14 June 2024
Mediterranean overturned slab holds earthquake secrets

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The Mediterranean Overturned Slab: A Surprising Discovery

In 2010, a seismic event beneath Spain led to a remarkable discovery beneath the western Mediterranean: an overturned subducted oceanic slab. This unexpected find was triggered by peculiar seismic wave arrivals from an earthquake under Spain, offering researchers a glimpse into the complex tectonic structure of the western Mediterranean basin.

The study, published in The Seismic Record, revealed that the subducted slab had descended rapidly into the Earth’s mantle and flipped over, resulting in the water it carried on its surface now residing beneath the slab. This discovery has significant implications for understanding the convergence of Africa and Eurasia in the Rif-Betic-Alboran region, an area encompassing the Betic and Rif mountain ranges and the Alboran Sea basin near the Straits of Gibraltar.

Deciphering the Strange Seismic Waves

Seismic waves from a magnitude 6.3 earthquake that struck below Granada in April 2010 provided the key insights into the overturned slab. Through the Program to Investigate Convective Alboran Sea System Overturn (PICASSO) project, the earthquake’s long-lasting coda waves and the unexpected arrival of an extra P-wave phase puzzled researchers. These abnormal wave characteristics hinted at a unique geological phenomenon beneath the surface.

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Strange Seismic Wave Arrivals Lead to Discovery of Overturned Slab in the Mediterranean!
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Upon closer examination of the seismic waveforms, researchers Daoyuan Sun and Meghan S. Miller identified a low-velocity layer at the base of the subducting Alboran slab. Such layers, indicative of slowed and absorbed seismic waves passing through liquid material, suggested the presence of a hydrous magnesium silicate layer beneath the overturned slab surface.

Implications for Tectonic Activity and Deep Earthquakes

The presence of the low-velocity layer beneath the overturned slab offers insights into the mechanisms driving deep earthquakes in southern Spain. The hydrous magnesium silicates within this layer, carrying water at depths of 600 kilometers, could undergo dehydration processes that make them more brittle, potentially triggering deep seismic events.

Moreover, the study suggests that the relatively young sea floor age in the western Mediterranean has led to the preservation of a cool slab due to the presence of hydrous silicates. This indicates a fast subduction speed of around 70 millimeters per year, shedding light on the speed of subduction in the region and the potential for similar geological processes in other seismic hotspots around the globe.

Future Directions in Seismic Research

The findings of the overturned Mediterranean slab study open up avenues for further research into deep earthquakes and subduction processes in various regions worldwide. Sun and Miller propose investigating seismic waveforms from deep earthquakes in other locations, such as northeastern China, South America, and the Fiji-Tonga region, to determine if similar mechanisms are at play.

To conduct such research effectively, dense seismic station networks would be essential to capture detailed waveforms and unravel the mysteries of subduction and deep earthquake occurrences. By expanding the study of these geological processes beyond the Mediterranean, scientists can gain a more comprehensive understanding of tectonic activity and seismic events across the globe.

Links to additional Resources:

https://www.nature.com/articles/s41561-022-01016-3 https://www.sciencedaily.com/releases/2022/08/220810110012.htm https://www.eurekalert.org/news-releases/964465

Related Wikipedia Articles

Topics: Mediterranean Sea, Tectonic plate, Seismic wave

Mediterranean Sea
The Mediterranean Sea ( MED-ih-tə-RAY-nee-ən) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Southern Europe and Anatolia, on the south by North Africa, and on the east by the Levant in West Asia. The Mediterranean...
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Plate tectonics
Plate tectonics (from Latin tectonicus, from Ancient Greek τεκτονικός (tektonikós) 'pertaining to building') is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since about 3.4 billion years ago. The model builds on the concept of continental drift, an idea developed...
Read more: Plate tectonics

Seismic wave
A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large man-made explosion that produces low-frequency acoustic energy. Seismic waves are studied...
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