Multiscale Brittle-Ductile Coupling and Genesis of Slow Earthquakes

We present the first attempt to explain slow earthquakes as cascading thermal-mechanical instabilities. To attain this goal we investigate brittle-ductile coupled thermal-mechanical simulation on vastly different time scales. The largest scale model consists of a cross section of a randomly perturbed elasto-visco-plastic continental lithosphere on the order of 100 × 100 km scale with no other initial structures. The smallest scale model investigates a km-scale subsection of the large model and has a local resolution of 40 × 40 m. The model is subject to a constant extension velocity applied on either side. We assume a free top surface and with a zero tangential stress along the other boundaries. Extension is driven by velocity boundary conditions of 1 cm/a applied on either side of the model. This is the simplest boundary condition, and makes it an ideal starting point for understanding the behavior of a natural system with multiscale brittle-ductile coupling. Localization feedback is observed as faulting in the brittle upper crust and ductile shearing in an elasto-viscoplastic lower crust. In this process brittle faulting may rupture at seismogenic rates, e.g., at 10²–10³ ms^?1, whereas viscous shear zones propagate at much slower rates, up to 3 × 10^?9 ms^?1. This sharp contrast in the strain rates leads to complex short-time-scale interactions at the brittle-ductile transition. We exploit the multiscale capabilities from our new simulations for understanding the underlying thermo-mechanics, spanning vastly different, time- and length-scales.     

The diffusion of Hong Kong cultural values to Mainland China: a case study in Shenzhen

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Workshop on Computational Studies of Interfacial Phenomena: Nanoscale to Mesoscale

This is a report of a workshop on nanoscale to mesoscale phenomena held at the Environmental Molecular Science Laboratory (EMSL) of the Pacific Northwest National Lab (PNNL) in Richland, Washington on September 24 to 25, 1998. Around thirty scientists from physics, chemistry, geology, geophysics, computer science, soil science, and applied mathematics gathered and presented 14 lectures covering many areas, which included interfacial mineral chemistry, large-scale molecular dynamics, constitutive relationships and quantum chemistry, cross-scaling studies, molecular dynamics of interfaces and new approaches in molecular dynamics. This workshop demonstrates a need for an interdisciplinary forum wherein many different issues crossing many scales and disciplinary boundaries can be discussed openly.     

On the Galactic disc age–metallicity relation

A comparison is made between the age–metallicity relations obtained from four different types of studies: F and G stars in the solar neighbourhood, analysis of open clusters, galactic structure studies with the stellar population synthesis technique and chemical evolution models. Metallicities of open clusters are corrected for the effects of the radial gradient, which we find to be −0.09 dex kpc⁻¹ and most likely constant in time. We do not correct for the vertical gradient, because its existence and value are not firmly established.
Stars and clusters trace a similar age–metallicity relation, showing an excess of rather metal-rich objects in the age range 5–9 Gyr. Galactic structure studies tend to give a more metal-poor relation than chemical evolution models. Neither relation explains the presence of old, relatively metal-rich stars and clusters. This might be caused by uncertainties in the ages of the local stars, or pre-enrichment of the disc with material from the bulge, possibly as a result of a merger event in the early phases of the formation of our Galaxy.     

Ubiquitous interactive visualization of 3D mantle convection using a web-portal with Java and Ajax framework

We have developed a new strategy and espouse a novel paradigm for large-scale computing and real-time interactive visualization. This philosophy calls for intense interactive sessions for a couple of hours at a time at the expense of storing data on many disk drives during regular or heroic runs on massively parallel systems. We have already carried out successfully real-time volume-rendering visualization by employing hundreds of processors for a grid with over 25 million unknowns. Both Cartesian and spherical 3D mantle convection are visualized. The volume-rendered images are viewed on a large display device, with many panels holding around 13 million pixels. We will employ a software strategy involving an hierarchical rendering service, which will have as software an Ajax interface for interactive visualization of large data sets on many different platforms from desktop PC’s to hand-held devices, such as the OQO and the Nokia N-800. An option for stereo viewing is also implemented. We have installed a user interface as web application, using Java and Ajax framework in order to achieve over the Internet reasonable accessibility to our ongoing runs. Our goal is to expand the array of interactive devices, which will make it feasible to carry out ubiquitous visualization and monitoring of large-scale simulations or onsite events and to allow for collaborations across oceans.     

Experiments in scientific computation on the PlayStation 3

The Sony PlayStation 3 (PS3) offers the computational power of a parallel processor at low cost, which makes it a great starter unit for development in parallel programming. To explore the capabilities of the unit, we took a simple ray tracing program and extended it to render triangulated height field data across the PS3’s 6 synergistic processing units (SPUs). We also implemented the heat averaging equation as a precursor to CFD analysis on the PS3. In our studies, we found the Cell engine in the PS3 to be a powerful machine, however great care must be taken while developing because its unique platform calls for many levels of optimization to ensure efficiency. For insight on early work done on modern stream computing and GPU processing look up the Merrimac project and Pat Hanrahan.     

Visualization of tsunami waves with Amira package

In recent years numerical investigations of tsunami wave propagation have been spurred by the magnitude 9.3 earthquake along the Andaman–Sumatra fault in December, 2004. Visualization of tsunami waves being modeled can yield a much better physical understanding about the manner of wave propagation over realistic seafloor bathymetries. In this paper we will review the basic physics of tsunami wave propagation and illustrate how these waves can be visualized with the Amira visualization package. We have employed both the linear and nonlinear versions of the shallow-water wave equation. We will give various examples illustrating how the files can be loaded by Amira, how the wave-heights of the tsunami waves can be portrayed and viewed with illumination from light sources and how movies can be used to facilitate physical understanding and give important information in the initial stages of wave generation from interaction with the ambient geological surroundings. We will show examples of tsunami waves being modeled in the South China Sea, Yellow Sea and southwest Pacific Ocean near the Solomon Islands. Visualization should be a part of any training program for teaching the public about the potential danger arising from tsunami waves. We propose that interactive visualization with a web-portal would be useful for understanding more complex tsunami wave behavior from solving the 3-D Navier–Stokes equation in the near field.