Picos de Europa: The Surprising Seismic Calm of a Geological Giant

A study reveals why the imposing mountains of the northern peninsula are an oasis of tectonic tranquility.

The Picos de Europa, that mountain range that rises majestically between Asturias, Cantabria and León, are much more than a landscape of vertigo and natural beauty. Considered the cradle of Spain's first National Park, these peaks, often associated with strength and rugged geology, keep a secret that defies expectations: almost absolute seismic tranquility. Researchers from the University of Oviedo have revealed that this iconic region is practically immune to earthquakes, a rare phenomenon, even in the context of low seismic activity in the Iberian northwest.

This fascinating discovery is based on an ambitious project that deployed ten seismic stations in the heart of the massif for six months, between July 2023 and January 2024. The result is the obtaining of the most detailed three-dimensional images to date of the most superficial layers of the Earth's crust beneath the Picos. The data are conclusive: during the entire observation period, only nineteen low-intensity earthquakes were recorded, most of them imperceptible to the human ear and only two of them detected by the National Seismic Network.

This almost total absence of seismic activity contrasts markedly with adjacent areas, especially to the west. There, well-documented active faults, such as the famous Ventaniella, act as hot spots where most of the energy released in the Cantabrian Mountains is concentrated. The research, which EFE has consulted, reveals a fundamental geological difference that explains this behavior.

To unravel this mystery, scientists used two innovative techniques: microseismicity analysis, which studies small ground movements, and ambient noise tomography. This latter method, a marvel of modern geophysics, uses the natural vibrations of the ground to reconstruct the internal structure of the Earth's crust, avoiding the need for artificial sources or explosions.

The results of these techniques are revealing. At a depth of approximately 5 to 6 kilometers, an abrupt limit in the speed of seismic waves is detected. This geological discontinuity coincides with the ancient Variscan thrust, a colossal fault that, more than 300 million years ago, during the formation of the supercontinent Pangea, stacked different layers of rock in a process of immense pressure and deformation.

However, the key to understanding the seismic serenity of the Picos de Europa lies even further down. Three-dimensional images have revealed the presence of an extensive body of low seismic velocity materials, oriented from northwest to southeast, extending to a depth of at least 8 kilometers.

The researchers postulate that these materials correspond to the syntectonic sediments of the ancient Variscan deformation front. These rocks, deposited as the range folded and formed, are notably softer and less consolidated than the rigid crystalline basement that characterizes the geology west of the Ventaniella fault.

This fundamental difference in the “hardness” of the rocks is, according to the study, the determining factor to explain why tectonic stresses are released in some areas and remain latent in others. The soft rocks of the Picos de Europa act as a “natural shock absorber”. Its ductile behavior reduces the probability of sufficient stresses accumulating to generate earthquakes.

In contrast, the rigid rocks of the west, subjected to similar pressures, store energy that is released more frequently through earthquakes, although generally of low magnitude. This energy “dissipation” mechanism explains the notable difference in seismic activity between both regions.

The Picos de Europa massif is located in a privileged geological position, in the transition between the ancient Variscan structure, inherited from the Paleozoic period, and the most recent Alpine deformations that gave rise to the current Cantabrian Mountains and the Pyrenees. This strategic location influences its geological behavior.

Furthermore, an exhaustive historical analysis of more than 7,700 earthquakes recorded in the region between 1999 and 2025 reinforces this conclusion. The data confirm that the Picos de Europa area marks the northern end of a strip of relative seismic calm that extends southwards across the Plateau.

Although the authors of the study warn that this research does not imply a total absence of seismic risk – since seismicity is never zero – it does provide a solid and detailed scientific basis to understand the distribution of earthquakes in northwest Spain. This knowledge is crucial for territorial planning and risk management in an area of great ecological and tourist value.

Frequently Asked Questions:

Why are the Picos de Europa seismically quiet?: The presence of soft, ductile rocks at considerable depths acts as a natural shock absorber, dissipating tectonic stresses without generating significant earthquakes.
When was the Variscan fault mentioned in the study formed?: The Variscan fault formed more than 300 million years ago, during the Variscan orogeny, a key geological event in the formation of the supercontinent Pangea.
What techniques were used to study the internal structure of the Picos de Europa?: Microseismicity analysis and environmental noise tomography were used, using natural ground vibrations.
How many earthquakes were recorded during the study?: During the six months of recording, nineteen small earthquakes were identified, most of them imperceptible.
What geological difference exists between the Picos de Europa and the areas to the west?: The Picos de Europa present soft rocks, while the areas to the west are dominated by a rigid crystalline basement.
What does “Variscan riding” mean?: It refers to a geological fault where one block of rock has shifted over another, stacking layers of rock during the formation of mountains.
What implications does this study have for security in the region?: Although it does not eliminate risk completely, it provides a better understanding of seismicity for planning and management.
Is it possible for strong earthquakes to occur in the Picos de Europa?: The study suggests that it is less likely due to the nature of the subsurface, but seismicity is never zero.
Did the research include historical earthquake data?: Yes, the record of more than 7,700 earthquakes between 1999 and 2025 was analyzed.
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