The paper presents basic formulae for the stress and strain components of the deformation and gravity changes due to source of heat of prismatic shape embedded in the elastic and viscoelastic halfspace (lithosphere) of the Kelvin type. Numerical results are presented in the numerous graphs which show gradual approaching stress, strain and gravity changes to the steady state. It is shown that the surface displacement causes a pronounced dome in the epicentral region of the source of heat and that the surface thermoviscoelastic stresses are mainly of tensile type and their values are well comparable with critical stresses required to cause creep or fractures of the surface of the halfspace.