Instantaneous deformation from continuous GPS: contributions from quasi-periodic loads   总被引：3，自引：0，他引：3  

Richard A. Bennett 《Geophysical Journal International》2008,174(3):1052-1064

Continuous GPS (CGPS) coordinate time-series are known to experience repeating deformation signals with seasonal and other periods. It is unlikely that these signals represent perfect sinusoids with temporally constant amplitude. We develop an analysis method that accommodates temporal variations in the amplitudes of sinusoidal signals. We apply the method to simulated coordinate time-series to numerically explore the potential consequences of neglecting decadal variation in amplitude of annual motions on the residual-error spectra of CGPS measurements, as well as potential bias in estimates for secular site velocity. We find that secular velocity bias can be appreciable for shorter time-series, and that residual-error time-series of longer duration may contain significant power in a broad band centred on semi-annual frequency if temporal variation in the amplitude of annual motions is not accounted for in the model used to reduce the observations to residuals. It may be difficult to differentiate the bandpass filtered signature of mismodelled loading signals from power-law noise, using residual-error spectra for shorter time-series. We provide an example application to a ∼9-yr coordinate time-series for a CGPS station located in southern California at Carbon Creek Control Structure (CCCS), which is known to experience large amplitude seasonal motions associated with the Santa Ana aquifer system.  相似文献   

Analyses on granular mass movement mechanics and deformation with distinct element numerical modeling: implications for large-scale rock and debris avalanches     

Nick Thompson  Matthew R. Bennett  Nick Petford 《Acta Geotechnica》2009,4(4):233-247

A large-scale avalanche of Earth material is modeled here as a granular flow using a distinct element numerical model PFC ^2D. Such failures occur in a variety of geological settings and are known to occur frequently over geologic time-scales transporting significant volumes of material basinward. Despite this, they remain poorly understood. The model used here begins with a listric failure, typical of the flank collapse of a volcanic cone, and describes the movement of an assembly of several thousand particles from failure to deposition. Within the model, each particle possesses its own material properties and interacts with its immediate neighbors and/or the basal boundary during emplacement. The general mechanics of the particle assembly are observed by monitoring the stresses, displacements, and velocities of distinct sections of the avalanche body. We monitor the avalanches’ energy regime (e.g., gravitational influence, energy dissipation by friction, kinetic energy evolution, and avalanche body strain). The addition of colored markers of varying geometry to the pre-failure avalanche was also used to make qualitative observations on the internal deformation that occurs during avalanche emplacement. A general stretching and thinning of the avalanche is observed. Monitoring of vertical and horizontal variations in stress, strain, porosity, and relative particle stability indicate that the lower more proximal sections of the avalanche are subject to higher stresses. These stresses are observed to be most significant during the initial phases of failure but decline thereafter; a situation likely to be conducive to block fragmentation and in developing a basal shear layer in real-world events. The model also shows how an avalanche which is initially influenced purely by gravity (potential energy) develops into a fully flowing assemblage as downslope momentum is gained and kinetic energy increases. The horizontal transition where the failure meets the run-out surface is recognized as a key area in emplacement evolution. The model has particular relevance to volcanic flank collapses and consequently the implications of the model to these types of failure and the geological products that result are considered in detail although the model is relevant to any form of large-scale rock or debris avalanche.  相似文献   

Ecological status of seagrass ecosystems: An uncertainty analysis of the meadow classification based on the Posidonia oceanica multivariate index (POMI)     

Bennett S  Roca G  Romero J  Alcoverro T 《Marine pollution bulletin》2011,62(8):1616-1621

Quantifying the uncertainty associated with monitoring protocols is essential to prevent the misclassification of ecological status and to improve sampling design. We assessed the Posidonia oceanica multivariate index (POMI) bio-monitoring program for its robustness in classifying the ecological status of coastal waters within the Water Framework Directive. We used a 7-year data set covering 30 sites along 500 km of the Catalonian coastline to examine which version of POMI (14 or 9 metrics) maximises precision in classifying the ecological status of meadows. Five factors (zones within a site, sites within a water body, depth, years and surveyors) that potentially generate classification uncertainty were examined in detail. Of these, depth was a major source of uncertainty, while all the remaining spatial and temporal factors displayed low variability. POMI 9 matched POMI 14 in all factors, and could effectively replace it in future monitoring programs.  相似文献   

Spatially enabled bushfire recovery   总被引：1，自引：0，他引：1  

Katie Elizabeth Potts  Rohan Mark Bennett  Abbas Rajabifard 《GeoJournal》2013,78(1):151-163

Over the last decade growth in spatial information use for disaster management has been considerable. Maps and spatial data are now recognized as critical elements in each of the four phases of disaster management: mitigation, preparedness, response, and recovery. The use of spatial information to support the phases of mitigation, preparedness and response to bushfires is widely understood. Less attention, however, has been given to the role of spatial information in the recovery. Moreover, the application of the spatially enabled society concept to bushfire recovery has not been explored. This paper explores the role that spatial information plays and could play in the recovery phase of a bushfire disaster. The bushfires in Victoria, Australia that took place during February 2009 are used as the primary case study. It is found that: Spatial information for recovery requires a pre-existing infrastructure; Spatial capacity must be developed across agencies dealing with recovery; Spatially enabled address and parcel information are the key dataset required to support all recovery tasks; Spatial integration of bushfire datasets (spread and intensity) require linking with planning regimes, and Spatial information that is volunteered could be incorporated into recovery activities.  相似文献   

Geological interpretation of ply structure of the Bulli Seam,Sydney Basin,N.S.W.     

M. Shibaoka  A. J. R. Bennett 《Australian Journal of Earth Sciences》2013,60(3):327-343

The ply structure of the Bulli seam in the Southern Coalfield of the Sydney Basin persists over the main part of the coalfield. Lateral variations were investigated using both petrographic profiles and swelling index profile sections. The results indicated that the thickness pattern of the whole Bulli seam was affected by three independent factors: (1) post‐depositional loss of the top portion of the seam; (2) pre‐depositional topography; and (3) differential subsidence during deposition. The lack of definite correlation between seam thickness and present geological structure suggests that no local tectonic movement took place during deposition of the seam. Tectonic movement cannot, therefore, be the main cause of variation in seam thickness. Subsidence during deposition of the Bulli seam in the northeastern margin of the coalfield appears to have been too rapid, and near the western margin too slow, to form a thick coal seam. However, in the main part of the coalfield, the rate of subsidence was suitable for peat accumulation and a thick seam was deposited under stable conditions, as indicated by the persistent ply structure.  相似文献   

Hydrothermal activity on the southern Mid-Atlantic Ridge: Tectonically- and volcanically-controlled venting at 4–5°S     

C.R. German  S.A. Bennett  D.P. Connelly  A.J. Evans  B.J. Murton  L.M. Parson  R.D. Prien  E. Ramirez-Llodra  M. Jakuba  T.M. Shank  D.R. Yoerger  E.T. Baker  S.L. Walker  K. Nakamura 《Earth and Planetary Science Letters》2008,273(3-4):332-344

We report results from an investigation of the geologic processes controlling hydrothermal activity along the previously-unstudied southern Mid-Atlantic Ridge (3–7°S). Our study employed the NOC (UK) deep-tow sidescan sonar instrument, TOBI, in concert with the WHOI (USA) autonomous underwater vehicle, ABE, to collect information concerning hydrothermal plume distributions in the water column co-registered with geologic investigations of the underlying seafloor. Two areas of high-temperature hydrothermal venting were identified. The first was situated in a non-transform discontinuity (NTD) between two adjacent second-order ridge-segments near 4°02′S, distant from any neovolcanic activity. This geologic setting is very similar to that of the ultramafic-hosted and tectonically-controlled Rainbow vent-site on the northern Mid-Atlantic Ridge. The second site was located at 4°48′S at the axial-summit centre of a second-order ridge-segment. There, high-temperature venting is hosted in an  18 km² area of young lava flows which in some cases are observed to have flowed over and engulfed pre-existing chemosynthetic vent-fauna. In both appearance and extent, these lava flows are directly reminiscent of those emplaced in Winter 2005−06 at the East Pacific Rise, 9°50′N and reference to global seismic catalogues reveals that a swarm of large (M 4.6−5.6) seismic events was centred on the 5°S segment over a  24 h period in late June 2002, perhaps indicating the precise timing of this volcanic eruptive episode. Temperature measurements at one of the vents found directly adjacent to the fresh lava flows at 5°S MAR (Turtle Pits) have subsequently revealed vent-fluids that are actively phase separating under conditions very close to the Critical Point for seawater, at  3000 m depth and 407 °C: the hottest vent-fluids yet reported from anywhere along the global ridge crest.  相似文献   

Modeling fluvial response to in‐stream woody vegetation: implications for stream corridor restoration     

Sean J. Bennett  Weiming Wu  Carlos V. Alonso  Sam S. Y. Wang 《地球表面变化过程与地形》2008,33(6):890-909

River restoration and bank stabilization programs often use vegetation for improving stream corridor habitat, aesthetic and function. Yet no study has examined the use of managed vegetation plantings to transform a straight, degraded stream corridor into an ecologically functional meandering channel. Experimental data collected using a distorted Froude‐scaled flume analysis show that channel expansion and widening, thalweg meandering and riffle and pool development are possible using discrete plantings of rigid, emergent vegetation, and the magnitudes of these adjustments depend on the shape of the vegetation zone and the density of the vegetation. These experimental results were verified and validated using a recently developed numerical model, and model output was then used to discuss mechanistically how rivers respond to the introduction of in‐stream woody vegetation. Finally, a hybrid method of meander design is proposed herein where managed vegetation plantings are used to trigger or force the desired morphologic response, transforming a straight, degraded reach into a more functional meandering corridor. It is envisioned that such numerical models could become the primary tool for designing future stream restoration programs involving vegetation and assessing the long‐term stability of such activities. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Challenging emotions     

Katy Bennett 《Area》2009,41(3):244-251

This paper contributes to work on emotional geographies by engaging with Liz Bondi's focus on relationality and the challenge to geographers to explore how their emotion might connect with the feelings of their subjects. Through the lens of a focus group meeting that created confusing feelings, it shows the hurdles that geographers face when they engage with practices developed in a psychotherapeutic setting. The paper is not so much a critique, more a desire to continue the conversation regarding how to approach and adopt psychotherapy's theory of practice in a research context .  相似文献   

Evidence for global circuit current flow through water droplet layers     

A.J. Bennett  R.G. Harrison 《Journal of Atmospheric and Solar》2009,71(12):1219-1221

Foggy air and clear air have appreciably different electrical conductivities. The conductivity gradient at horizontal droplet boundaries causes droplet charging, as a result of vertical current flow in the global atmospheric electrical circuit. The charging is poorly known, as both the current flow through atmospheric water droplet layers and the air conductivity are poorly characterised experimentally. Surface measurements during three days of continuous fog using new instrument techniques show that a shallow (of order 100 m deep) fog layer still permits the vertical conduction current to pass. Further, the conductivity in the fog is estimated to be approximately 20% lower than in clear air. Assuming a fog transition thickness of one metre, this implies a vertical conductivity gradient of order 10 fS m^?2 at the boundary. The actual vertical conductivity gradient at a cloud boundary would probably be greater, due to the presence of larger droplets in clouds compared to fog, and cleaner, more conductive clear air aloft.  相似文献   

Polar non-hydrocarbon contaminants in reservoir core extracts     

B Bennett  SR Larter 《Geochemical transactions》2000,1(1):34-4

A geochemical investigation of oils in sandstone core plugs and drill stem test oils was carried out on samples from a North Sea reservoir. A sample of diesel used as a constituent of the drilling fluids was also analysed. The aliphatic and aromatic hydrocarbons and polar non-hydrocarbons were isolated using solid phase extraction methods. GC analysis of the hydrocarbon fraction of the core extract indicated that contamination may be diesel derived. From analysis of diesel some compound classes are less likely to be affected by contamination from diesel itself including: steranes, hopanes, aromatic steroid hydrocarbons, benzocarbazoles and C₀–C₃-alkylphenols.  相似文献