The Vrancea Seismic Cycle Revisited: A Double-Percolation Framework and Vertical Stress Resetting at Intermediate Depths
The Vrancea seismic zone represents a unique case of concentrated intermediate-depth seismicity in Europe, characterized by recurrent large earthquakes occurring within a narrow subcrustal volume between approximately 70 and 180 km depth. Observational studies indicate that seismic activity is confined to a small, nearly vertical seismogenic body, commonly interpreted as a remnant subducted slab or a delaminated lithospheric fragment. Seismic catalog analyses further reveal the presence of two depth-separated active segments, centered around 90 km and 140 km, which appear to participate alternately in the seismic cycle. In addition, independent investigations document a depth-dependent stress regime, with evidence for vertical extension in the 100-130 km depth range, as well as a correlation between intermediate-depth seismicity and dehydration reactions in hydrous minerals.