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

Abstract

[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 frequencyindependent 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.

Knickpoint initiation and distribution within fluvial networks: 236 waterfalls in the Waipaoa River, North Island, New Zealand

“…Along this subduction margin, the thinned, leading edge of the Australian plate obliquely overrides the west-dipping and overthickened portion of the Pacific Plate called the Hikurangi Plateau (Davy, 1992). As the two plates converge at a rate of ∼ 45 mm/year (DeMets et al, 1994), seamounts entering the trench deform and destabilize the trench slope suggesting that the oceanic plate topography and thickness strongly influence the time evolution of wedge deformation (Lewis and Pettinga, 1993;Collot et al, 2001;Eberhart-Phillips and Chadwick, 2002). In the Waipaoa drainage basin, the exposed forearc is composed of latest Cretaceous to Pliocene shelf and slope sediments.…”

Three-dimensional P- and S-wave attenuation structures around the source region of the 2016 Kumamoto earthquakes

“…We first determine the path-averaged attenuation factor t * from the waveform data through a spectral analysis. The seismic displacement spectra of P-and S-waves for event i observed at station j may be expressed as where f is the frequency, Ω 0i is a frequency-independent term related to the seismic moment, and f ci is the corner frequency of the source spectrum S i f (Scherbaum 1990;Eberhart-Phillips and Chadwick 2002). The attenuation factor t * ij contains information on Q along the ray path from the hypocenter i to station j.…”

Methodology of Seismic Tomography

“…where α is a frequency-dependent factor (e.g., Scherbaum 1990;Eberhart-Phillips and Chadwick 2002;Eberhart-Phillips et al 2008;Ko et al 2012 …”