Pore pressure changes due to a ramp introduction of slip on permeable and impermeable faults in a fluid-saturated rock mass are calculated for the purpose of evaluating water well level fluctuations. The calculations demonstrate the importance of coupling between deformation and fluid diffusion at observation points less than 5(4ct0)1/2, where c is the diffusivity and t0 is the rise time. The decay of pore pressure in the results here is due entirely to fluid mass diffusion. An approach that neglects diffusion and assumes that the pore pressure is proportional to the mean normal stress would predict a ramp pore pressure response. At distances greater than 5(4ct0)1/2 the pore pressure decays so slowly that the neglect of diffusion may be appropriate. For both permeable and impermeable faults, the pore pressure decays more rapidly for shorter slip zone lengths and longer rise times. However, the pore pressure change calculated for the impermeable fault is larger, particularly for observation points near the fault, and decays less rapidly than for the permeable fault. These differences suggest that fault permeability can be a significant factor in the response of water wells near faults and care should be used in inferring details of the slip distribution if hydrologic conditions are not known. These results are applied to a water well level change observed by Lippincott et al. A satisfactory fit to the data is obtained by uniform slip over a fault length of about 1.5 km and a rise time of 8 hours. Althouth the slip magnitude is not well constrained by the fit, the range of possible values includes the 0.5 to 1.0 cm inferred by Lippincott et al. using a different approach. ¿ American Geophysical Union 1988