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Two of the most destructive forces in nature – earthquakes and tsunamis – can be a bigger threat than thought

Tsunami Illustration

Two of the most destructive forces of nature – earthquakes and tsunamis – may actually be more of a threat than current estimates, according to new research conducted by researchers at the University of New Mexico and Nanyang Technological University published today (May 3, 2021

) in Nature Geoscience is a monthly peer-reviewed scientific journal published by the Nature Publishing Group, covering all aspects of geoscience, including theoretical research, modeling, and fieldwork. Other related work is also published in areas including atmospheric science, geology, geophysics, climatology, oceanography, paleontology and space science. It was established in January 2008.
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The researchers developed a new method for assessing earthquakes and tsunami hazards represented by the farthest part of offshore subduction zones and found that the hazard may have been systematically underestimated in some areas, meaning that tsunami risk assessments should be reoriented given the new findings. The results have important implications for reducing the risk in affected areas around the world, including Southeast Asia and the Pacific Rim, in the event of future earthquakes and tsunamis.

Megathrust earthquakes are among the most powerful earthquakes experienced around the world and occur in subduction zones where two tectonic plates converge and one slides beneath the other. The plates move continuously towards each other, but if the interface or the fault between them is stuck, a slip deficit builds up over time. Like a debt, this slip deficit must eventually be paid, and for tectonic plates, payday is earthquake day. When these earthquakes affect the lowest part of the fault near the seabed, they have the potential to move the seabed upwards and create devastating tsunamis.

Understanding the potential rupture behavior of megatrusters, especially in the low offshore part of the fault, where most destructive tsunamis are generated, is therefore a critical task for geoscientists predicting the dangers of seismic and tsunami floods. The probability of seismic behavior is often assumed to be somewhat low in the low part of the fault, based on laboratory investigations of recovered fault zone material.

GPS Station P028

Located in the desert of northern New Mexico, data from GPS site P028 contribute to geological surveys of the Rio Grande Rift. A continental rift is a place where the earth’s crust is pulled very slowly apart. Credit: UNAVCO

The speed of the fault for building slip deficits can also be measured using geodetic observations that track how the earth’s surface moves over time, for example using very accurate GPS sensors installed on land along with a model that tells how to drop the fault. affects the movement of these stations. However, it is difficult for scientists to use this technique to “see” what is going on in the lowest part of the fault because it is far from land, below kilometers of water, where traditional GPS instruments cannot work.

Now, researchers at the University of New Mexico and Nanyang Technological University (NTU) in Singapore have developed a new geodetic method to derive this value, which accounts for the interaction between different parts of the fault, resulting in a much more physically accurate result. Lindsey’s team noted that previous models have not taken into account the fact that if the deep part of the fault is stuck between earthquakes, the low part can not move either – it is in what they call a ‘stress shadow’, and there is no build-up of energy available that causes it to slip. Taking this effect into account, the team developed a technique that uses the same land-based data but results in a huge improvement in their ability to “see” the fault slip in the areas furthest from the coast, allowing scientists to reassess danger. from offshore parts of subduction zones most prone to tsunami formation.

“We applied this technique to Cascadia and Japan subduction zones and found that where deeper locked spots are present, the low fault must also have a high slip deficit – regardless of its own friction properties,” said Eric Lindsey, an assistant professor at the UNM Department of Earth and Planetary Sciences, who conducted the research while at the Earth Observatory of Singapore at NTU. “If these areas can slide seismically, the global tsunami danger could be higher than currently recognized. Our method identifies critical locations where seabed observations could provide information on friction properties at these faults to better understand their sliding behavior. ”

This study is important because it requires a reassessment of previous models of tsunami danger on mega-threats worldwide. Because this can be done with existing data, the reassessment can also be performed relatively quickly. Hopefully this will lead to better preparedness among coastal communities for future events.

Reference: May 3, 2021, Natural geoscience.
DOI: 10.1038 / s41561-021-00736-x

Other institutions involved in the research include the School of Earth Sciences, Energy and Environment, Universidad Yachay Tech, (Ecuador) and the Department of Earth and Planetary Science at the University of California Berkeley. The study is supported by, among others, the National Research of Singapore, the Ministry of Education in Singapore and the National Science Foundation.

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