Using Laboratory Earthquake Ruptures and Ultra-High Speed DIC to Reveal the Structure of Dynamic Friction
About the Event:
Friction plays a central role in determining how ruptures propagate along faults in the earth’s crust and release waves that cause destructive shaking threatening our infrastructure and endangering our lives. Yet, the detailed nature of the dynamic frictional laws, which operate on such faults, is one of the biggest uncertainties in earthquake source mechanics. This presentation discusses unprecedented measurements of evolving local, on-fault, friction recorded dynamically during spontaneous mini-earthquakes, which are created in the laboratory. The measurements are enabled by a new high-speed full-field imaging technique (a dynamic version of Digital image correlation-DIC) and digital, ultra-high-speed, photography. This is a new way of inferring friction directly from individual transient rupture events without having to ever invoke assumptions of uniform sliding along frictional interfaces as is done in all previous frictional studies. The newly developed imaging technique quantitatively captures the full-field evolution of particle velocities, strains, and stresses of both sub-Rayleigh and Supershear ruptures created in the laboratory under conditions mimicking spontaneous rupture nucleation and tectonic loading. The technique combines pattern-matching algorithms with ultra-high-speed photography and highly tailored analysis to obtain full-field time histories in the presence of dynamic sliding discontinuities. Dynamic imaging of particle velocities, strains stresses and transient surface tractions during rupture enables unique observations of key rupture features as well as detailed analysis of dynamic friction in a fully transient setting. Our measurements do not support classical slip weakening as the operant frictional law. Instead, they show that friction is strongly velocity dependent and has a complex (history dependent) evolution, qualitatively consistent with a rate-and-state frictional law, supplemented with flash heating.
About the Speaker:
California Institute of Technology
Ares Rosakis graduated from Athens College, a Greek-American high school in June of 1975. In September of 1975, he moved to the United Kingdom to attend University College Oxford and to study engineering science. He received his bachelor's (B.A.) and Masters of Arts (M.A.) degrees from Oxford University in 1978 and 1986 respectively. He went on to earn his ScM. (1980) and PhD (1982) degrees in Engineering (solid mechanics and structures) from Brown University. He joined the California Institute of Technology (Caltech) as an assistant professor in 1982 as the Institute's youngest tenure track faculty member. He was promoted to the ranks of associate and full professor in 1988 and 1993 respectively. In 2004, he was named the Theodore von Kármán Professor of Aeronautics and Professor of Mechanical Engineering. In 2013, he was honored as the inaugural recipient of the Otis Booth Leadership Chair, Division of Engineering and Applied Science.