New research reveals how water deep in the Earth causes earthquakes and tsunamis

In a new study, published in the journal. Nature, an international team of scientists provides the first conclusive evidence that directly links the deep Earth water cycle and its expressions with magmatic productivity and seismic activity.

Water (H_twoO) and other volatiles (eg CO_two and sulfur) that are recycled through the deep Earth have played a key role in the evolution of our planet, including the formation of continents, the beginning of life, the concentration of mineral resources and the distribution of volcanoes and earthquakes.

Subduction zones, where tectonic plates converge and one plate sinks below another, are the most important parts of the cycle, with large volumes of water flowing in and out, mainly through volcanic eruptions. However, historically how (and how much) water is transported by subduction, and its effect on natural hazards and natural resource formation, has historically been misunderstood.

The study’s lead author, Dr. George Cooper, an honorary researcher at the University of Bristol School of Earth Sciences, said: “As the plates travel from where they are first made on ocean ridges to subduction zones, seawater enters rocks through cracks, faults, and by binding to minerals. Upon reaching a subduction zone, the sinking plate is heated and squeezed, resulting in the gradual release of some or all of its water. As the water is released, the melting point of the surrounding rocks decreases and generates magma. This magma floats and moves upward, ultimately leading to arc eruptions overlying volcanic. These eruptions are potentially explosive due to the volatiles contained in the melt. The same process can cause earthquakes and can affect key properties such as their magnitude and whether or not they trigger tsunamis. “

Exactly where and how volatiles are released and how they modify host rock remains an area of ​​intense research.

Most studies have focused on subduction along the Pacific Ring of Fire. However, this research focused on the Atlantic plate and, more specifically, on the volcanic arc of the Lesser Antilles, located on the eastern edge of the Caribbean Sea.

“This is one of only two zones that currently subduct slow-spreading plates. We hope this hydrates more penetratingly and heterogeneously than the fast-spreading Pacific plate, and that the expressions of water release are more pronounced. “said Professor Saskia. Va, Imperial College London.

The Volatile Recycling in the Lesser Antilles (VoiLA) project brings together a large multidisciplinary team of researchers including geophysicists, geochemists, and geodynamics from Durham University, Imperial College London, University of Southampton, University of Bristol, University of Liverpool, the Karlsruhe Institute of Technology, the University of Leeds, the Museum of Natural History, the Institute of World Physics in Paris and the University of the West Indies.

“We collected data on two marine scientific cruises on the RRS James Cook, temporary deployments of seismic stations that recorded earthquakes below the islands, geological field work, chemical and mineral analysis of rock samples and numerical modeling,” said Dr. Cooper. .

To trace the influence of water throughout the subduction zone, the scientists studied compositions of boron and isotopes of molten inclusions (small pockets of magma trapped within volcanic crystals). Boron fingerprints revealed that the mineral, water-rich serpentine contained in the sinking plate is a dominant provider of water in the central arc region of the Lesser Antilles.

“By studying these micron-scale measurements, it is possible to better understand large-scale processes. Our combined geochemical and geophysical data provide the clearest indication to date that the structure and amount of water in the sinking plate are directly connected to the volcanic evolution of the arc and its associated dangers, “said Professor Colin Macpherson of Durham University

“The wettest parts of the descending plate are where there are major cracks (or fracture zones). By making a numerical model of the history of fracture subduction below the islands, we found a direct link to the locations of the highest rates of small earthquakes and low shear wave velocities (indicating fluids) in the subsoil, “said Professor Saskia Goes.

The history of subduction of water-rich fracture zones may also explain why the central islands of the arc are the largest and why, throughout geological history, they have produced the greatest amount of magma.

“Our study provides conclusive evidence that directly links the parts of the water inlet and outlet cycle and their expressions in terms of magmatic productivity and seismic activity. This may encourage studies in other subduction zones to find such water-bearing fault structures in the subduction plate to help understand patterns in earthquake and volcanic hazards, “said Dr. Cooper.

“In this research we discovered that variations in water correlate with the distribution of smaller earthquakes, but we would really like to know how this pattern of water release can affect the potential and act as a warning system for larger and possible earthquakes tsunamis, “said Professor Colin Macpherson.