hide
Free keywords:
-
Abstract:
Numerical investigations of 2D and 3D modes of large-scale convection in faulted aquifers are presented with the aim to infer possible transport mechanisms supporting the ormation of thermal springs through fractured aquicludes. The transient finite elements models are based on dealized structural features that can characterize many hydrothermal systems. The sensitivity analysis of the fault permeability showed that faults cross-cutting the main regional flow direction allow groundwater to be driven laterally by convective forces within the fault planes. Therein thermal waters can either discharge along
the fault traces or exit the fault through adjacent permeable aquifers. In the latter case, the resulting flow
is helicoidally and transient. The location and the spacing between discharge areas can migrate with time, is not strictly constrained to the damage zones and reflects the wavelength of the multicellular regime in the fault zone.
An illustrative example based on simplified structural data of the Lower Yarmouk Gorge (LYG) is presented. The numerical calculations indicate that crossing flow paths result from the coexistence of fault convection, developing for example along NE-SW oriented faults within the Gorge, and additional flow fields. The latter are induced either by topography NeS gradients, e.g. perpendicular to the major axe of the Gorge, or by local thermal convection in permeable aquifers below the Eocene aquiclude. Sensitivity analysis of fault hydraulic conductivity (K) and the analytical solutions based on viscousdependent Rayleigh theory show that K values between 2.3e_7 m/s and 9.3ee 7 m/s (i.e. 7 m/yr and
30 m/yr, respectively) favor coexisting transport processes. The uprising thermal plumes spread over
several hundred meters forming clusters of springs, in agreement with observation, and which temperature
fall within the measured ranges, i.e. 20 _C_60 _C. To some extent the models also reproduced the transient behavior of the spring temperature. Owing to the idealized nature of the presented models, the numerical results and the associated analytical solution can be applied to study the onset of thermal convection and resulting flow patterns of any fractured hydrothermal basin.
