The discontinuities in the rock mass generate diffused wavefields, along with the coherent fields, which need to be accessed using seismic signals. This study novelly investigates the dissipation and diffusivity characteristics of seismic signals in an Agaria marble rock specimen containing a pre-existing flaw. For this, a diffused ultrasound technique to study the evolving incoherent field of propagating seismic signals through the intact and flawed region of the Agaria marble specimen was examined. The signal was bandpass filtered within a frequency range, and then, the spectral energy densities of the seismic signals within an intact and damaged Agaria marble specimen were compared. The influence of various frequency ranges on the diffusion properties of the signals was also explored for both intact and damaged Agaria marble samples. By comparing the results of these two cases, i.e., intact and flawed, a deeper understanding of how the presence of the flaw (damage) alters the diffusion characteristics of the propagating seismic signals in the Agaria marble specimen can be harnessed. Specifically, the inherent damage in the flawed specimen decreases diffusivity and conversely increases the dissipation of the ultrasonic signal due to the incoherent wave field. This technique can be more sensitive to small-scale damage present in a material than conventional methods.