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

Abstract

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 diffusion 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 m•o 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.

Clues to the identification of a seismogenic source from environmental effects: the case of the 1905 Calabria (Southern Italy) earthquake

“…We assumed that the observed streamflow variations are the hydrological response to coseismic strain changes (MuirWood and King, 1993). Several studies demonstrate that the polarities of calculated deformation are in agreement with those of the observed hydrological effects so that extensional strain produces a discharge fall and compressive strain a discharge rise, especially in the near field (Grecksch et al, 1999;Ge and Stover, 2000;Lee et al, 2002;Montgomery and Manga, 2003;Caporali et al, 2005).…”

“…In particular, MuirWood and King (1993) found that hydrological changes would accompany major normal fault, showing increase in streamflow and spring rise; reverse faults, on the contrary, would show negligible or undetectable effects, whilst strike slip and oblique faults would generate a combination of responses. Recently, the spatial pattern of water level changes has been compared with simulated coseismic strain changes (Grecksch et al, 1999;Ge and Stover, 2000;Lee et al, 2002;Montgomery and Manga, 2003;Caporali et al, 2005). The area interested by contractional volumetric strain seems to be in good agreement with the water level rise and water excess in streamflows.…”

Coseismic response of groundwater level in the Three Gorges well network and its relationship to aquifer parameters

“…Such changes can include step-changes in water level, water-level oscillations, and sustained change in water level [8][9][10][11]. Usually, a step-change in water level is considered to be caused by static stress release as fault slips [12][13][14][15]. Seismic waves can also lead to step-changes [10] and oscillations [2,[16][17][18] in groundwater level.…”

Streamflow Changes in the Vicinity of Seismogenic Fault After the 1999 Chi–Chi Earthquake

“…Generally, larger changes, up to 11.09 m, were found in wells closer to the fault. These co-seismic changes were likely caused by coseismic strain induced by fault displacement (Wakita 1975;Roeloffs 1988;Grecksch et al 1999;Ge and Stover 2000;Chia et al 2001Chia et al , 2008b. The distribution of the sustained changes in the footwall revealed that crustal extension dominated near the Chelungpu fault during the earthquake, while compression prevailed away from the fault.…”