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Hydrological effects of dip‐slip fault rupture on a hydrothermal plume
Author(s) -
Dempsey D. E.,
Archer R. A.,
Ellis S. M.,
Rowland J. V.
Publication year - 2013
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2012jb009395
Subject(s) - geology , fluid dynamics , petrology , permeability (electromagnetism) , geothermal gradient , pore water pressure , slip (aerodynamics) , fault (geology) , hydrothermal circulation , plume , mass flux , geotechnical engineering , seismology , geophysics , mechanics , physics , membrane , biology , genetics , thermodynamics
Abstract Earthquakes cause a variety of hydrological effects, including changes in well levels, streamflow, hot‐spring temperatures, and geyser periodicity. These may be produced by changes in pore‐fluid pressure or by changes in permeability. We investigate near‐field effects of normal earthquakes on fault‐controlled hydrothermal plumes, e.g., at the Te Kopia geothermal system on the Paeroa Fault, New Zealand. A numerical model is detailed that addresses the effects of coseismic pore‐pressure and permeability perturbations on geothermal upflow along a dip‐slip fault. Fluid flow is modeled using the heat and mass transfer code Finite Element Heat and Mass transfer. The 2 m wide fault is impermeable and thus behaves as a partition between fluid flow in the adjacent fault blocks, as well as a structure for upflow to localize upon. A realistic distribution for the coseismic change in mean rock stress is obtained from a plane‐strain mechanical model for normal fault rupture in an elastic‐plastic‐viscous crust. These stress changes are imported into the fluid flow model as pore‐fluid pressure changes. In addition, we consider the effects of fault core fracture and damage by introducing an increase in permeability at the fault plane. Results show that short‐term effects are dominated by pore‐pressure changes, which cause increased heat and mass fluxes at the surface for a period of several weeks. Longer‐term, an elevated mass flux remains due to the increase in subsurface permeability. Upflow migrates from the footwall scarp into the hanging wall and away from the fault, because rising fluids are no longer deflected by the fault.