An experimental design for laboratory simulation of periglacial solifluction processes

An experimental slope of gradient 12° was constructed, comprising two 5 m × 2 m × 0·3 m contiguous strips of natural soils. Soil freezing and thawing took place from the surface downwards in an open hydraulic system, water being supplied at the base of each soil. Thermal conditions, porewater pressures and soil displacements were monitored using a PC-based logging system, with readings taken at half-hourly intervals. Soil surface displacements due to frost heave and solifluction were measured using linear voltage displacement transducers. Soil temperatures were determined using thermistors and semiconductor temperature sensors. Antifreeze-filled miniature ceramic-tipped pressure transducers were used to determine porewater pressure variations. The potential of this experimental approach for precise monitoring of mass movement processes associated with thawing of ice-rich soils is demonstrated.     

Development of the HEFT and NuSTAR focusing telescopes

Hard X-ray/soft gamma-ray astrophysics is on the verge of a major advance with the practical realization of technologies capable of efficiently focusing X-rays above 10 keV. Hard X-ray focusing telescopes can achieve orders of magnitude improvements in sensitivity compared to the instruments based on coded apertures and collimated detectors that have traditionally been employed in this energy band. Compact focal planes enable high-performance detectors with good spectral resolution to be employed in efficient, low-background configurations. We have developed multilayer coated grazing incidence optics and solid state Cadmium Zinc Telluride focal plane systems for the High Energy Focusing Telescope (HEFT) balloon-borne experiment, and for the Nuclear Spectroscopic Telescope Array (NuSTAR) Small Explorer satellite. In this paper we describe the technologies, telescope designs, and performance of both experiments.     

On the evaluation of snow water equivalent estimates over the terrestrial Arctic drainage basin

Comparisons between snow water equivalent (SWE) and river discharge estimates are important in evaluating the SWE fields and to our understanding of linkages in the freshwater cycle. In this study, we compared SWE drawn from land surface models and remote sensing observations with measured river discharge (Q) across 179 Arctic river basins. Over the period 1988‐2000, basin‐averaged SWE prior to snowmelt explains a relatively small (yet statistically significant) fraction of interannual variability in spring (April–June) Q, as assessed using the coefficient of determination (R²). Averaged across all basins, mean R²s vary from 0·20 to 0·28, with the best agreement noted for SWE drawn from a simulation with the Pan‐Arctic Water Balance Model (PWBM) forced with data from the European Centre for Medium‐Range Weather‐Forecasts (ECMWF) Re‐analysis (ERA‐40). Variability and magnitude in SWE derived from Special Sensor Microwave Imager (SSM/I) data are considerably lower than the variability and magnitude in SWE drawn from the land surface models, and generally poor agreement is noted between SSM/I SWE and spring Q. We find that the SWE versus Q comparisons are no better when alternate temporal integrations–using an estimate of the timing in basin thaw–are used to define pre‐melt SWE and spring Q. Thus, a majority of the variability in spring discharge must arise from factors other than basin snowpack water storage. This study demonstrates how SWE estimated from remote sensing observations, or general circulation models (GCMs), can be evaluated effectively using monthly discharge data or SWE from a hydrological model. Copyright © 2007 John Wiley & Sons, Ltd.     

Impacts of climate variability on stream-flow in the Yellow River

This paper examines the impacts of climate variability upon the regional hydrological regimes of the Yellow River in China. Results indicate that the average annual precipitation is 494·8 mm in La Niña years and only 408·8 mm in El Niño years. The difference is 86·0 mm, or 18·8% over the long-term average. The stream-flows in the La Niña years are higher than that in El Niño years: 9·2% at the Lan-Zhou station, 9·5% for Tou-Dao-Guai station, 11·8% for Long-Men, 17·6% for San-Men-Xia, 19·2% at the Hua-Yuan-Hou station, and 22·0% at the Li-Jin station. Both precipitation and stream-flow responses show temporal and spatial patterns. The relationship among the stream-flow, precipitation, and temperature, which was obtained by ArcGIS Geostatistical Analyst based on observed data, indicates stream-flow is sensitive to both precipitation and temperature. For small precipitation increases (less than 13%), the stream-flow percentage change is less than the precipitation change for the Yellow River. The results of this paper can be used as a reference for watershed water resources planning and management to maintain the healthy life and proper function of the river. Copyright © 2007 John Wiley & Sons, Ltd.     

Spatial patterns of ice storm disturbance on a forested landscape in the Appalachian Mountains, Virginia

Ice storms (major freezing rain events) periodically disturb forests in eastern North America. The damage may vary spatially, especially in complex terrain. This study uses satellite imagery to investigate spatial heterogeneity of forest damage caused by ice storms that affected the Appalachian Mountains, Virginia during 1994. The results display a region-scale (southwest-to-northeast) gradient in damage that apparently corresponds to a gradient in the depth of ice that accumulated during the storms. Damage also varied topographically, particularly by aspect. Damage was most extensive on east-, southeast- and south-facing slopes; at middle elevations; and on slopes of moderate steepness.     

Temporal and spatial variations of post-seismic deformation following the 1999 Chi-Chi, Taiwan earthquake

We use GPS displacements collected in the 15 months after the 1999 Chi-Chi, Taiwan earthquake  ( M _w 7.6)  to evaluate whether post-seismic deformation is better explained by afterslip or viscoelastic relaxation of the lower crust and upper mantle. We find that all viscoelastic models tested fail to fit the general features in the post-seismic GPS displacements, in contrast to the satisfactory fit obtained with afterslip models. We conclude that afterslip is the dominant mechanism in the 15-month period, and invert for the space–time distribution of afterslip, using the Extended Network Inversion Filter. Our results show high slip rates surrounding the region of greatest coseismic slip. The slip-rate distribution remains roughly stationary over the 15-month period. In contrast to the limited coseismic slip on the décollement, afterslip is prominent there. Maximum afterslip of 0.57 m occurs downdip and to the east of the hypocentral region. Afterslip at hypocentral depths is limited to the southern part of the main shock rupture, with little or no slip on the northern section where coseismic slip was greatest. Whether this results from along strike variations in frictional properties or dynamic conditions that locally favour stable sliding is not clear. In general, afterslip surrounds the area of greatest coseismic slip, consistent with post-seismic slip driven by the main shock stress change. The total accumulated geodetic afterslip moment is  3.8 × 10¹⁹ N m  , significantly more than the seismic moment released by aftershocks,  6.6 × 10¹⁸ N m  . Afterslip and aftershocks appear to have different temporal evolutions and some spatial correlations, suggesting that aftershock rates may not be completely controlled by the rate of afterslip.     

Fault throw determination using 4 component VSP: Aigion fault (Greece) case study

The present paper presents the results of a technique based on Vertical Seismic Profiling (VSP) to quantify the offset of a fault in a context where seismic reflection profiles do not image any reflectors. The case study is located in Greece, in the Aigion area, on the south border of the Corinth Gulf. The Aigion fault, oriented East–West, and dipping at 60°N, has been intersected by the scientific well Aig-10 at 760 m in depth, but some uncertainty remained concerning its exact offset since the depth of the pre-rift sequence is open to debate due to the lack of subsurface data. The pre-rift consists of a Mesozoic low-porosity series (carbonates and radiolarite), while the syn-rift consists of poorly compacted conglomerates and turbidites.

Seismic diffractions on fault edges are expected to be present along the fault surface. We find that a few diffracted events are effectively recorded in P and S wave mode by the 4 components of the VSP survey, and critically refracted arrivals along the Aigion fault plane. These singular events have been used in order to refine the fault geometry and to determine its throw. Additionally, results from a 2D finite difference elastic seismic model of a single fault step geometry have been closely examined in order to illustrate the generation of the singular seismic events observed on the field data, such as P-wave and S-wave refracted and diffracted events, and support their interpretation with higher confidence. As a result, the seismic arrival patterns from full waveform seismic modelling confirm the characterisation of the main fault geometry (mainly its throw: about 200 m) in the well vicinity derived from the actual analysis of the 4 Component Aigion VSP data.