Yang Bailin's study in the Guizhou Province of China used Landsat TM data to study the effects of hydrocarbon seepage on plants. Abnormally low and high thermal areas were found on the August 1987 image. Eighteen days prior, an earthquake of 5.1 magnitude occurred in the area. The abnormally low areas coincide with existing oil fields, the abnornally high areas do not. It is believed that the earthquake enhanced the thermal radiation of the entire area, but effusion of hydrocarbon gases augmented soil moisture content and created a lower thermal signature in the oil field area.
Oil rises from the seafloor to the ocean surface and spreads out over the more dense water.
This tends to smooth out the ocean surface by reducing the surface tension of the sea water. This results in a dark area on radar images. The same concept can be applied in environmental monitoring . A relatively calm ocean surface makes seep detection easier. Care must be taken in interpreting apparent oil seeps, however.