Dan J. Bower
Caltech Geophysics Division, MC 252-21, Pasadena, CA 91125, USA
Refereed publications
| Authors | Title | Year | Journal / Proceedings | BibTeX type |
|---|---|---|---|---|
| Bower, D.J.; Wicks, J.K.; Gurnis, M. & Jackson, J.M. | A geodynamic and mineral physics model of a solid-state ultralow-velocity zone | 2011 |
Earth Planet. Sc. Lett. Vol. 303 , pp. 193-202 |
article |
| Abstract: Recent results (Wicks et. al., 2010) suggest that a mixture of iron-enriched (Mg,Fe)O and ambient mantle is consistent with wavespeed reductions and density increases inferred for ultralow-velocity zones (ULVZs). We explore this hypothesis by simulating convection to deduce the stability and morphology of such chemically-distinct structures. The buoyancy number, or chemical density anomaly, largely dictates ULVZ shape, and the prescribed initial thickness (proxy for volume) of the chemically-distinct layer controls its size. We synthesize our dynamic results with a Voigt-Reuss-Hill mixing model to provide insight into the inherent seismic tradeoff between ULVZ thickness and wavespeed reduction. Seismic data are compatible with a solid-state origin for ULVZs, and a suite of these structures may scatter seismic energy to produce broadband PKP precursors. | ||||
BibTeX:
@article{BWGJ11,
author = {D. J. Bower and J. K. Wicks and M. Gurnis and J. M. Jackson},
title = {A geodynamic and mineral physics model of a solid-state ultralow-velocity zone},
journal = {Earth Planet. Sc. Lett.},
year = {2011},
volume = {303},
pages = {193--202},
doi = {10.1016/j.epsl.2010.12.035}
}
|
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| Gurnis, M.; Zahirovic, S.; Turner, M.; DiCaprio, L.; Spasojević, S.; Müller, R.D.; Boyden, J.; Seton, M.; Manea, V.C. & Bower, D.J. | Plate Tectonic Reconstructions with Continuously Closing Plates | 2010 | Comput. Geosci. | article |
| Abstract: We present a new algorithm for modeling a self-consistent set of global plate polygons. Each plate polygon is composed of a finite list of plate margins, all with different Euler poles. We introduce a "Continuously Closed Plate" (CCP), such that, as each margin moves independently, the plate polygon remains closed geometrically as a function of time. This method solves emerging needs in computational geodynamics to combine kinematic with dynamic models. Because they have polygons that are too widely spaced in time and have inconsistent motions between margins and plates, traditional global plate tectonic reconstructions have become inadequate for geodynamics. The CCP algorithm has been incorporated into the GPlates open-source paleogeographic system. The algorithm is a set of procedures and data structures that operate on collections of reconstructed geometric data to form closed plate polygons; the main data structures used for each plate polygon are based on a nested hierarchy of topological elements. Reconstructions with CCPs can be created, edited, visualized and exported with GPlates. The native storage of the dynamic reconstructions is the GPlates Markup Language, GPML, which uses an XML-based file format called GML. We demonstrate the utility of the CCP method by creating a global reconstruction with continuously closing plates from 140 Ma to the present using data from existing, traditional reconstructions. |
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BibTeX:
@article{GURNIS09,
author = {Michael Gurnis and S. Zahirovic and M. Turner and L. DiCaprio and S. Spasojević and R. D. Müller and J. Boyden and M. Seton and V. C. Manea and D. J. Bower},
title = {Plate Tectonic Reconstructions with Continuously Closing Plates},
journal = {Comput. Geosci.},
year = {2010},
note = {in review}
}
|
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| Bower, D.J.; Gurnis, M.; Jackson, J.M. & Sturhahn, W. | Enhanced Convection and Fast Plumes in the Lower Mantle Induced by the Spin Transition in Ferropericlase | 2009 |
Geophys. Res. Lett. Vol. 36 |
article |
| Abstract: Using a numerical model we explore the consequences of the intrinsic density change (Δρ/ρ ≈ 2–4%) caused by the Fe2+ spin transition in ferropericlase on the style and vigor of mantle convection. The effective Clapeyron slope of the transition from high to low spin is strongly positive in pressure-temperature space and broadens with high temperature. This introduces a net spin-state driving density difference for both upwellings and downwellings. In 2-D cylindrical geometry spin-buoyancy dominantly enhances the positive thermal buoyancy of plumes. Although the additional buoyancy does not fundamentally alter large-scale dynamics, the Nusselt number increases by 5–10%, and vertical velocities by 10–40% in the lower mantle. Advective heat transport is more effective and temperatures in the core-mantle boundary region are reduced by up to 12%. Our findings are relevant to the stability of lowermost mantle structures. | ||||
BibTeX:
@article{BGJS09,
author = {D. J. Bower and M. Gurnis and J. M. Jackson and W. Sturhahn},
title = {Enhanced Convection and Fast Plumes in the Lower Mantle Induced by the Spin Transition in Ferropericlase},
journal = {Geophys. Res. Lett.},
year = {2009},
volume = {36},
doi = {10.1029/2009GL037706}
}
|
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| Sun, D.; Helmberger, D.; Ni, S. & Bower, D. | Direct measures of lateral velocity variation in the Deep Earth | 2009 |
J. Geophys. Res. Vol. 114 |
article |
| Abstract: Current tomographic models of the Earth display perturbations to a radial stratified reference model. However, structures in the deep mantle that are chemically dense with low Rayleigh numbers can develop enormous relief, perhaps with boundaries closer to vertical than radial. Such features are hard to detect with present tomographic modeling technique because the timing anomalies are based on long-period filtered waveforms with complexity removed. Here we develop a new tool for processing array data on the basis of a decomposition referred to as a multipath detector, which can be used to distinguish between horizontal structure (in-plane multipathing) and vertical (out-of-plane multipathing) directly from processing array waveforms. A lateral gradient coefficient based on this detector provides a direct constraint on the sharpness of the boundaries and material properties. We demonstrate the usefulness of this approach by processing samples of both P and S data from the Kaapvaal array in southern Africa, which are compared with synthetic predictions from a metastable dynamic model containing sharp edges. Both data and simulations produce timing gradients larger than 2 s/deg in azimuthal changes for S-waves, where only minor effects are obtained for P-waves. These results further validate the case for distinct chemistry inside the African Low Shear Velocity Province. | ||||
BibTeX:
@article{SHNB09,
author = {D. Sun and D. Helmberger and S. Ni and D. Bower},
title = {Direct measures of lateral velocity variation in the Deep Earth},
journal = {J. Geophys. Res.},
year = {2009},
volume = {114},
doi = {10.1029/2008JB005873}
}
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| Bower, D.J.; Caulfield, C.P.; Fitzgerald, S. & Woods, A.W. | Transient ventilation dynamics following a change in strength of a point source of heat | 2008 |
J. Fluid Mech. Vol. 614 , pp. 15-37 |
article |
| Abstract: We investigate the transient ventilation flow within a confined ventilated space, with high- and low-level openings, when the strength of a low-level point source of heat is changed instantaneously. The steady-flow regime in the space involves a turbulent buoyant plume, which rises from the point source to a well-mixed warm upper layer. The steady-state height of the interface between this layer and the lower layer of exterior fluid is independent of the heat flux, but the upper layer becomes progressively warmer with heat flux. New analogue laboratory experiments of the transient adjustment between steady states identify that if the heat flux is increased, the continuing plume propagates to the top of the room forming a new, warmer layer. This layer gradually deepens, and as the turbulent plume entrains fluid from the original warm layer, the original layer is gradually depleted and disappears, and a new steady state is established. In contrast, if the source buoyancy flux is decreased, the continuing plume is cooler than the original plume, so that on reaching the interface it is of intermediate density between the original warm layer and the external fluid. The plume supplies a new intermediate layer, which gradually deepens with the continuing flow. In turn, the original upper layer becomes depleted, both as a result of being vented through the upper opening of the space, but also due to some penetrative entrainment of this layer by the plume, as the plume overshoots the interface before falling back to supply the new intermediate layer. We develop quantitative models which are in good accord with our experimental data, by combining classical plume theory with models of the penetrative entrainment for the case of a decrease in heating. Typically, we find that the effect of penetrative entrainment on the density of the intruding layer is relatively weak, provided the change in source strength is sufficiently large. However, penetrative entrainment measurably increases the rate at which the depth of the draining layer decreases. We conclude with a discussion of the importance of these results for the control of naturally ventilated spaces. | ||||
BibTeX:
@article{BCFW08,
author = {D. J. Bower and C. P. Caulfield and S. Fitzgerald and A. W. Woods},
title = {Transient ventilation dynamics following a change in strength of a point source of heat},
journal = {J. Fluid Mech.},
year = {2008},
volume = {614},
pages = {15--37},
doi = {10.1017/S0022112008003479}
}
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