Gravity tides and ocean loading in southern Alaska

Short tidal gravity series were recorded at five stations in Alaska between latitudes of 61° and 65°N with a LaCoste earth tide meter. Gravimetric factors for semidiurnal tides are anomalously small by an average of 15%, whereas diurnal tides have gravimetric factors too large by an average of 2.5%. The corresponding phase lags are between 4° and −5° for semidiurnal tides and between 0° and −4° for diurnal tides. The ocean load effects were computed for the M2 and O1 tides from cotidal charts. The ocean load tides explain more than 80% of the discrepancy between the theoretically predicted earth tide and the observations. Finite element calculations demonstrate that the residuals cannot be explained by geological structure associated with the downgoing lithospheric slab beneath Alaska.