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61.
62.
Mohammad Parsa Abbas Maghsoudi Emmanuel John M. Carranza Mahyar Yousefi 《Natural Resources Research》2017,26(4):443-455
In this study, stream sediment geochemical data have been subjected to robust principal components analysis (RPCA) and singularity mapping (SM) to enhance and map significant multivariate geochemical anomalies (i.e., mineralization-related) in Ahar area, NW Iran. The RPCA was applied to (a) account for the compositional nature of stream sediment geochemical data using suitable log-ratio transformation, (b) modulate the effect of outliers in component estimation and (c) derive a multivariate geochemical footprint of mineralization. The SM was applied to extract anomalous patterns of the multivariate geochemical footprint of mineralization. The exploration targets were then delineated using Student’s t-statistics analysis. The correlations of mapped exploration targets with the known mineral occurrences and mineralization-related patterns were further evaluated using normalized density index and overall accuracy analyses. 相似文献
63.
Earthquake detection probability within a seismically quiet area: application to the Bruchsal geothermal field 下载免费PDF全文
Emmanuel Gaucher 《Geophysical Prospecting》2016,64(2):268-286
In applications such as oil and gas production, deep geothermal energy production, underground storage, and mining, it is common practice to implement local seismic networks to monitor and to mitigate induced seismicity. For this purpose, it is crucial to determine the capability of the network to detect a seismic event of predefined magnitude in the target area. The determination of the magnitude of completeness of a network is particularly required to properly interpret seismic monitoring results. We propose a method to compute the detection probability for existing local seismic networks, which (i) strictly follows the applied detection sequence; (ii) estimates the detection capability where seismicity has not yet occurred; and (iii) delivers the results in terms of probabilities. The procedure includes a calibration of a local magnitude scale using regional earthquakes recorded by the network and located outside the monitored area. It involves pre‐processing of the seismograms recorded at each station as performed during the triggering sequence, which is assumed based on amplitude thresholds. Then, the calibrated magnitude–distance–amplitude relations are extrapolated at short distances and combined to reproduce the network detection sequence. This generates a probability to detect a seismic event of a given magnitude at a specified location. This observation‐based approach is an alternative to a fully theoretical detection capability modelling and includes field conditions. Seismic wave attenuation by geometrical spreading and intrinsic attenuation, site effect, and instrumental responses are partly accounted for by the calibration. We apply this procedure on the seismic network deployed in the Bruchsal geothermal field (Germany). Although the system was in good working order, no induced seismicity was identified in the area between June 2010, when monitoring started, and November 2012. The recording of distant seismicity during this time period, however, allowed the application of the proposed procedure. According to the applied network detection parameters, the results indicate that the absence of seismicity can be interpreted as a 95% probability that no seismic event with ML ≥ 0.7 occurred below the network at 2.4‐km depth, i.e., in the geothermal reservoir. 相似文献
64.
An evaluation of the genesis and suitability of groundwater for irrigation in the Volta Region,Ghana 总被引:1,自引:0,他引:1
Stable isotope data and concentrations of the major cations and anions of groundwater from the northern part of the Volta
Region, Ghana, were used to determine the source of recharge and the suitability of groundwater in the area for irrigation.
This study finds that the delta deuterium (δD) and delta Oxygen-18 (δ18O) data from the area fall along the global meteoric water line (GMWL). An equation of regression derived for the relationship
between δD and δ18O bears very close semblance to the equation which describes the GMWL. On the basis of this, groundwater in the study area
is probably meteoric and fresh. The apparently low salinities and sodicities of the groundwater seem to support this interpretation.
The suitability of groundwater for domestic and irrigation purposes is related to its source, which determines its constitution.
A plot of the sodium adsorption ratio (SAR) and electrical conductivity (EC) data on a semilog axis, suggests that groundwater
serves good irrigation quality in the area. Sixty percent (60%), 20% and 20% of the 67 data points used in this study fall
within the medium salinity–low sodicity (C2–S1), low salinity–low sodicity (C1–S1) and high salinity–low sodicity (C3–S1)
fields, which ascribe good irrigation quality to groundwater from this area. Salinities range from 28.1 to 1,956 μS/cm, whilst
SAR values fall within the range 0–3. Extremely low sodicity waters of this kind, with salinities lower than 600 μS/cm, have
the tendency to affect the dispersive properties of irrigation soils when used for irrigation. About 50% of the groundwater
in the study area fall within this category and need prior treatment before usage. 相似文献
65.
Using the SPICAV-UV spectrometer aboard Venus Express in nadir mode, we were able to derive spectral radiance factors in the middle atmosphere of Venus in the 170-320 nm range at a spectral resolution of R ? 200 during 2006 and 2007 in the northern hemisphere. By comparison with a radiative transfer model of the upper atmosphere of Venus, we could derive column abundance above the visible cloud top for SO2 using its spectral absorption bands near 280 and 220 nm. SO2 column densities show large temporal and spatial variations on a horizontal scale of a few hundred kilometers. Typical SO2 column densities at low latitudes (up to 50°N) were found between 5 and 50 μm-atm, whereas in the northern polar region SO2 content was usually below 5 μm-atm. The observed latitudinal variations follow closely the cloud top altitude derived by SPICAV-IR and are thought to be of dynamical origin. Also, a sudden increase of SO2 column density in the whole northern hemisphere has been observed in early 2007, possibly related to a convective episode advecting some deep SO2 into the upper atmosphere. 相似文献
66.
Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain 总被引:4,自引:4,他引:0
An application of the grain size trend analysis (GSTA) is used in an exploratory approach to characterize sediment transport on Camposoto beach (Cádiz, SW Spain). In May 2009 the mesotidal beach showed a well-developed swash bar on the upper foreshore, which was associated with fair-weather conditions prevailing just before and during the field survey. The results were tested by means of an autocorrelation statistical test (index I of Moran). Two sedimentological trends were recognized, i.e. development towards finer, better sorted and more negatively skewed sediment (FB–), and towards finer, better sorted and less negatively or more positively skewed sediment (FB+). Both vector fields were compared with results obtained from more classical approaches (sand tracers, microtopography and current measurements). This revealed that both trends can be considered as realistic, the FB+ trend being identified for the first time in a beach environment. The data demonstrate that, on the well-developed swash bar, sediment transported onshore becomes both finer and better sorted towards the coast. On the lower foreshore, which exhibits a steeper slope produced by breaking waves, the higher-energy processes winnow out finer particles and thereby produce negatively skewed grain-size distributions. The upper foreshore, which has a flatter and smoother slope, is controlled by lower-energy swash-backwash and overwash processes. As a result, the skewness of the grain-size distributions evolves towards less negative or more positive values. The skewness parameter appears to be distributed as a function of the beach slope and, thus, reflects variations in hydrodynamic energy. This has novel implications for coastal management. Figure
GSTA model for Camposoto Beach, Cádiz, with FB– (finer, better sorted, more negatively skewed) and FB+ (finer, better sorted, less negatively/more positively skewed) textural trends dominating the lower and upper foreshore respectively 相似文献
67.
François Charlet Marc De Batist Emmanuel Chapron Sébastien Bertrand Mario Pino Roberto Urrutia 《Journal of Paleolimnology》2008,39(2):163-177
Prior to the collection of a series of sediment cores, a high- and very-high-resolution reflection seismic survey was carried
out on Lago Puyehue, Lake District, South-Central Chile. The data reveal a complex bathymetry and basin structure, with three
sub-basins separated by bathymetric ridges, bedrock islands and interconnected channels. The sedimentary infill reaches a
thickness of >200 m. It can be sub-divided into five seismic-stratigraphic units, which are interpreted as: moraine, ice-contact
or outwash deposits (Unit I), glacio-lacustrine sediments rapidly deposited in a proglacial or subglacial lake at the onset
of deglaciation (Unit II), lacustrine fan deposits fed by sediment-laden meltwater streams in a proglacial lake (Unit III),
distal deposits of fluvially derived sediment in an open, post-glacial lake (Unit IV) and authigenic lacustrine sediments,
predominantly of biogenic origin, that accumulated in an open, post-glacial lake (Unit V). This facies succession is very
similar to that observed in other glacial lakes, and minor differences are attributed to an overall higher depositional energy
and higher terrigenous input caused by the strong seismic and volcanic activity in the region combined with heavy precipitation.
A long sediment core (PU-II core) penetrates part of Unit V and its base is dated as 17,915 cal. yr. BP. Extrapolation of
average sedimentation rates yields an age of ca. 24,750 cal. yr. BP for the base of Unit V, and of ca. 28,000 cal. yr. BP
for the base of Unit IV or for the onset of open-water conditions. This is in contrast with previous glacial-history reconstructions
based on terrestrial records, which date the complete deglaciation of the basin as ca. 14,600 cal. yr. BP. This discrepancy
cannot be easily explained and highlights the need for more lacustrine records from this region.
This is the second in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of
Lago Puyehue, Chilean Lake District. The papers in this special issue were collected by M. De Batist, N. Fagel, M.-F. Loutre
and E. Chapron. 相似文献
68.
Leo Eisner Aldo Vesnaver Emmanuel Gaucher Xander Campman 《Geophysical Prospecting》2010,58(5):725-726
69.
Rock slope instability assessment using spatially distributed structural orientation data in Darjeeling Himalaya (India) 总被引:1,自引:0,他引:1
Saibal Ghosh Andreas Günther Emmanuel John M. Carranza Cees J. van Westen Victor G. Jetten 《地球表面变化过程与地形》2010,35(15):1773-1792
We discuss a geographic information system (GIS)‐based methodology for rock slope instability assessment based on geometrical relationships between topographic slopes and structural discontinuities in rocks. The methodology involves (a) regionalization of point observations of orientations (azimuth and dip) of structural discontinuities in rocks in order to generate a digital structural model (DStM), (b) testing the kinematical possibility of specific modes of rock slope failures by integrating DStMs and digital elevation model (DEM)‐derived slope and aspect data and (c) computation of stability scenarios with respect to identified rock slope failure modes. We tested the methodology in an area of 90 km2 in Darjeeling Himalaya (India) and in a small portion (9 km2) within this area with higher density of field structural orientation data. The results of the study show better classification of rock slope instability in the smaller area with respect to known occurrences of deep‐seated rockslides than with respect to shallow translational rockslides, implying that structural control is more important for deep‐seated rockslides than for shallow translational rockslides. Results of scenario‐based analysis show that, in rock slopes classified to be unstable, stress‐induced rock slope instability tends to increase with increasing level of water saturation. The study demonstrates the usefulness of spatially distributed data of orientations of structural discontinuities in rocks for medium‐ to small‐scale classification of rock slope instability in mountainous terrains. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
70.