Hawaiian earthquake swarm caused by magma moving across ‘seals’ – Eurasia Review

Magma pumping through a huge complex of flat, interconnected chambers deep within Hawaii’s volcanoes appears to be responsible for an unexplained swarm of small earthquakes that have been felt on the Big Island over the past seven years, particularly since the 2018 eruption and collapse of the Kulauea summit.

Pancake-like chambers, called “sills,” channel magma laterally and upward to recharge the magma chambers of at least two of the island’s active volcanoes: Mauna Loa and Kuluea. Using a machine learning algorithm, geoscientists at Caltech were able to use data collected from seismic stations on the island to map the structure of the sills, mapping them with unprecedented precision and demonstrating that they connect volcanoes.

Furthermore, the researchers were able to monitor the progression of magma as it hurtled upwards through the sills, linking this to Kīlauea’s activity. They analyzed the period ending in May 2022, so it’s not yet possible to say if they can detect the magma flow that led to Mauna Loa’s November 27 eruption, but the team plans to look into that next.

“Prior to this study, we knew very little about how magma was stored and transported deep in Hawaii. Now, we have a high-resolution map of an important part of the plumbing system,” says John D. science. The study marks the first time that scientists have been able to observe the structure of magma deep within Earth. “We know very well what magma is doing in the shallow part of the system above 15 kilometers deep, but until now, everything below that has been a matter of speculation,” says Wilding.

With data on more than 192,000 small (less than 3.0 magnitude) tremors that occurred over a 3.5-year period from 2018 to mid-2022, the team was able to plot more than a dozen tremors stacked on top of each other. The largest is about 6 kilometers by 7 kilometers. The sills tend to be about 300m thick, and separated by about 500m.

“Volcanic earthquakes are typically characterized by their small size and frequency during magmatic disturbances,” says Weiqiang Zhu, a postdoctoral researcher in geophysics and co-lead author of the Science paper. “We are excited about recent advances in machine learning, particularly deep learning, that are helping to accurately detect and quantify these small seismic signals that have been recorded by dense seismic networks. Machine learning can be an effective tool for seismologists to analyze large archived datasets, and to identify patterns in small earthquakes, and gain insights into underlying structures and physical mechanisms.”

Wilding and Zou worked with Jennifer Jackson, William E. Leonhard Professor of Metallurgical Physics. Zachary Ross, Associate Professor of Geophysics and William H. Hurt Scholar; Both are senior authors on the paper. In October, Ross was selected as one of the 2022 Packard Science and Engineering Fellows, which will provide funding to support this research moving forward.

The team didn’t have to put together a single piece of hardware to conduct the study; Instead, they relied on data collected by United States Geological Survey seismographs on the island. However, a machine learning algorithm developed in Ross’s lab gave them an unprecedented ability to separate signal from noise—that is, to clearly identify earthquakes and their locations, creating a kind of three-dimensional “point cloud” that shows thresholds.

“It’s similar to taking a CT scan [computerized tomography] Scanning, the way a doctor can visualize inside a patient’s body,” says Ross. “But instead of using controlled sources with X-rays, we use passive sources, which are earthquakes.”

The team was able to classify about 10 times as many earthquakes as previously possible, and they were able to locate them with a margin of error of less than a kilometer; Previous sites have been determined with margins of error of a few kilometres. The work was done with a deep learning algorithm taught to detect earthquake signals using a training dataset of millions of pre-selected earthquakes. Even with small earthquakes, which may not stand out to the human eye on a seismogram, the algorithm detects patterns that distinguish earthquakes from background noise. Ross previously used this technique to reveal how a natural injection of fluid underground drove a four-year-old earthquake near Cahuila, California.

The thresholds appear to be at depths of approximately 36 to 43 kilometers. (For reference, the deepest depth humans have ever dug into the ground is just over 12 kilometers.) Scientists have long known that phase boundaries exist about 35 kilometers below Hawaii; At this stage boundary, a rock with the same chemical composition transitions from one group of minerals above to a different group below. By examining the new data, Jackson realized that transformations occurring in this rock combined with magma injection could host chemical reactions and processes that compress or weaken the rock, possibly explaining the presence of sills–and, by extension, active seismic activity.

“The transition of spinel to plagioclase within the lithospheric rock may occur through diffuse migration, entrapment, and crystallization of molten magma within the shallow sub-Hawaiian lithosphere mantle,” says Jackson. “Such aggregates can exhibit transient weakening caused by coupled deformation and chemical interactions, which can facilitate crack growth or activate faults. Repeated magma injections will continuously modify grain sizes in the sill complex, prolonging seismic deformation conditions in the rocks. It could This process exploits lateral differences in force to produce and preserve the laterally integrated seismic features that we observe.”

Researchers say it’s unclear whether the sills below the Big Island are unique to Hawaii or whether this type of volcanic structure is common. “Hawaii is the best-watched island in the world, with dozens of seismic stations giving us a window into what’s going on below the surface. We have to wonder, how many other locations is this happening?” says Wilding.

It is also unclear how the movement of magma causes small earthquakes. Earthquakes delineate structures, but the actual mechanism of earthquakes is not well understood. Researchers say that injecting a lot of magma into space causes a lot of stress.

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