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How water in deep Earth triggers earthquakes and tsunamis

Date: 26 June 2020 Tags: Geography & Environment

Issue

Scientists provide the first conclusive evidence directly linking deep Earth's water cycle and its expressions with magmatic productivity and earthquake activity.

 

Background

Water (H2O) and other volatiles (e.g. CO2 and sulphur) that are cycled through the deep Earth have played a key role in the evolution of our planet, including in the formation of continents, the onset of life, the concentration of mineral resources, and the distribution of volcanoes and earthquakes.

 

Details

  • Subduction zones, where tectonic plates converge and one plate sinks beneath another, are the most important parts of the cycle with large volumes of water going in and coming out, mainly through volcanic eruptions.

  • As plates journey from 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.

  • To trace the influence of water along the length of the subduction zone, the scientists studied boron compositions and isotopes of melt inclusions.

  • The 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.

  • The history of subduction of water-rich fracture zones can also explain why the central islands of the arc are the largest and why, over geologic history, they have produced the most magma.

  • In this research scientists found that variations in water correlate with the distribution of smaller earthquakes, but further studies are required to know how this pattern of water release may affect the potential and act as a warning system for larger earthquakes and possible tsunami.

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