in Lengai’s magma chamber is not well constrained, which is why they have designed different sizes of magma chamber. The next step of this work is to define uncertainties, and the project is ongoing.”

Another virtual day in AGU

The samples above are just a small part of the interesting and important work that graduate students presented today at Arabian Gulf University. Other notable work includes this talk by Sydney Deping, a student at the University of Oregon, who wakes up at 4:00 a.m. to discuss her work on characterizing early earthquake rupture using instruments placed deep in wells to measure stress. She wants to know “when can we find out how big an earthquake is.” A poster by Doctor Simona Colombelli of the University of Naples Federico II discussed the same question as Dybing’s work, but focused on seismic data. Spoiler alert: It says it’s possible. Had it been in the actual poster hall, her next-door neighbor, Haoran Meng of the University of California, San Diego, would have argued the opposite of that a few meters away – that how the earthquake started has little effect on how large it becomes.

Thank you for joining Temblor’s coverage of the Fall 2020 AGU Virtual Meeting.

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