Fault Permeability Structure From Reservoir Induced Seismicity (Ris) Observations And 3D Flow Modeling In Ne Brazil

We use observations of RIS beneath Açu Reservoir, NE Brazil, to investigate the damage zone permeability of geological faults. High-resolution digital seismic monitoring of the reservoir has provided unusually detailed information on the locations of seismic events. The temporal distribution of these events shows them to be directly related to annual fluctuations in the reservoir level. Model simulations show that for pressure-diffusion to be a hydrogeologically consistent mechanism for RIS, preferential flow must occur within 2D fault planes embedded in a 3D low permeability matrix. The observed spatial and temporal variability of earthquakes indicate that these faults must have heterogeneous permeability fields with significant spatial structure; Our simulations indicate that <0.05 kPa of pressure change at hypocentral depth is required to trigger seismic events.