The following is a useful collection of geophysical terms. Search through using the alphabetical shortcuts or the “Find” function in your web browser.


The distance a nuclear logging probe moves during one time constant.

last reading

The depth of the shallowest value recorded on a log.

lateral log

A multielectrode, resistivity-logging technique that has a much greater radius of investigation than the normal techniques, but requires thick beds and produces an unsymmetrical curve.


A focused-resistivity logging technique; see also guard log.

layered Earth

A common geophysical model which assumes that the Earth is horizontally layered – the physical parameters are constant to infinite distance horizontally, but change vertically.

light non aqueous phase liquids (lNAPls)

Organic fluids that are less dense than water. They are capable of forming an immiscible layer that floats on the water table (e.g. petroleum hydrocarbons or other organic liquids). Also referred to as Floaters.

long normal log

A resistivity log with AM spacing usually 64 in.; see normal logs.

microresistivity log

Refers to a group of short-spaced resistivity logs that are used to make measurements of the mud cake and invaded zone.