Seismic Waves Reveal Upside-Down Oceanic Slab Beneath Western Mediterranean Post-2010 Spain Earthquake

As Africa and Eurasia gradually converge, seismic activity reveals an intriguing geological tale: a portion of the Earth's surface now rests inverted beneath the Mediterranean. These unusual seismic waves from a 2010 Spanish earthquake could guide scientists to an unforeseen revelation.

As detailed in a paper, titled "Revealing the Secrets of the Western Mediterranean: A Deep Earthquake and the Overturned Slab" published in The Seismic Record, the seismic patterns depict a swift descent and flip of a subducted oceanic slab into the Earth's mantle, positioning the water it carried beneath the slab.

Tectonic Slab Flipping and Deep Earthquakes in Spain's Western Mediterranean Tectonics

Spain experiences uncommonly frequent and deep earthquakes, with a recent study proposing a connection to a flipped tectonic slab. Geologists Daoyuan Sun and Meghan Miller have noted five significant deep-focus earthquakes beneath Granada since 1954, challenging the typical aftershock pattern seen at such depths.

Tectonic collisions often involve subduction, where one plate slides beneath another, creating mountains or intertwining the plates. The Mediterranean floor, at the African-Eurasian plate border, is sinking beneath Europe in a stacked slab formation.

Subducted slabs develop hydrous magnesium silicates when exposed to ocean water, becoming dehydrated and brittle as they sink. This heightened vulnerability to earthquakes and slowed seismic waves is detectable by seismologists.

The prolonged and uniquely phased seismic waves from the 2010 Granada earthquake indicate slower movement at the bottom of the Alboran slab. The study suggests a relatively cold slab due to a significant amount of water carried to the mantle transition zone. To maintain this coolness, a fast subduction speed of approximately 70 millimeters per year is necessary.

The swift sinking of the slab prompts the Earth's crust to flip, carrying water along. The study concludes that the slab completely overturned, shedding light on the complex tectonics and deep earthquakes in the region.

The confirmation of a subducted oceanic lithosphere beneath southern Spain, forming the Beltic-Rif arc, explains the unique tectonic structures in the western Mediterranean.

Insights from Deep Earthquakes in Spain's Western Mediterranean Basin

The research has significant implications for unraveling the intricate tectonic structure of the western Mediterranean basin, specifically the Rif-Betic-Alboran region, where Africa and Eurasia converge.

This area encompasses the Betic mountain ranges in Spain, the Rif mountain ranges in Morocco, and the Alboran Sea basin east of the Straits of Gibraltar. The findings promise valuable insights into the complexities of the convergence between Africa and Eurasia in this geographical zone.

Furthermore, the study provides a unique perspective on the mechanisms underlying rare and deep earthquakes, those exceeding 600 kilometers, in southern Spain. The team highlights the significance of comprehending seismic activity in this region.

While the initial intention was not to delve into the mechanisms of deep earthquakes, the close examination of seismic waveforms led to the discovery of these peculiar seismic waves, enhancing our understanding of the seismic intricacies associated with the 2010 Spain earthquake.

Looking ahead, Sun suggests the potential extension of this waveform analysis to deep earthquakes in various regions globally, such as northeastern China, South America, Sunda-Banda, and the Fiji-Tonga region.

However, such research endeavors would require the strategic deployment of dense seismic stations directly above these seismic events, mirroring the fortunate circumstances surrounding the 2010 Spain earthquake.

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