How Water in the Deep Earth Triggers Earthquakes and Tsunamis

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In a brand-new research study, released in the journal Nature, a worldwide group of researchers offers the very first definitive proof straight connecting deep Earth’s water cycle and its expressions with magmatic efficiency and earthquake activity.

Water (WATER) and other volatiles (e.g. CO2 and sulfur) that are cycled through the deep Earth have actually played a crucial function in the advancement of our world, consisting of in the development of continents, the start of life, the concentration of mineral resources, and the circulation of volcanoes and earthquakes.

Subduction zones, where tectonic plates assemble and one plate sinks underneath another, are the most vital parts of the cycle — with big volumes of water entering and coming out, generally through volcanic eruptions. Yet, simply how (and just how much) water is transferred through subduction, and its result on natural threats and the development of natural deposits, has actually traditionally been badly comprehended.

Lead author of the research study, Dr. George Cooper, Honorary Research Fellow at the University of Bristol’s School of Earth Sciences, stated: “As plates journey from where they are first made at mid-ocean ridges to subduction zones, seawater enters the rocks through cracks, faults and by binding to minerals. Upon reaching a subduction zone, the sinking plate heats up and gets squeezed, resulting in the gradual release of some or all of its water. As water is released it lowers the melting point of the surrounding rocks and generates magma. This magma is buoyant and moves upwards, ultimately leading to eruptions in the overlying volcanic arc. These eruptions are potentially explosive because of the volatiles contained in the melt. The same process can trigger earthquakes and may affect key properties such as their magnitude and whether they trigger tsunamis or not.”

Exactly where and how volatiles are launched and how they customize the host rock stays a location of extreme research study.

Quill Island of Statia

Quill, on the island of Statia. One of the islands in the Lesser Antilles. Credit: Dr. George Cooper

Most research studies have actually concentrated on subduction along the Pacific Ring of Fire. However, this research study concentrated on the Atlantic plate, and more particularly, the Lesser Antilles volcanic arc, situated at the eastern edge of the Caribbean Sea.

“This is one of only two zones that currently subduct plates formed by slow spreading. We expect this to be hydrated more pervasively and heterogeneously than the fast spreading Pacific plate, and for expressions of water release to be more pronounced,” stated Prof. Saskia Goes, Imperial College London.

The Volatile Recycling in the Lesser Antilles (VoiLA) task unites a big multidisciplinary group of scientists consisting of geophysicists, geochemists and geodynamicists from Durham University, Imperial College London, University of Southampton, University of Bristol, Liverpool University, Karlsruhe Institute of Technology, the University of Leeds, The Natural History Museum, The Institute de Physique du Globe in Paris, and the University of the West Indies.

“We collected data over two marine scientific cruises on the RRS James Cook, temporary deployments of seismic stations that recorded earthquakes beneath the islands, geological fieldwork, chemical and mineral analyses of rock samples, and numerical modeling,” stated Dr. Cooper.

To trace the impact of water along the length of the subduction zone, the researchers studied boron structures and isotopes of melt additions (small pockets of caught lava within volcanic crystals). Boron finger prints exposed that the water-rich mineral serpentine, consisted of in the sinking plate, is a dominant provider of water to the main area of the Lesser Antilles arc.

“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 of the sinking plate are directly connected to the volcanic evolution of the arc and its associated hazards,” stated Prof. Colin Macpherson, Durham University

“The wettest parts of the downgoing plate are where there are major cracks (or fracture zones). By making a numerical model of the history of fracture zone subduction below the islands, we found a direct link to the locations of the highest rates of small earthquakes and low shear wave velocities (which indicate fluids) in the subsurface,” stated Prof. Saskia Goes.

The history of subduction of water-rich fracture zones can likewise describe why the main islands of the arc are the biggest and why, over geologic history, they have actually produced the most magma.

“Our study provides conclusive evidence that directly links the water-in and water-out parts of the cycle and its expressions in terms of magmatic productivity and earthquake activity. This may encourage studies at other subduction zones to find such water-bearing fault structures on the subducting plate to help understand patterns in volcanic and earthquake hazards,” stated Dr. Cooper.

“In this research we found that variations in water correlate with the distribution of smaller earthquakes, but we would really like to know how this pattern of water release may affect the potential — and act as a warning system — for larger earthquakes and possible tsunami,” stated Prof. Colin Macpherson.

Reference: “Variable water input controls evolution of the Lesser Antilles volcanic arc” by George F. Cooper, Colin G. Macpherson, Jon D. Blundy, Benjamin Maunder, Robert W. Allen, Saskia Goes, Jenny S Collier, Lidong Bie, Nicholas Harmon, Stephen P. Hicks, Alexander A. Iveson, Julie Prytulak, Andreas Rietbrock, Catherine A. Rychert, Jon P. Davidson and the VoiLA group, 24 June 2020, Nature.
DOI: 10.1038/s41586-020-2407-5



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