No matter how hard science tries, it’s still not possible to predict earthquakes. So, when in doubt, every second counts as soon as there are signs of an earthquake. Researchers are working on complex early warning systems that aim to help give people in affected areas at least a little more time to protect themselves. Not least in metropolises like Istanbul. Researchers have long expected an imminent “superquake” here.
Unfortunately, there are earthquakes for which an early warning is not possible and certainly not early. According to Marco Bohnhoff of the German Research Center for Geosciences (GFZ) Potsdam, the most recent earthquake in southeastern Turkey is one of them. The reason for this is that the densely populated region is in the immediate vicinity of the epicenter. It’s not always like that. Many earthquakes, which also cause damage on land, occur under the sea, for example.
In any case, researchers are working intensively on warning systems that should alert people in affected regions as early as possible. They’ve been looking for sure signs of a nearby earthquake for decades, but so far none of the approaches have been entirely reliable. So the only thing left is advance notice when an earthquake strikes.
Approaches to earthquake early warning
Measurement of seismic waves
Regional warning systems are often installed in areas that are at risk for earthquakes along tectonic plate boundaries. There, a system of ground sensors directly records vibrations in the ground. This is because earthquakes produce different types of seismic waves, including low vibration compression waves (P waves) and shear waves (S waves). The S wave is the dangerous wave that causes destruction. According to professor of seismology Stefano Parolai of the University of Trieste, there are only a few seconds between the two waves. “The further away you are, the more time there is for an alarm,” he explains.
However, if you are very close to the epicenter, the alarm will reach you after the dangerous S wave. If the affected area is far enough away to be warned in advance, the alarm is triggered directly by the real-time signals from the monitoring network . Connected infrastructure also shuts down electricity and gas lines to trains and alerts industry.
However, seismic measurements can also be made in the place to be protected from the earthquake – for example, in a city or at an industrial plant. According to Parolai, the measuring devices recorded the P wave and derived from it how strong the S wave was about to be and immediately triggered measurements accordingly.
Gravity signals and artificial intelligence
Strong earthquakes can be accurately estimated using machine learning and real-time analysis of gravity signals, say French researchers. They came up with a method last year using signals called immediate elastogravity signals (PEGS). These are the result of sudden rock shifts and cause short-term gravity changes. And the most important thing about these PEGS is that they travel at the speed of light, which allows for faster acquisition and analysis than seismic P and S waves. Using an AI algorithm, the research team was able to use these signals for an early warning system eight seconds faster than the best seismic wave measurement system.
One often-debated approach is the change in electromagnetic signals in the ionosphere. Apparently, they can trigger earthquakes and are therefore considered possible precursors to larger earthquakes. In fact, these changes have been successfully linked to earthquakes, but so far they have not proven reliable as an early warning method.
The strange behavior of animals
Is it possible that some animals know before humans that the earth is about to shake? Do they possibly have a “sixth sense” that tells them this? Time and again, the animals’ abnormal behavior is discussed as a harbinger of earthquakes. Several research projects deal with anecdotal observations of fleeing frogs or nervous goats. Experts from the German Research Center for Geosciences GFZ closely analyzed the studies on the strange behavior of the animals. But until now, no research group has really been able to reliably predict earthquakes through systematic observations of animals. In the ICARUS project, the Max Planck Society is researching an early warning system for animals. However, this is on hold due to the Russian war in Ukraine. Because the data is collected at the ISS space station by antenna, and it came from Moscow in March 2022. After that it was over.
In some cases, minor forehocks herald a larger earthquake. Experts suspect that this is also a possible explanation for the strange behavior of some animals. They can feel it and be scared by it. Of course, we humans can also measure these aftershocks, but whether it really was one of these earthquakes can only be known for sure after the main earthquake. And besides, not every major earthquake has such aftershocks.
There are several studies that indicate an increase in radon concentrations before an earthquake. But even this is not a reliable sign: only in a few cases was this increase causally related to seismic activity. Depending on the distance to the epicenter, the measured values differed so much that no significant connection could be proven so far.
statistics from the past
Researchers are also trying to predict earthquakes using statistical methods. To do this, they use data from the past and examine the frequency and strength of many small earthquakes, which measuring instruments register but which humans do not normally feel. But even that hasn’t been very successful so far: none of these statistical evaluations have so far provided results that would be adequate for predicting earthquakes.
To actually be able to develop an earthquake prediction at some point, science requires better research options. A team of seismologists therefore proposed building “key observatories” near fault zones on land and at the bottom of the sea.
Sea of Marmara: Tides as a Trigger
In particular, southeastern Europe to the Middle East is an area where severe earthquakes can occur repeatedly, as several tectonic plates meet here. For the region around the Turkish metropolis of Istanbul, for example, researchers have long expected an imminent “superquake” that could cause significant damage. Namely, it is part of the active North Anatolian fault system – a large tectonic plate boundary known for destructive earthquakes. The fault’s main branch runs directly between Istanbul and the Schwachlu Peninsula, a little further south, and is called the “seismic gap”: a major earthquake is about to occur here, experts are sure. Therefore, the Sea of Marmara, south of Istanbul, is exciting for seismological research.
The team led by Patrizia Martínez-Garzón of the German Research Center for Geosciences GFZ addressed sea level change in the Sea of Marmara in a recently published study. To do this, they collected and analyzed seismic data there. For this analysis, they used new methods of artificial intelligence and image processing, because the seismic effects triggered by natural sea level fluctuations are so small that the data could only be tracked this way. And yet, they showed that sea level change can trigger earthquakes.
The North Anatolian Fault runs alongside the megacity of Istanbul. Image copyright: Image reproduced from the GEBCO 2014 world map, www.gebco.net
Indeed, the fact that seismic effects occur with such weak initial forces may indicate that faults in the studied area are on the brink of collapse, the research team said. Then more earthquakes could be triggered. This means that the team’s analytics can, in turn, be a step towards better risk prediction.
Fault A so-called fault is an existing fracture in the Earth’s crust.
It’s crucial, the research team writes, to understand how much stress is needed to cause a fault to trigger an earthquake. And that’s where tides come in, because a natural touchstone of how the Earth responds to a stress disturbance are quasi-periodic phenomena, like tidal movement, or seasonal effects, like additional water due to precipitation.
Whether these stress changes are enough to trigger earthquakes has been studied for decades. Thanks to new AI analysis methods and image processing technology, it is now possible to evaluate data that was previously difficult to analyze. As a result, the research team was able to prove this. Using data from November 2018 to May 2019, they were able to demonstrate for the first time in this region a strong influence of sea level changes in the Sea of Marmara on local seismicity.
We document for the first time in this hydrothermal region in the eastern Sea of Marmara a strong influence of tidal water level changes on local seismicity.
Patricia Martínez-Garzón, GFZ
That relationship is usually weak, explains lead author Patricia Martínez-Garzón. The sea level varies here by only 0.8 meters. But the analysis shows “that local rates of seismicity are significantly higher in the periods just after sea level minima, when sea levels are rising again.”
The results can now help estimate which voltage changes are sufficient to activate local faults and trigger earthquakes, explains the researcher and summarizes: indication that the local fault lines in Armenlu are on the verge of collapse.”
Martínez-Garzón, P. et. al.: Sea level changes affect seismicity rates in a hydrothermal system near Istanbul. Geophysical Research Letters, 50. 2023. https://doi.org/10.1029/2022GL101258.
This topic in the program:3 sat | nano | February 10, 2023 | 6:30 pm