Three-dimensional attenuation model of the shallow Hikurangi subduction zone in the Raukumara Peninsula, New Zealand

[1] The material properties of the shallow subduction zone are imaged with data from a passive seismic deployment in the Raukumara Peninsula. Attenuation images are obtained using t* values measured from 2848 spectra of P wave arrivals. The t* values are inverted for frequency-independent three-dimensional (3-D) Q(p), using a 3-D velocity model. Linked nodes in a preliminary 2-D inversion are used to obtain the most reliable initial model for 3-D inversions. The results show the benefits of obtaining 3-D Q in addition to 3-D V-p and V-p/V-s. Q is related to localized permeability and heterogeneity, and thus 3-D Q is an important tool for interpreting active tectonic regions. Q(p) in the shallow overlying plate generally corresponds to the mapped geology. Two high Q(p) features (>600) represent subducted seamounts or Cretaceous volcanics within the overlying plate. The gradient above the subducting plate is the strongest feature in the Q(p) model, with the slab having high Q(p) (600-900). Below 20-km depth and above the plate interface, there is a zone of 50% decrease in Q(p) and high V-p/V-s about 10 km thick which represents actively subducting sediment and has distributed microearthquake activity associated with active underplating.