The Silent Fault
Beneath the Catalan Coastal Ranges, a network of faults marks the slow but persistent tectonic collision between the Eurasian and African plates. One of the most significant structures here is the Amer-Brugent Fault System, a slow-moving fault that is a source of seismic hazard for the region, including the densely populated city of Barcelona. This region experiences low to moderate seismicity, but its geological history contains evidence of powerful and destructive earthquakes.
The last major event to rupture this fault system was part of the 1427-1428 seismic crisis, which culminated in the Catalonia earthquake on February 2, 1428. With an estimated magnitude of around 6.5, the quake's epicenter was near Camprodon, but its effects were widespread and devastating. It completely destroyed villages like Queralbs and Tortellà and caused hundreds of casualties across the region. In Barcelona, roughly 90 kilometers from the epicenter, the shaking reached an intensity of VI or VII (Very Strong), causing panic and collapsing the large rose window of the Santa Maria del Mar church. For nearly 600 years since, this segment of the fault has been quiet, accumulating stress in what geologists identify as a seismic gap.
Evidence from the Earth
To understand the fault's behavior, paleoseismologists dig trenches directly across the fault line, creating a cross-section of the upper sediment layers. These trenches expose a record of past earthquakes. Displaced soil horizons, liquefaction features, and filled-in fissures are physical evidence of ancient ruptures. By using radiocarbon dating on organic materials found within these disturbed layers, scientists can construct a timeline of prehistoric seismic events.
Studies of the fault systems in the Catalan Coastal Ranges, such as the El Camp Fault, reveal a complex history. While major, surface-rupturing earthquakes with magnitudes up to 6.7 may have recurrence intervals measured in thousands of years, the broader fault system experiences significant seismic events more frequently. The historical record itself shows a cluster of damaging quakes in the 14th and 15th centuries. The 1428 event was preceded by a series of tremors in 1427 that weakened structures, contributing to the widespread destruction when the mainshock hit. The long period of silence since 1428 suggests that the accumulated tectonic strain may be due for release. Modern assessments consider a return period of around 1,000 years for a maximum intensity VII earthquake in Barcelona.