Data Services Products: EMC-Alaska_SurfTTI_2024 3D crustal TTI model across Alaska from surface wave database

Summary

Alaska_SurfTTI_2024 (Liu & Ritzwoller, 2024) is a tilted transversely isotropic (TTI) anisotropy model for the Alaskan continental crust, derived from an MCMC inversion using a surface wave database (Liu et al., 2022) that includes Rayleigh and Love waves from both ambient noise and earthquake data.

Description

Name Alaska_SurfTTI_2024
Title 3D crustal TTI model across Alaska from surface wave database
Type 3-D Seismic Tomography Earth Model
Sub Type TTI anisotropy
Year 2024
Data Version v1.0 (version history))
Data Revision r0.0 (revision history)
 
Short Description   Alaska_SurfTTI_2024 (Liu & Ritzwoller, 2024) is a TTI anisotropy model of the Alaskan continental crust, derived from a Markov Chain Monte Carlo inversion of a surface wave dataset that includes Rayleigh and Love waves isotropic phase speed and Rayleigh wave azimuthal anisotropy from both ambient noise and earthquake data (Liu et al., 2022). This model resolves the spatial variation of inherent anisotropy by inferring the depth-dependent tilt of the hexagonally symmetric elastic tensor. The authors also thank Aakash Gupta and Carl Tape for their constructive comments and efforts in testing the model.
 
Authors: Chuanming Liu, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, US

Michael Ritzwoller, Department of Physics, University of Colorado Boulder, Boulder, CO, USA
 
Previous Model None
Reference Model Alaska-LFeng-2019_vsv_gamma, PREM
Model Home Page None
 
Model Download AK-tti-tensor.v1.0.r0.0-n4.nc (see metadata) in compressed netCDF 4 Classic format contains elastic tensor components for the TTI model, including variables such as C11, C22, and others. The coordinate system is defined north-east-down.

AK-tti-independent-vars-unc.v1.0.r0.0-n4.nc (see metadata) in compressed netCDF 4 Classic format contains the independent variables and corresponding uncertainties from the TTI inversion, including:
  • L: L=Vsv^2*density (Love parameter)
  • Gamma: Amplitude of inherent shear wave radial anisotropy, gamma=(N-L)/2L
  • Dip: Dip angle of the anisotropy foliation plane
  • Strike: Strike angle of the anisotropy foliation plane
  • Eta: η=F/(A−2L)
  • layer_type: 1- Sedimentary layer; 2 – Crystalline crust layer; 3 – Uppermost mantle layer

    AK-tti-model-depths.txt contains the depths to the base of sediment and the Moho used in the inversion at each grid point.
 
Depth Coverage 0 to 100 km
 
Area Alaska and northwestern Canada (approx. 58°/70° latitude and -164°/-133° longitude)
 
Data Set Description The dataset includes TTI anisotropic parameters across Alaska, derived from the joint inversion of Rayleigh and Love wave phase speeds, and Rayleigh wave azimuthal anisotropy extracted from both ambient noise and earthquake data spanning periods of 8 – 85 s.
 
 

Alaska_SurfTTI_2024-1
Figure 1. Surface wave anisotropy inversion results: means of the posterior distribution. Horizontal slices of dip angle (θ) in degrees in the (a) upper crust and (b) lower crust, as well as S-wave anisotropy (γ) at depths of© 8 km and (d) 25 km which is in the lower crust across Alaska. Major faults are shown with black lines, while the Denali fault as the major boundary is shown as a blue line. The profile AA’ in (a) is used in Fig. 2. DF: the Denali fault, KF: the Kobuk fault, CMF: the Castle Mountain fault, BRF: Border Ranges fault.

Alaska_SurfTTI_2024-2
Figure 2. Surface wave anisotropy inversion results: mean of the posterior distribution. Vertical transects of (a) dip angle (θ) and (b) inherent S-wave anisotropy (γ) along the profile AA’ identified in Fig. 1a.

Alaska_SurfTTI_2024-3
Figure 3. The same as Figure 2 but for different transects along profiles (blue lines) of BB’, CC’, DD’, EE’, and FF’ identified in (i) topography map. WA: West Alaska, TR: Transition Region, CA: Central Alaska, NS: North Slope, DF: the Denali fault, INF: the Iditarod-Nixon Fork fault, TCF: the Totschunda fault, SF: the Susulatna fault; KF: the Kobuk fault; BR: the Brooks Range.

Citations and DOIs

To cite the original work behind this Earth model:

  • Liu, C., & Ritzwoller, M. H. (2024). Seismic Anisotropy and Deep Crustal Deformation Across Alaska. Journal of Geophysical Research: Solid Earth, 129(5). https://doi.org/10.1029/2023jb028525

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, https://doi.org/10.1785/0220120032.

DOI for this EMC webpage: doi:https://doi.org/10.17611/dp/emc.2025.alaskasurftti.1

References

  • Liu, C., Zhang, S., Sheehan, A. F., & Ritzwoller, M. H. (2022). Surface Wave Isotropic and Azimuthally Anisotropic Dispersion Across Alaska and the Alaska-Aleutian Subduction Zone. Journal of Geophysical Research: Solid Earth, 127(11). https://doi.org/10.1029/2022jb024885

Credits

  • v1.0 r0.0 model provided by Chuanming Liu, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, US.
    h2. Revision History

version v1.0, revision r0.0: uploaded April 4, 2025.

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