For nearly three centuries, the catastrophic 1755 Lisbon earthquake has remained an enigma, defying conventional geological explanations. This seismic event, which devastated the Portuguese capital and profoundly influenced European thought, occurred in a region seemingly devoid of the typical tectonic features that trigger such large-scale tremors. However, recent scientific endeavors, culminating in a new publication in 'Nature Geoscience,' may finally offer a comprehensive understanding of this historical disaster. The research introduces a novel geological mechanism, proposing 'oceanic delamination' as the primary cause, a concept previously thought impossible in oceanic crust. This groundbreaking theory challenges established paradigms and could redefine our understanding of seismic activity in stable oceanic environments, providing a much-anticipated answer to a persistent geological puzzle.

The 1755 Lisbon earthquake, striking on All Saints' Day, sent shockwaves through both the physical and intellectual landscapes of 18th-century Europe. Its immense destruction, claiming tens of thousands of lives, sparked profound philosophical debate, famously influencing Voltaire's satirical work, 'Candide.' The earthquake's theological implications were equally unsettling; its occurrence on a holy day led many to question divine providence, challenging the prevailing notion of a benevolent God. From a geological perspective, the event was equally perplexing. Unlike most major earthquakes that originate from visible fault lines or active subduction zones where tectonic plates collide and one slides beneath another, the seabed off Lisbon appears geologically placid, presenting no clear indicators of significant seismic activity. This apparent contradiction has long puzzled geologists, making the Lisbon earthquake a unique case study in seismology.

Earthquakes are primarily driven by two main types of geological processes: delamination and subduction. Delamination typically occurs in continental crust, where the dense, pliable mantle beneath the Earth's brittle upper crust detaches, allowing lighter magma to rise, causing the overlying crust to buckle and fracture. This process leads to mountain formation, volcanic eruptions, and seismic events. Conversely, subduction involves one tectonic plate being forced beneath another, usually an oceanic plate sliding beneath a continental or another oceanic plate. This interaction generates immense friction and stress, resulting in powerful earthquakes. However, neither delamination nor traditional subduction appeared to be occurring off the coast of Lisbon, rendering the 1755 event an anomaly that did not fit established models of plate tectonics.

The new research, detailed in 'Nature Geoscience,' proposes a revolutionary concept: oceanic delamination. This theory suggests that under specific conditions, even the typically impermeable oceanic mantle can undergo delamination. Evidence supporting this radical idea includes the detection of an anomalous magma body, dubbed the 'southwest Iberia anomaly,' deep beneath the seafloor off Portugal. Furthermore, a cluster of deep-seated earthquakes (originating at depths exceeding 20 kilometers) has been identified in the same region, yet without visible subduction. The deep origin of these tremors indicates a decoupling between the upper crust and the underlying mantle, a characteristic consistent with delamination rather than typical fault-line activity. Simulations conducted by the research team bolster this theory, further suggesting that the presence of highly slippery serpentinite rock off the Portuguese coast might facilitate this unusual oceanic delamination process.

The proposed 'oceanic delamination' model offers a compelling explanation for the 1755 Lisbon earthquake, resolving a long-standing geological puzzle. While the theological questions raised by the disaster may continue to inspire contemplation, the scientific understanding of its mechanics appears to be finally within reach. This novel theory not only clarifies a historical seismic event but also expands our comprehension of the complex dynamics within Earth's crust and mantle, potentially opening new avenues for earthquake prediction and hazard assessment in previously underestimated regions.