Many 'safest' places suddenly had earthquakes, what happened?

Places considered 'absolutely safe' on earthquake maps are suddenly shaking. Even faults that have been dormant for millions of years are 'moving'. Not only the people, but also the scientific community is worried.

The earthquake in the villages near Huizinge (Netherlands) caused many houses to be forced to brace afterwards. Notably, this is an area that is considered to have almost no natural earthquakes - Photo: ANP

For decades, world earthquake risk maps have largely ignored places like the Netherlands, India's Deccan Plateau, and the US state of Oklahoma.

These places are far from tectonic plate boundaries, have no history of strong shaking and are considered absolutely safe land.

But a new line of research is forcing scientists to rethink how humans are triggering earthquakes, and how the most stable areas are sometimes the most fragile.

When a fault that has been dormant for millions of years suddenly "bursts" into an earthquake

On August 16, 2012, the small village of Huizinge in the Netherlands was suddenly shaken by a 3.6 magnitude earthquake. People were shocked: "How could there be an earthquake here?"

But the answer was right under their feet: a gas project at the Groningen field, one of the world’s largest, that changed the pressure underground and triggered shallow faults that had been dormant for millions of years.

Groningen is no exception. From India to the United States, regions that were thought to be “earthquake-proof” have recorded tremors directly related to human activities such as mining, oil and gas exploitation, dam construction, liquid pumping, geothermal exploitation…

Why are stable zones more vulnerable?

The answer lies in a little-known process called “frictional healing.”

In a recent study published in Nature Communications , a team led by seismologist Ylona van Dinther (Utrecht University, Netherlands) discovered that shallow faults in stable regions become stronger the longer they remain dormant.

“In the Netherlands, the faults have not moved for millions of years,” says van Dinther. “When they get stuck, the contact area between the two rock faces increases, making them stick together more tightly. We call this frictional healing.”

Map of earthquake-prone areas, in which red is earthquakes caused by mining activities, dark blue is from reservoir activities and orange is oil and gas exploitation - Photo: HIQUAKE

At first glance, a stronger fault might seem like a good thing. But in reality, this is exactly what makes it so that even a small change from human activity can upset the balance , releasing all the accumulated energy in a single slip.

The Utrecht team's computer simulations show that when underground pressure changes, for example due to gas withdrawal or fluid injection, shallow faults will begin to take on more load.

In just 35 years , that pressure can overcome millions of years of accumulated frictional force, causing the fault to “pop” and create an unusually strong earthquake.

Once the energy is released, the fault goes dormant and takes millions of years to build up again. But the problem is that there are more than a thousand of these faults in the world , meaning the risk of a triggering earthquake could be widespread.

Concerns that infrastructure is not designed to withstand shaking

The sudden 5.4 magnitude earthquake was determined to be "man-made" in Pohang (South Korea) in 2017 - Photo: SIM1992

What worries experts is not just the earthquake, but also the surface impact .

Shallow faults lie close to the ground, so when they slide, energy is transmitted straight to the surface, causing stronger shaking than the deep faults commonly found in Japan or Türkiye.

“Infrastructure in stable areas is not built to withstand earthquakes,” warned geophysicist Daniel Faulkner (University of Liverpool, UK).

He cited the 2017 magnitude 5.4 earthquake in Pohang, South Korea, where a geothermal project was found to have contributed to the tremor, forcing the government to shut it down. The city was unprepared for an earthquake.

Van Dinther said there are ways to reduce the risk. That is, control the amount and speed of fluid injected into the ground, starting slowly, increasing gradually or pumping in cycles to avoid sudden pressure build-up.

Some previous studies in the journal Geophysical Research Letters ( 2021) also showed that cyclic pumping methods can limit the magnitude of triggering earthquakes.

However, she stressed: “No matter how cautious, businesses must clearly communicate that earthquakes can occur. In the risk assessment, we must take into account the healing process and the strengthening of the fault."

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HOANG THI

Source: https://tuoitre.vn/nhieu-noi-an-toan-nhat-bong-bi-dong-dat-co-chuyen-gi-20251205140808307.htm