QuakeSim and the Solid Earth Research Virtual Observatory

We are developing simulation and analysis tools in order to develop a solid Earth Science framework for understanding and studying active tectonic and earthquake processes. The goal of QuakeSim and its extension, the Solid Earth Research Virtual Observatory (SERVO), is to study the physics of earthquakes using state-of-the-art modeling, data manipulation, and pattern recognition technologies. We are developing clearly defined accessible data formats and code protocols as inputs to simulations, which are adapted to high-performance computers. The solid Earth system is extremely complex and nonlinear, resulting in computationally intensive problems with millions of unknowns. With these tools it will be possible to construct the more complex models and simulations necessary to develop hazard assessment systems critical for reducing future losses from major earthquakes. We are using Web (Grid) service technology to demonstrate the assimilation of multiple distributed data sources (a typical data grid problem) into a major parallel high-performance computing earthquake forecasting code. Such a linkage of Geoinformatics with Geocomplexity demonstrates the value of the Solid Earth Research Virtual Observatory (SERVO) Grid concept, and advances Grid technology by building the first real-time large-scale data assimilation grid.     

iSERVO: Implementing the International Solid Earth Research Virtual Observatory by Integrating Computational Grid and Geographical Information Web Services

We describe the goals and initial implementation of the International Solid Earth Virtual Observatory (iSERVO). This system is built using a Web Services approach to Grid computing infrastructure and is accessed via a component-based Web portal user interface. We describe our implementations of services used by this system, including Geographical Information System (GIS)-based data grid services for accessing remote data repositories and job management services for controlling multiple execution steps. iSERVO is an example of a larger trend to build globally scalable scientific computing infrastructures using the Service Oriented Architecture approach. Adoption of this approach raises a number of research challenges in millisecond-latency message systems suitable for internet-enabled scientific applications. We review our research in these areas.     

Twenty-first century Arctic climate change in the CCSM3 IPCC scenario simulations

Arctic climate change in the Twenty-first century is simulated by the Community Climate System Model version 3.0 (CCSM3). The simulations from three emission scenarios (A2, A1B and B1) are analyzed using eight (A1B and B1) or five (A2) ensemble members. The model simulates a reasonable present-day climate and historical climate trend. The model projects a decline of sea-ice extent in the range of 1.4–3.9% per decade and 4.8–22.2% per decade in winter and summer, respectively, corresponding to the range of forcings that span the scenarios. At the end of the Twenty-first century, the winter and summer Arctic mean surface air temperature increases in a range of 4–14°C (B1 and A2) and 0.7–5°C (B1 and A2) relative to the end of the Twentieth century. The Arctic becomes ice-free during summer at the end of the Twenty-first century in the A2 scenario. Similar to the observations, the Arctic Oscillation (AO) is the dominant factor in explaining the variability of the atmosphere and sea ice in the 1870–1999 historical runs. The AO shifts to the positive phase in response to greenhouse gas forcings in the Twenty-first century. But the simulated trends in both Arctic mean sea-level pressure and the AO index are smaller than what has been observed. The Twenty-first century Arctic warming mainly results from the radiative forcing of greenhouse gases. The 1st empirical orthogonal function (explains 72.2–51.7% of the total variance) of the wintertime surface air temperature during 1870–2099 is characterized by a strong warming trend and a “polar amplification”-type of spatial pattern. The AO, which plays a secondary role, contributes to less than 10% of the total variance in both surface temperature and sea-ice concentration.     

Pattern analysis of dune‐field parameters

As a basic form of pattern analysis, the parameters of dune spacing, defect density, crest orientation and crest length are measured from remote images and treated statistically for dunes at White Sands in New Mexico, the Algodones in California, the Agneitir in Mauritania, and the Namib in Namibia. Statistical populations are identified from frequency plots of dune spacing and crest length, field‐scale calculations of defect density, and rose diagrams of crest orientation. Single populations characterize simple dune fields (White Sands), whereas multiple populations characterize compound/complex dunes (Algodones, Namib), and complex dune fields (Agneitir). As time increases, dune fields show an increase in dune spacing and crest length, a decrease in defect density, more tightly clustered crest orientation, and a reduction in the variance associated with measurements of these parameters. The results are consistent with models of dune fields as self‐organizing complex systems in which a characteristic pattern emerges as a function of constructional time. Because pattern evolution is a function of time, it may be possible to use pattern analysis to augment current methods of age determination. Statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns, and to reconstruct each generation in terms of construction time and palaeo‐wind regime. Copyright © 2006 John Wiley & Sons, Ltd.     

Evaluation of an upscaled model for DNAPL dissolution kinetics in heterogeneous aquifers

Estimates of contaminant fluxes from DNAPL sources as a function of time and DNAPL mass reduction are important to assess the long-term sustainability and costs of monitored natural attenuation and to determine the benefits of partial source removal. We investigate the accuracy of the upscaled mass transfer function (MTF) proposed by Parker and Park [Parker JC, Park E. Modeling field-scale dense nonaqueous phase liquid dissolution kinetics in heterogeneous aquifers. WRR 2004;40:W05109] to describe field-scale dissolved phase fluxes from DNAPL sources for a range of scenarios generated using high-resolution 3-D numerical simulations of DNAPL infiltration and long-term dissolved phase transport. The results indicate the upscaled MTF is capable of accurately describing field-scale DNAPL dissolution rates as a function of time. For finger-dominated source regions, an empirical mass depletion exponent in the MTF takes on values greater than one which results in predicted mass flux rates that decrease continuously with diminishing DNAPL mass over time. Lens-dominated regions exhibit depletion exponents less than one, which results in more step-function like mass flux versus time behavior. Mass fluxes from DNAPL sources exhibiting both lens- and finger-dominated subregions were less accurately described by the simple MTF, but were well described by a dual-continuum model of the same form for each subregion. The practicality of calibrating a dual-continuum model will likely depend on the feasibility of obtaining spatially resolved field measurements of contaminant fluxes or concentrations associated with the subregions using multilevel sampling or some other means.     

Water quality in Lemoa, Guatemala

A variety of water supply sources are used in the rural Guatemalan Highlands. Formal municipal systems are rare, but villagers frequently form local water committees that construct spring-based supply systems. Recent work has indicated that groundwater may be a viable water supply source. The water quality from these two sources was characterized as well as water from other common sources including surface water and precipitation collection systems. Typically, all of the water sources contained unacceptable levels of coliform bacteria except for groundwater from a drilled well. Water monitoring indicated that not only did the water contain coliforms at the actual sources, but the infrastructure used to transmit the water to points of use may also be a source of coliforms. A cost comparison indicates that groundwater may be a cost-competitive, higher quality alternative to traditional spring-fed water systems.     

Differential supply of autochthonous organic carbon and nitrogen to the microbial loop in the Delaware Estuary

Using stable isotope tracer techniques in 4-h bottle incubations, the importance of organic matter transfer from phytoplankton to heterotrophic bacteria (bacteria) has been re-evaluated in the Delaware Estuary, considering carbon (C) and nitrogen (N) cycles separately. The hypothesis is that the transfer of C and N from phytoplankton to bacteria varies both temporally and spatially along estuarine gradients in response to variation in factors such as terrestrial organic C supply, inorganic N speciation and concentrations, and extracellular release of dissolved organic matter by phytoplankton. The percentage of autochthonous dissolved organic C being assimilated by bacteria varied between 3% and 10% of primary production and was not related to the rate of primary production. The transfer of N was considerably more variable when compared to C transfer, averaging ca. 20% of phytoplankton N assimilation; individual experiments yielded rates as high as 50%. Unlike C, autochthonous dissolved organic N transfer appears to vary with the magnitude of primary production, and its assimilation by bacteria accounted for 0–56% of the total measured bacterial N uptake. The results highlight the importance of separate consideration of C and N elemental cycles in evaluating sources of organic matter to the estuarine microbial loop.     

Oxygen, silicon, and Mn-Cr isotopes of fayalite in the Kaba oxidized CV3 chondrite: Constraints for its formation history

The iron-rich olivine end-member, fayalite, occurs in the matrix, chondrules, Ca-Al-rich inclusions (CAIs), silicate aggregates, and dark inclusions in the Kaba and Mokoia oxidized CV3 chondrites. In most occurrences, fayalite is associated with magnetite and troilite. To help constrain the origin of the fayalite (Fa_98-100), we measured oxygen and silicon isotopic compositions and Mn-Cr systematics in fayalite from two petrographic settings of the Kaba meteorite. One setting consists of big fayalite laths embedded in the matrix and radiating from a core of fine-grained magnetite and sulfide, while the other setting consists of small fayalite-magnetite-sulfide assemblages within or at the surface of Type I barred or porphyritic olivine chondrules. Oxygen in the big fayalite laths and small chondrule fayalites falls on the terrestrial fractionation line, and is distinct from that in chondrule forsterites, which are enriched in ¹⁶O (Δ¹⁷O = ∼−4‰). Oxygen in the big fayalite laths may be isotopically heavier than that in chondrule fayalites. Silicon isotopes suggest that forsterite is ∼1‰/amu heavier than adjacent fayalite within Kaba chondrules. However, we were unable to confirm large silicon isotopic differences among fayalites reported previously. The Mn-Cr data for big Kaba fayalites give an initial ⁵³Mn/⁵⁵Mn ratio of (2.07 ± 0.17) × 10⁻⁶, consistent with literature results on Mokoia chondrule fayalites. The combined data suggest that fayalites in both petrographic settings formed at about the same time, ∼9.7 Ma after the formation of CAIs. Our data indicate that those fayalite-magnetite-troilite assemblages replacing metal inside and around chondrules formed by aqueous alteration on the meteorite parent body. The formation site and mechanism for the big fayalite laths is less clear, but the petrographic setting indicates that they did not form in situ. None of the models that have been suggested for formation of these fayalites is entirely satisfactory.     

A simple,efficient starting value for the iterative solution of Kepler's equation

A simple starting value for the iterative solution of Kepler's equation in the elliptic case is presented. This value is then compared against five other starting values for 3750 test cases. In addition, bounds are given for the solution of Kepler's equation.