Estimating the Compensation Depth of the Hawaiian Swell With Linear Filters

Abstract

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. 13,91513,916 MCNUTT AND SHURE: COMPENSATION DEPTH OF THE HAWAIIAN SWELL sea

Crustal structure of rifted and convergent margins : the U.S. East Coast and Aleutian margins

“…Studies of hotspot swells suggest compensation depths of 70 to 200 krn [e.g. Haxby and Turcotte, 1978;Detrick et al, 1986;Courtney and White, 1986;McNutt and Shure, 1986]. We consider compensation down to a depth Zc such that for depths ZL ~z ~Zc, p=p(T=Ta·), and for depths z > Zc, p=p(T=Ta), making no requirement that Zc be either greater or less than the current lid thickness Za (Figure 11).…”

The effect of a shallow low viscosity zone on mantle convection and its expression at the surface of the earth

“…at most swells, however, give a depth of compensation for the swell topography which appears shallower than the thermal plate thickness (Haxby and Turcotte, 1978;Crough, 1978). Estimates at various hotspot chains indicate depths of compensation of 60-90 kmfor the Hawaiian swell (Crough, 1978;McNutt and Shure, 1986), 40-70 km for the Bermuda Rise (Haxby and Turcotte, 1978), and 40-60 km for the Marquesas swell (Crough and Jarrard, 1981;Fischer et al, 1986).…”

“…Such a thermal anomaly can also explain the geoid, gravity and topography anomalies (Dietz and Menard, 1953;Crough, 1978;Detrick and Crough, 1978;Von Herzen et al, 1982;McNutt and Shure, 1986). Many researchers believe that this thermal anomaly is created by an upwelling in the mantle and that mid-plate swells are the surface expression of concentrated upwellings in a convective flow (Dietz and Menard, 1953;McKenzie et al, 1980).…”

“…Finally, recent studies of the flexure at swells have shown that they can also be characterized by thin elastic plates, which are thinner than the thickness expected for lithosphere of equivalent age (Watts, 1978;McNutt and Shure, 1986). (Watts, 1978;Detrick and Crough, 1978;Von Herzen et al, 1982;Haxby and Weissel, 1986;McNutt and Shure, 1986).…”

“…The geoid and heat flow anomalies for most swells range between 6-13 m and 6-16 mW/m 2 , respectively, with Cape Verde again the largest with a geoid anomaly of nearly 13 m and a heat flow anomaly of 16 mW/m 2 Von Herzen et al, 1982;Detrick et al, 1986;Courtney and White, 1987;McNutt, 1987). Second, the geoid and topography anomalies are in general linearly related, giving depths of compensation which lie between 45-70 km, well within the thermal plate thickness (Crough, 1978;Haxby and Turcotte, 1978;Detrick et a1., 1981;McNutt and Shure, 1986;Fischer et al, 1986):…”