麻豆淫院

One of the worst earthquakes in European history ripped through Portugal in 1755, causing a tsunami, fires and shaking that killed tens of thousands of people and caused widespread destruction. Another less well-documented earthquake occurred in the same region in 1356, and a more recent 7.9 magnitude earthquake occurred in 1969. The most recent event was recorded by seismic instruments and has been found to have originated from the flat Horseshoe Abyssal Plain, which is not near any known major tectonic faults.

The reason for such destructive earthquakes far away from major fault lines has long been a mystery to scientists. However, a recent find off the coast of the Iberian Peninsula has shed some light on the events. The study, in Nature Geoscience, describes a high-velocity anomaly beneath the Horseshoe Abyssal Plain, found using seismic imaging from land and ocean-bottom seismometer data and simulations testing out different convergence scenarios among structures of Earth's crust.

The tomography data revealed the anomaly to be a delaminating block of old oceanic lithosphere鈥攎eaning the usually rigid oceanic plate was splitting and the bottom part had started sinking into Earth. This seemed like an odd occurrence, as prior delamination was only observed in continental plates and not oceanic plates. However, the group's models showed that the ocean mantle began to decouple from the overlying crust due to "serpentinization," a process where water seeps into rock, hydrating it and turning it into hydrous serpentinite rocks. This allows for easier separation.

This activity is believed to be the cause of Portugal's earthquakes. The models also show that the delamination may have been preceded by two fracture zones. The researchers believe that the oceanic plate delamination could be related to the start of the subduction process, which was previously a poorly understood process in plate tectonics. However, it is well documented that subduction causes powerful earthquakes.

"The two fracture zones isolated a lithospheric block undergoing delamination that began sinking northwards, leading to the formation of a major thrust fault at the present-day location of high-magnitude seismicity (for example, the 1969 earthquake, and possibly the 1755 Great Lisbon Earthquake)," the authors explain.

"This process may explain why, under specific conditions, delamination may precede (and even facilitate) subduction initiation. Once part of the lithosphere starts to sink by delamination, subduction may be easily initiated."

This work has finally helped explain why Portugal continues to experience high magnitude earthquakes and can help to improve earthquake preparedness and risk mitigation in Portugal and Spain in the future. Additional research may help to explain similar anomalous tectonic activity.

漏 2025 Science X Network