No matter how hard science tries, it is still not possible to predict earthquakes. Therefore, when in doubt, every second counts as soon as there are signs of an earthquake. Researchers are working on complex early warning systems that are intended to help give people in the affected areas at least a little more time to get to safety. Not least in metropolises like Istanbul. Researchers have long been expecting an impending “superquake” here.
Unfortunately there are earthquakes for which a warning is not possible and certainly not an early one. According to Marco Bohnhoff from the German Research Center for Geosciences (GFZ) Potsdam, the most recent severe earthquake in south-east Turkey is one of them. The reason for this is that the densely populated region is in the immediate vicinity of the epicenter. That’s not always like that. Many earthquakes, which also cause damage on land, occur on the seabed, 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 coming quake for decades, but so far none of the approaches have been entirely reliable. So the only thing that remains is the early warning when an earthquake occurs.
Approaches to earthquake early warning
Measurement of seismic waves
In areas that are in a danger zone for earthquakes along the boundaries of tectonic plates are common regional warning systems installed. There, a system of sensors in the ground 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 seismology professor Stefano Parolai from 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 later than 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 observation network. The linked infrastructure then also switches off electricity and gas lines, stops trains and warns the industry.
However, the seismic measurements can also be made at the location that is to be protected from the earthquake – for example in a city or at an industrial plant. According to Parolai, the measuring devices then registered the P wave and derived from it how strong the S wave was about to be and immediately triggered measures 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 presented a method last year using signals called prompt elastogravity signals (PEGS). These are the result of sudden rock shifts and cause short-term changes in gravity. 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 managed to use these signals for a warning system that is eight seconds faster than the best measuring system for seismic waves.
Electromagnetic Signals
A frequently debated approach is the change in electromagnetic signals in the ionosphere. Apparently they can trigger earthquakes and are therefore considered as possible precursors of larger earthquakes. In fact, such changes have been successfully linked to earthquakes, but have so far proved unreliable as a 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 that? Again and again, abnormal behavior of animals is discussed as a harbinger of earthquakes. Several research projects deal with the anecdotal observations of fleeing toads or nervous goats. The experts from GFZ German Research Center for Geosciences looked closely at the studies on the strange behavior of the animals. But so far, no research group has actually been able to reliably predict earthquakes through systematic animal observations. The Max Planck Society conducts research in Project ICARUS in an early warning system for the animals. However, that is on hold due to the Russian war in Ukraine. Because the data is collected on the ISS space station by antenna and came from Moscow by March 2022. After that it was over.
In some cases, smaller foreshocks herald a larger earthquake. Experts suspect that this is also a possible explanation for the strange behavior of some animals. They may sense it and be startled by it. Of course, we humans can also measure these foreshocks, but whether it was really one of those earthquakes can only be known with certainty after the main earthquake. And besides, not every major earthquake has such foreshocks.
There are various studies that indicate an increase in radon concentrations in the run-up to an earthquake. But even that is not a reliable sign: Only in a few cases has this increase been causally linked to seismic activity. Depending on the distance to the epicenter, the measured values differed so much that no meaningful 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 normally do not feel. But even that has not been very successful so far: none of these statistical evaluations has so far provided results that would be suitable for predicting earthquakes.
In order to actually be able to develop an earthquake prediction at some point, science calls for better research options. A team of seismologists has therefore Construction of “key observatories” near geological fault zones on land and on the seabed.
Sea of Marmara: Tides as a trigger
In particular, the south-east of Europe to the Middle East is an area in which severe earthquakes can occur again and again, as several tectonic plates meet here. For the region around the Turkish metropolis of Istanbul, for example, researchers have long been expecting an impending “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 main branch of the fault runs directly between Istanbul and the Schwachlu Peninsula a little further south and is referred to as a “seismic gap”: A major earthquake is overdue here, experts are certain. Therefore, the Sea of Marmara, south of Istanbul, is exciting for seismological research.
The team led by Patrizia Martínez-Garzón from the GFZ German Research Center for Geosciences has dealt with the change in sea level 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 that are triggered by the natural fluctuations in sea level are so small that the data could only be tracked down in this way. And yet they showed that changing sea levels can trigger earthquakes.
Bildrechte: Image reproduced from the GEBCO world map 2014, www.gebco.net
In fact, the fact that seismic effects occur at all with such weak initiating forces could indicate that the faults in the studied area are on the verge of failure, the research team said. Then more earthquakes could be triggered. This means that the team’s analyzes could in turn be a step towards better risk prediction.
warpA so-called fault is an existing fracture in the earth’s crust.
It is crucial, the research team writes, to understand how much stress it takes to cause a fault to fail and trigger an earthquake. And that’s where the tides come in, because a natural touchstone for how the Earth responds to a stress perturbation is quasi-periodic phenomena like tidal movement, or seasonal effects like additional water due to precipitation.
Whether such stress changes are sufficient to trigger earthquakes has been studied for decades. Thanks to new AI analysis methods and image processing technology, it has now been possible to evaluate the previously difficult-to-analyze data. As a result, the research team actually succeeded in proving it. 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 Martinez-Garzon, GFZ
This 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 seismicity rates are significantly higher in the periods just after sea-level minimums, when sea levels are rising again.”
The results can now help to estimate which voltage changes are sufficient to activate the local faults and trigger earthquakes, explains the researcher and sums up: “If such small voltage fluctuations due to changes in sea level are sufficient to trigger seismicity, this could be an indication that the local fault lines in Armenlu are on the verge of failure.”
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 p.m
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