Near‐surface in situ stress: Introduction

Abstract

From plots of in situ stress versus depth it is apparent that horizontal stress is several times the vertical stress at depths of <100 m within the earth's crust [ Hast , 1958; Herget , 1973; Haimson , 1978]. Brown and Hoek 's [1978] compilation of earth stress shows that the average of principal horizontal stresses at zero depth varies between 2.7 and 40.5 MPa. The literature contains no consensus on why the horizontal stresses should be so high at shallow depths. Possible mechanisms include plastic yield and subsequent elastic deformation accompanying unloading on removal of overburden [ Seagar , 1964], topography [ Voight , 1966], and creep under tectonic forces [ Hast , 1969].