As a supplementary study,we use passive seismic data recorded by one OBS station near the Southwest Indian Ridge hydrothermal vent(49°41.8'E)to inverse the crustal structure and mantle transition zone thickness by receiver functions,in order to investigate previous active seismic experiment models and to find the influence of deep mantle thermal anomaly on seafloor hydrothermal venting at an ultra-slow spreading ridge.The P-to-S converted wave velocity model shows that the shallow crust has an abnormal velocity variation decreasing downward from 3.4 km/s to 2.6 km/s,and the deep crust has a velocity increasing from 2.6 km/s to 3.0 km/s and has a low velocity zone(~3.0–2.8 km/s)between 6-9km with Moho discontinuity at~9.0 km.The velocity spectrum stacking plot made from passive seismic data shows that the 410 discontinuity is depressed by~15km,the 660 discontinuity is elevated by~18km,and a positive thermal anomaly between 182 K and 237 Kis inferred.