Vertical seismic profiling (commonly abbreviated to the name VSP) is a major technique in geophysical exploration, which involves measuring downgoing and upgoing seismic wavefields through a stratigraphic sequence.
The shallow seismic reflection technique is relatively straightforward from a conceptual perspective. A high-frequency, short-duration impulse of acoustic energy is generated at the Earth’s surface. Seismic waves propagate downwards and reflect back from subsurface acoustic horizons (i.e., water table, bedrock, lithologic and facies contacts, etc.) towards the surface. There, a number of sensors (geophones) record them. The recorded signals can be used to create a 2-D or 3-D model of the subsurface.
The shallow reflection seismic technique is complex – mostly because the echoes (reflected energy or seismic events) of interest are not the only waves present in the recordings. Field data are contaminated by the presence of ground-roll, refractions and both coherent and random noise. To compensate, sophisticated acquisition and processing methodologies must be used in order to enhance the relative amplitudes of the reflected seismic events of interest. Many of these methodologies are site and target dependent. The interpretation of reflection seismic data is also complex. Interpreted models can be unreliable because of either inaccurate velocity control or incorrect seismic event identification. Similarly, seismic amplitudes can be misinterpreted because of attenuation and improperly applied gain control. The combination with external geological and geophysical constraints is often the key to successful interpretations and the development of a reasonable subsurface model and geologic image.