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- Title
Densely Sampled Global Dynamic Topographic Observations and Their Significance.
- Authors
Holdt, M. C.; White, N. J.; Stephenson, S. N.; Conway‐Jones, B. W.
- Abstract
Topography and bathymetry are principally supported by some combination of crustal and sub‐crustal density variations. However, dynamic topography is generated by vertical deflection of the Earth's surface as a result of mantle convection. Isolating and quantifying observable dynamic topography yields valuable information about mantle processes. Here, we investigate global dynamic topography by calculating residual depth anomalies throughout the oceanic realm and residual topographic anomalies across the continents. We correct for sedimentary and crustal loading by exploiting a variety of seismologic datasets that include seismic reflection profiles, wide‐angle/refraction surveys, and receiver functions. In this way, an extensively revised and augmented global compilation of 10,874 oceanic residual depth measurements and 3,777 continental residual topographic measurements is constructed. In the oceanic realm, the methodology has been revised to improve accuracy and resolution. First, quartz/clay content of the sedimentary column is adjusted to remove minor skewness of residual depth anomalies as a function of plate age. Secondly, variation of bulk density as a function of crustal thickness is taken into account. Our global compilation is used to generate spherical harmonic representations of observable dynamic topography out to degree 40 (i.e., ∼1,000 km). Resultant spectra demonstrate that dynamic topographic power varies linearly with inverse wavenumber. The spectral slope directly reflects the way by which dynamic topography is generated by Stokes' flow. Our global results are consistent with independent and diverse geologic markers of uplift and subsidence together with Neogene‐Quaternary intraplate basalt magmatism. Plain Language Summary: The Earth's surface consists of interlocking tectonic plates that move with respect to each other at rates which we can now observe using the global positioning system. The story of how plate tectonics was discovered in the late 1960s is a very exciting one but the emphasis on horizontal movement of plates has tended to deflect attention away from a significant and related topic. Plate motion must be caused by slow stirring of the Earth's interior and this stirring should also generate lazy up‐and‐down displacement of the surface we live on. Unfortunately, these vertical movements are probably very slow and so hard to directly measure. In this study, we build upon previous attempts to measure vertical movements across the globe that we think can be attributed to slow stirring of the interior. Our analysis of depth measurements from the oceans and of anomalous topography onshore has enabled us to pinpoint the surface effects of stirring, which appear to occur on a whole host of length scales from hundreds of kilometers to tens of thousands of kilometers. Key Points: 7,601 seismic profiles yield residual depth measurements throughout the oceanic realmSpherical harmonic representations of dynamic topography are generated from combined oceanic and continental measurementsResultant power spectra are consistent with Stokes' flow of convecting mantle
- Subjects
INTERNAL structure of the Earth; SEISMIC reflection method; SURFACE of the earth; GLOBAL Positioning System; SEISMIC anisotropy; STOKES flow; MAGMATISM
- Publication
Journal of Geophysical Research. Solid Earth, 2022, Vol 127, Issue 7, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2022JB024391