INVITED FACULTY TALK - Earthquake Induced Fluid Flow As Natural Hydrogeologic Tests
Ge, Shemin 1 ; Cutillo, Paula 2
1 University of Colorado
2 US National Park Service
Hydrogeologic systems are known to respond to earthquakes, manifested by ground water level changes, abnormal temperature and chemical concentrations in ground water. The implication of these phenomena is manifold. This presentation focuses on the effects of earthquake on ground water and interpretation of earthquake induced water level transients. Post seismic recovery of water level is a diffusion process, and the recovery reflects system hydraulic diffusivity, which can be used to constrain hydraulic conductivity. Water level changes and subsequent recovery can be viewed as natural analogs to hydrologic tests. A framework is developed to integrate co-seismic deformation, co-seismic pore pressure change, and post-seismic diffusion, by linking deformation and pressure. Application of this framework is discussed through case studies. One involves water level fluctuations in Devils Hole, Death Valley National Park. The water level has been observed to vary in response to external stresses. Short-term variations of large magnitude are linked to known earthquakes. Modeling estimated a hydraulic diffusivity of 0.03 m2/s. Another case involves ground water level from Parkfield, CA. The co-seismic change and post-seismic recovery following an earthquake were examined. A hydraulic diffusivity of 10-4 m2/s was found to fit the observed data. This study has also been applied to study fluid pressure transients associated with seismicity in subduction zones.