Earthquake fracture energy relates to how a quake stops
Date:
March 8, 2022
Source:
Cornell University
Summary:
By examining earthquake models from a fresh perspective, engineers
now show that the earthquake fracture energy -- once thought to
relate to how faults in the Earth's crust weaken -- is related to
how quakes stop.
FULL STORY ==========================================================================
By examining earthquake models from a fresh perspective, Cornell
University engineers now show that the earthquake fracture energy --
once thought to relate to how faults in the Earth's crust weaken --
is related to how quakes stop.
==========================================================================
This modeling revelation could help science inch closer to making accurate earthquake forecasts.
"We realized that observations we thought were related to how faults
weaken are actually data related to how an earthquake stops," said Greg McLaskey, assistant professor in the School of Civil and Environmental Engineering, in the College of Engineering. "We've observed that
earthquake fracture energy is more related to the overall rupture style
-- such as crack-like or pulse-like rupture -- instead of a specific slip-weakening relationship (the way the crust weakens when plates slide
past each other)." The work, "Earthquake Breakdown Energy Scaling
Despite Constant Fracture Energy," was published Feb. 22 in Nature Communications. In addition to McLaskey, the lead author was Chun-Yu
(Huey) Ke, Ph.D. '21, and David S. Kammer at the Institute for Building Materials, ETH Zu?rich, Switzerland. The research was supported by the
National Science Foundation.
Research over the past 25 years has focused on earthquake fracture energy
or breakdown energy usually estimated from ground shaking, McLaskey said.
That research had linked earthquake fracture energy to the way the Earth's crust weakens during an earthquake. But by studying large-scale rock experiments -- at the Bovay Laboratory Complex -- between two two-ton
granite slabs, the researchers at Cornell found that those models may
have been slightly askew.
==========================================================================
The lab's computer models suggested that those seismic observations are
not directly related to fracture energy, but instead, the new research indicated, the seismic observations depend on how the earthquake ends,
as related to either a pulse-like or crack-like rupture style.
For a pulse-like rupture, the fault resembles an inchworm moving along a surface. The inchworm doesn't jump, McLaskey said, and only a little bit
moves at a time. In a crack-style rupture, the fault resembles a zipper.
Seismologists have been measuring the fracture energy (sometimes called breakdown energy) of earthquakes. "That parameter of an earthquake should
not be interpreted as a weakening of the crust," he said, "but whether
the earthquake rupture is a pulse or a crack." When earthquakes do occur,
they end. The slipped part of the fault tapers off and eventually merges
with part of the crust that is not ruptured. "Think of a car approaching
a stop sign," he said. "You don't stop abruptly. You see the sign and you
apply the brakes -- but the factor we've introduced is whether you're
coming to a stop sign going uphill, downhill or on a flat surface."
The engineers found that when they slammed on the experimental brakes,
they could not get the ruptures to stop. "The only way we could get
our ruptures in the lab to stop is by making 'a hill,' so to speak,"
McLaskey said. "We introduced that factor into our model and it began
to make sense." Earthquakes are unpredictable, he said, discussing
early warning technology used around the world in Japan and Mexico,
and now being developed in California.
"If you get a 1-second warning because of sensors that there will be an earthquake -- maybe a 10-second warning -- you'll be lucky," he said.
"One of the reasons why it is difficult to predict earthquakes is
because scientific modeling equations don't always add up," McLaskey
said. "This paper is a step in the right direction. We're getting a
better understanding of these models -- hopefully leading to an ability
to predict earthquakes." McLaskey is a faculty fellow at the Cornell
Atkinson Center for Sustainability.
========================================================================== Story Source: Materials provided by Cornell_University. Original written
by Blaine Friedlander. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Chun-Yu Ke, Gregory C. McLaskey, David S. Kammer. Earthquake
breakdown
energy scaling despite constant fracture energy. Nature
Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-28647-4 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/03/220308155631.htm
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