Scientists recently discovered something surprising in southern Poland: a 13-foot scarp stretching two miles across a pasture. This edge in the soil points to a hidden crack in the Earth, which indicates that powerful earthquakes struck this area thousands of years ago, even though today it seems calm and low-risk.
Dr. Piotr Kłapyta, a geomorphologist from Jagiellonian University in Krakow, mapped this line and connected it to an unknown fault. The research team initially looked for simpler explanations like erosion or landslides but found deeper signs of a geological break.
Using advanced airborne laser maps, the team tracked the edge across difficult terrain. They noticed that it remained straight, a pattern rarely caused by everyday erosion. Further underground scans revealed a sharp discontinuity beneath the scarp, supporting the idea of a fault line.
Next, the researchers dug a trench through the scarp near Brzegi. Inside, they found layers of sediment that ended sharply and then resumed at different levels. This pointed to quick geological changes rather than slow soil shifts. While the trench couldn’t uncover every past quake, it confirmed that significant movements did disturb the area.
The team also needed to estimate when this fault last ruptured. They used diffusion modeling, a method that estimates how long it takes for sharp edges to soften. Their findings suggest the rupture occurred between 10,000 and 50,000 years ago, likely during the last ice age.
Interestingly, modern maps label Podhale, the region near Slovakia, as quiet. Little seismic activity in recent years makes it seem safe. However, seismometers have only been monitoring this area for a short time, and it’s important to remember that older quakes may not appear in current records. Written accounts can’t capture what shook the ground before modern settlements.
Kłapyta emphasizes that studying ancient earthquake patterns through trenches provides better risk assessments than relying solely on modern catalogs. Many destructive earthquakes happen infrequently and thus escape detection.
Another notable point is how the Brzegi fault doesn’t fit the typical model connecting fault lengths to surface break sizes. Usually, longer faults yield larger breaks, but this fault, despite its short length, signals significant energy that modern systems might miss.
The forces driving the Brzegi fault stem from the collision of the Alps and the Carpathians. This pressure affects distant faults, affecting the region’s geology. The team linked the Brzegi fault’s movement to larger regional forces—crucial for understanding other hidden faults in Central Europe.
The implications of these findings are significant. Planners must recognize that the ground can hold clues about past seismic activity. New high-resolution maps can help identify other potential fault lines. Understanding how often a fault ruptures is essential. Each ancient rupture adds vital information about earthquake risks.
The Brzegi fault turns what seemed like a tranquil area into a complex history written in the layers of the Earth. More research and digging could reveal whether this fault has a record of multiple breaks, which will be critical for future planning and safety measures in Poland.
For more information, check out the study published in Geomorphology here.
