Using scaling parameters of induced seismicity in size and space domains (seismic b value and spatial correlation dimension D, respectively), we analyze the fracturing pattern of the gas reservoir of Lacq in correlation with the production rate. On the basis of previous observations and a previous model <Segall et al., 1994>, we assume that the cause of induced seismicity is a poroelastic stressing, such that the production rate can be viewed as a stress rate for the rocks adjacent to the reservoir. During the 20-year study period the production rate has decreased dramatically, leading to a change of poroelastic stress rate from 4.5¿10-3 to 1.5¿10-3 MPa/yr. Accordingly, we observe a significant decrease in the size of activated fractures and a reduction of the spatial clustering of fracturing, both arguing for a stress rate impact on the fracturing pattern in the gas field. We interpret these changes in terms of a change in the deformation mode of stressed rocks from a more brittle to a more ductile behavior as the stress rate was decreased. This hypothesis is supported by independent evidence from a number of experimental, numerical, and field studies. The loading rate thus appears as a possible candidate to drive changes of b and D in time and space. The apparent sensitivity of the Earth's crust fracturing pattern to loading rate variations of much lower frequency than the tidal variations suggests that the Earth's crust deformation mode itself be frequency dependent. Also, our observations may have strong implications in contexts where the loading rate is induced by human intervention (e.g., hydrocarbon recovery, mines), suggesting the possibility of adjusting the loading rate so as to shape the fracturing pattern locally according to human needs. ¿ 1999 American Geophysical Union