Synopsis: Acoustic Trigger For Earthquakes

Numerical simulations support the idea that acoustic waves can trigger earthquakes by reducing friction between the rocks within a fault.

Big earthquakes often induce smaller quakes, or aftershocks, in geological faults that are sometimes thousands of kilometers away. One explanation is that the acoustic vibrations generated by seismic waves can trigger an aftershock by creating a low-friction, fluidlike state within the fault. New numerical simulations support this so-called acoustic fluidization hypothesis. The work also shows that faults may self-induce seismic activity by spontaneously generating acoustic waves.

The typical earthquake occurs when compressed rocks suddenly slide past each other along a fault line. The rate of these slips is higher than expected from measurements of rock-on-rock friction. Scientists have therefore proposed that sound waves—generated locally or externally—cause fluidlike motion in small grains lodged within the fault. Evidence for this has come from experiments showing that acoustic vibrations can reduce friction in granular materials.

Eugenio Lippiello from the Second University of Naples in Italy and his colleagues explored whether acoustic waves could affect the slip dynamics in a simulated fault system. Their model consisted of two rough plates pressed together with a bed of spherical grains in between. Under an applied shear stress, the plates exhibited occasional slips, just as in real faults. But when the team perturbed their system with externally produced acoustic waves, they found that slipping occurred earlier. As predicted by acoustic fluidization, this “triggering” occurs at a resonant frequency corresponding to waves bouncing back and forth inside the fault. The researchers found that these same resonant waves appeared spontaneously in unperturbed systems a short time before each slip, suggesting that acoustic waves may internally arise inside a fault and trigger a slip a few seconds later.

This research is published in Physical Review Letters.

–Michael Schirber


Features

More Features »

Announcements

More Announcements »

Subject Areas

GeophysicsMaterials Science

Previous Synopsis

Quantum Information

Connecting Qubits with Sound

Read More »

Next Synopsis

Topological Insulators

Hunting Grounds for Dirac Electrons

Read More »

Related Articles

Viewpoint: Acoustic Experiments without Borders
Interdisciplinary Physics

Viewpoint: Acoustic Experiments without Borders

A new approach to laboratory acoustic experiments could remove unwanted effects caused by the reflections of acoustic waves from the boundaries of the experimental setup. Read More »

Focus: Glue or Ink Improves Soft Metal Cuts
Industrial Physics

Focus: Glue or Ink Improves Soft Metal Cuts

Coating a soft metal with any compound that adheres leads to smoother cuts because the coating makes the surface more brittle. Read More »

Synopsis: Beat Strong, My Liquid Gallium Heart
Fluid Dynamics

Synopsis: Beat Strong, My Liquid Gallium Heart

Applying a current across a drop of liquid gallium induces an oscillatory motion reminiscent of that of a beating heart. Read More »

More Articles