Observed very long period Rayleigh-wave phase velocities across the Canadian shield

summary . The recent Indonesian earthquake (1977 August 19; M_s =8.0) makes possible a direct determination of Rayleigh-wave phase velocities at very long periods (200 to 300 s) over a pure shield path (College, Alaska-State College, Pennsylvania) by the two-station method. Results are in good agreement with previous models derived by regionalization of great-circle phase velocities and discussed in a previous paper (Okal, Paper I). Great-circle phase velocities computed at College and State College are correctly predicted by the models derived in Paper I, and further substantiate one of its main conclusions: no substantial structural differences between oceans and continents at depths greater than 240 km, are necessary to account for the presently available seismic data.