Imaging the Hikurangi subduction zone, New Zealand, using teleseismic receiver functions: crustal fluids above the forearc mantle wedge

We image the Hikurangi subduction zone using receiver functions derived from teleseismic earthquakes. Migrated receiver functions show a northwest dipping low shear wave feature down to 60 km depth, which we associate with the crust of the subducted Pacific Plate. Receiver functions (RF) at several stations also show a pair of negative and positive polarity phases with associated conversion depths of similar to 20-26 km, where the subducted Pacific Plate is at a depth of similar to 40-50 km beneath the overlying Australian Plate. RF inversion solutions model these phases with a thin low S-wave velocity zone less than 4 km thick, and an S-wave velocity contrast of more than similar to 0.5 km s(-1) with the overlying crust. We interpret this phase pair as representing fluids near the base of the lower crust of the Australian Plate, directly overlying the forearc mantle wedge.