Slip-weakening and interactive dynamics of an heterogeneous seismic source

A theoretical 3D model of a fault region includes a slip-dependent friction, tectonic loading from the sides, and deterministic, continuous time formulation of governing equations. The model reproduces such properties of real faults as earthquake nucleation, earthquake complex rupture and nonregular recurrence. In particular, it is observed that the style of faulting changes from one event to another. Since all parameters related to the constitutive law are fixed during computer simulations, it is concluded that interactions between fault segments are responsible for such behavior. Neither the constitutive law nor fault spatial heterogeneities solely create complexity; rather it is the whole interactive dynamics of the system that determines the character of its evolution. Results are illustrated by time variations of global (i.e., related to the state of the whole fault) functions, such as energy release rate, seismic moment release rate, tectonic stresses, and local characteristics, such as driving and cohesive stresses, slip rates, slip displacements and mutual relations between them.     

Evidence for extreme fractionation of peralkaline silicic magmas, the Boseti volcanic complex, Main Ethiopian Rift

Matrix glass and melt inclusions in phenocrysts from pantellerite lavas of the Boseti volcanic complex, Ethiopia, record extreme fractionation of peralkaline silicic magma, with Al₂O₃ contents as low as 2.3?wt.%, FeO* contents up to 17?wt.% and SiO₂ contents ~65?wt.%. The new data, and published data for natural and experimental glasses, suggest that the effective minimum composition for peralkaline silicic magmas has ~5?wt.% Al₂O₃, 13?wt.% FeO* and 66?±?2?wt.% SiO₂. The dominant fractionating assemblage is alkali feldspar?+?fayalite?+?hedenbergite?+?oxides?±?quartz. Feldspar – melt relationships indicate that the feldspar is close to the minimum on the albite-orthoclase solid solution loop through the entire crystallization history. There is petrographic, mineralogical and geochemical evidence that magma mixing may have been a common process in the Boseti rhyolites.     

A 2300-year record of environmental change from SW Anatolia, Lake Burdur, Turkey

This work deals with changes recorded by lacustrine sediments from SW Anatolia in Turkey in the context of increasing stress on the Mediterranean environment in relation to human-climate-environmental interactions. Paleolimnological investigations were carried out on Lake Burdur (Lake District geographical subregion of Turkey), which has been subject to rapid changes in its hydrological system that caused a ~10-m water-level drop in the last 30 years. Study of a 5-m-long sediment core, taken from the recently dried out part of the lake, shows significant variation in granulometry, clay mineralogy, nitrogen and organic carbon content and its isotopic composition (?¹³C_org) throughout the sedimentary sequence, which represents the last 2,300 years. Chronology is based on radiocarbon dates obtained from plant fragments. The results provide a record of environmental changes, including biological productivity and erosion intensity, in relation to changes in water level and humidity of the area. The lowest previous water level, which is the same as observed today, occurred at approximately 300 BC, after which time a water-level increase led to a maximum stage between AD 200 and 1200. From AD 1200 to the present, the climate became drier accompanied by an overall lowering of water level, with periods of water-level fluctuations superimposed. The lake never dried out as is observed today at the coring site. The present drop in the lake water level is attributed to human activity rather than to climate change. This record of climate and environmental change in the Lake Burdur area appears to be stratigraphically complete. This study provides rare data for the late Holocene in Anatolia as well as information about rapid climate changes during specific periods. The influence of both the Northern hemisphere atmospheric circulation and Indian monsoon on the east Mediterranean remains unclear. Nevertheless, the North Sea—Caspian atmospheric teleconnection could be an important factor that explains local differences in climatic evolution of Anatolia during the period considered.     

On the complex disc–corona interactions in the soft spectral states of soft X-ray transients

Accreting black holes show a complex and diverse behaviour in their soft spectral states. Although these spectra are dominated by a soft, thermal component which almost certainly arises from an accretion disc, there is also a hard X-ray tail indicating that some fraction of the accretion power is instead dissipated in hot, optically thin coronal material. During such states, best observed in the early outburst of soft X-ray transients, the ratio of power dissipated in the hot corona to that in the disc can vary from ∼ 0 (pure disc accretion) to ∼ 1 (equal power in each). Here we present results of spectral analyses of a number of sources, demonstrating the presence of complex features in their energy spectra. Our main findings are: (1) the soft components are not properly described by a thermal emission from accretion discs: they are appreciably broader than can be described by disc blackbody models even including relativistic effects, and (2) the spectral features near     commonly seen in such spectra can be well described by reprocessing of hard X-rays by optically thick, highly ionized, relativistically moving plasma.     

Choice Modeler: A Web-based Spatial Multiple Criteria Evaluation Tool

This article presents a concept of a Web-based spatial multiple criteria evaluation tool for individual and group use called Choice Modeler (CM). CM was originally conceived as part of a larger Participatory Geographic Information System for Transportation project (PGIST; http://www.pgist.org ) aimed at developing and evaluating Internet-hosted capabilities to support participatory decision processes. CM is designed to be either a part of a larger information system such as PGIST or a standalone tool used for evaluation of decision variants. The decision support functions provided by CM aid in reducing the cognitive complexity of the decision space characterized by multiple decision options, evaluation criteria, and criterion weights. This is achieved by incorporating in CM the sensitivity analysis functions for the identification of criteria that do not influence the decision option ranking. Users can remove such criteria from further consideration and thus lessen the cognitive burden of evaluation, which may be essential in multi-stakeholder participatory decision processes. The additional capabilities of CM include a vote aggregation function to collate individual option rankings into a group ranking, and measures of agreement/disagreement to inform the participants about a group-derived desirability of specific decision options. The design of CM was implemented using Web-service architecture. In the article we describe the design of CM and discuss its advantages and limitations.     

Privacy and spatial pattern preservation in masked GPS trajectory data

Personal trajectory data are increasingly collected for a variety of academic and recreational pursuits. As access to location data widens and locations are linked to other information repositories, individuals become increasingly vulnerable to identification. The quality and precision of spatially linked attributes are essential to accurate analysis; yet, there is a trade-off between privacy and geographic data resolution. Obfuscation of point data, or masking, is a solution that aims to protect privacy and maximize preservation of spatial pattern. Trajectory data, with multiple locations recorded for an entity over time, is a strong personal identifier. This study explores the balance between privacy and spatial pattern resulting from two methods of obfuscation for personal GPS data: grid masking and random perturbation. These methods are applied to travel survey GPS data in the greater metropolitan regions of Chicago and Atlanta. The rate of pattern correlation between the original and masked data sets declines as the distance thresholds for masking increase. Grid masking at the 250-m threshold preserves route anonymity better than other methods and distance thresholds tested, but preserves spatial pattern least. This study also finds via linear regression that median trip speed and road density are significant predictors of trip anonymity.     

Geologic factors controlling groundwater chemistry in the coastal aquifer system of Douala/Cameroon: implication for groundwater system functioning

Douala city, located in the littoral province of Cameroon, receives abundant rainfall quantities due to its geographical position in the Gulf of Guinea and bears considerable surface water and groundwater resources. Due to socioeconomic development and rapid demographic growth in the city and its consequences of unplanned urbanization and improper sanitation system, these water resources are poorly protected and managed. Streams in the Wouri watershed receive large amounts of wastewater discharge, and hundreds of boreholes have been drilled into the aquifer system without any management plan. A detailed hydrodynamic and hydrogeochemistry study in Douala town and its environs was conducted to get a better insight into the groundwater system functioning in order to provide information for the sustainable management and protection of the groundwater resource. Two field campaigns were carried out with 187 samples collected and analyzed for major ions, stable isotopes (¹⁸O, ²H), and tritium ³H. The results of the sampling have shown that the weathering of silicate minerals is the dominant geochemical process affecting groundwater chemistry in this system. However, acid rainfall in the humid climate has also caused carbonate mineral dissolution, amorphous silica deposition, and ion exchange reactions to occur in aquifers in the region. The various water types identified were categorized into four major clusters C1 to C4, based on the major ion composition and the local hydrogeological conditions. Environmental isotope data reveal that modern-to-submodern waters occur in the phreatic Quaternary/Mio-Pliocene and Oligocene/Upper Eocene aquifers, respectively. These results corroborate with the conceptual model built where modern groundwater types indicated silicate mineral weathering and calcite dissolution (C1 and C2), whereas submodern groundwater mostly showed silica deposition, ion exchange, and, to a lesser extent, carbonate mineral dissolution (C3 and C4). This improved understanding of the aquifer system functioning is essential to provide a reasonable basis for effective control measures and sustainable water management.     

Internal catchment process simulation in a snow‐dominated basin: performance evaluation with spatiotemporally variable runoff generation and groundwater dynamics

Hydrologic models have increasingly been used in forest hydrology to overcome the limitations of paired watershed experiments, where vegetative recovery and natural variability obscure the inferences and conclusions that can be drawn from such studies. Models are also plagued by uncertainty, however, and parameter equifinality is a common concern. Physically‐based, spatially‐distributed hydrologic models must therefore be tested with high‐quality experimental data describing a multitude of concurrent internal catchment processes under a range of hydrologic regimes. This study takes a novel approach by not only examining the ability of a pre‐calibrated model to realistically simulate watershed outlet flows over a four year period, but a multitude of spatially‐extensive, internal catchment process observations not previously evaluated, including: continuous groundwater dynamics, instantaneous stream and road network flows, and accumulation and melt period spatial snow distributions. Many hydrologic model evaluations are only on the comparison of predicted and observed discharge at a catchment outlet and remain in the ‘infant stage’ in terms of model testing. This study, on the other hand, tests the internal spatial predictions of a distributed model with a range of field observations over a wide range of hydroclimatic conditions. Nash‐Sutcliffe model efficiency was improved over prior evaluations due to continuing efforts in improving the quality of meteorological data collection. Road and stream network flows were generally well simulated for a range of hydrologic conditions, and snowpack spatial distributions were well simulated for one of two years examined. The spatial variability of groundwater dynamics was effectively simulated, except at locations where strong stream–groundwater interactions exist. Model simulations overall were quite successful in realistically simulating the spatiotemporal variability of internal catchment processes in the watershed, but the premature onset of simulated snowmelt for one of the simulation years has prompted further work in model development. Copyright © 2011 John Wiley & Sons, Ltd.     

Interannual Variation in Photosynthetically Significant Optical Properties and Water Quality in a Coastal Blackwater River Plume

Surface water optical characteristics, nutrients, and planktonic chlorophyll a concentrations were analyzed in the Cape Fear River (CFR) plume over a 2-year period. CFR discharge during the dry year (109 ± 105 m³s⁻¹) was only 25% of the wet year discharge (429 ± 337 m³s⁻¹). Partitioning the contributions of phytoplankton pigments, non-pigmented particles, and colored dissolved organic matter (CDOM) to the absorption of photosynthetically active radiation (PAR) indicated that CDOM was the dominant contributor to PAR absorption. Particulate absorption was relatively greater during the dry year. Pigment absorption was minor and varied little among stations or between years. Chlorophyll a concentrations were reduced at the most plume-influenced stations during the wet year, despite lower turbidity and higher nitrate concentrations. Ammonium and orthophosphate concentrations were not different between years. CDOM absorption [a _CDOM (412)] ranged from 0.05 to 8.25 m⁻¹ with highest values occurring near the CFR mouth. Our results suggest that for coastal ecosystems with significant blackwater river inputs, CDOM may exert a major limiting influence over near-shore primary production.