scholarly journals Land Magnetic survey along a profile from Akaz to Rutba town and its applications

2012 ◽  
Vol 9 (1) ◽  
pp. 63-71
Author(s):  
Baghdad Science Journal
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Measurements ◽  
Continuation Method ◽  
Vertical Component ◽  
Base Station ◽  
Western Desert ◽  
Magnetic Survey ◽  
Fracture Density ◽  
Geological Time ◽  
Near Surface

A land magnetic survey was carried out along regional profile, which is located at the north part of the Iraqi western desert. It starts from al –Qaam City (at north) toward Rutba City (at south) with a total length of 238km. The survey was carried out along the paved road between the two cities, About 113 measuring points were done with inter-station distance of 2 km (for 198 km) and 2 to 5km (for 40km). Two proton magnetometers were used in this survey. One of them is used for base station monitoring, which was fixed as of Salah Aldin field (Akkas). Its readings were used for diurnal corrections. All magnetic measurements were corrected for normal and topographic corrections. The readings were reduced to a certain base level. The resulted magnetic anomalies show a good correlation with those of Arial - magnetic survey anomalies conducted by (C.G.G, 1974). This is true for those anomalies with wavelength more than 50km. While the land magnetic survey has shown more small anomalies which may reflect near surface sources. In addition, there is a considerable difference between the magnetic intensity values of both surveys. The downward continuation method was used in this study for detecting the depth of magnetic anomaly source. But before applying this method the total magnetic field was converted to its vertical component using computer program packages. The 2.5 mathematical modeling techniques were used for interpreting magnetic anomaly. Several models were suggested according to the geological and geophysical surface and subsurface data. These models clearly suggest that the tectonic of the studied area may be completely affected by deep faults that could reach the basements or even cut it. These faults resulted in tectonic blocks with relative movements that could happen through the geological time, and they may be responsible for the tectonic features of the western desert. These faults could also responsible for the lateral and vertical variations that are noticed in subsurface rocks of the studied area. The subsurface lateral susceptibility variation between the different blocks could result from the variation in physical parameter of the rocks (like porosity, fracture density…) and there is a possibility that rocks beneath 18km (lower crust) still possess some magnetic properties.

A multi-scale ground and drone-borne magnetic survey approach for the detection and investigation of archaeological structures

2021 ◽  
Author(s):  
Bruno Gavazzi ◽  
Hugo Reiller ◽  
Marc Munschy ◽  
Gilles Pierrevelcin ◽  
Florian Basoge ◽  
...  
Keyword(s):  
Vertical Component ◽  
High Amplitude ◽  
Magnetic Survey ◽  
Rhine River ◽  
Near Surface ◽  
Multi Scale ◽  
Electric Power Line ◽  
Frequency Magnetic Field ◽  
Ground Magnetic

<p><span>Ground magnetic surveys are commonly used for imaging near-surface structures in archaeological studies. Usually, surveys are conducted using vertical component gradiometers or scalar gradiometers to produce a vertical pseudo-gradient map. Scalar magnetometers can also be used, albeit less frequently, to produce maps of the total magnetic anomaly. In all these cases, the equipment is pushed or pulled by an operator or carried behind a vehicle. Here we present a third approach made available by the use of three-component fluxgate magnetometers: fast surveys over large areas using a compact lightweight drone flying automatically 1 to 2 m above the ground and high precision surveys acquired by an operator 0,2 to 1 m above the ground. A case study on the gallo-roman site of Oedenburg, </span><span>located</span><span> along the Rhine River in its upper valley, illustrates the results that can be obtained with the approach. A comparison with previously acquired pseudo-gradient surveys show</span><span>s</span><span> that the presented method allows a faster coverage, a greater resolution for the imaging of short wavelength structures (such as walls) and a better capacity of imaging large wavelength structures (such as pathways, palaeochannels or soil composition variations). As the site is crossed by a high voltage electric power line, a method to suppress the high-amplitude 50 Hz frequency magnetic field is presented.</span></p>

scholarly journals Matlab tool REGCONT2: effective source depth estimation by means of Tikhonov’s regularized downwards continuation of potential fields

2018 ◽  
Vol 48 (3) ◽  
pp. 231-254 ◽  
Author(s):  
Roman Pašteka ◽  
David Kušnirák ◽  
Roland Karcol
Keyword(s):  
Continuation Method ◽  
Downward Continuation ◽  
Potential Fields ◽  
Magnetic Survey ◽  
Unexploded Ordnance ◽  
Size Estimation ◽  
Source Depth ◽  
Sampling Step ◽  
Real World Data ◽  
Near Surface

Abstract Transformation based on downward continuation of potential fields is an important tool in their interpretation – depths of shallowest important sources can be determined by means of stable downward continuation algorithms. We analyse here selected properties of one from these algorithms (based on Tikhonov’s regularization approach) from the scope of two most important discretization parameters – dimensions of the areal coverage of the interpreted field and the sampling interval size. Estimation of the source depth is based on the analysis of computed LP-norms for various continuation depths. A typical local minimum of these norms disappears at the source depth. We show on several synthetic bodies (sphere, horizontal cylinder, vertical rod) and also real-world data-sets (results from a magnetic survey for unexploded ordnance detection) that there is a need for relatively large surroundings around the interpreted anomalies. Beside of this also the sampling step plays its important role – grids with finer sampling steps give better interpretation results, when using this downward continuation method. From this point of view, this method is more suitable for the interpretation of objects in near surface and mining geophysics (anomalies from cavities, unexploded ordnance objects and ore bodies). Anomalies should be well developed and separable, and densely sampled. When this is not valid, several algorithms of interpolation and extrapolation (grid padding methods) can improve the interpretation properties of studied downward continuation method.

scholarly journals Isotopically “heavy” pyrite in marine sediments due to high sedimentation rates and non-steady-state deposition

Geology ◽  
2021 ◽  
Author(s):  
Jiarui Liu ◽  
Gilad Antler ◽  
André Pellerin ◽  
Gareth Izon ◽  
Ingrid Dohrmann ◽  
...  
Keyword(s):  
Critical Role ◽  
Global Ocean ◽  
Sedimentation Rates ◽  
Geological Time ◽  
Near Surface ◽  
Reactive Iron ◽  
Depositional Processes ◽  
Pyrite Formation ◽  
Ocean Chemistry ◽  
Sedimentary Pyrite

Sedimentary pyrite formation links the global biogeochemical cycles of carbon, sulfur, and iron, which, in turn, modulate the redox state of the planet’s surficial environment over geological time scales. Accordingly, the sulfur isotopic composition (δ34S) of pyrite has been widely employed as a geochemical tool to probe the evolution of ocean chemistry. Characteristics of the depositional environment and post-depositional processes, however, can modify the δ34S signal that is captured in sedimentary pyrite and ultimately preserved in the geological record. Exploring sulfur and iron diagenesis within the Bornholm Basin, Baltic Sea, we find that higher sedimentation rates limit the near-surface sulfidization of reactive iron, facilitating its burial and hence the subsurface availability of reactive iron for continued and progressively more 34S-enriched sediment-hosted pyrite formation (δ34S ≈ –5‰). Using a diagenetic model, we show that the amount of pyrite formed at the sediment-water interface has increased over the past few centuries in response to expansion of water-column hypoxia, which also impacts the sulfur isotopic signature of pyrite at depth. This contribution highlights the critical role of reactive iron in pyrite formation and questions to what degree pyrite δ34S values truly reflect past global ocean chemistry and biogeochemical processes. This work strengthens our ability to extract local paleoenvironmental information from pyrite δ34S signatures.

scholarly journals Environmental monitoring of soil pollution in urban areas (a case study from Heraklion city, Central Crete, Greece)

2017 ◽  
Vol 47 (2) ◽  
pp. 963
Author(s):  
E. Kokinou ◽  
C. Belonaki ◽  
D. Sakadakis ◽  
K. Sakadaki
Keyword(s):  
Magnetic Susceptibility ◽  
Urban Areas ◽  
Magnetic Measurements ◽  
Topographic Map ◽  
Near Surface ◽  
Thermomagnetic Analysis ◽  
Geological Features ◽  
Digital Elevation ◽  
Elevation Model

Main scope of the present study is to combine topographic and geological data, magnetic susceptibility and thermomagnetic analysis in order to investigate the magnetic properties of the near surface soils in possible polluted urban areas. For this purpose, a power plant with a dense traffic net around it, located in the NW section of Heraklion city in Crete was selected to be the study area. Surface soil samples have been collected from the area under investigation and they were analyzed in order to estimate the spatial distribution of the magnetic susceptibility. Loci of high values of the magnetic susceptibility within the study area gave rise to further proceed to thermomagnetic analysis of the selected samples. GIS techniques were used for mapping the magnetic measurements on the various topographic and geological features of the area. The digital elevation model was created by the digitization of the topographic map contours (1:5000 scale maps). The combination of the above techniques indicate high values of the magnetic susceptibility especially in the northeastern part of the investigated area, possibly related to pollution due to the presence of heavy metals.

Robust Empirical Time–Frequency Relations for Seismic Spectral Amplitudes, Part 1: Application to Regional S Waves in Southeastern Iran

2020 ◽  
Author(s):  
Maryam Safarshahi ◽  
Igor B. Morozov
Keyword(s):  
Seismic Waves ◽  
Joint Inversion ◽  
Vertical Component ◽  
Transverse Component ◽  
Model Parameters ◽  
S Wave ◽  
Near Surface ◽  
S Waves ◽  
Time Frequency ◽  
Frequency Independent

ABSTRACT Empirical models of geometrical-, Q-, t-star, and kappa-type attenuation of seismic waves and ground-motion prediction equations (GMPEs) are viewed as cases of a common empirical standard model describing variation of wave amplitudes with time and frequency. Compared with existing parametric and nonparametric approaches, several new features are included in this model: (1) flexible empirical parameterization with possible nonmonotonous time or distance dependencies; (2) joint inversion for time or distance and frequency dependencies, source spectra, site responses, kappas, and Q; (3) additional constraints removing spurious correlations of model parameters and data residuals with source–receiver distances and frequencies; (4) possible kappa terms for sources as well as for receivers; (5) orientation-independent horizontal- and three-component amplitudes; and (6) adaptive filtering to reduce noise effects. The approach is applied to local and regional S-wave amplitudes in southeastern Iran. Comparisons with previous studies show that conventional attenuation models often contain method-specific biases caused by limited parameterizations of frequency-independent amplitude decays and assumptions about the models, such as smoothness of amplitude variations. Without such assumptions, the frequency-independent spreading of S waves is much faster than inferred by conventional modeling. For example, transverse-component amplitudes decrease with travel time t as about t−1.8 at distances closer than 90 km and as t−2.5 beyond 115 km. The rapid amplitude decay at larger distances could be caused by scattering within the near surface. From about 90 to 115 km distances, the amplitude increases by a factor of about 3, which could be due to reflections from the Moho and within the crust. With more accurate geometrical-spreading and kappa models, the Q factor for the study area is frequency independent and exceeds 2000. The frequency-independent and Q-type attenuation for vertical-component and multicomponent amplitudes is somewhat weaker than for the horizontal components. These observations appear to be general and likely apply to other areas.

Three-dimensional numerical modeling of gravity and magnetic anomaly in a mixed space-wavenumber domain

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. G41-G54 ◽  
Author(s):  
Shikun Dai ◽  
Dongdong Zhao ◽  
Shunguo Wang ◽  
Bin Xiong ◽  
Qianjiang Zhang ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Fourier Transform ◽  
Differential Equations ◽  
Numerical Solution ◽  
Magnetic Anomaly ◽  
Large Scale ◽  
Vertical Component ◽  
Wavenumber Domain ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Anomaly

Fast and accurate numerical modeling of gravity and magnetic anomalies is the basis of field-data inversion and quantitative interpretation. In gravity and magnetic prospecting, the computation and memory requirements of practical modeling is still a significant issue, which leads to the difficulty of using efficient and detailed inversions for large-scale complex models. A new 3D numerical modeling method for gravity and magnetic anomaly in a mixed space-wavenumber domain is proposed to mitigate the difficulties. By performing a 2D Fourier transform along two horizontal directions, 3D partial differential equations governing gravity and magnetic potentials in the spatial domain are transformed into a group of independent 1D differential equations wrapped with different wavenumbers. Importantly, the computation and memory requirements of modeling are greatly reduced by this method. A modeling example with 4,040,100 observations can be finished in approximately 28 s on a desktop using a single core, and the independent differential equations are highly parallel among different wavenumbers. The method preserves the vertical component in the space domain, and thus a mesh for modeling can be finer at a shallower depth and coarser at a deeper depth. In general, the new method takes into account the calculation accuracy and the efficiency. The finite-element algorithm combined with a chasing method is used to solve the transformed differential equations with different wavenumbers. In a synthetic test, a model with prism-shaped anomalies is used to verify the accuracy and efficiency of the proposed algorithm by comparing the analytical solution, our numerical solution, and a well-known numerical solution. Furthermore, we have studied the balance between computational accuracy and efficiency using a standard fast Fourier transform (FFT) method with grid expansion and the Gauss-FFT method. A model with topography is also used to explore the ability of modeling topography with our method. The results indicate that the proposed method using the Gauss-FFT method has characteristics of fast calculation speed and high accuracy.

Analysis of the Czech magnetic anomaly data obtained by ground-based and airborne magnetic surveys

2020 ◽  
Author(s):  
Pavel Hejda ◽  
Dana Čápová ◽  
Eva Hudečková ◽  
Vladimír Kolejka
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Data File ◽  
Ore Deposits ◽  
Substantial Contribution ◽  
Magnetic Survey ◽  
Contour Maps ◽  
Anomaly Map ◽  
Ground Magnetic ◽  
Airborne Survey

<p>The modern epoch of ground magnetic surveying activity on the Czech territory was started by the Institute of Geophysics by setting up a fundamental network of the 1<sup>st</sup> order in 1957-58. It consists of 199 points and was reoccupied in 1976-78 and 1994-96. The anomaly maps were constructed by subtraction of the IGRF model.</p><p>Extensive aeromagnetic measurements have been performed from 1959 to 1972 by permalloy probe of Soviet provenience. The accuracy of the instrumentation was about (and often above) 10 nT. The second period of airborne survey started in 1976. Thanks to the deployment of proton precession magnetometer, the accuracy improved to ~ 2 nT. Since 2004 the measurements were carried out by caesium magnetometer. The data were digitized, known anthropogenic anomalies were cleared away and data were transformed to the regular grid with step 250 m. The final data file of magnetic anomalies ΔT, administered by the Czech Geological Survey, represents a substantial contribution to the exploration of ore deposits and to the structure geology in general.</p><p>In view of the fact that data file of magnetic anomalies was compiled from data acquired by heterogeneous methods in the course of more than 50 years, our recent study is aimed at looking into the homogeneity of the data by comparison them with ground-based magnetic survey. A simple comparison of the contour maps showed good similarity of the large regional anomalies. For more detailed analysis, the variation of ΔT in the neighbourhood of all points of the fundamental network was inspected and the basic statistic characteristics were computed. Summary results as well as several examples will be presented accordingly as the INSPIRE compliant services and eventually as the user-friendly web map application and made available on the CGS Portal http://mapy.geology.cz/ and on the updated web of the CzechGeo/EPOS consortium www.czechgeo.cz. Incorporating the map into the World Digital Magnetic Anomaly Map (WDMAM – IAGA) is also under consideration. This data will also be interesting for the EPOS.</p>

scholarly journals Converted‐wave seismic exploration: Applications

Geophysics ◽  
2003 ◽  
Vol 68 (1) ◽  
pp. 40-57 ◽  
Author(s):  
Robert R. Stewart ◽  
James E. Gaiser ◽  
R. James Brown ◽  
Don C. Lawton
Keyword(s):  
Seismic Waves ◽  
Seismic Exploration ◽  
Fracture Density ◽  
Converted Wave ◽  
P Waves ◽  
Near Surface ◽  
S Waves ◽  
Subsurface Fluid ◽  
Processing Techniques ◽  
Gas Bearing

Converted seismic waves (specifically, downgoing P‐waves that convert on reflection to upcoming S‐waves are increasingly being used to explore for subsurface targets. Rapid advancements in both land and marine multicomponent acquisition and processing techniques have led to numerous applications for P‐S surveys. Uses that have arisen include structural imaging (e.g., “seeing” through gas‐bearing sediments, improved fault definition, enhanced near‐surface resolution), lithologic estimation (e.g., sand versus shale content, porosity), anisotropy analysis (e.g., fracture density and orientation), subsurface fluid description, and reservoir monitoring. Further applications of P‐S data and analysis of other more complicated converted modes are developing.

MICROEARTHQUAKE INVESTIGATION OF THE MESA GEOTHERMAL ANOMALY, IMPERIAL VALLEY, CALIFORNIA

Geophysics ◽  
1977 ◽  
Vol 42 (1) ◽  
pp. 17-33 ◽  
Author(s):  
Jim Combs ◽  
David Hadley
Keyword(s):  
Vertical Component ◽  
Surface Expression ◽  
High Gain ◽  
Strike Slip ◽  
Imperial Valley ◽  
Natural Period ◽  
Near Surface ◽  
Geothermal Fluids ◽  
First Motion ◽  
Motion Studies

Microearthquakes associated with the Mesa geothermal anomaly were recorded for five weeks during the summer of 1973 using an array of six portable, high‐gain seismographs equipped with vertical‐component 1-sec natural period seismometers. Background seismicity of the area is thus determined prior to development for geothermal power and water. The local seismicity changed considerably over the recording period. Most daily activity was characterized by only one or two potentially locatable events, while two microearthquake swarms of two‐ and three‐day duration included as many as 100 or more distinct local events per day. Hundreds of small events (nanoearthquakes), some clustered in swarms, were recorded by each seismograph; however, most were not detected on four or more seismograms so that hypocentral locations usually could not be determined. Locations were determined for 36 microearthquakes having epicenters situated in the [Formula: see text] areal extent of the geothermal anomaly. Focal depths ranged from near‐surface to about 8 km. More than half of the located events have hypocenters greater than the 4.0 km which is approximately the depth to crystalline basement. Stress associated with the Mesa geothermal anomaly is relieved by a combination of continuous microseismic activity and intermittent microearthquake swarms. Based on the results of the present study, a new right‐lateral strike‐slip fault, the Mesa fault, was defined. First motion studies indicate strike‐slip faulting although there is no surface expression of the fault. The northwest‐southeast trending Mesa fault is an active fault functioning as a conduit for rising geothermal fluids of the Mesa geothermal anomaly. This investigation is another demonstration that geothermal areas are characterized by enhanced microearthquake activity.

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