Sand blows as a potential tool for magnitude estimation of pre-instrumental earthquakes     

Raymi A. Castilla  Franck A. Audemard 《Journal of Seismology》2007,11(4):473-487

A worldwide database of liquefaction-induced sand blows has been compiled to generate empirical relationships between earthquake parameters and sand blow geometries. Curves resulting from these empirical relationships can be used afterwards for the study of historic and pre-historic earthquakes that formed sand blows. This database only incorporates instrumental earthquakes inducing sand blows, characterised in terms of magnitude (Mw), hypocentral location and focal mechanism solution. Two relationships are herein presented. The first curve, minimum likelihood of liquefaction occurrence (magnitude/epicentral distance), displays a logarithmic behaviour, as others already proposed. The second curve of sand-blow diameter vs epicentral distance is the first proposal of this kind, whose shape follows a negative power-law. Magnitude estimations of (pre-)historic earthquakes then may be attempted through these empirical relationships. Resulting magnitudes derived from these curves should be mostly considered as underestimated. The curves will reflect actual magnitudes only if, correspondingly, the farthest and largest blow has ever been reported during the after-earthquake survey. Following the same principle, a magnitude estimation resulting from the measuring of a sand blow can only be considered as minimal because it is almost impossible to ascertain that the measured feature is the biggest one produced by the earthquake under evaluation. Finally, these results call for thorough surveys of induced effects after every future moderate-to-large earthquake, as any empirical relationship simply improves by incorporating new data.  相似文献   

Hydromechanical reactivation of natural discontinuities: mesoscale experimental observations and DEM modeling     

Tsopela  Alexandra  Donzé  Frédéric-Victor  Guglielmi  Yves  Castilla  Raymi  Gout  Claude 《Acta Geotechnica》2019,14(5):1585-1603

Fracture interaction mechanisms and reactivation of natural discontinuities under fluid pressurization conditions can represent critical issues in risk assessment of caprock integrity. A field injection test, carried out in a damage fault zone at the decameter scale, i.e., mesoscale, has been studied using a distinct element model. Given the complex structural nature of the damage fault zone hydraulically loaded, the contribution of fracture sets on the bulk permeability has been investigated. It has been shown that their orientation for a given in situ stress field plays a major role. Based on these results, a simpler model with a fluid-driven fracture intersecting a second fracture has been set up to perform a sensitivity analysis. It is in presence of a minimum differential stress value with a minimum angle with the maximum principal stress that the second fracture could be both, hydraulically and mechanically reactivated. Results also showed that in the vicinity of the fluid-driven fracture, a natural fracture will offer contrasted hydromechanical responses on each side of the intersection depending on the stress conditions and its orientation with respect to the stress field. In this case, we show that a hydromechanical decoupling can occur along the same plane. These results provide insights into fracture-controlled permeability of fault zones depending on the properties of the fractures and their hydromechanical interactions for a given in situ stress field.

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