iTi – Institute of Triggering and Instability

Introduction

iTi exists to link researchers studying instabilities leading to failure in granular materials.  These include the study of the new slip behaviors observed in Earth ranging from stick-slip to slow-slip, Earth tremor and dynamic wave triggering of these phenomena.

Summary

In the past 20 years or so, an extremely rich spectrum of slip behaviors has been observed in Earth.  Fast slip of faults results in earthquakes and associated radiation of seismic waves.  Slow-slip (measured from global positioning satellites, surface-based strain meters, or tilt meters) can take place over minutes hours or days and is common along active tectonic boundaries.  Slow slip can occur silently or with a noise-like rumbling termed non-volcanic tremor.  Tremors can occur on their own, but some believe that they are a manifestation of slow slip and can be used as a proxy for slow-slip.

All of these phenomena can be triggered by various means.  Seismic waves from one earthquake, principally surface waves, may trigger other earthquakes nearby, in what is known as the aftershock region or well beyond and thousands of kilometers from the triggering earthquake.  This has been known since the well known Landers Earthquake that occurred in the early 1990’s in California, USA. Slow-slip too can be triggered.  Slow slip too may be triggered by seismic waves. More recently it was discovered that tremor could be triggered by seismic waves as well.  Moreover, triggering can be induced by quasi-static forcing, for instance by Earth and ocean tides.

Fault zones are comprised of gouged granular material that has been created by communication over geologic time and multiple faulting episodes.  The behavior of the granular material is thought to control the slip process through initiation and failure.

The work of collaborators associated with iTi is devoted to understanding how all types of slip initiate, proceed and terminate. We are focused particularly on the behavior of granular material that controls these processes. We are applying laboratory experiments, Earth observations, and modeling in order to elucidate the physics of slip.  Our laboratory work at Pennsylvania State Univsity (USA) in the laboratory of Chris Marone includes controlled studies of slip in a bi-axial configuration.  Our model studies include molecular dynamical (MD) studies of sheared beads in contact and brittle-ductile frictional (BDF) modeling of sliding blocks.  The model work is shared between ETH and EMPA in Zurich and the Los Alamos National Laboratory.


Publications

Daub, E. G., D. R. Shelly, R. A. Guyer, and P. A. Johnson (2011), Brittle and ductile friction and the physics of tectonic tremor, Geophys. Res. Lett. 38, L10301. (PDF File – 571 KB)

The Dynamics of Tectonic Tremor Throughout the Seismic Cycle, Daub, et. al. (HTML Poster)

Discrete Element Method modeling of granular friction, stick-slip dynamics and the investigation of dynamic earthquake triggering (HTML Poster)

The micromechanics of fault gouge and dynamic earthquake triggering: investigation by Discrete Element Method numerical simulations (HTML Poster)


Collaborators

  • Pennsylvania State University
  • USGS
  • University of Tokyo
  • University of Nevada
  • University of Bath (UK)
  • University of Grenoble (France)
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