Do earthquakes and tectonic plates have a two-way relationship?

The residents of Izmit, Turkey, were asleep when the ground began to shake on August 17, 1999. The earthquake recorded a magnitude of 7.4, triggered aftershocks, and proved to be completely destructive, leaving more than 17,000 dead, tens of thousands injured, and billions of dollars. damages. But it was exceptional for another reason: it affected the movement of the tectonic plate. This discovery may lead to a rethinking of how earthquake risk models are pieced together.

Scientists have long known that earthquakes occur when slips occur along fault lines. These can be generated by pressing on the edges of tectonic plates, which are constantly moving over the Earth’s mantle. But researchers who investigated the İzmit earthquake made unprecedented observations of plate motion and concluded that the earthquakes themselves could influence plate motion, which in turn could influence subsequent earthquakes. “These findings suggest a full-plate kinetic signal associated with stress from large earthquakes,” they wrote in a Geophysical Journal International study.

GPS data detects movement change

The theory of plate tectonics, generally accepted since the mid-20th century, assumes that large earthquakes do not cause a disturbance in plate motion; Rather, motion is the result of energy transfer via stress accumulated over long periods of time. The researchers conclude that although this one-way relationship is the case for large plates, finer plates may be more susceptible to impact from earthquakes due to their lower area covering the boundary between the lithosphere and the asthenosphere.

The Anatolian Miniature Panel provided a good opportunity to test this idea, not only because it is small and stretches across most of Turkey and heads towards the Mediterranean, but also because it supports an area that has had good GPS data coverage for decades. GPS data is used in geodetic surveys, which analyze points on the Earth’s surface, including how they have been affected by earthquakes. Comparing the data over time can reveal the movement of the plate.

“Seismicity and plate motions are linked by a feedback mechanism, which means that large seismic events are able to alter the rigid motion of the plates.”

The researchers calculated that the rotational force, or torque, required to change the course of the tectonic plate is very close to the torque produced by earthquakes. In an analysis of GPS data, they found that not only did the Anatolian plate change its direction, but also the frequency of earthquakes around Turkey after the Izmit earthquake.

“In our study, we observe a change in Anatolian kinematics from before to after the Izmit earthquake, and we discover that the force change needed to change Anatolian motion to the degree determined by geodetic observations corresponds to the force shift transmitted,” said co-author Juan Martin de Blas, a postdoctoral geology researcher at University of Copenhagen “Izmit Earthquake”.

“Earthquakes are not just a product of plate movements,” he added. Instead, earthquakes and plate motions are linked by a feedback mechanism, which means that large seismic events are capable of altering the rigid motion of the plates. This link has other implications because it suggests that plate motions may also differ in the years to decades before an earthquake.”

Lots of new questions

This feedback mechanism could represent a major new insight into plate tectonics. The challenge of one of the basic tenets of tectonics – that plate motions are essentially constant during an earthquake cycle – met some resistance during the study review process. However, de Blas said, the team found open-minded reviewers who made suggestions that helped advance the paper.

The researchers believe that the insight should be incorporated into the computer models used to calculate earthquake risk. Rather than assuming that plate motions are constant, the feedback mechanism between earthquakes and plates should be taken into account, they say. This calculation also includes greater use of data from GPS devices located further away from the edges of the plate to give a better overall picture of the plate’s dynamics, according to the team.

Richard Styron, an active fault specialist with the Italy-based Earthquake Risk Foundation, said the global earthquake model was not involved in the study. “Future research will be needed to better understand the mechanisms of this change, in particular the response of the viscoelastic lower crust and upper mantle that modulate plate motions and the frequency of the earthquake cycle.”

Among other unknowns is whether the change in plate motion is permanent, associated with a greater evolution in regional tectonics, or a transient change that will be reversed, said Styron, who praised the work as a “remarkable study.”

Meanwhile, de Blas and his colleagues plan to investigate other areas for clues to the feedback mechanism. They are looking for geological settings where similar dynamics apply and will test whether the feedback mechanism also applies to the overlap period, when energy builds up before it is suddenly released by earthquakes.

—Tim Horniak (@robotopia), science writer

Citation: Horniak, T. (2022), Do earthquakes and plate tectonics have a bidirectional relationship?, Eos, 103, https://doi.org/10.1029/2022EO220189. Posted on April 18, 2022. Text © 2022. authors. CC BY-NC-ND 3.0 Unless otherwise noted, images are subject to copyright. Any reuse without the express permission of the copyright owner is prohibited. Related

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