A groundbreaking study reveals the intricate process of how earthquakes form, shedding light on the gradual buildup of stress that eventually leads to a catastrophic release of energy. Conducted by physicist Jay Fineberg and his team at The Hebrew University of Jerusalem, the research investigates the mechanisms behind tectonic movements and their eventual transformation into seismic events. Published in the journal Nature, this study utilizes lab experiments to simulate real-world conditions, offering valuable insights into the precursors of earthquakes.
Earthquakes occur when two tectonic plates moving against each other become momentarily stuck, allowing stress to accumulate along the fault line. Fineberg's team explored this phenomenon by clamping sheets of plexiglass together and applying a shear force, mimicking the conditions found in strike-slip faults such as California's San Andreas Fault. These experiments reveal that before a crack forms, the material undergoes a precursor phase known as a nucleation front, which plays a critical role in the formation of earthquakes.
"The plates are increasingly stressed by the forces trying to move them, but are stuck at the brittle part of the interface that separates them," said Jay Fineberg.
The study's findings indicate that a period of slow, creeping movement without any noticeable shaking may be an essential prelude to earthquakes. This creeping phase is characterized by the gradual buildup of stress at the brittle part of the interface between the tectonic plates. Fineberg emphasizes that the material composition of the contacting plates does not significantly impact this process.
"The material composing the contacting plates will not matter," noted Fineberg.
In their experiments, Fineberg and his team observed that a crack begins as a patch within the plane where two plexiglass "plates" meet. This crack then transitions from a two-dimensional model into a one-dimensional line, ripping through the material with increasing speed. The researchers discovered that modeling nucleation fronts in two dimensions, rather than one, was crucial to understanding this transition.
"The fracture process doesn’t happen all at once. First, a crack needs to be created," explained Fineberg.
As the crack progresses, it reaches the borders of the brittle interface and accelerates rapidly to speeds approaching the speed of sound. This rapid acceleration is what triggers the shaking that characterizes an earthquake.
"When that crack reaches the borders of the brittle interface, that crack accelerates rapidly to speeds close to the speed of sound. That's what makes the earth shake," Fineberg stated.
The study highlights how a slow creep before a crack can swiftly transition into an earthquake, emphasizing the importance of detecting these signs in laboratory materials. Fineberg and his team are currently working to identify indicators of this transition from aseismic (non-shaking) to seismic (shaking) activity.
"This extra energy now causes the explosive motion of the crack," Fineberg remarked.
By combining lab experiments with theoretical calculations, this research provides a comprehensive understanding of how tectonic stress evolves into destructive seismic events. The findings offer a new perspective on earthquake prediction and prevention, potentially leading to improved strategies for mitigating their impact.
