Pore water pressure

About: Pore water pressure is a research topic. Over the lifetime, 11455 publications have been published within this topic receiving 247670 citations. The topic is also known as: pwp.

Hydrodynamic response to strike- and dip-slip faulting in a half-space

Abstract: Field observations have shown strong coupling between earthquake-induced stress-strain fields and subsurface hydrodynamics, reflected by water level change in wells and stream flow fluctuations. Various models have been used in an attempt to interpret the coseismic fluctuations in groundwater level, predict water table rise in the event of an earthquake, and explain stream flow variations. However, a general model integrating earthquake-induced stress-strain fields, coseismic pore pressure generation, and postseismic pore pressure diffusion is still lacking. This paper presents such a general framework with which one can approach the general problem of postseismic pore pressure diflusion in three dimensions. We first use an earthquake strain model to generate the stress-strain field. We then discuss the linkage coupling stress and strain with pore pressure and present an analytical solution of time-dependent pore pressure diffusion. Finally, we use two examples, a strike-slip and a dip-slip fault, to demonstrate the application of the analytical model and the effects of earthquakes on fluid flow. The application to the two fault systems shows that the diffusion time is shorter than conventional estimates, which are based on a diffusivity and a length scale. We find that the diffusion time is predominately a function of the diffusivity of the system, while the length scale influences the magnitude of the initial pore pressure. A diffusion time based on the diffusivity and a length may be misleading because significant localized flow occurs in complex three-dimensional systems. Furthermore, the induced patterns of a pore pressure change resemble the strain field when shear stress effects are neglected but are significantly modified when shear stresses are included in the coupling relation. The theoretical basis of this work is developed assuming a single episode dislocation. However, the methodology and the results can be readily applied to studying pore pressure conditions after multifaulting events by simple superposition.

Settling, dissolution and burial of biogenic silica in the sediments off Somalia (northwestern Indian Ocean)

Abstract: Particle fluxes of biogenic silica through the water column, silica burial fluxes into the sediments, and the flux of dissolved silica across the sediment-water interface estimated from pore water profiles are used to assess the behaviour of biogenic silica at two stations 80 and 270 km offshore along a transect off the Somali coast in the northwestern Indian Ocean. Particulate biogenic silica fluxes varied from 0.3 mmol m−2 day−1 in the non-upwelling season to 6 mmol m−2 day−1 during upwelling on the Somali slope. Fluxes were lower in the Somali Basin, from 0.2 to 2.3 mmol m−2 day−1. Evaluation of the dissolution curves derived by wet chemical leaching in sediment trap and sediment samples shows that the Km values, the apparent reactivity rates in alkaline medium, are higher for the shallow sediment traps than for deep trap and boxcore sediments. Modelling of pore water profiles shows that in the sediment most dissolution occurs in the top halfcentimetre, and pore water effluxes are in close agreement with those from in situ benthic incubations. Our results show that less than 10% of the biogenic silica arriving on the Somali Margin is buried in the sediments, giving a burial efficiency lower than the approximately 20% reported from the open Arabian Sea.