Two powerful earthquakes hundreds of years apart struck the same spot off the coast of Portugal. The possible cause is the peeling of tectonic plates.
Tectonic Plates And Powerful Portugal Quakes
According to the United States Geological Survey, tectonic plates or lithospheric plates are slabs of solid rock that make up the crusts and uppermost mantle of the Earth. They are commonly oceanic and continental plates.
Marine geologist Joao Duarte from the Instituto Dom Luiz of the University of Lisbon presented his theory and arguments arising from his study of the 8.9-magnitude quake that caused a tsunami and resulted to over a dozen deaths in Lisbon and Morocco. Surprisingly, some 300 years before the said quake, in November 1755, the Great Lisbon earthquake, one of the deadliest in history, struck and killed about 10,000 to 100,000 people. The 8.7-magnitude quake flattened the city of Lisbon.
Possible Peeling Of The Earth's Crust
Duarte and geologist Nicolas Riel of the Johannes Gutenberg University Mainz in Germany started their research in 2012 and used seismic waves to study the region where the two quakes struck. They found a particularly dense structure deep below the crust.
Other researchers have also identified small quakes coming from the mass that spans 155 miles, or about 250 kilometers, below the Earth's crust. The researchers explained the possibility of the birthing of subduction zones or an area in which one tectonic plate is rammed beneath another.
In the case of the tectonic plate beneath Portugal, the top layer is peeling off from the bottom layer, creating deep fractures or delamination of oceanic lithosphere. It is likely that the peeling is driven by a water-absorbing layer in the middle of the tectonic plate and the particular layer might have undergone a geological process called serpentinization. They said the old oceanic lithosphere may be prone to gravitational instabilities, which may be fundamental in the process of subduction initiation.
There were previous studies zeroing in on subduction behind the Duarte's team was the first to provide data on this theory which they presented at European Geosciences Union General Assembly held in Vienna. They tested their hypothesis using simple 2D numerical simulations.
Effects On The Atlantic Ocean
If the peeling theory is confirmed, it may mark one of the earliest stages of the Atlantic Ocean shrinking which suggests that the ocean plate will dive beneath the continental plate in about 200 years when the Iberian and North American regions are pulled closer together. If that happens, the Atlantic Ocean will vanish.
This theory is related to super-ocean cycle hypothesis that suggests that every billion years or so, superoceans will form and will sink the Atlantic ocean beneath the continental plates.
"The identification of the first case of oceanic lithospheric delamination will certainly contribute to further our understanding of tectonic plates," the authors wrote.