RESEARCH
AREAS OF RESEARCH
Background
It is increasingly apparent that faults are zones with a complex internal structure that typically involves localized deformation on slip surfaces within a fault core surrounded by damage zone of distributed fractures. High-resolution map traces of large continental earthquakes and measurements from exhumed faults show that the slip surfaces are non-planar with a fractal geometry at all scales.
We use numerical simulations and laboratory experiments to study the effects of the complex structure of faults on the rupture process during earthquakes or aseismic deformation and to explain key field observations.
The effects of fault roughness and rock rheology on the seismic cycle
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Rupture complexity
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Rupture speed
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Slip patterns
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Earthquake nucleation
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Transition between seismic and aseismic slip
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Reoccurrence time and magnitude of small earthquake
The movie shows simulation results for the spatiotemporal evolution shear stress during the nucleation and propagation of a frictional rupture on a rough fault.
Background
The asymmetric geometry of thrust faults with respect to the Earth’s surface leads to complex dynamic behavior of up-dip ruptures with amplification of ground motions, asymmetry between the hanging and footwall, and reduction in normal stress.
We characterize the interaction of thrust ruptures with the free surface with an experimental technique that combines ultra-high speed photography with digital image correlation. (In collaboration with Profs. Ares Rosakis and Nadia Lapusta and Dr. Vito Rubino from Caltech)
Generating and imaging laboratory earthquakes
Schematics of the laboratory setup to generate and visualize laboratory earthquake. Using a combination ultrahigh-speed photography and digital image correlation (Rubino, Rosakis, and Lapusta, 2017; 2019), we study the spatiotemporal evolution of frictional ruptures with full-field maps of displacements, velocities, strain, and stresses at time intervals of 0.5 - 1 microseconds.
The interaction of thrust ruptures with the free surface
In the movie, the experimental technique is used to observe the spatiotemporal evolution of a laboratory thrust rupture near the free surface with maps of particle velocity magnitude and overlaid velocity vectors
Background
The common view is that because earthquakes occur by sudden slippage along a pre-existing fault or plate interface, they are a frictional phenomenon. The evolution of frictional resistance controls the nucleation and propagation of shear ruptures and the transition between stable and unstable sliding.
We study the evolution of frictional resistance with the following approaches:
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Performing our own experiments, in which we observe laboratory frictional ruptures with a coupled ultra-high speed photography and digital image correlation method.
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Numerical modelling of laboratory experiments.
Study the friction resistance by imaging of laboratory ruptures
Using an experimental setup that combines ultrahigh-speed photography and digital image correlation (Rubino, Rosakis, and Lapusta, Nature communications, 2017; Experimental Mechanics 2019; and Tal, Rubino, Rosakis, and Lapusta, Applied Sciences, 2019), we study the spatiotemporal evolution of frictional ruptures with full-field maps of displacements, velocities, strain, and stresses at time intervals of 0.5 - 1 microseconds. These measurements enable to study the evolution dynamic friction as function of slip, slip rate, and normal stress directly at the experimental interface.
Frictional resistance response to variations in normal stress
While friction traditionally is defined as being proportional to normal stress, experimental studies have shown that frictional shear resistance does not change instantaneously in response to a step changes in normal stress but evolves gradually with slip. In a recent paper (Tal, Rubino, Rosakis, and Lapusta, PNAS, 2020), we monitored the interaction of laboratory thrust ruptures with the free surface, demonstrated that the shear frictional resistance exhibits a significant lag in response to normal stress variations, and identified a predictive frictional formulation that captures this delay.
Modelling friction experiments
The frictional behavior observed in rock friction experiments usually represents a combined response of the frictional interface and the bulk of the sample. This can lead to a misinterpretation of the local frictional behavior on the interface. Modelling of friction experiments enables to (1) relate the macroscopic behavior of the sample to the local frictional behavior on the interface; (2) better understand the effects of fault geometry, sample dimensions, and boundary conditions; and (3) constrain the frictional properties of the interface.
An example from a study in which we modelled experimental data of the slip behavior of rough granite surfaces (Tal, Goebel, Avouac, EPSL 2020) is shown in the movie.
Background
Geological and geophysical observations of fault zones reveal that fault cores are surrounded by regions of damaged rocks consist of fractures at a wide range of length scales, with decaying intensity with distance from the fault core. The main mechanisms proposed for the development of off-fault damage include slip on rough faults, dynamic damage from the passage of earthquake ruptures, and static migrating process zones.
We study the the production of damage by comparing numerical models with field data from exhumed faults and by experimental observations of damage production during rock deformation.
Modelling the damage extent near faults
We investigate effects of fault non-planarity and earthquake ruptures on the production of damage by comparing numerical models with field data from exhumed small displacement faults within the Atacama fault zone in northern Chile. (In collaboration with Prof. Daniel Faulkner from the university of Liverpool).
