1 ] P and S -P arrival time data from 311e arthquakes and several thousand offshore and onshore shots have been used in simultaneous inversion for hypocenters, three-dimensional (3-D) Vp and Vp/ Vs models in the Southern Alps region, New Zealand. The combined data result in ah ighly nonuniform ray path distribution, and linked nodes are used in sparsely sampled areas. Gravity data are used to improve the model below 20-km depth, where it is poorly sampled by local earthquakes. The crustal Vp from 5to25 km depth is fairly uniform, generally ranging from 5.5 to 6.5 km/s, typical of graywacke and schist. Active fault zones tend to be correlated with low-velocity zones. Where the Alpine fault is primarily strike slip, it is characterized by avertical low-velocity zone, to at least 15-km depth. Where the fault is dipping and has al arge dip-slip component, it is characterized by alarge region of low velocity above and southeast of the fault, to at least 14-km depth, consistent with fluids and fracture density from active deformation. Al arge high-velocity,h igh-resistivity feature in the eastern Southern Alps may represent Mesozoic schist of higher metamorphic grade than its surroundings, which is relatively rigid and serves to both reduce deformation in the overlying basin and concentrate deformation in the adjoining low-velocity region. The imaged crustal root is deepest 80-km south of Mt. Cook and is asymmetric with as harper gradient on the northwestern side. The approximate Moho shows regional variation, with 5–10 km thicker crust in Otago than Canterbury