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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.06.035 Byline: Ja-Ren Lin (a)(b), Taras V. Gerya (b), Paul J. Tackley (b), David A. Yuen (c), Gregor J. Golabek (b) Keywords: Planetary formation Abstract: We developed and tested an efficient 2D numerical methodology for modeling gravitational redistribution processes in a quasi spherical planetary body based on a simple Cartesian grid. This methodology allows one to implement large viscosity contrasts and to handle properly a free surface and self-gravitation. With this novel method we investigated in a simplified way the evolution of gravitationally unstable global three-layer structures in the interiors of large metal-silicate planetary bodies like those suggested by previous models of cold accretion [Sasaki, S., Nakazawa, K., 1986. J. Geophys. Res. 91, 9231-9238; Karato, S., Murthy, V.R., 1997. Phys. Earth Planet Interios 100, 61-79; Senshu, H., Kuramoto, K., Matsui, T., 2002. J. Geophys. Res. 107 (E12), 5118. 10.1029/2001JE001819]: an innermost solid protocore (either undifferentiated or partly differentiated), an intermediate metal-rich layer (either continuous or disrupted), and an outermost silicate-rich layer. Long-wavelength (degree-one) instability of this three-layer structure may strongly contribute to core formation dynamics by triggering planetary-scale gravitational redistribution processes. We studied possible geometrical modes of the resulting planetary reshaping using scaled 2D numerical experiments for self-gravitating planetary bodies with Mercury-, Mars- and Earth-size. In our simplified model the viscosity of each material remains constant during the experiment and rheological effects of gravitational energy dissipation are not taken into account. However, in contrast to a previously conducted numerical study [Honda, R., Mizutani, H., Yamamoto, T., 1993. J. Geophys. Res. 98, 2075-2089] we explored a freely deformable planetary surface and a broad range of viscosity ratios between the metallic layer and the protocore (0.001-1000) as well as between the silicate layer and the protocore (0.001-1000). An important new prediction from our study is that realistic modes of planetary reshaping characterized by a high viscosity protocore and low viscosity molten silicate and metal [Senshu, H., Kuramoto, K., Matsui, T., 2002. J. Geophys. Res. 107 (E12), 5118. 10.1029/2001JE001819] may result in the transient exposure of the protocore to the planetary surface and a strongly (up to 8% of the planetary diameter) aspherical deviation of the planetary shape during the early stages of core formation. Exposure of the protocore might happen in the early stages of iron core formation. This process may conceivably convert a large amount of potential energy into temperature increase and a transient strongly non-uniform depth of the magma ocean around the protoplanet. Our simplified model also predicts that the time for metallic core formation out of the metal-rich layer depends mainly on the dynamics of the deformation of the solid strong protocore. In nature this dynamics will be strongly dependent on the effective viscosity of the protocore, which should generally have non-Newtonian pressure-, temperature-, and stress-dependent rheology with strong thermomechanical feedbacks from gravitational energy dissipation. Author Affiliation: (a) Institute of Oceanography, National Taiwan University, Taiwan (b) Geophysical Fluid Dynamics Group, Institute of Geophysics, Department of Geosciences, ETH-Zurich, Switzerland (c) University of Minnesota Supercomputing Institute, Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN55455, USA Article History: Received 30 May 2008; Revised 25 April 2009; Accepted 21 June 2009

Subduction of the lithosphere at convergent-plate boundaries takes place asymmetrically--the subducted slab sinks downward, while the overriding plate moves horizontally (one-sided subduction). In contrast, global mantle convection models generally predict downwelling of both plates at convergent margins (two-sided subduction). We carried out two-dimensional (2-D) numerical experiments with a mineralogical-thermomechanical viscoelastic-plastic model to elucidate the cause of one-sided subduction. Our experiments show that the stability, intensity, and mode of subduction depend mainly on slab strength and the amount of weak hydrated rocks present above the slab. Two-sided subduction occurs at low slab strength (sin[[phi]] < 0.15, where [phi] is effective internal friction angle), regardless of the extent of hydration. In contrast, steady-state one-sided subduction requires a weak hydrated slab interface and high slab strength (sin[[phi]] > 0.15). The weak interface is maintained by the release of fluids from the subducted oceanic crust as a consequence of metamorphism. The resulting weak interplate zone localizes deformation at the interface and decouples the strong plates, facilitating asymmetric plate movement. Our work suggests that high plate strength and the presence of water are major factors controlling the style of plate tectonics driven by self-sustaining one-sided subduction processes. Keywords: subduction zones, water, numerical modeling, slab dehydration, fluid flow.

Using a regional upper-mantle model with an unprecedented spatial resolution of ~100 m, we have investigated at multiple resolutions the character of incipient magma chambers forming under oceanic arcs. The magma chambers are formed from wave-like structures propagating upward along descending slabs and consist of compositionally buoyant, hydrated, partially molten subducted crustal and mantle material. These wave structures are 300-500 [degrees]C colder than the mantle wedge and may have an upward velocity of >1 m/yr. Inverted temperature structures and transitory bimodal magmatism are plausible consequences of finger-like penetration of relatively cold, hydrated material of the incipient magma chambers into the hot mantle wedge. Apart from forming and periodic feeding of the magma chambers, 'cold' waves may also transport upward thousands of cubic kilometers of subducted material and may cause the rapid exhumation of ultrahigh-pressure rocks along slabs. Keywords: subduction zones, numerical modeling, partial melting, mantle plumes, exhumation of ultrahigh-pressure rocks.

Double-diffusive convection (D.D.C.) is a nonlinear fluid-dynamical phenomenon, driven by thermal and compositional effects on the density. We discuss the nature of subcritical, finite-amplitude, double-diffusive convection for infinite Prandtl number and large Lewis number, Le, which have applications in magma chambers and at the D'-layer at the core-mantle boundary (CMB). Numerical solutions by two-dimensional, finite-element method are presented to portray the nature of time-dependent D.D.C. in both the diffusive and the finger regimes. The compositional heterogeneities at the CMB are far more complex than the local thermal structure because of the large Le and may have important implications for the scattering of seismic waves off the CMB. The effects of increasing the buoyancy ratio [R.sub.[rho]] are to suppress time-dependent D.D.C. even at high Ra. In narrow slots shear-heating instabilities can be triggered in the finger regime by the abrupt overturn of the compositional interface. This phenomenon may occur in tall magma chambers with low dissipation numbers of of order 0 (0.01).

Convective magma mixing is driven by thermal and compositional effects on melt density. We investigated the role of compositional buoyancy in convective magma mixing by means of two-dimensional numerical simulation. Two kinds of self-organization phenomena were observed in our simulations: (1) temporally-local unmixing events associated with flow reversals; and (2) long-lived segregations (ocular structures) in the center of convection cells. Statistical quantities of scale, scale ratio, and intensity of segregation are useful abstractions of the composition field for quantifying mixing and self-organization phenomena. The trajectory of scale ratio and intensity exhibits attractor behavior and provides a compact way of monitoring the evolution of mixing and self-organization. The ratio of compositional buoyancy to thermal buoyancy is given by the parameter Rr, where Rr = 0 implies passive mixing and Rr > 0 implies dynamic mixing. Ocular structures which form in both passive and dynamic mixing tend to decrease the mixing rate. Flow reversals and associated unmixing events which occur only in dynamic mixing further slow mixing. However, passive mixing is slower in our simulations than is mixing with small Rr because a strong and persistent ocular structure forms in passive mixing. At high Rr (Rr > 1), however, mixing is generally inhibited by compositional buoyancy because of the gravitational stability of the initial state.

Numerical modelling of geological processes, such as mantle convection, flow in porous media, and geothermal heat transfer, has become quite common with the increase in computing and the availability of usable software. Today modelling these dynamical processes entails the solving of the governing equations involving the mass, momentum, energy and chemical transport. These equations represent partial differential equations and must be solved on powerful enough computers because they require sufficient spatial and temporal resolution to be useful. We describe here the salient and outstanding features of the SEPRAN software package, developed in the Netherlands, as a case study for a robust and user-friendly software, which the geological community can utilize in handling many thermal-mechanical-chemical problems found in geology, which will include geothermal situations, where many types of partial differential equations must be solved at the same time with thermodynamical input parameters. [ABSTRACT FROM AUTHOR]

We have designed a web-based software system for real-time interactive visualization of results taken from large-scale simulations of 3-D mantle convection and other large-scale modeling efforts. This approach allows for intense visualization sessions for a couple of hours as opposed to storing massive amounts of data in a storage system. Our data sets consist of 3-D data with over 10 million unknowns at each time-step to be used for volume rendering. Large-scale interactive visualization on a display wall holding 15 million pixels has already been accomplished. With the advent of the age of the mobile web, we have now extended this tactic to hand-held devices, such as the OQO, Nokia N800, netbooks, iPHONE, and Android OS phones. We are developing web-based software in Java to extend the ubiquitous use of this system across long distances. The software is aimed at creating an interactive and functional application capable of running on multiple browsers by taking advantage of two AJAX-enabled web frameworks: Echo2 (http://echo.nextapp.com/site/echo2) and Google Web Toolkit (http://code.google.com/webtoolkit/). Modular building of the system allows for components to be swapped out so that other forms of visualization can be accommodated, such as molecular dynamics in mineral physics or 2-D data sets from the regional convection models. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We have extended our previous 2D method [Gerya, T.V., Yuen, D.A., 2003. Characteristics-based marker-in-cell method with conservative finite-differences schemes for modeling geological flows with strongly variable transport properties. Phys. Earth Planet. Interiors 140, 295–320], which is a combination of conservative finite-differences with marker-in-cell techniques to include the effects of visco-elasto-plastic rheology, self-gravitation and a self-consistently derived evolving curvilinear planetary surface. This code is called I2ELVIS and can solve a new class of computationally challenging problems in geodynamics, such as shear localization with large strains, crustal intrusion emplacement of magmas, bending of realistic visco-elasto-plastic plates and core-formation by vigorous shell tectonics activities related to a global Rayleigh–Taylor instability of a metal layer formed around silicate-rich lower density (primordial) core during planetary accretion. We discuss in detail the computational strategy required the rheological constraints to be satisfied at each time step and spatial location. We show analytical benchmarks and examples drawn from comparing between numerical and analogue experiments in structural geology, subducting slab bending with a visco-elasto-plastic rheology and equilibrium spherical configurations from self-gravitation. We have also tested possibilities of future applications by addressing 3D geometries based on multigrid method and including inertial effects in the momentum equation with tracers in order to simulate meteoritic impact events and eventually earthquake instabilities. [Copyright &y& Elsevier]

Visualizing and analyzing datasets in the geosciences is becoming increasingly complicated as their volumes are growing explosively. This poses a challenging problem for researchers who must sift through terabytes of data to discover useful relationships inside the information. There is a great need for geophysicists to interactively explore their data sets. Conventional visualization systems lack adequate bandwidth and rendering capabilities necessary for the largest data sets. CAVE and Powerwall display devices are necessary for researchers to explore their data sets in an immersive setting. We describe a utilitarian system targeted specifically at the cost-effective interactive exploration of data sets tens of terabytes in size and harness this system for visualization and analysis of geophysical simulations. Webcams can be used as a steering device to track a local region of interest, which is useful for remote visualization of large data sets. This system will be employed as a web-service under the auspices of Narada-Brokering, while using webcam technologies to enable remote visualization for collaborating researchers. Webcams can be incorporated in a point-to-point network for rapid exchange of information and quickly announcing natural disasters, such as tsunamis, landslides and earthquakes. [ABSTRACT FROM AUTHOR]

Abstract: Although the Amira visualization package has been available since 1999, not much effort has been made to use this powerful package for addressing the challenging problem that geodynamicists have in visualizing 3-D features of cold downwellings in spherical mantle convection simulations with high spatial resolution. In this paper, we present three approaches that exploit the functionalities of Amira to meet the needs of visualizing the complexity of these dynamic processes. The first task is to use the multiple isosurfaces combined with different colors and transparencies for showing the large-scale features from a global perspective. The second task is to localize the small-scale features of interest by cutting off the rest or splitting off a small part of image from the entire picture so that the details can be viewed locally. The third one is the use of multiple windows simultaneously for showing different portions of the same set data in different displaying formats from various angles of view. We will also present new geophysical findings based on these visualization approaches. [Copyright &y& Elsevier]

Abstract: Wavelet compression methodologies promise significant computational and storage cost savings through the benefit of producing results on adapted grids that significantly reduce storage and data manipulation costs. Yet, with these storage methodologies come new challenges in the visualization of temporally adaptive datasets. Wavelet compressed three-dimensional mantle convection simulations are visualized as a challenging case study. We employ adaptive 3D visualization using cache friendly octal tree volume visualization as an effective visualization approach. To explore the localized multi-scale structures in the datasets, the wavelet coefficients are also visualized allowing visualization of energy contained in local physical regions as well as in local wavenumber space. Our technique allows for exploring localized multi-scale structures using multi-resolution visualization from the compressed state of large geophysical simulations. [Copyright &y& Elsevier]

Calculation of phase diagrams for terrestrial and planetary materials exerts a growing impact in geosciences today. In this work, we demonstrate the feasibility of efficient delineation and visualization of complicated realistic multi-phase diagrams and related in situ physical properties of rocks by using discontinuous second generation wavelets, allowing a representation of both isotropic and anisotropic properties with arbitrary resolution. This is done by combining adaptive wavelet-based meshing technology with recently developed efficient “phase diagram function” designed as a Gibbs free energy minimization. The proposed automated strategy allows one to obtain an efficient delineation of physical properties using a uniform set of wavelet nodes regardless of whether these variables are continuous or discontinuous functions of pressure, temperature, or composition. The use of this strategy captures very small details of phase diagram morphology allowing both acceleration of the calculations and compression of results on the order of 102 by comparison to uniform grids of the same effective resolution. The web-based application of the proposed methodology for phase diagram visualization with interactive zooming capabilities is also discussed. [Copyright &y& Elsevier]

Abstract: This paper brings an overall view of the service-oriented architecture (SOA) used in VLab, a system aimed to handle concurrent calculations of geo-materials participating in extensive workflows. We recap the algorithms of physical importance that underly the system requirements. The system architecture then emerges naturally. A usage view diagram is shown and thoroughly discussed. We also show how analysis tools are integrated in the SOA. [Copyright &y& Elsevier]

Abstract: High dynamic range data, the magnitudes of which span a wide range of scales, are pervasive in the geosciences. Simulations or measurements of many important geophysical processes, such as earthquakes, mantle temperature fluctuations, generate various high dynamic range data sets, in the form of volume or surface. Effective visualization of such datasets is vital for understanding such complex geophysical phenomena and poses a new challenge for both geoscientists and visualization scientists. We describe the general aspects of high dynamic range datasets in the geophysical sciences and provide three case studies of visualizing such data using the techniques we have developed recently. They include: (1) visualizing the Earth’s mantle structures using high dynamic volume volume visualization (HDR VolVis); (2) visualizing surface ruptures during earth quakes using an interference-based method; (3) visualizing tsunami waves again using interference-based method. To improve the performance of visualizing these datasets, which are usually large in size, modern commodity graphics hardware are leveraged to provide simultaneously efficient simulation and visualization. [Copyright &y& Elsevier]

Abstract: Virtual organizations are rapidly changing the way scientific communities perform research. Web-based portals, environments designed for collaboration and sharing data, have now become the nexus of distributed high performance computing. Within this paper, we address the infrastructure of the Virtual Laboratory for Earth and Planetary Materials (VLab), an organization dedicated to using quantum calculations to solve problems in mineral physics. VLab provides a front-end portal, accessible from a browser, for scientists to submit large-scale simulations and interactively analyze their results. The cyber-infrastructure of VLab concentrates on scientific workflows, portal development, responsive user-interfaces and automatic generation of web services, all necessary to ensure a maximum degree of flexibility and ease of use for both the expert scientist and the layperson. [Copyright &y& Elsevier]

Abstract: Software for geodynamic modeling has not kept up with the fast growing computing hardware and network resources. In the past decade supercomputing power has become available to most researchers in the form of affordable Beowulf clusters and other parallel computer platforms. However, to take full advantage of such computing power requires developing parallel algorithms and associated software, a task that is often too daunting for geoscience modelers whose main expertise is in geosciences. We introduce here an automated parallel computing environment built on open-source algorithms and libraries. Users interact with this computing environment by specifying the partial differential equations, solvers, and model-specific properties using an English-like modeling language in the input files. The system then automatically generates the finite element codes that can be run on distributed or shared memory parallel machines. This system is dynamic and flexible, allowing users to address different problems in geosciences. It is capable of providing web-based services, enabling users to generate source codes online. This unique feature will facilitate high-performance computing to be integrated with distributed data grids in the emerging cyber-infrastructures for geosciences. In this paper we discuss the principles of this automated modeling environment and provide examples to demonstrate its versatility. [Copyright &y& Elsevier]

Abstract: The pair of earthquakes off Taiwan on December 26, 2006 and the subsequent disruption of the Internet traffic have called attention to the potential destructive hazards along the Chinese coast from tsunamis. Historical records show past tsunami earthquakes in this region. Using GPS, earthquake focal mechanisms and geological evolution, we have delineated the dangerous zones in the Philippine Sea plate where major earthquakes may occur. The Manila Trench is identified as being most susceptible to future major earthquakes. We have obtained the local Gutenberg–Richter relationship for five sections along the Philippine Sea plate boundary and use this information for determining the probability distribution for tsunami waves of various heights to impinge on various Chinese cities. We devise a new method called the probabilistic forecast of tsunami hazard (PFTH), which determines this probability distribution by direct numerical simulation of the waves excited by hypothetical earthquakes in these zones. We have employed the linear shallow-water equations over the South China Sea. We have also compared them with results from the nonlinear version and found that the linear treatment serves our purpose sufficiently well. In the next century the probability of a wave with a height of over 2.0m to hit near-coast ocean of Hong Kong and Macau is about 10%. Cities in Taiwan are less vulnerable than those on the mainland coast. [Copyright &y& Elsevier]

Abstract: Small-scale convection of the upper mantle beneath the Chinese Tian Shan (Tien Shan) is investigated in terms of numerical modeling. The finite element method combined with the marker-in-cell technique is used to describe the flow of the heterogeneous upper mantle. The density model is derived from the P-wave velocity structure of the crust and upper mantle along the Kuche–Kuitun profile across the Chinese Tian Shan, which is obtained using the seismic travel time tomography technique. Our computational results reveal the southward-counterclockwise and northward-clockwise upper mantle convective cells underneath the Junggar-north Tian Shan and Tarim-south Tian Shan, respectively. Our results also show the convective scale reaches to ∼500km and the convective speed at the top of the upper mantle should not be less than 20mm/year for a normal viscosity model. The northward extrusion of the Tarim block plays a key role in the Tian Shan mountain building since the Cenozoic period, but it nearly does not influence the upper mantle convection. The present-day tectonic deformation in the Chinese Tian Shan is related to the small-scale convection of the upper mantle. [Copyright &y& Elsevier]