Ocean bottom seismograph orientation and crustal structure of the Woodlark Rift

The Woodlark Rift in southeastern Papua New Guinea is a young continental rift and develops within the collision zone between the Australian and SW Pacific Plates, which offers an ideal location to explore the crustal structure beneath the incipient rift under a convergent setting. However, the sea water layer makes it difficult to collect high-quality seismic data, and the common step is to deploy the ocean bottom seismographs （OBSs） in a free-fall way. Therefore, mis-orientation of horizontal components of the OBS usually leads to failure of applying the inversion techniques such as the receiver function to the three-component waveforms. In this study, we employed both P-wave and Rayleigh-wave polarization analyses to determine all available OBS orientations, and then used the recorded teleseismic waveforms to conduct a receiver function study on the crustal structure beneath the Woodlark rift. The number of the receiver function traces has greatly increased after the orientation corrections and the crustal structures can be better constrained based on the results from P-wave polarization analysis. Contrasting crustal structures were revealed beneath the Kiribishi Basin and the Goodenough Basin where the rift axis is located. The crust beneath the Goodenough Basin is deciphered to thin towards the rift axis with an average of （33.3±2.42） km, while a much thinner crust is observed beneath the Kiribisi Basin with a mean value of （24.1±5.44） km. High v_P/v_S ratios were determined at all stations, which may be attributed to the Papuan ultramafic body and dehydration melting of fossil subducted slab segments.