Signal and noise in deep wells

Deep-well measurements at Grapevine, Texas; Hobart, Oklahoma; and Orlando, Florida, show that the noise is composed of surface waves that decrease in amplitude with depth. At Hobart, a low-velocity wave guide contains wave-guided noise. Fundamental and higher mode Rayleigh waves appear to be present in the noise at each site. The amplitudes of incident P waves depend on the depth at which the deep-well seismometer is operated. High-frequency P waves from quarry blasts are clearly visible in recordings from the deep-well seismometer because the high-frequency noise is suppressed at depth.