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Two Papers Regarding Dynamic Fault Weakening Mechanisms by Dr. Yao Lu et al. Were Rated as Research Focus in Geology and Highlight in GRL, Respectively

2016/12/29 15:21:26

Dr. Yao Lu, Professor Ma Shengli and Distinguished Visiting Professor Toshihiko Shimamoto of State Key Laboratory of Earthquake Dynamics, IGL, and two cooperators (Dr.John Platt and Dr. Andre Niemeijer) published two research papers about dynamic fault weakening mechanisms in Geology and Geophysical Research Letter (GRL) in January andJuly 2016, respectively. Through cleverlydesigned high-velocity friction experiments, these two studies explore the dominant mechanisms for dynamic fault weakening during an earthquake. The results have important implications for a better understanding of the physical process of coseismic faulting. Therefore, these two papers were rated as Research Focus in Geology or and Highlight in GRL, respectively.

The paper Dr. Yao Lu et al. published in the January 2016 issue of Geologyis entitled as “The crucial role of temperature in high-velocity weakening of faults: Experiments on gouge using host blocks with different thermal conductivities”. Dr. Yao and his collaborators conducted high-velocity friction experiments on fault gouges using host blocks (“wall rocks”) made of materials with different thermal conductivities, through which the fault-zone temperature becomes a controllable variable that is to some degree independent of the applied normal stress and slip rate in the experiment. The experimental results revealed that the high-velocity weakeningof gouge becomes more pronounced as the thermal conductivity of host block decreases and the dynamic fault weakening only occurs in the case of dramatic temperature rise. The observed differencesin frictional behaviors, deformation microstructures, and calculated temperaturedemonstrate that temperature rise driven by frictional heating is essential in causing dynamicweakening of gouge at seismic velocities. These results also reveal the important roles of dynamic temperature rise of faults in flash heating process during seismic slip.In RESEARCH FOCUS of the January 2016 issue of Geology, Professors Marone and Richardson from Pennsylvania State University gave high praise to two papers published in the same issue, and the paper published by Dr. Yao Lu et al. is one of them. Some of the comments on Yao et al. (2016) from Professors Marone and Richardson are given as follows (Marone and Richardson, 2016):

“…Yao et al. have made a major advance using a clever experimental design that disentangles the main effects. Their results show that temperature rise is the key factor causing frictional weakening in laboratory faults sheared at high velocity. Yao et al. conducted identical experiments with a variety of thermal boundary conditions to isolate the effect of temperature on fault weakening. They find that when heat is removed from the fault zone more efficiently, faults are stronger than in cases where the fault zone is better insulated and temperature rises more quickly with slip …”

“…Yao et al.’s data may also shed light on a puzzle related to the application of high-velocity friction data to earthquakes…”

“…Yao et al.’s work suggests the existence of a critical slip velocity for dynamic weakening. Could this have a structural signature within fault zones? The works of Yao et al. and Brodsky et al. point to a number of interesting questions about the connections between fault roughness, dynamic weakening and earthquake source properties that are likely to guide future work in this area for many years.”

Dr. Yao Lu and his collaborators published a companion paper entitled “Is frictional heating needed to cause dramatic weakening of nanoparticle gouge during seismic slip? Insights from friction experiments with variable thermal evolutions thermal evolutions” in GRL in July. This paper explores the effects of preexisting and newly formed nanoparticles have on dynamic fault weakening. By performing high-velocity friction experiments on periclase (MgO) nanoparticles and on bare surfaces of Carrara marble cylinders/slices under variable temperature conditions that are simulated by using host blocks of different thermal conductivities, they observed high friction in nano-MgO tests and unexpected slip strengthening following initial weakening in marble slice tests in the case of relatively low temperature rise, suggesting that the dominant weakening mechanisms are of thermal origin. Furthermore, the paper also discusses possible superplastic behaviors of the nano fault gouge at seismic slip rates, and gave a different viewpoint on flash heating for nanograins that was thought to be impossible in previous studies. The reviewers and the editor think that this paper is of great importance to a better understanding on the dynamic weakening of nano-sized fault gouge, so the Editor of GRL evaluate this paper as Highlight (http://agupubs.onlinelibrary.wiley.com/agu/article/10.1002/2016GL069053/ editor-highlight/).

Link of paper 1: http://geology.gsapubs.org/content/44/1/63.abstract

Link of paper 2: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2016GL069053/abstract