Scientists studied the impact of underwater mountains dragged into subduction zones and the geodynamic processes that occur near them.
Sea-mountains are geologic formations that rise at least 1000 meters above the ocean floor but do not reach the seawater level (so they do not form islands). A new study focuses on the effect of the underwater mountains that are pulled into subduction zones (where Earth's tectonic plates collide) on seismic shocks.
The study was recently published in Nature Geoscience journal.
Researchers performed computer simulations to examine the geological phenomena that occur when a seamount reaches an ocean trench in a subduction zone. They discovered that seamounts may either favor strong quakes or mitigate them.
Analyzing these phenomena has been a challenging task since subduction occurs at great depths and deriving the conditions in this environment has been difficult. Scientists addressed the lack of data by utilizing rock samples extracted by drilling at offshore zones near Japan to create a realistic simulation of the subduction zone and sea-mountain.
The data showed that, during subduction, the rock formations in front of the underwater mountain are squeezed and become more brittle, meaning that they break with little elastic deformation and with almost no plastic deformation. Brittle failure triggers strong earthquakes as accumulated stress is quickly released when the material fails. The data were surprising since researchers anticipated that the bedrock would have been broken down due to the increase of stress and water pressure (and would present less brittle behavior).
However, the analyses also showed that seamount leaves behind a softer, weakened material that presents a ductile behavior and mitigates the impact of seismic shocks.
According to the researchers, the developed model can be considered valid since it is verified with data from real earthquakes.
In addition, the softened rock material may shed light on the characteristics of slow-slip earthquakes that occur when faults move slowly against each other and can last for a significant amount of time (even months). According to Dr. Laura Wallace, a researcher from the University of Texas Institute for Geophysics and the New Zealand research institute GNS Science, who has studied slow-slip earthquakes in New Zealand, the findings can be utilized to show how geological structures impact the behavior of seismic shocks.
Dr. Tian Sun, lead author of the study and a researcher at the Geological Survey of Canada, stated that the study has provided new evidence on the impact of underwater mountains in a reduction zone on seismic shocks. However, the scientific team will continue the research in order to better understand the whole spectrum of the phenomenon. "We still need high-resolution geophysical imaging and offshore earthquake monitoring to better understand patterns of seismic activity,” Dr. Sun explained.
Source: University of Texas
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