A sensor network in the foothills of Chile's Valparaíso region has detected 803 hidden microearthquakes in the commune of San Esteban, revealing that the Andes mountain range continues to actively deform.
The small tremors registered magnitudes ranging from approximately 1 to 2 Mw at depths between two and six kilometres beneath the surface. Spread across an area of roughly 100 square kilometres, the events were too weak to be felt by the local population and had gone completely unnoticed by conventional monitoring networks.
San Esteban is a rural commune situated in Los Andes Province within Chile's central Valparaíso Region, approximately 100 kilometres northeast of the capital city of Santiago. Microearthquakes, or microsisms, are extremely minor seismic tremors that register below human perception thresholds, requiring specialized high sensitivity instruments to detect their signals.
Fault line activity
Researchers found that the cluster of 803 microearthquakes is concentrated around the Cariño Botado fault system. Geologists noted that this local geological structure is directly related to the historic uplift of the western edge of the Andes mountains.
The spatial distribution pattern of the tremors indicates that the Earth's crust in central Chile is actively continuing to absorb structural deformation. Rather than remaining static, the rock formations along the fault system are absorbing ongoing tectonic strain in real time.
The Andes represent the longest continental mountain range in the world, stretching over 7,000 kilometres along the western spine of South America. Chile sits directly along the Pacific Ring of Fire, a geologically active zone characterized by frequent earthquakes and volcanic eruptions caused by colliding tectonic plates.
Artificial intelligence and advanced sensing
To detect the hidden seismic events, the research team combined seismic wave recordings with high-precision gravity measurements, magnetotelluric studies, and artificial intelligence tools. This integrated analytical approach enabled scientists to locate hundreds of tiny signals and reconstruct the subsurface activity occurring deep beneath the ground.
Conventional seismic monitoring networks rely on widely spaced ground stations designed to trigger on stronger tremors, which often causes them to miss low amplitude microseismic events. Magnetotellurics is an electromagnetic geophysical technique used to map subterranean electrical conductivity, while artificial intelligence algorithms can scan continuous seismic data to extract subtle signals that human analysts might miss.
Tectonic interaction and slab subduction
Scientists linked the underlying activity to the subduction of the oceanic Nazca plate beneath the continental South American plate. In this specific region of central Chile, the subduction zone features a low angle geometry known to geophysicists as a flat slab.
Because the subducting plate moves horizontally at a shallow angle rather than diving steeply into the mantle, this flat slab configuration can transfer compressive forces further inland toward geological structures located in the interior of the continent.
Implications for seismic hazard
Researchers emphasized that the discovery of these 803 microearthquakes does not indicate that a major, destructive earthquake is imminent, nor does the data allow scientists to predict future seismic events. Instead, the finding demonstrates that the Andes are continuing to deform, with the minor tremors functioning as small signals that allow scientists to observe how the mountain range continues to evolve.
