isopachn.

1918 Private Let. U.S. Geol. Surv. (G. & C. Merriam Co. files) 10 May Isopach, isopachous—noun and adjective, referring to lines on a map that shows equal thicknesses of beds, e.g. coal beds.

1925 Bull. Amer. Assoc. Petroleum Geologists 9 890 The term ‘isopach’ is used to designate lines through points of equal thickness.

1925 Bull. Amer. Assoc. Petroleum Geologists 9 890 The isopachs swing from a general east-and-west direction to the north.

1957 Bull. Geol. Surv. Great Brit. 12 55 The total stratigraphical thickness in feet at each locality was plotted and isopachs drawn through points of equal thickness.

1969 Nature 8 Nov. 536/2 The measured thickness of the pyroclastic deposits at various localities and the proposed isopachs are shown in Fig. 2. The isopachs generally extend south-eastwards from the eruptive centres, indicating distribution under the influence of a prevailing north-westerly wind.

1936 Jrnl. Royal Aeronaut. Soc. 40 55 An isopach is defined..as lines along which the sum of the principal stresses is constant.

1962 J. C. Jaeger Elasticity, Fracture & Flow (ed. 2) iv. 182 Isopachs are curves of constant mean stress σ₁ + σ₂.