Coseismic damage generation and pulverization in fault zones: insights from dynamic Split Hopkinson Pressure Bar experiments. In “Fault Zone Properties and Processes during Dynamic Rupture”
Published by: Aben, F., Doan, M.-L., Gratier, J.-P., and Renard, F.
Conceptual damage zone geometries for several different rupture types. The red line indicates the fault plane with sense of movement (black arrows). The pulverized interval is bordered by a blue line, the damage zone boundary by black. (a) Geometry for systematic bilateral sub‐Rayleigh rupture. The zone of pulverized rocks has a small width and thins quickly with depth. (b) Geometry for unilateral sub‐Rayleigh ruptures with a preferred direction. The damage would be concentrated in the tensional quadrant, including pulverized rocks. (c) Bilateral supershear rupture geometry with a much larger zone of pulverized rocks within the same order of magnitude as the damage zone boundary. Pulverized rocks can extend to much greater depths relative to sub‐Rayleigh ruptures. (d) Asperity‐ and barrier‐controlled damage zone geometry that shows a much more patchy distribution of damage along the fault due to dynamic rupture velocities from sub‐ to supershear. See electronic version for color representation.
Coseismic damage in fault zones contributes to the short‐ and long‐term behavior of a fault and provides a valuable indication of the parameters that control seismic ruptures. This review focuses on the most extreme type of off‐ fault coseismic damage: pulverized rock. Such pervasively fractured rock that does not show any evidence of shear strain is observed mainly along large strike‐slip faults. Field observations on pulverized rock are briefly examined and would suggest that dynamic (high strain rate) deformation is responsible for its generation. Therefore, these potential paleo‐seismic markers could give an indication of the constraints on rupture propagation conditions. Such constraints can be determined from dynamic loading experiments, typically performed on a Split‐Hopkinson Pressure Bar apparatus. The principle of this apparatus is summarized and experimental studies on dynamic loading and pulverization are reviewed. For compressive dynamic loading, these studies reveal a strain rate thresh- old above which pulverization occurs. The nature of the pulverization threshold is discussed by means of several fracture mechanics models. The experimental pulverization conditions are correlated with field observations by analyzing and discussing several earthquake rupture models. An indisputable rupture mechanism could not be established owing to a gap in experimental knowledge, especially regarding tensile dynamic loading.