The Tonga subduction zone in the south-west Pacific is the fastest convergent plate boundary in the world with the most active mantle seismicity. This zone shows unique tectonic features including Samoan volcanic lineament of plume-driven origin near the northern rim of the Tonga subducting slab. The proximity of the Samoa hotspot to the slab is enigmatic and invokes debates on interactions between the Samoa plume and the Tonga subduction. Based on long-term observations of intermediate and deep-focus Tonga earthquakes reported in the Global Centroid Moment Tensor (CMT) catalog, we provide novel detailed imaging of this region. Accurate traveltime residua of the P- and S-waves recorded at two nearby seismic stations of the Global Seismographic Network are inverted for the P- and S-wave velocities and their ratio and reveal their pronounced lateral variations. In particular, they differ for the southern and northern parts of the Tonga subduction region. While no distinct anomalies are detected in the southern Tonga segment, striking low-velocity anomalies associated with a high Vp/Vs ratio are observed in the northern Tonga segment close to the Samoa plume. These anomalies spread through the whole upper mantle down to depths of ~ 600 km. Together with the fast extension of the northern back-arc Lau Basin, slab deformation and geochemical enrichment in the northern Tonga region, they trace deep-seated magmatic processes and evidence an interaction of the Tonga subduction with the Samoa plume.

西南太平洋汤加俯冲带是世界上收敛速度最快、地幔地震活动最活跃的板块边界。该区域显示出独特的构造特征，包括汤加俯冲板块北缘附近由羽流驱动的萨摩亚火山线。萨摩亚热点与板块的接近程度是一个谜，并引发了关于萨摩亚羽流和汤加俯冲之间相互作用的争论。基于对全球质心矩张量 (CMT) 目录中报告的中、深震源汤加地震的长期观测，我们提供了该地区的新颖详细成像。在全球地震台网的两个附近地震台站记录的 P 波和 S 波的准确走时残差被反演 P 波和 S 波速度及其比率，并揭示了它们明显的横向变化。尤其是汤加俯冲区的南部和北部，它们是不同的。虽然在汤加南部段没有检测到明显的异常，但在靠近萨摩亚羽流的汤加北部段观察到与高 Vp/Vs 比相关的显着低速异常。这些异常通过整个上地幔向下传播到约 600 公里的深处。加上北弧后刘盆地的快速伸展、汤加北部地区的板片变形和地球化学富集，