(1) (n.) Geophysics. A Stoneley wave that occurs at the low frequencies of seismic data. See: Stoneley wave, surface wave. (2) (n.) Geophysics. An interface wave hat occurs in cased wellbores when a Rayleigh wave encounters a wellbore and perturbs the fluid in the wellbore. The tube wave travels down the wellbore along the interface between the fluid in the wellbore and the wall of the wellbore. A tube wave suffers little energy loss and typically retains a very high amplitude which interferes with reflected arrivals occurring later in time on vertical seismic profile (VSP) data. Because the tube wave is coupled to the formationthrough which it is traveling, it can perturb the formation across open fractures intersecting the borehole. This squeezing effect can generate secondary tube waves which travel both up and down from the fracture location. Such events can be diagnostic of the presence of open fractures and their amplitude related qualitatively to the length and width, e. g. , volume of the fluid-filled fracture space. This effect is generally seen only in shallow formations where the overburden pressure is lower. See: Coupling, Rayleigh Wave, Vertical Seismic Profile