A comparison of the upper‐mantle structure beneath Eurasia and the North Atlantic and Arctic Oceans

Abstract

Summary. A travel‐time curve for P seismic waves recorded at NORSAR from earthquakes in the North Atlantic and Arctic Oceans is of a significantly different character from those for rays bottoming under western Russia and southeast and central Europe. The differences arise principally from variations in the outer 200–300 km of the three regions and from the apparently anomalous nature of the velocity distribution between 300 and 500km beneath southern and central Europe. Extremal ‘tau’ inversion is extended to the calculation of bounds on vertical transit time for different depth ranges beneath the three regions. A maximum difference of 5 s is permitted by the bounds in the two‐way vertical transit times of P waves between 50 and 800 km below western Russia and the oceans. The bounds obtained on transit times between 300 and 800 km demand no significant difference between the two regions and permit a maximum difference of 2.5 s in two‐way transit time. This is consistent with the observation that the oceanic travel‐time curve may be fitted to within observational error by a model which is substantially the same as that for western Russia below 300 km. Copyright © 1978, Wiley Blackwell. All rights reserved