Microfiche. Although It Is Recognized That Certain Portions Are Illegible, It Is Being Released in the Interest of Making Available as Much Information as Possible

Candidate models of the forces which oppose the sinking of slabs are all constrained to produce results consistent with the following observation: relative geoid highs, which one assumes are due to slabs, characteristically occur over subduction zones. Certain models which are otherwise plausible, such as those based on a Newtonian half-space mantle, yield geoid lows instead of highs. This study has extended a published model of viscous corner flow in subduction zones in ordl.r to demonstrate that it can — in certain cases — produce the requisite geoid highs. Specifically the relative geoid highs ar.produced if mantle flow is distinctly non-Newtonian (stress exponent n > 2). Results in the form of deflection of vertical (or geoid slope) profiles are cony puted for typical values of the slab parameters; they are compared with a representative profile of geoid slopes derived from Seasat altimeter data in order to show qualitative similarities. It is concluded that the effect of non-Newtonian flow as opposed to Newtonian, is to spread out the induced surface deformation, thereby stretching out the regional compensation to waverengths. (transverse to the trench) of several thousand kilometers. `'•,