Two of nature’s most destructive forces – earthquakes and tsunamis – may in fact pose a greater threat than current estimates, according to a new study by scientists from the University of New Mexico and Nanyang University of Technology published today (May 3, 2021
“class =” glossaryLink “> Nature Geoscience.
Researchers have developed a new method for assessing the dangers of earthquakes and tsunamis presented by the outermost part of the offshore subduction zones and found that the danger may have been systematically underestimated in some areas, which means that tsunami risk assessments should be be reviewed in the light of new results. The findings have important implications for risk mitigation in affected areas of the world, including Southeast Asia and the Pacific, in the event of future earthquakes and tsunamis.
Megaathrust earthquakes are among the most powerful earthquakes experienced worldwide and occur in subduction zones, where two tectonic plates converge and one slides beneath the other. The plates move towards each other continuously, but if the interface or damage between them is stuck, then over time a deficit of slippage accumulates. Like debt, this slip deficit must be paid off eventually, and for tectonic plates, the payday is the day of the earthquake. When these earthquakes affect the shallowest part of the fault near the seabed, they have the potential to displace the seabed and create devastating tsunamis.
Therefore, understanding the potential rupture behavior of megatrusts, especially in the shallow offshore part of the fault where the most destructive tsunamis are generated, is a critical task for geologists predicting seismic and tsunami floods. The probability of seismic behavior is often considered to be slightly low in the shallow part of the fault based on laboratory studies of recovered material from the fault area.
The rate of accumulation of slip deficit can also be measured by using geodetic observations that track the movement of the earth’s surface over time, for example by using high-precision GPS sensors installed on land, along with a model that connects how slip on fault affects the movement of these stations. However, it is difficult for scientists to use this technique to “see” what is happening in the shallowest part of the fault, because it is far from land, under kilometers of water, where traditional GPS instruments cannot work.
Now scientists from the University of New Mexico and Nanyang University of Technology (NTU) in Singapore have developed a new geodetic method to derive this value, which takes into account the interaction between different parts of the fault, leading to a much more accurate physical result. Lindsay’s team noted that previous models have failed to take into account the fact that if the deep part of the fault is stuck between earthquakes, the shallow part also cannot move – this is what they call a “stress shadow”. “And there is a lack of accumulation of energy to make him slip away. Taking this effect into account, the team developed a technique that uses the same terrestrial data but significantly improves their ability to “see” the fault slipping in the farthest coastal areas, allowing researchers to reassess the danger posed by offshore parts of the subduction zones most prone to tsunami generation.
“We applied this technique to subduction zones in Cascadia and Japan and found that wherever there are deeper locked sections, the shallow fault should also have a high slip deficit – regardless of its own frictional properties,” said Eric Lindsey, assistant at the UNM Department of Earth and Planetary Sciences, who conducted the study while at the Earth Observatory in Singapore at NTU. “If these areas can slip away seismically, the global tsunami threat could be higher than currently recognized. Our method identifies critical locations where seabed observations can provide information on the frictional properties of these faults to better understand their sliding behavior. “
This study is important because it calls for a reassessment of previous models of tsunami hazards worldwide. As this can be done with existing data, the revaluation can also be done relatively quickly. We hope that this will lead to better preparedness among coastal communities for future events.
Reference: May 3, 2021, Nature Geoscience.
DOI: 10.1038 / s41561-021-00736-x
Other institutions involved in the study include the School of Earth Sciences, Energy and Environment, Universidad Yachay Tech (Ecuador) and the Department of Earth and Planetary Sciences at the University of California, Berkeley. The study is supported by the National Studies of Singapore, the Ministry of Education of Singapore and the National Science Foundation, among others.