Difference traveltimes SKKS-SKS for 12 Tonga-Fiji events observed from 96--117¿ at North and South America WWSSN and CSN stations exceed the difference times of standard earth model PREM by 2--3 s. Also the amplitude ratios SKS/SKKS at American stations from 96--107¿ are lower than the PREM ratios. No such anomalies occur in directions from Tonga-Fiji towards Eurasia and Africa and for a Sea of Japan event and paths to North America and Africa. The regional variations in the data point to pronounced lateral variations in earth structure. The anomalous difference times imply either an advance of SKS or a delay of SKKS relative to PREM. The interpretation of the anomalies is not unique. Our preferred explanation involves S-velocity anomalies in the lower mantle on the source side, east of Tonga-Fiji.