As of: March 1, 2024, 7:38 p.m
By: Lisa Metzger
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Tremors occur again and again in the Alpine region.
Other environmental influences also play a role.
Professor Heiner Igel from LMU explains the background.
Munich – The earth has been shaking repeatedly in the Alpine region since the beginning of the year.
The seismologists from the Austrian earthquake service
GeoSphere Austria
see this as an unusual accumulation, especially in Tyrol.
The strength of the individual, successive earthquakes also puzzles experts.
The tremors can now even be felt in southern Bavaria; most recently, an earthquake with a magnitude of 3.8 shook the region near Bad Reichenhall on January 23rd.
Heiner Igel from the Institute for Earth and Environmental Sciences at the Ludwig Maximilian University (LMU) in Munich is also concerned with the series of earthquakes.
As a professor of seismology, he knows about the geophysical peculiarities of the region.
In an interview, he explains why even the weather can play a role in earthquakes and what that means for Bavaria.
Earthquakes in the Alpine region happen again and again.
The danger is particularly high in the Austrian Inn Valley.
© Imago/Eibner Europa/Panthermedia
Mr. Igel, the Austrian seismologists see an unusual frequency in the series of earthquakes. They have a different opinion. For what reason?
Professor Heiner Igel:
First of all, it should be said that the earthquakes are absolutely nothing unusual.
In the Alpine region there are faults in which earthquakes occur again and again.
It is a young mountain range, the African continent presses on the Eurasian plate - so maximum magnitudes of 3 to 4 are relatively normal in this region.
How do you think the earthquakes should be assessed?
Hedgehog:
From what we've observed, we're seeing swarm quake activity.
Swarm earthquakes differ from normal tectonic earthquakes in that they increase and decrease in strength, with the greatest magnitude often being in the middle.
Do you see the potential for a larger earthquake in these swarms?
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Igel:
Historically, very large damaging earthquakes are not to be expected in these regions.
For a large earthquake you need a large fault surface, and there are fewer of these in an area as heavily deformed as the Alps.
“The earth’s crust is like a windshield.”
Can you explain this in more detail?
Hedgehog:
Think of the Earth's crust as a windshield.
Like the earth's crust, the windshield is under tension and can crack at any time if a crack occurs.
The question is always how far it will break until resistance occurs and it stops breaking further.
Due to the complex topography and morphology of the Alps, there are fewer large fracture surfaces.
In Sumatra, for example, we have a fracture length of 1,500 kilometers.
This situation does not exist in the Alpine region.
But that is all relative.
We have, for example, the Inntal Fault
(a fault that exists in the Tyrolean Lower Inn Valley east of Innsbruck and separates the northern Limestone Alps from the central Alpine areas over large areas; editor's note)
.
The fault is relatively long and vertical in depth and can sometimes produce a magnitude of 6 or larger.
Does that mean there is no risk of stronger earthquakes in Bavaria?
Igel:
There are several regions in Bavaria that are seismically active.
But we assume that large damaging earthquakes are very unlikely.
Professor Heiner Igel teaches seismology at the LMU Munich.
Among other things, he researches earthquakes that can be triggered by heavy rain.
© Heiner Igel
Many natural phenomena are increasing in intensity due to changing climatic conditions. Extreme weather events, for example, are becoming more frequent. Are there external influences that can also affect earthquakes in the Alpine region?
Igel:
Two things about it: wherever glaciers retreat, there is a relief, a so-called 'glacial rebound'.
As glaciers melt, mass is removed and the earth's crust rises slightly.
These aren't big movements, but any relief increases the likelihood of earthquakes because it takes the pressure off faults, making them easier to break.
The second is rain-induced earthquakes – a very local and specific effect.
Heavy rain as a consequence of the climate in Bavaria – earthquakes are also more likely
What is meant by a rain-induced earthquake?
Hedgehog:
These are tremors that are triggered by heavy rainfall.
Typically with magnitudes around 2.0.
Importantly, this is a very regionally limited phenomenon.
It also depends on the rock.
Porous limestone, for example, can play a big role in this.
They were the first to establish a causal connection between heavy rainfall events and earthquakes. How did they manage to do that?
Igel:
We developed a physical model with which we were able to explain the increase in 'pore water pressure' at depth caused by the inflowing water and the associated increase in seismicity.
Essentially, the water acts like lubricant on the fault, making quakes easier.
The region below the Hochstaufen near Bad Reichenhall is very well known for swarm earthquakes, which are proven to be triggered by rain.
Heiner Igel, Professor of Seismology at the Geo and Environmental Sciences Institute at LMU Munich
Now the scientists' forecasts about the effects of climate change for Bavaria are largely unanimous: the Free State will have to struggle primarily with longer periods of heat and drought, but also with heavy rain events. This raises the question: even with stronger earthquakes?
Igel:
If you assume that there are more heavy rain events, it cannot be ruled out that there will be more frequent tremors.
The region below the Hochstaufen near Bad Reichenhall is very well known for swarm earthquakes, which are proven to be triggered by rain.
This is a relatively recent finding.
It has to be said: We do not assume that major damaging earthquakes are to be expected in the region.
(By the way: Our Bayern newsletter informs you daily about all the important stories from Bavaria.)
Political demand for fracking: high probability of causing earthquakes
If liquids can trigger earthquakes, so-called fracking as a means of generating energy is also questionable. Bavaria's Prime Minister Markus Söder (CSU) made this proposal in 2022 in the wake of the gas crisis. In the current government program, the state government is clearly positioning itself for this. As a scientist, do you see a threat here?
Hedgehog:
Anytime you put liquid into the earth, there's a high chance you'll cause small earthquakes.
The crucial question is always: Is there a large fault nearby where a large earthquake could occur?
In Bavaria this can be ruled out with relative certainty.
Mr. Igel, thank you for the interview.
Different types of earthquakes
Swarm earthquakes
are multiple earthquakes in a region during a specific period of time.
They differ from normal tectonic earthquakes in that they rise and fall in strength, with the greatest magnitude often being in the middle.
Tectonic earthquakes
are caused by long-standing built-up tension, often over centuries.
In the event of a large earthquake, this build-up of tension is suddenly reduced.
There is a large quake and many aftershocks that decrease in magnitude and number over time.
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