CIG April Webinars

CIG April Webinars


What can we learn about friction evolution and rupture behavior from laboratory experiments?
Vito Rubino, Ecole Central de Nantes

Characterizing the rheology of faults is of paramount importance to improve our understanding of frictional ruptures and earthquake physics, as friction controls key processes of rupture nucleation, propagation, and arrest and also influences how damaging earthquakes can be. In this presentation, I will describe the evolution of frictional strength during the propagation of dynamic ruptures using laboratory experiments. Our innovative experimental approach allows us to capture the full-field evolution of particle velocities of dynamic ruptures and decode the nature of friction by tracking its evolution and studying its dependence on slip, slip velocity and their history. We find that friction evolution is consistent with the rate-and-state friction laws combined with flash heating weakening mechanism but not with the widely used slip-weakening laws. Our recent experiments along interfaces enriched with fault gouge, the pulverized rock present in natural fault, reveal an even more complex behavior characterized by intermittent rupture propagation. The measured friction behavior allows us to challenge existing friction laws and formulate new ones. This approach gives a new perspective on the study of friction and provides important insights into earthquake and rupture physics. [more info] [register]


Making the Ocean Floor: Two-phase dynamics of mantle melting and formation of oceanic lithosphere
Adina Pusok, Oxford University

The theory of plate tectonics established fifty years ago has formed a robust framework for understanding how the Earth works across a range of scales. While the kinematics of plate tectonics is well established, the dynamics remain a challenge. A key component is understanding the nature of the oceanic lithosphere–asthenosphere system. The classic view suggests that mid-ocean ridges (MORs) are places of passive mantle upwelling driven by plate divergence, and that the oceanic lithosphere forms by conductive cooling away from the ridge axis. Melt represents a passive component in this model – a view that has been questioned by recent seismic and magnetotelluric data from the sea floor. Here I present two-phase flow numerical models of MORs and oceanic lithospheric extension that highlight the dynamic role of melt in the oceanic lithosphere–asthenosphere system. In a first part, I show that melting-induced buoyancy effects may induce time-dependent flow and provide an explanation for both the asymmetric distribution of melt beneath the axis and the inferred short-wavelength variations in the lithosphere–asthenosphere boundary (LAB). In a second part, I show some preliminary results using a new poro-viscoelasto-viscoplastic theory that allows for the formation and evolution of fluid-driven fractures, such as dikes and sills. I investigate how magma interacts with the solid-rock closer to the MOR axis, and whether magma supply controls fragmentation of oceanic lithosphere. Finally, these results were obtained using the FD-PDE framework, which is a computational framework for building flexible, testable and robust geodynamic models. [more info] [register]

Mechanical behavior of lubricated faults during earthquake nucleation and propagation
Marie Violay, EPFL

Natural and human Induced Fluid Earthquakes (FIEs) have been observed and recorded for decades. These events can be responsible for significant human, economical and infrastructure damage. FIEs result from the interaction between fluid pressure perturbations, in-situ stresses, frictional and rupture processes at micro to macro scales, and the geometric complexity of the fault zone. Methods for risk assessment and forecasting (in terms of time, location and magnitude) of FIEs require a sound physical basis. However, much of the primary parameters controlling FIE dynamics cannot be measured by geophysical methods. Thus, to establish new general constitutive physical FIE laws, the temporal- and spatial-scale dependence of FIEs should first be properly investigated in the laboratory. here we studied the influence of viscous lubricant in the nucleation and propagation of spontaneous frictional ruptures. [more info] [register]

Nicola Tisato, University of Texas at Austin

See our calendar for a full list of upcoming events.