LAUSR

13 Fluid pressure diffusion occurring on the microscopic scale is believed to be a significant 14 source of intrinsic attenuation of seismic waves propagating through fully saturated porous 15 rocks. The so-called squirt flow arises from compressibility heterogeneities in the 16 microstructure of the rocks. To study squirt flow experimentally at seismic frequencies the 17 forced oscillation method is the most adequate, but these studies are still scarce. Here we 18 present the results of forced hydrostatic and axial oscillation experiments on dry and 19 glycerine-saturated Berea sandstone, from which we determine the dynamic stiffness moduli 20 and attenuation at micro-seismic and seismic frequencies (0.004 – 30 Hz). We observe 21 frequency-dependent attenuation in response to the drained-undrained transition (~0.1 Hz) 22 and squirt flow (>10 Hz). The frequency-dependent attenuation and associated modulus 23 dispersion at 5 MPa effective stress is in fairly good agreement with the results of the 24 analytical solutions for the drained-undrained transition and squirt flow. The comparison with 25