Sinking seamount offers clues to slow motion earthquakes

Date:
June 22, 2023
Source:
University of Texas at Austin
Summary:
The first ever 3D seismic imaging of a subducting seamount shows
a previously unknown sediment trail in Earth's crust off the coast
of New Zealand. Scientists think the sediment patches help release
tectonic pressure gradually in slow slip earthquakes instead of
violent tremors.

The findings will help researchers search for similar patterns at
other subduction zones like Cascadia in the U.S. Pacific Northwest.


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==========================================================================
FULL STORY ========================================================================== Scientists have long puzzled over what happens when seamounts -- mountains
and volcanoes on the seafloor -- are pulled into subduction zones. Now,
new research from The University of Texas at Austin shows that when
seamounts sink, they leave behind a trail of soft sediments. The
researchers think the sediment patches help tectonic pressure escape
gradually in slow slip earthquakes instead of violent tremors.

The findings, published June 7, 2023, in the journal Nature Geoscience,
can be used to adjust earthquake models and help scientists unravel the mechanisms that drive earthquakes.

The research was led by Nathan Bangs, a senior research scientist at
the University of Texas Institute for Geophysics. In 2018, Bangs led an
ocean seismic survey that resulted in the first ever 3D scan of a large subducting seamount. Known as the Pāpaku Seamount, the long extinct volcano lies some three miles under the seafloor inside the Hikurangi subduction zone off the coast of New Zealand.

Images from the scan show the seamount colliding with the subduction
zone and the pattern of stresses, fluids and sediments surrounding
it. Previous models suggested sediments are pushed down the subduction
zone ahead of the seamount, but the scan revealed something different:
a massive sediment trail in Pāpaku's wake.

In another surprise, the scientists spotted the fading trail of a much
larger seamount that had long since sunk beneath New Zealand's North
Island.

According to Bangs, the discovery suggests that sinking seamounts drag
down enough water-rich sediment to create conditions in the crust suitable
for slow slip earthquakes, at least in New Zealand.

"That older one seems to be very much linked to an uplifted ridge that's
really in the bullseye of where recent slow slip activity has been,"
Bangs said.

"There could be other places like Cascadia (in the U.S. Pacific Northwest)
that have subducting seamounts and a lot of sediment, but because the subducting crust there typically has less water than Hikurangi, they may
be less likely to have the same kind of shallow slow slip activity."
Slow slip earthquakes are slow motion versions of large earthquakes,
releasing similar levels of pent-up tectonic energy but in a harmless
creeping fashion that can take days or weeks to unfold. Scientists believe
that the make-up of the crust is a major factor in how tectonic energy
is released, with softer, wetter rocks allowing plates to slip slowly,
while drier, brittle rocks store energy until they fail in violent and
deadly megaquakes.

The new findings reveal how those conditions sometimes come about and importantly, said Bangs, tell scientists what to look for at the world's
other subduction zones.

The research and seismic survey were funded by the National Science
Foundation and similar scientific agencies in New Zealand, the United
Kingdom and Japan.

The University of Texas Institute for Geophysics is a research unit of
the Jackson School of Geosciences.

* RELATED_TOPICS
o Earth_&_Climate
# Earthquakes # Natural_Disasters # Geography # Geology
o Fossils_&_Ruins
# Early_Climate # Paleontology
* RELATED_TERMS
o Earthquake o Geologic_fault o Alpine_Fault o Sedimentary_rock
o Crust_(geology) o Mid-ocean_ridge o Paleoclimatology o Volcano

========================================================================== Story Source: Materials provided by University_of_Texas_at_Austin. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Nathan L. Bangs, Julia K. Morgan, Rebecca E. Bell, Shuoshuo Han,
Ryuta
Arai, Shuichi Kodaira, Andrew C. Gase, Xinming Wu, Richard Davy,
Laura Frahm, Hannah L. Tilley, Daniel H. N. Barker, Joel H. Edwards,
Harold J.

Tobin, Tim J. Reston, Stuart A. Henrys, Gregory F. Moore, Dan
Bassett, Richard Kellett, Valerie Stucker, Bill Fry. Slow slip
along the Hikurangi margin linked to fluid-rich sediments trailing
subducting seamounts.

Nature Geoscience, 2023; 16 (6): 505 DOI: 10.1038/s41561-023-01186-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230622120919.htm

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