Seismic source

A natural or artificial generator of seismic waves. For an active survey its bandwidth, pulse duration, directivity and energy influence penetration, resolution and acquisition design.

A controlled vibratory seismic source that transmits a known frequency sweep through a coupled ground contact. Repeated sweeps can improve useful signal strength, and Vibroseis correlation compresses the long source signal into a shorter wavelet. Access, ground coupling, finite source force, bandwidth and nonlinear harmonics affect the resulting survey data.

Let a linear Earth response $h$ be recorded using a known source sweep $s$, giving $d=s\ast h+n$. Cross-correlating the record with the sweep yieldsThus a compact sweep autocorrelation $R_{ss}$ produces pulse-compressed arrival wavelets, while unrelated noise has a smaller coherent response. The Fourier transform of the result is $H(\omega )|S(\omega ){|}^2+N(\omega )\overline{S(\omega )}$. Correlation is a matched-filter operation, not an exact inversion of missing source frequencies. Spectral shaping or stabilized deconvolution can further adjust the wavelet within the measured bandwidth.^[ref]

A seismic source producing an impulsive disturbance by a professionally managed subsurface explosion. Its applications include surveys needing strong, broad-band energy, but source coupling, repeatability, ground disturbance, site access and specialist operational requirements influence suitability. Vibroseis instead distributes controlled energy over a known frequency sweep.

An array of compressed-air sources fired in water to generate repeatable broadband pressure pulses for a seismic reflection survey. Source tuning reduces coherent bubble oscillations but does not eliminate seismic source ghosts. Its energy and low-frequency content can provide greater penetration than small high-frequency boomer seismic sources or sparker seismic sources.

A delayed, usually polarity-reversed copy of source radiation reflected at the water free surface. Interference with the direct wave shapes the usable spectrum; source depth controls the delay.

A marine acoustic source using a rapid underwater electrical discharge and its expanding bubble to generate a pulse. Its energy and spectrum can be chosen to investigate shallow sub-bottom structure; bubble behaviour and seismic wavelet shape affect resolution.

An impulsive marine acoustic source in which an electrically driven plate displaces water. The emitted broadband pulse is useful for shallow seismic reflection profiling, with effective penetration and resolution depending on source energy and substrate.

A shallow marine acoustic profiling system transmitting a swept-frequency pulse and using matched processing to resolve interfaces below the seabed. Fine vertical seismic resolution must be balanced against penetration and seismic attenuation.