Harvard Year 1 Accomplishments
for Geoinformatics: Community Computational Platforms for Developing
Three-Dimensional Models of Earth Structure, Phase II
We have developed a first-generation California statewide Unified Structural
Representation (USR) that incorporates the latest faults from the SCEC Statewide
Community Fault Model and major basin structures. The USR will be used in 3D
waveform tomographic inversions to refine our understanding of crust and upper mantle
velocity structure and facilitate improved strong ground motion forecasting. The model
includes a new description of the Central Valley (San Joaquin and Sacramento Basin),
components from the USGS San Francisco Bay Area Model (Brocher et al., 2005), the
SCEC southern California Community Velocity Model (CVM-H v. 15.1) (Shaw et al.,
2015). This new USR include tens of thousands of direct velocity and density
measurements that span scales from decimeter borehole observations to 100 km long
basin structures. Thus, careful attention has been paid to preparing and integrating
these data into compatible model components.
One of the goals of our project is to extend numerical wave propagation studies to higher
frequencies (> 2 Hz), which requires that we enhance the new velocity models using
statistical descriptions of fine-scale velocity heterogeneities. These heterogeneities can
be strong in sedimentary basins and have spatially anisotropic statistical distributions
(Magistrale et al., 1996; Süss and Shaw, 2003; Brocher, 2005). While we have local
measures of fine-scale velocity structure (down to meter scales) along boreholes with
sonic logs, there is not a sufficient density of such samples to facilitate the development
of a deterministic regional model. Thus, in collaboration with SCEC investigators we
have developed a statistical description of fine-scale velocity structure, informed by more
than one million measurements in borehole sonic logs and geological correlations.
Specifically, we have defined the Vp and Vs variability (≈ 6.5 and 7.6 %, respectively)
present in the well data but not represented in the basin models, and established vertical
(80 m) and horizontal (2000 m) correlation lengths for fine-scale velocity structures using
wells across the LA basin as well as in tightly clustered oil fields. We anticipate using
these results in year two of our study to develop a statistical representation of fine scale
wave speed structure as an enhancement to the new Statewide USR.
Finally, we have developed new data and metadata standards for the representation and
delivery of the various geological and geophysical constraints used to develop these
models. These datasets include borehole measurements of Vp, Vs, or density, stacking
velocity measurements, and constraints on geological interfaces such as the top of
crystalline basement or Moho. These metadata structures will enable the direct
comparison of perturbations from seismic tomography with the original data coverages
used to parameterize the starting model. Such comparisons can determine if large
perturbations from the inversions correspond to regions of rich or poor data constraints
in the original models, thereby helping to assess the validity of the inversion results.
Ultimately, we anticipate that waveform tomography will directly consider these
constraints in the inversions, weighting values in the starting models based on the
degree to which they are directly constrained. This will help to focus perturbations from
the inversions in areas where the starting models are less certain, likely yielding
improvements in the resolved velocity structures. We plan to disseminate these new
models and their data and metadata components through the UCVM framework.
References
Brocher, T.M., R.C. Jachens, R. W. Graymer, C. W. Wentworth, B. Aagaard, and R. W.
Simpson, 2005, A new community 3D seismic velocity model for the San Francisco
bay Area: USGS Bay Area Velocity Model 05.00, SCEC Annual Meeting,
Proceedings and Abstracts, Volume XV, p. 110.
Brocher, T.M., 2005, A regional view of urban sedimentary basins in Northern California
based on oil industry compressional-wave velocity and density logs, Bulletin of the
Seismological Society of America, vol.95, no.6, pp.2093-2114.
Magistrale, H., S. Day, R. W. Clayton, and R. Graves (2000), The SCEC Southern
California Reference Three-Dimensional Seismic Velocity Model Version 2, BSSA
90, S65-S76.
Süss, P., and J. H. Shaw, P wave seismic velocity structure derived from sonic logs and
industry reflection data in the Los Angeles basin, California, JGR 108(B3),
doi:10.1029/2001JB001628.
Shaw, J. H., A. Plesch, C. Tape, M. P. Suess, T. H. Jordan, G. Ely, E. Hauksson, J.
Tromp, T. Tanimoto, R. Graves, K. Olsen, C. Nicholson, P. J. Maechling, C. Rivero,
P. Lovely, C. M. Brankman, J. Munster, 2015, Unified Structural Representation of
the southern California crust and upper mantle, Earth and Planetary Science Letters,
415, 1–15.
Broader Impacts
This work directly addresses the goal of improving seismic hazards assessment by
advancing the methodology for defining regional 3D fault systems and seismic velocity
structure. These models are used as the starting point for 3D seismic waveform
inversions, which further refine our understanding of wave speed structure and therefore
help to improve the accuracy of strong ground motion predictions. Our goal is to develop
model development workflows, data structures, and computational platforms that can be
used to address seismic hazards in earthquake prone regions worldwide.
Publications
Shaw, J. H., A. Plesch, C. Tape, M. P. Suess, T. H. Jordan, G. Ely, E. Hauksson, J.
Tromp, T. Tanimoto, R. Graves, K. Olsen, C. Nicholson, P. J. Maechling, C. Rivero,
P. Lovely, C. M. Brankman, J. Munster, 2015, Unified Structural Representation of
the southern California crust and upper mantle, Earth and Planetary Science Letters,
415, 1–15.
Abstracts
Gill, D., P. Small, P. Maechling, T. Jordan, J.H. Shaw, A. Plesch, P. Chen, E. Lee, R.
Taborda, K. Olsen, S. Callaghan, 2014, UCVM: Open Source Software for
Understanding and Delivering 3D Velocity Models, IN23D-3752, AGU Annual
Meeting, San Francisco, CA.
Nicholson, C., A. Plesch, C. Sorlien, J.H. Shaw, and E. Haukson, 2014, The SCEC 3D
Community Fault Model (CFM-v5): An updated and expanded fault set of oblique
crustal deformation and complex fault interaction for southern California T31B-4584,
AGU Annual Meeting, San Francisco, CA.
Plesch, A., C. Nicholson, C. Sorlien, J. H. Shaw, and E. Hauksson, 2014, SCEC
Community Fault Model Version 5.0, SCEC Annual Meeting, Palm Springs, CA.
Plesch, A., Shaw, J. H., Song, X., Jordan, T. H., 2014, Stochastic Descriptions of FineScale Basin Velocity Structure from Well Logs and the SCEC Community Velocity
Model (CVMH), SSA Annual Meeting, Alaska, p431.
Song, X., T.H. Jordan, A. Plesch, J.H. Shaw, 2014, Stochastic Descriptions of SmallScale, Near-Surface Velocity Variations in the Los Angeles Basin for Modeling
Earthquake Ground Motions, T33A-4649, AGU Annual Meeting, San Francisco, CA.
Personnel
This grant support Senior Research Associate Andreas Plesch. Dr. Plesch is the chief
developer of the SCEC Statewide CFM and CVM-H, and played a leading role in
constructing the Statewide USR. Dr. Plesch also worked collaboratively with the PI’s
(Jordan, Shaw) to examine the velocity variability with the goal of developing a
stochastic representation of fine scale velocity structure.
Travel
None
Additional Collaborators
The Harvard group works closely with various groups in the energy industry and
software developers that have contributed datasets and applications that contributed to
this project.
Figure
Perspective view of the California Statewide USR, including components from the SCEC
Statewide Community Fault Model (SCFM). Basin structures are outlined in red, and
include a new Central Valley basin model, the USGS Bay Area Model, and basins from
the latest generation SCEC southern California USR.