Hydraulic fracture treatments induce microsensitivity (i.e., discrete events plus noise) which can be recorded only by seismometers located in or near the treatment well bore. Seismograms recorded in the treatment well bore are composed of interacting phases which to data defay discrete identification and preclude standard inversion techniques to determine source characteristics, propagation path characteristics, or both. To understand the recorded data, synthetic seismograms have been generated using treatement-induced, low-velocity zone (LVZ). The LVZ is produced by pore dilatancy in response to formation fluid pressurization caused by pressure diffusion from the treatment fluid and fracture opening. Borehole, seismometer coupling, fluid transport, and dynamic fracture effects are not considered. The models examined showed that a fixed-aperture fracture plus surrounding LVZ acted as a leaky waveguide confining the seismic energy and altering propagation characteristics which resulted in unconventional seismograms. The seismograms were composed of multiple transient phases caused by phase interactions and conversions at the waveguide boudaries and stationary phases corresponding to the eigenfrequency structure of the fracture-LVZ waveguide. ¿ American Geophysical Union 1987