Dim spot
Downward spike in a seismic attribute, often indicative of hydrocarbons / From Wikipedia, the free encyclopedia
In reflection seismology, a dim spot is a local low-amplitude seismic attribute anomaly that can indicate the presence of hydrocarbons[1] and is therefore known as a direct hydrocarbon indicator. It primarily results from the decrease in acoustic impedance contrast when a hydrocarbon (with a low acoustic impedance) replaces the brine-saturated zone (with a high acoustic impedance) that underlies a shale (with the lowest acoustic impedance of the three), decreasing the reflection coefficient.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/1/1d/Seismic_dim_spot.png/320px-Seismic_dim_spot.png)