Data Services Products: EMC-nz_atom_north_chow_etal_2021_vp+vs New Zealand Adjoint TOMography velocity model (North Island)


This is a 3D velocity model of the North Island of New Zealand derived using earthquake-based adjoint tomography.


Name nz_atom_north_chow_etal_2021_vp+vs
Title New Zealand Adjoint TOMography velocity model (North Island)
Type 3-D Tomography Earth Model
Sub Type Shear-wave velocity (km/s) and Compressional-wave velocity (km/s)
Year 2021
EMC Data Revision r0.0 (revision history)
Short Description   This is a 3D velocity model of the North Island of New Zealand derived using earthquake-based adjoint tomography. The starting model is defined as the ray-based NZ-Wide2.2 Velocity Model from Eberhart-Phillips et al. (2021). To derive this velocity model, we iteratively improve fits between earthquake observations from New Zealand-based broadband seismometers and synthetically generated waveforms from spectral element simulations. The waveform bandpass of interest is 4-30s.
This velocity model defines the following quantities: Vp (km/s), Vs (km/s), density (kg/m3), Qp and Qs, however only Vp and Vs are updated during our inversion. The remaining quantities are defined by the starting velocity model.
Authors: Bryant Chow, Victoria University of Wellington, Wellington, New Zealand
GNS Science, Lower Hutt, New Zealand
(Now at University of Alaska Fairbanks)

Yoshihiro Kaneko, Department of Geophysics, Kyoto University, Kyoto, Japan

Carl Tape, Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA

Ryan Modrak, Los Alamos National Laboratory, Los Alamos, NM, USA

Nick Mortimer, GNS Science, Dunedin, New Zealand

Stephen Bannister, GNS Science, Lower Hutt, New Zealand

John Townend, Victoria University of Wellington, Wellington, New Zealand
Contact Bryant Chow (
Previous Model
Reference Model NZ-Wide2.2 Velocity Model (Eberhart-Phillips et al.) Note: The provided reference model has been rotated and interpolated from its original format for use in our tomographic inversion. Additionally, this reference model encompasses a domain that is larger than the velocity model, but its values are only valid within the volume defined by the NZ ATOM North velocity model, stated explicitly in the Area section below.
Usage Notes   The geodetic datum of the original model is EPSG:32760 WGS 84/ UTM zone 60S. Two-dimensional latitude, longitude, coordinate variables in the netCDF 4 CLASSIC files for this model are expressed as a function of the UTM X and Y axis (see netCDF CF Metadata Conventions).
Data Files Description The velocity model is separated into three files covering overlapping depth ranges and with differing grid spacing:
  • shallow defines depths -3 to 9 km (BSL)
  • crust defines depths 7 to 47 km (BSL)
  • mantle defines depths 44 to 400 km (BSL)
Model Download Please see the above Data Files Description and Usage Notes sections about these files.
Model files in netCDF 4 Classic format:
Depth Coverage -3.0 to 400.0 km (below earth surface)
Area North Island of New Zealand and the Hikurangi subduction zone Coordinate system: UTM 60S x-axis 17000,635000, y-axis 5286000, 5905000 Coordinate system: WGS84 latitude -42.5°, -37.0°, longitude 173.0°, 178.5°
Data Set Description Dataset includes seismic waveforms filtered at 4-30s period. Waveforms from 60 earthquakes recorded on up to 88 broadboad three-component seisimic stations, resulting in 1800 unique source-receiver pairs. Broadband stations include the following networks:

Comparisons of initial (M00; reference) and final (M28) shear-wave velocity (Vs) models at various depth slices. Columns represent initial model (M00; left), final model (M28; center), and net model update (ln(M28/M00); right). Rows represent depth slices at 5 km (top), 15 km (middle), and 25 km (bottom). Annotated letters A–E relate to notable velocity features not seen in the initial model. Note the differing color scales between rows and columns. Numerical artefacts related to mesh coarsening layers are visible in panels D, E, F, H, and I.

Zeroth moment test
Zeroth moment test: This volumetric field (HSS) approximates the sensitivity of the entire set of waveform measurements to perturbations in Vs structures. Darker colors represent higher relative sensitivity. The solid yellow lines outline a threshold sensitivity value. A) HSS at 5 km depth. Pink lines show surface traces of cross sections in (D) and (E). Earthquakes and receivers used in inversion are depicted as green circles and white inverted triangles. B) HSS at 15 km depth. C) HSS at 25 km depth. D) HSS A–A’ cross section to 60 km depth at 2x vertical exaggeration. E) HSS B–B’ cross section. White lines in cross sections correspond to the plate interface model of Williams et al. (2013).

Citations and DOIs

To cite the original work behind this Earth model:

  • Chow, Bryant, Yoshihiro Kaneko, Carl Tape, Ryan Modrak, Nick Mortimer, Stephen Bannister, and John Townend. “Strong upper-plate heterogeneity at the Hikurangi subduction margin (North Island, New Zealand) imaged by adjoint tomography.” Journal of Geophysical Research: Solid Earth, accepted Dec. 9, 2021,

To cite IRIS DMC Data Products effort:

  • Trabant, C., A. R. Hutko, M. Bahavar, R. Karstens, T. Ahern, and R. Aster (2012), Data Products at the IRIS DMC: Stepping Stones for Research and Other Applications, Seismological Research Letters, 83(5), 846–854,

DOI for this EMC webpage:


  • Chow, Bryant, Yoshihiro Kaneko, and John Townend. “Evidence for deeply-subducted lower-plate seamounts at the Hikurangi subduction margin: implications for seismic and aseismic behavior.” Journal of Geophysical Research: Solid Earth, accepted Dec. 28, 2021,
  • Chow, Bryant, Yoshihiro Kaneko, Carl Tape, Ryan Modrak, and John Townend. “An automated workflow for adjoint tomography—waveform misfits and synthetic inversions for the North Island, New Zealand.” Geophysical Journal International 223, no. 3 (2020): 1461-1480.
  • Eberhart-Phillips, Donna, Bannister, Stephen, Reyners, Martin, & Henrys, Stuart. (2020). New Zealand Wide model 2.2 seismic velocity and Qs and Qp models for New Zealand [Data set]. Zenodo.
  • Charles A. Williams, Donna Eberhart‐Phillips, Stephen Bannister, Daniel H. N. Barker, Stuart Henrys, Martin Reyners, Rupert Sutherland; Revised Interface Geometry for the Hikurangi Subduction Zone, New Zealand. Seismological Research Letters 2013; 84 (6): 1066–1073.


  • Model provided by Bryant Chow

Revision History

revision r0.0: uploaded December 17, 2021.




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