The link between temperature, drought and tectonic tremors in Alaska

A Kobe University research group has highlighted how low-frequency tectonic tremors occur; These findings will contribute to better predictions of future giant earthquakes.

In addition to the merging Pacific plate, the Alaskan subduction zone also features a submerged oceanic plateau called the Yakutta terrain. Low-frequency tectonic tremors, a type of slow earthquake, have only been detected in the Yakutta sloping terrain. However, the mechanism by which these events occur is not well understood.

Researchers at Kobe University conducted a 3D thermal digital simulation of convection in the Alaskan subduction zone with the aim of revealing the mechanism behind these low-frequency tremors. Based on the 3D thermal structure obtained from the simulation, and the signals of the hydrated minerals in the slab, the researchers calculated the water content distribution and compared the results of these calculations in the area where the tremors occur.

The results showed the presence of high levels of aridity in the marine sediment layers and ocean crust in the earthquake zone. Researchers believe that the reason for the occurrence of tremors in the Yakutat terrain is that the layers of marine sediment and ocean crust are thicker there, which means that the level of dryness is higher than in the west of the adjacent Pacific Plate (where tectonic tremors do not occur).

The Kobe University research group consisted of second-year master’s student IWAMOTO Kaya (Department of Planetary Science, Graduate School of Science), academic researcher SUENAGA Nobuaki and Professor Yoshida Shuichi (both from the Center for Urban Safety and Security Research).

These results were published in the online British scientific journal “Scientific Reports” (Nature Publishing Group) on 14 April 2022.

the main points

Elucidating the mechanism by which low-frequency tremors occur is important for understanding the plate subduction process. It is believed that this will also help shed light on how shallow giant earthquakes occur. In this study, the research group built a 3D thermomechanical model of the Alaskan subduction zone and calculated the maximum aridity water content and aridity level. Drought levels from the marine sediment layers and ocean crust of the subducted plate were highest in the region of low-frequency tremors. Therefore, water expelled from the merging plate is thought to contribute to these tectonic tremors.

Search background

An oceanic plateau called the Yakutat terrain descends into the Alaskan subduction zone. Low-frequency tectonic tremors occur at this slope plateau. The region where slow earthquakes (such as low-frequency tectonic tremors) occur is deeper and adjacent to the region where super earthquakes occur, suggesting a link between the two. Therefore revealing the mechanism behind how low-frequency tectonic tremors occur is important for understanding the occurrence of different earthquake events in subduction zones. This research group built a 3D thermomechanical model of the Alaskan subduction zone so that they could check the temperature and level of aridity in regions close to where the low-frequency tremors occur.

Research Methodology

The researchers performed a 3D thermo-numerical simulation of the subduction of the Yakutta terrain and the Pacific Plate in the Alaskan subduction zone. It is believed that when the Pacific plate subsides, it brings the hydrated minerals in the plate into the deep regions of high temperature and high pressure, and these conditions cause a dehydration reaction as the water is expelled from the hydrated minerals. Based on the 3D thermal structure obtained from numerical simulations, the researchers determined the dryness levels of the hydrated minerals in the slab. From these results, it was understood that in the low-frequency tremors region, a large amount of water is expelled due to the high temperature and high pressure conditions causing drought-degradation reactions. It is believed that low-frequency earthquakes do not occur in the Pacific plate because it has thin layers and therefore suffers from little drought. On the other hand, the ocean crust and marine sediment layers in the Yakut terrain are relatively thicker, which means that it experiences high levels of aridity. The researchers concluded that this is why low-frequency tectonic tremors occur only in sapphire terrain.

More research

In 1964, a massive earthquake occurred in Alaska. This is the largest earthquake that occurred in the Alaskan subduction zone and the second most powerful earthquake ever recorded in world history. The low-frequency tectonic tremors that were the subject of this research occur near the epicenter of the 1964 earthquake, at the lower slope of the plate front. Next, the research group will continue to make thermomechanical models of different subduction zones to search for global and regional characteristics of the causal mechanisms behind massive undersea earthquakes and slow earthquakes. This research will contribute to a better understanding of how earthquakes occur and our ability to predict massive earthquakes in the future.

glossary of terms

1. Low-frequency tectonic tremors: A seismic event characterized by lower-frequency seismic waves than an ordinary earthquake.

2. Slow earthquake: the phenomenon of fault slippage at a slower speed than an ordinary earthquake.

3. Oceanic plateau: a relatively flat area on the sea floor.

4. Plate: refers to the split plate.

5. Hydro minerals: Minerals containing OH groups in their crystalline structure.

6. Dehydration decomposition reaction: As the plate erupts, the resulting temperature and pressure lead to phase shifts of hydrated minerals and expulsion of water.

Story source:

Materials provided by Kobe University. Note: Content can be modified according to style and length.

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