A geophysical model of the Precambrian of the Albany 1:1M sheet, Western Australia, and its relevance to economic geology

1989 ◽  
Vol 20 (2) ◽  
pp. 195
Author(s):  
A. Whitaker
Keyword(s):  
Granite Gneiss ◽  
Western Boundary ◽  
Block Boundary ◽  
The North ◽  
Geophysical Model ◽  
Eastern Zone ◽  
Western Zone ◽  
Dense Zone ◽  
Wide Zone ◽  
East West

In the Albany 1:1M sheet, the 10-50 km wavelength gravity and aeromagnetic anomalies define major boundaries and subdivisions of the Precambrian blocks/provinces and large bodies of granite, while the short wavelength magnetic anomalies define lithological banding and lineaments. The Yilgarn Block in the sheet area is readily subdivided into two major north-northwest to north trending zones of low magnetization separated by a 30 km wide zone of high magnetization. The eastern zone is considered to be due to granite-greenstone terrane, the western boundary of which is located 100 km west of that currently recognised from outcrop geology. The western zone is considered to be due to granite-geiss terrane while the 30 km wide zone between coincides with strongly magnetised granulites. The Albany Province is composed of two structurally distinct east-west trending zones. The southern zone of relatively low magnetization and density coincides with acid gneiss and granites, whereas the highly magnetised, relatively dense zone to the north and west, correlates with highly metamorphosed acid and mafic granulites. Thrusting of the Albany Province during the Mid-Proterozoic has demagnetised and or deformed the margin of the southern Yilgarn Block to at least 50 km north of the block boundary. Throughout the region, significant mineral deposits of Au, Ni, Sn, Ti, and Fe are located within greenstone and high grade metamorphic belts. These belts have characteristic signatures which contrast with extensive areas of relatively homogeneous, low economic mineral potential, granite-gneiss terrane.

Analysis of Complex Surface Displacements above a Storage Cavern Field in NW-Germany, Observed by InSAR

2021 ◽  
Author(s):  
Markus Even ◽  
Malte Westerhaus ◽  
Verena Simon
Keyword(s):  
Displacement Field ◽  
Pressure Response ◽  
Phase Model ◽  
Basic Method ◽  
Elastic Displacement ◽  
The North ◽  
Geophysical Model ◽  
Surface Displacements ◽  
Pressure Changes ◽  
East West

<p>The cavern field at Epe has been brined out of a salt deposit belonging to the lower Rhine salt flat, which extends under the surface of the North German lowlands and part of the Netherlands, and is used to store e.g. natural gas, brine and petroleum. Cavern convergence and operational pressure changes cause surface displacements that have been studied for this work with the help of SAR interferometry (InSAR) using distributed and persistent scatterers. Vertical and East-West movements have been determined based on Sentinel-1 data from ascending and descending orbit. Simple geophysical modeling is used to support InSAR processing and helps to interpret the observations. In particular, an approach is presented that allows to relate the deposit pressures with the observed surface displacements. Seasonal movements occurring over a fen situated over the western part of the storage site further complicate the analysis. Findings are validated with ground truth from levelling and groundwater level measurements.</p><p>For porous storage sites the geomechanic response can be described as elastic: displacement is almost proportional to reservoir pressure and displays the same pronounced seasonal behavior. At Epe the visco-elastic response of the salt layer has to be considered. The general appearance of the surface displacement is that of a strongly smoothed and shifted version of the cavern pressure curve. To deal with this situation a temporal model for displacement with pressure changes (pressure response) is derived that relates cavern pressure with observed displacement based on the theory for visco-elastic behavior of a Kelvin-Voigt body.</p><p>In order to deal successfully with the challenging displacement field at Epe several algorithmic improvements were implemented. To obtain a more complete picture of the displacement field DS pre-processing has been combined with StaMPS. Furthermore, StaMPS was modified in order to support unwrapping with a phase model composed of linear trend, pressure response and a seasonal component (caused by ground water level changes). Finally, refining the iterative estimation scheme of StaMPS helped avoiding leakage of the displacement signal to the spatially correlated noise term.</p><p>Determining vertical and east-west displacements from InSAR line-of-sight displacements is fundamental for interpretation and integration with levelling data. In this study, a basic method of orbit combination and another one supported by a simplistic geophysical model were applied in order to obtain 2D-displacements. For the basic method the north-south component was handled as if it were zero, while the geophysical model predicts the LOS effect of NS displacements. It assumes that caverns act as spherical pressure/volume sources embedded in an elastic half space (“Mogi” sources). To incorporate the visco-elastic component, each cavern is encompassed by a spherical salt shell that obeys the Kelvin-Voigt differential equations. The model is used here to describe either the parameters of the linear component of the displacement model or of the pressure response. A novelty of the orbit combinations implemented for this study is that the different components of the phase model are combined separately. This allows for a better understanding of the phenomena that contribute to the displacement field.</p>

A sub-regional approach for the analysis of atmospheric teleconnection influence on precipitation in Calabria (southern Italy)

2020 ◽  
Author(s):  
Giulio Nils Caroletti ◽  
Roberto Coscarelli ◽  
Tommaso Caloiero
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Monthly Precipitation ◽  
The South ◽  
The North ◽  
Eastern Zone ◽  
Teleconnection Indices ◽  
Western Zone ◽  
The Mediterranean ◽  
Mediterranean Oscillation

<p>Due to the importance of precipitation as a climatic and meteorological variable, it is paramount to detect the relationships between teleconnections and precipitation at different temporal and spatial scale. In fact, large-scale systems can i) influence precipitation directly, ii) establish a favourable environment to deep moist convection, and thus extreme precipitation, but also iii) help triggering dry conditions and drought.</p><p>In this study, developed within the INDECIS EU project, the teleconnection influence on precipitation in the Calabria region has been evaluated over the 1981-2010 time period, by means of a database of 79 rain gauge stations and seven teleconnections indices. Calabria, the southernmost region of peninsular Italy, was chosen as a valuable test bed mainly because it is located in the centre of the Mediterranean region, which constitutes a hot spot for climate change. Moreover, Calabria has a high-density, long-time network of precipitation gauges, recently validated and homogenized.</p><p>Statistical relationships between teleconnection indices and precipitation are often developed through well-known correlation analyses techniques, e.g. Pearson, Spearman and Kendall, where a teleconnection index is compared to cumulated precipitation values. In this study, three types of correlation analysis were performed: i) seasonal indices vs seasonal cumulated precipitation; ii) three-month indices vs monthly cumulated precipitation; iii) monthly indices vs monthly cumulated precipitation. These analyses have been performed in five Rainfall Zones (RZs) of the study area, characterised by different climatic conditions: the North-Eastern Zone (I1), the Central-Eastern Zone (I2) and the South-Eastern Zone (I3) on the Ionian side of Calabria and the North-Western Zone (T1) and the South-Western Zone (T2) on the Tyrrhenian part.</p><p>Results showed that the Mediterranean Oscillation and the North Atlantic Oscillation are the most important large-scale contributors to the precipitation regime of Calabria. Moreover, seasonal Eastern Atlantic pattern influenced seasonal precipitation in the RZs I1 and T1; three-monthly East Atlantic/Western Russian pattern influenced monthly precipitation in the RZs I2 and T1; three-monthly Western Mediterranean Oscillation influenced monthly precipitation in the RZs I3 and T1; while three-monthly El Nino-Southern Oscillation influenced monthly precipitation in the RZ T2.</p><p>Investigating changes in the response of local precipitation and teleconnections throughout the 1951-2010 and 1951-1980 time periods, a change in precipitation response to teleconnection patterns emerged, i.e., in the impact that the Mediterranean Oscillation has on the East coast precipitation (RZs I1-I3), a possible result of natural variation or climate change. In addition, these results have been compared to those obtained with the classical correlation analyses between teleconnection indices and single-station precipitation.</p><p>The approach developed for this study is a general method that, in principle, can be reproduced for any variable for any region and for every teleconnection.</p><p>Acknowledgments:</p><p>The Project INDECIS is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462).</p>

Strain patterns of Sichuan and Yunnan, China from GPS data and comparison between seismic and geodetic moment release

2020 ◽  
Author(s):  
Jingyang Zhao ◽  
Yanqiang Wu ◽  
Hongbao Liang ◽  
Kaifu Du
Keyword(s):  
Strain Rate ◽  
Shear Strain ◽  
Earthquake Catalog ◽  
Shear Strain Rate ◽  
The South ◽  
Maximum Shear Strain ◽  
Block Boundary ◽  
The North ◽  
Geodetic Strain ◽  
East West

<p>We processed data from ~600 GPS stations, covering the period 1999-2018, to provide new insights into the crustal motion and deformation of Sichuan and Yunnan, China. We used the derived velocity field to evaluate two-dimensional strain rate tensors, and mapped the main, maximum shear, dilatation, east-west and north-south strain rates.The spatial distribution of the main strain rate in the Sichuan-Yunnan region generally shows an orderly deflection. The minimum principal strain rate is northeastward in the west of the Sichuan-Yunnan block boundary, gradually deflects eastward and southeastward toward the east and south, and returns to the northeast direction until the southwestern edge of Sichuan-Yunnan. This reflects the complex tectonic dynamics background of the study area. The high value of the maximum shear strain rate is mainly distributed along the eastern boundary of the Sichuan-Yunnan block, especially near the Xianshuihe-Xiaojiang fault, where the maximum shear strain rate exceeds 4.0 × 10<sup>-8</sup> / a. The area strain rate in the study region shows that the areas of compression and expansion are comparable, with weak tensions prevailing in the interior and compression in the marginal areas. The strain rate result also shows that the east-west strain rate component in the southern Sichuan-Yunnan is dominated by positive value, and the north is dominated by negative value. It indicates that the east-west deformation in the south of the Sichuan-Yunnan is dominated by expansion, and in the north is dominated by contraction. The north-south component strain rate shows that there is a significant positive high-value zone in and around the Xianshuihe fault zone, while southern Sichuan-Yunnan is a more significant negative-value zone, and the distribution of negative high-value zones is controlled by the south boundary of the Sichuan-Yunnan block. Based on the fault activity and focal mechanism data, the study area was divided into several seismic source zones. We translated the geodetic strain rates into rates of seismic moment release in each zone and compared them with earthquake catalog-based moment rates, to evaluate the potential of seismic activity of the region. The analysis shows the geodetic strain is completely released seismically for most of the study area. However, for the southern Yunnan，the geodesy-based moment rates are more than 2 times higher than the earthquake-based rates. This result indicates that at least a large earthquake may occur in southern Yunnan in the future.</p>

scholarly journals Comparison of climatic variables among different climatic sub-regions of Bangladesh

2016 ◽  
Vol 29 (1) ◽  
pp. 63-71
Author(s):  
Md Younus Mia ◽  
Md Ramjan Ali ◽  
Shimul Roy
Keyword(s):  
Minimum Temperature ◽  
Moving Average ◽  
Maximum Temperature ◽  
Annual Average ◽  
Change Rate ◽  
The North ◽  
Eastern Zone ◽  
North Eastern ◽  
Western Zone ◽  
North Western

The study was conducted to compare the rate of change of selective climatic variables such as annual maximum and minimum temperature, annual total rainfall and annual average humidity among the three different climatic sub-regions (Western zone, northwestern zone and north-eastern zone) of Bangladesh. Annual averages of climatic parameters were calculated to analyze the trend lines, variation and change rate of climatic parameter during the study period. Five years moving average rainfall and humidity were also determined. It was observed that change rate of annual maximum temperature and annual average maximum temperature both were highest in north-eastern zone at the rate of 0.048 and 0.046°C per year, respectively. Highest annual minimum temperature change rate (0.003°C per year) was also found in the north-eastern zone but highest annual average minimum temperature change rate (0.034°C per year) was found in the north-western zone. Average annual rainfall was decreasing insignificantly in all the three climatic sub-regions whereas the highest change rate (21.50 mm per year) was observed in the north-eastern zone of Bangladesh. Highest annual average humidity change rate (0.113% per year) was found in the north-western zone of Bangladesh and five years moving average of annual average humidity was increasing at the highest rate of 0.132% per year in the north-western zone of Bangladesh.Bangladesh J. Sci. Res. 29(1): 63-71, June-2016

scholarly journals A Low frequency Southern Sky Survey Using the Mauritius Radio Telescope

2002 ◽  
Vol 199 ◽  
pp. 25-31
Author(s):  
N. Udaya Shankar
Keyword(s):  
Radio Telescope ◽  
Low Frequency ◽  
Fourier Synthesis ◽  
North East ◽  
The North ◽  
Sky Survey ◽  
Correlation Receiver ◽  
Complex Correlation ◽  
Right Ascension ◽  
East West

The Mauritius Radio Telescope (MRT) is a Fourier synthesis instrument which has been built to fill the gap in the availability of deep sky surveys at low radio frequencies in the southern hemisphere. It is situated in the north-east of Mauritius at a southern latitude of 20°.14 and an eastern longitude of 57°.73. The aim of the survey with the MRT is to contribute to the database of southern sky sources in the declination range −70° ≤ δ ≤ −10°, covering the entire 24 hours of right ascension, with a resolution of 4' × 4'.6sec(δ + 20.14°) and a point source sensitivity of 200 mJy (3σ level) at 151.5 MHz.MRT is a T-shaped non-coplanar array consisting of a 2048 m long East-West arm and a 880 m long South arm. In the East-West arm 1024 fixed helices are arranged in 32 groups and in the South arm 16 trolleys, with four helices on each, which move on a rail are used. A 512 channel, 2-bit 3-level complex correlation receiver is used to measure the visibility function. At least 60 days of observing are required for obtaining the visibilities up to the 880 m spacing. The calibrated visibilities are transformed taking care of the non-coplanarity of the array to produce an image of the area of the sky under observation.This paper will describe the telescope, the observations carried out so far, a few interesting aspects of imaging with this non-coplanar array and present results of a low resolution survey (13' × 18') covering roughly 12 hours of right ascension, and also present an image with a resolution of 4' × 4'.6sec(δ + 20.14°) made using the telescope.

Coastline Vulnerability Assessment through Landsat and Cubesats in a Coastal Mega City

2020 ◽  
Vol 12 (5) ◽  
pp. 749 ◽  
Author(s):  
Majid Nazeer ◽  
Muhammad Waqas ◽  
Muhammad Imran Shahzad ◽  
Ibrahim Zia ◽  
Weicheng Wu
Keyword(s):  
Spatial Resolution ◽  
Land Reclamation ◽  
Anthropogenic Activities ◽  
Monsoon Season ◽  
Coastal Protection ◽  
Landsat Images ◽  
Intergovernmental Panel ◽  
Eastern Zone ◽  
Stable Conditions ◽  
Western Zone

According to the Intergovernmental Panel on Climate Change (IPCC), global mean sea levels may rise from 0.43 m to 0.84 m by the end of the 21st century. This poses a significant threat to coastal cities around the world. The shoreline of Karachi (a coastal mega city located in Southern Pakistan) is vulnerable mainly due to anthropogenic activities near the coast. Therefore, the present study investigates rates and susceptibility to shoreline change using a 76-year multi-temporal dataset (1942 to 2018) through the Digital Shoreline Analysis System (DSAS). Historical shoreline positions were extracted from the topographic sheets (1:250,000) of 1942 and 1966, the medium spatial resolution (30 m) multi-sensor Landsat images of 1976, 1990, 2002, 2011, and a high spatial resolution (3 m) Planet Scope image from 2018, along the 100 km coast of Karachi. The shoreline was divided into two zones, namely eastern (25 km) and western (29 km) zones, to track changes in development, movement, and dynamics of the shoreline position. The analysis revealed that 95% of transects drawn for the eastern zone underwent accretion (i.e., land reclamation) with a mean rate of 14 m/year indicating that the eastern zone faced rapid shoreline progression, with the highest rates due to the development of coastal areas for urban settlement. Similarly, 74% of transects drawn for the western zone experienced erosion (i.e., land loss) with a mean rate of −1.15 m/year indicating the weathering and erosion of rocky and sandy beaches by marine erosion. Among the 25 km length of the eastern zone, 94% (23.5 km) of the shoreline was found to be highly vulnerable, while the western zone showed much more stable conditions due to anthropogenic inactivity. Seasonal hydrodynamic analysis revealed approximately a 3% increase in the average wave height during the summer monsoon season and a 1% increase for the winter monsoon season during the post-land reclamation era. Coastal protection and management along the Sindh coastal zone should be adopted to defend against natural wave erosion and the government must take measures to stop illegal sea encroachments.

scholarly journals Optimal design of the solar tracking system of parabolic trough concentrating collectors

2020 ◽  
Vol 15 (4) ◽  
pp. 613-619
Author(s):  
Li Kong ◽  
Yunpeng Zhang ◽  
Zhijian Lin ◽  
Zhongzhu Qiu ◽  
Chunying Li ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Solar Radiation ◽  
Tracking System ◽  
Low Cost ◽  
Parabolic Trough ◽  
The North ◽  
Tracking Mode ◽  
Solar Tracking ◽  
East West

Abstract The present work aimed to select the optimum solar tracking mode for parabolic trough concentrating collectors using numerical simulation. The current work involved: (1) the calculation of daily solar radiation on the Earth’s surface, (2) the comparison of annual direct solar radiation received under different tracking modes and (3) the determination of optimum tilt angle for the north-south tilt tracking mode. It was found that the order of solar radiation received in Shanghai under the available tracking modes was: dual-axis tracking > north-south Earth’s axis tracking > north-south tilt tracking (β = 15°) > north-south tilt tracking (β = 45) > north-south horizontal tracking > east-west horizontal tracking. Single-axis solar tracking modes feature simple structures and low cost. This study also found that the solar radiation received under the north-south tilt tracking mode was higher than that of the north-south Earth’s axis tracking mode in 7 out of 12 months. Therefore, the north-south tilt tracking mode was studied separately to determine the corresponding optimum tilt angles in Haikou, Lhasa, Shanghai, Beijing and Hohhot, respectively, which were shown as follows: 18.81°, 27.29°, 28.67°, 36.21° and 37.97°.

scholarly journals Spatial Patterns and Intensity of the Surface Storm Tracks in CMIP5 Models

2017 ◽  
Vol 30 (13) ◽  
pp. 4965-4981 ◽  
Author(s):  
James F. Booth ◽  
Young-Oh Kwon ◽  
Stanley Ko ◽  
R. Justin Small ◽  
Rym Msadek
Keyword(s):  
Storm Track ◽  
Storm Tracks ◽  
Cmip5 Models ◽  
Western Boundary ◽  
Spatial Correlations ◽  
Boundary Current ◽  
Near Surface ◽  
Surface Stability ◽  
The North ◽  
Basin Scale

To improve the understanding of storm tracks and western boundary current (WBC) interactions, surface storm tracks in 12 CMIP5 models are examined against ERA-Interim. All models capture an equatorward displacement toward the WBCs in the locations of the surface storm tracks’ maxima relative to those at 850 hPa. An estimated storm-track metric is developed to analyze the location of the surface storm track. It shows that the equatorward shift is influenced by both the lower-tropospheric instability and the baroclinicity. Basin-scale spatial correlations between models and ERA-Interim for the storm tracks, near-surface stability, SST gradient, and baroclinicity are calculated to test the ability of the GCMs’ match reanalysis. An intermodel comparison of the spatial correlations suggests that differences (relative to ERA-Interim) in the position of the storm track aloft have the strongest influence on differences in the surface storm-track position. However, in the North Atlantic, biases in the surface storm track north of the Gulf Stream are related to biases in the SST. An analysis of the strength of the storm tracks shows that most models generate a weaker storm track at the surface than 850 hPa, consistent with observations, although some outliers are found. A linear relationship exists among the models between storm-track amplitudes at 500 and 850 hPa, but not between 850 hPa and the surface. In total, the work reveals a dual role in forcing the surface storm track from aloft and from the ocean surface in CMIP5 models, with the atmosphere having the larger relative influence.

scholarly journals On the Relationship between Synoptic Wintertime Atmospheric Variability and Path Shifts in the Gulf Stream and the Kuroshio Extension

2009 ◽  
Vol 22 (12) ◽  
pp. 3177-3192 ◽  
Author(s):  
Terrence M. Joyce ◽  
Young-Oh Kwon ◽  
Lisan Yu
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Western Boundary ◽  
Atmospheric Variability ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

Abstract Coherent, large-scale shifts in the paths of the Gulf Stream (GS) and the Kuroshio Extension (KE) occur on interannual to decadal time scales. Attention has usually been drawn to causes for these shifts in the overlying atmosphere, with some built-in delay of up to a few years resulting from propagation of wind-forced variability within the ocean. However, these shifts in the latitudes of separated western boundary currents can cause substantial changes in SST, which may influence the synoptic atmospheric variability with little or no time delay. Various measures of wintertime atmospheric variability in the synoptic band (2–8 days) are examined using a relatively new dataset for air–sea exchange [Objectively Analyzed Air–Sea Fluxes (OAFlux)] and subsurface temperature indices of the Gulf Stream and Kuroshio path that are insulated from direct air–sea exchange, and therefore are preferable to SST. Significant changes are found in the atmospheric variability following changes in the paths of these currents, sometimes in a local fashion such as meridional shifts in measures of local storm tracks, and sometimes in nonlocal, broad regions coincident with and downstream of the oceanic forcing. Differences between the North Pacific (KE) and North Atlantic (GS) may be partly related to the more zonal orientation of the KE and the stronger SST signals of the GS, but could also be due to differences in mean storm-track characteristics over the North Pacific and North Atlantic.

The mineralogical composition of some Scottish soils

1925 ◽  
Vol 15 (3) ◽  
pp. 257-271 ◽  
Author(s):  
James Hendrick ◽  
George Newlands
Keyword(s):  
Mineralogical Composition ◽  
Fine Sand ◽  
Plant Food ◽  
Sand Fraction ◽  
Extensive Survey ◽  
North East ◽  
The North ◽  
Local Origin ◽  
East West ◽  
Made In

1. Previous investigations showed that certain Scottish soils were of glacial drift origin, that they were comparatively rich in unweathered silicates and therefore in reserves of plant-food, that they showed considerable variation in such silicates and were capable of classification accordingly. Some indication was also shown that the glacial drift, and hence the resulting soil, was sometimes of local origin, its character being determined by the underlying rock. In the present investigation a more extensive survey of Scottish soils has been made in order to discover to what extent these preliminary findings might be applicable generally.2. For this purpose soils have been collected from various localities in the north, north-east, west and south of Scotland, and have been analysed mechanically and the “fine sand” fraction examined mineralogically.

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