New Research Opportunities in the Earth Sciences - New Research Opportunities in the Earth Sciences - page 24

Disciplinary advances underlying the progress in characterizing deep chemical
reservoirs include improved global seismic data sets accumulated from fixed and
portable seismic networks; improved three-dimensional (3D) waveform modeling and
imaging capabilities for resolving complex, deep structures; improved resolution of
3D thermo-chemical convection models enabled by faster computers and enhanced
numerical codes; novel 3D petrographic analyses for lower-mantle conditions enabled
by 3D x-ray tomography with nanoscale resolution; greatly expanded experimental
determinations of deep-mantle properties enabled by synchrotron radiation facilities;
and greatly improved molecular dynamics models implemented on fast computer
networks. The rapid accumulation of new data, models, and properties positions the
community to integrate the separate advances into new understanding of thermo-
chemical convection throughout the upper and lower mantles, including effects of the
subducted lithosphere, deep chemical piles, and thermo-chemical plumes.
While near-term progress can be anticipated based on the improved data,
analysis techniques, and facilities that support research on the deep Earth system,
final resolution of many of the key issues will require a significant improvement in
high-resolution observational, theoretical, experimental, and modeling capabilities.
On the observational end, the primary challenge is the big step to fully 3D seismic
imaging with short scale-length resolution. This is achieved in the shallow oil
exploration industry using very fine wavefield sampling that is not approached by
current global seismic networks or even large-scale deployments of continental-scale
arrays such as the EarthScope transportable array (e.g., Rost et al., 2008). There is a
need for moderate aperture (~100 km) dense (100 to 200 stations) broadband arrays
deployed in multiple locations around the world that can provide high-resolution
imaging of specific regions of the deep mantle within the large-scale framework
structures that can be imaged by existing global networks. An “Array of Arrays”
concept is being developed in the seismological community as a means to achieve the
high-resolution capabilities essential to resolving detailed structures in boundary
layers, in deep subducting slabs, and in deep plumes as well as for improving models
of statistical heterogeneity of small-scale structures that cannot be deterministically
imaged. This undertaking will require strong international partnerships.
Advances in theoretical and computational capabilities for 3D seismic
processing, for ab initio mineral physics calculations of material properties, and for
multiscale 3D spherical geodynamics are all required to take a big step forward in
resolving fine-scale structures and dynamics. Access to massive computational
resources is also needed for dealing with the complexity of high-resolution
seismological imaging and modeling, theoretical mineral physics, and especially
global geodynamics calculations. These global geodynamics calculations will include
fine-scale boundary layers on thermal and chemical boundaries, phase changes
including iron (Fe) spin-state transitions, and partial melting effects, with long-time
evolution. Improved experimental resolution of high P-T elasticity and transport
properties will also be required, which will likely involve establishing new NSF-
supported analysis nodes on large U.S. Department of Energy (DOE) high-energy
facilities. The overall scope of facilities needed to make the next large steps in
understanding the deep Earth thermo-chemical dynamic system will likely require
major instrumentation initiatives and interagency partnerships. While the EarthScope