1. n. [Geology] A contour connecting points of equal true vertical thickness of strata, formations, reservoirs or other rock units. A map that displays isochores is an isochore map. The terms isopach and isopach map are incorrectly used interchangeably to describe isochores and isochore maps.

What does an Isochore map represent?

Isochore maps measure the thickness from a point on the upper surface straight down to the corresponding point on the lower surface. Isopach maps display the stratigraphic thickness between an upper and lower horizon. It is measured as the shortest distance between the two surfaces.

What is an isopach map used for?

An isopach map (/ˈaɪsoʊpæk/) illustrates thickness variations within a tabular unit, layer or stratum. Isopachs are contour lines of equal thickness over an area. Isopach maps are utilized in hydrographic survey, stratigraphy, sedimentology, structural geology, petroleum geology and volcanology.