Low-frequency vibroseis data with maximum displacement sweeps

摘要

Several recent advances in land-seismic acquisition equipment and processing algorithms have encouraged exploration geophysicists to reconsider the potential benefits of energetic low frequencies for geophysical applications, imaging beneath high-velocity and highly absorbing formations, deep imaging, acoustic impedance inversion, velocity model estimation in geophysically complex areas, and inversion of surface waves to characterize near-surface elastic properties. On the receiver side, the growing use of accelerometers in surface and borehole seismic surveys has enabled acquisition with high signal-to-noise ratio of frequencies lower than 2 Hz. Hydraulic vibrators, which are the most widely used onshore seismic sources, have their output energy limited at low frequencies by mechanical constraints, such as the maximum reaction mass displacement. Only low-actuator forces can be used to drive the vibrators at these low frequencies which, in turn, can yield extremely long sweeps in the absence of a design criterion or if a design is used that is too conservative.