Magyar Pedagógia

We examine the relation between the locations of hotspots on the surface of the Earth and mantle structure as determined from seismic tomography. In particular, we correlated hotspot locations with Tanimoto's (1989) shear wave velocity structure throughout the mantle. A spherical harmonic representation of both fields enables us to perform a "degree by degree" correlation, and to test possible relationships between features of the same scale. A statistical significance analysis is applied to these results. A similar analysis was performed by Richards et al. (1988) in studying hotspot - geoid relations. Two major phenomena were observed in the hotspot - shear velocity correlation: 1. Very good correlation between the hotspots and slow (hot) regions in degree 2, and only degree 2, in the bottom half of the lower mantle. The correlation gradually decays to zero in the upper mantle. 2. A good correlation of degree 6 with the deeper upper mantle (200-670 km) which decays rapidly below 670 km. These good correlations are significant both statistically and by the fact that these degrees show peaks in the hotspot amplitude spectrum. The length scales we are looking at are too large to determine the origin of a single hotspot However, if we believe that hotspots reflect the general convection pattern in the mantle, we can hope to learn something about the style of this convection. The above observations suggest the possibility of two, not necessarily independent, regions in different depths in the mantle, which control the location of different hotspots. To check whether this is reasonable, we excluded those hotspots which give a negative contribution to the l=6 correlation in the upper mantle. The correlation of these excluded hotspots with the lower mantle at degree 2 improves slightly relative to the already significant correlation that the complete set of 47 hotspots demonstrates. This set of observations presents a constraint on mantle convection models

Structure of the Kerguelen Plateau province from Seasat altimetry and seismic reflection data

The Kerguelen Plateau in the southern Indian Ocean stands 2−4 km above the adjacent sea floor and is 2,500 km long (Fig. 1)1,2. Seasat provided a unique data set for deriving the free-air gravity field of the region (Fig. 2)3−5. Here we report the results of a new analysis of the plateau province's structure employing both Seasat and newly-acquired multichannel seismic (MCS) data6,7 for ground truth. The northern sector is characterized by volcanism and a sedimentary basin; the southern sector by a broad anticlinal arch, major faulting, and a sedimentary basin; and the eastern sector by an abyssal basin (Labuan) and bounding ridge (William's). The three sectors argue for a more complex tectonic evolution of the feature than has been previously proposed