Broad areas of anomalously shallow seafloor surround regions of active or recently active hot spot volcanism. The cause of these midplate swells has been modeled both as elevated temperatures in a convecting layer and as thermal expansion within the conducting portion of the lithosphere. According to the former explanation, we would expect the low-density material compensating the swell to lie beneath the conducting lid, whereas the latter model allows compensation at shallower depths. We present a technique based on the application of linear filters for determining the compensation depth of midplate swells given observations of topography and geoid or gravity anomalies. Our method does not require an a priori estimate of swell height or width, nor does it assume complete spatial or spectral separation between the swell topography and the signal from the hot spot volcanoes, which are compensated by flexure of the oceanic Moho. Rather, we exploit the difference in the predicted sign and amplitude of the Moho deflection beneath elevated topography produced by loading above versus loading below the elastic plate in order to separate the two effects.

An application of these linear filters to residual topography and geoid data from the region surrounding the Hawaiian hot spot yields a compensation depth of 70¿10 km, within the lower lithosphere.