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.