1. n. [Geophysics]

A type of local seismic event that, in contrast to a bright spot, shows weak rather than strong amplitude. The weak amplitude might correlate with hydrocarbons that reduce the contrast in acoustic impedance between the reservoir and the overlying rock, or might be related to a stratigraphic change that reduces acoustic impedance.

Antonyms: bright spot

See: acoustic impedance,  anomaly,  hydrocarbon indicator,  polarity standard