Presence Of Magnetic Anomalies Research Articles

The Study of Geomagnetic Field Southeastern Part of an Najaf-Karbala Plateau, Central Iraq, by World Magnetic Model 2015

Abstract In this paper numerical simulations of the Earth’s magnetic field in the south-eastern part of an Najaf-Karbala Plateau and to the north of the centre of An-Najaf governorate have been investigated using the WMM2015 model. The study area is located at (Latitude = 32.3180°-31.99°) N, (Longitude = 44.5160°-44.0690°) E, and ranging altitude between 20-90 m above sea level). The study area was divided into grid of (2000 points) by drawing parallel lines, the interspacing distance between two lines (1 Km). Each line would be divided into several nodes. The space between any two nodes about (0.25 Km), this is done by using Google earth program v.6, Collected the data were latitude, longitude, and elevation from sea level. The data applied by (WMM2015) model and the result data of earth magnetic field elements drawn by Surfer v.13 and converted to the contour map by using the gridding method to find the characteristics of Earth magnetic elements ( Total intensity (F), the East component(Y), Horizontal intensity (H), Down component(Z), the North component(X), Declination (D) ) and Inclination (I)). The contour maps of F, Y, and D have magnetic anomalies that observed the changing in the values in the north western part of the study area. This may be indicating the presence of magnetic anomalies as a result of the presence of subsurface rock structures caused by them, including base rocks or various faults.

Investigation of Magneto-/Radio-Metric Behavior in Order to Identify an Estimator Model Using K-Means Clustering and Artificial Neural Network (ANN) (Iron Ore Deposit, Yazd, IRAN)

The study area is located near Toot village in the Yazd province of Iran, which is considered in terms of its iron mineralization potential. In this area, due to radioactivity, radiometric surveys were performed in a part of the area where magnetometric studies have also been performed. According to geological studies, the presence of magnetic anomalies can have a complex relationship with the intensity of radioactivity of radioactive elements. Using the K-means clustering method, the centers of the clusters were calculated with and without considering the coordinates of radiometric points. Finally, the behavior of the two variables of magnetic field strength and radioactivity of radioactive elements relative to each other was studied, and a mathematical relationship was presented to analyze the behavior of these two variables relative to each other. On the other hand, the increasing and then decreasing behavior of the intensity of the Earth’s magnetic field relative to the intensity of radioactivity of radioactive elements shows that it is possible to generalize the results of magnetometric surveys to radiometry without radiometric re-sampling in this region and neighboring areas. For this purpose, using the general regression neural network and backpropagation neural network (BPNN) methods, radiometric data were estimated with very good accuracy. The general regression neural network (GRNN) method, with more precision in estimation, was used as a model for estimating the radiation intensity of radioactive elements in other neighboring areas.

Detailed bathymetry and magnetic anomaly in the Central Ryukyu Arc, Japan: implications for a westward shift of the volcanic front after approximately 2.1 Ma

Detailed bathymetry and magnetic anomalies in the southern part of the Central Ryukyu Arc reveal recent volcanic structures in a southwestward extension of the active volcanic front of the Ryukyu Arc. A line of bathymetric highs running subparallel to this recent volcanic front was observed approximately 20 km to the east. A set of small, sharply defined magnetic anomalies extends southward from this line of bathymetric highs to the islands Kume-jima and Aguni-jima, suggesting the former existence of an ancient volcanic front. The ages of volcanic rocks from these islands indicate that magmatic activity along the ancient volcanic front continued until at least approximately 2.1 Ma. The presence of magnetic anomalies between the two volcanic fronts suggests that the volcanic front has moved gradually westward. This shift can be explained by the termination of asthenospheric upwelling and/or the rapid retreat of the Ryukyu Trench after its change in subduction direction.

Ocean‐generated magnetic field study based on satellite geomagnetic measurements: 2. Signal inference

The work presented here is the second part of an ocean‐generated magnetic field study and provides a procedure for inferring the ocean‐generated magnetic field from satellite geomagnetic measurements. The procedure was first tested on synthetic data. The simulation employed a hypothetical satellite measuring the magnetic field at an altitude of 400 km. The “measurements” (generated by the CM4 and CHAOS models) included the core field, the lithospheric field, the ionospheric and magnetospheric fields, the secular variation, and the ocean‐generated magnetic field. The search algorithm, as proposed in part 1, converts irregular measurements into fields on a regular grid. The filtration procedure is based on the Savitzky‐Golay algorithm. The procedure includes four steps providing seven unknown filter parameters. Parameter values were obtained by solving the problem of minimizing the spatially averaged squared residuals between the inferred field and the model field. Then, the parameters were used in the filter to infer the ocean‐generated magnetic field that was initially added to the “measurements.” The inferred signal, although spatially corrupted and having a smaller magnitude (60% of the magnitude of the initial signal), indicated the presence of magnetic anomalies within the Southern Ocean. The technique was then applied to CHAMP geomagnetic measurements. The result of filtering was clear magnetic anomalies within the Southern Ocean with a spatial character that were close to what models of the ocean‐generated magnetic field provided. The magnitude of the inferring signal was 5 nT, the corrected values were 7–8 nT, 1–2 nT larger than the modeled field magnitude. To compare the temporal variability of the inferred field with the variability of sea surface height, ten 10° by 10° areas were selected within the Southern Ocean and the root‐mean‐square of both SSH and the magnetic field were computed for each area. A comparison of the results indicated a close similarity between SSH and the magnetic field temporal variability, which allowed the identification of the inferred field as the ocean‐generated magnetic field.

Magnetic properties of Martian olivine basalts studied by terrestrial analogues

Here we present a comparison study of terrestrial olivine basalt and relatively un-weathered basalt studied by the Mars Exploration Rover Spirit on Mars. The Mossbauer spectra of terrestrial olivine basalt exhibit some characteristics that can also be seen in the Mars spectra. The results from Mossbauer spectroscopy on Mars indicate that the olivine in the rocks has undergone alteration at high temperatures (600–1,000°C), a process known to give rise to anomalously magnetic rocks on Earth. This suggests that if the rocks at Gusev crater had solidified in an external magnetic field of terrestrial magnitude, these would have become highly magnetic enough to explain the presence of magnetic anomalies on Mars.

Docking for an autonomous ocean sampling network

In this paper, we examine the issues associated with docking autonomous underwater vehicles (AUVs) operating within an Autonomous Ocean Sampling Network (AOSN). We present a system based upon an acoustic ultrashort baseline system that allows the AUV to approach the dock from any direction. A passive latch on the AUV and a pole on the dock accomplish the task of mechanically docking the vehicle. We show that our technique for homing is extremely robust in the face of the two dominant sources of error-namely the presence of currents and the presence of magnetic anomalies. Our strategy for homing is independent of the initial bearing of the dock to the AUV, includes a method for detecting when the vehicle has missed the dock, and automatically ensures that the AUV is in a position to retry homing with a greater chance of success. Our approach is seen to be extremely successful in homing the vehicle to the dock, mechanically attaching itself to the dock, aligning inductive cores for data and power transfer, and undocking at the start of a fresh mission. Once the AUV is on the dock, we present a methodology that allows us to achieve the complex tasks with ensuring that the AUV is securely docked, periodically checking vehicle status, reacting to a vehicle that requires charging, tracking it when it is out on a mission, archiving and transmitting via satellite the data that the AUV collects during its missions, as well as providing a mechanism for researchers removed from the site to learn about vehicle status and command high-level missions. The dock is capable of long-term deployments at a remote site while respecting the constraints - low power, small size, low computational energy, low bandwidth, and little or no user input - imposed by the amalgamation of acoustic, electronic and mechanical components that comprise the entire system.

Morphology and origin of the Osbourn Trough

The Osbourn Trough is a 900 km long, east‐west trending gravity low, visible in satellite altimetry data, which intersects the Tonga Trench at 25°30′S. A recent survey collected gravity, magnetic, echo sounder, and swath bathymetry data on three adjacent, north‐south trending ship tracks centered on the trough. The linear gravity low is 20–30 mGal less than the regional value and is accompanied by a flat‐lying, 200–500 m deep sediment‐filled valley. Swath bathymetry images reveal several parallel, east‐west trending linear ridges and valleys on either side of the main trough as well as other morphologic features characteristic of relict spreading centers, including a prominent inside corner high and possible pseudo‐fault trace. The presence of magnetic anomalies (possibly anomalies 33 and 32) suggests that the seafloor here was formed after the end of the Cretaceous Normal Superchron (anomaly 34). These data support the conclusion that this trough is a spreading center, which stopped spreading in Late Cretaceous time. The existence of this feature has important implications for tectonic reconstructions in this region. The Osbourn Trough could be part of the fossil spreading center between the Pacific Plate and a fragment of the Phoenix Plate, the Bellingshausen Plate. This would require the seafloor between the Osbourn Trough and the Chatham Rise to the south to be a remnant fragment of the Bellingshausen Plate. This remnant may have joined to the Pacific Plate when the Hikurangi Plateau entered the Gondwana subduction zone at the Chatham Rise possibly causing the cessation of spreading on the Osbourn Trough.

Removing varying directional trends in aeromagnetic data

Both qualitative and quantitative interpretations of aeromagnetic data can be hindered by the presence of magnetic anomalies caused by mafic dykes. Such anomalies obscure the magnetic signatures due to basement lithology and structure, and their effects will often dominate when automated interpretation methods are applied to gridded data sets. Since dyke swarms are often nonparallel, simple frequency‐domain strike‐sensitive filtering based on a single directional trend is not a viable method for removing their signatures. We use a coordinate transformation to project anomalies of various strikes onto one direction, which is then suppressed using a standard decorrugation method. The resulting grid is subsequently transformed back to the original projection. This approach is illustrated by the removal of the magnetic signature of the Proterozoic Mackenzie dyke swarm occurring in the Slave structural province, Northwest Territories, Canada.

Transitional Tectonics and Late Cenozoic Structure of the Continental Margin off Northernmost California

The continental margin north of the Cape Mendocino triple junction is a region of tectonic transition between structures related to underthrusting on the continental slope and those related to right-lateral strike-slip along the coast. Underthrusting of late Cenozoic rocks of the continental slope by the Gorda lithospheric plate is seen by the presence of magnetic anomaly 3, age 5 m.y., beneath the slope. Folds and faults mapped by reflection profiling on the continental slope are parallel to it, and the faults have dip separations predominantly with west side down. These structures are best explained as resulting from oblique underthrusting, with structural trends controlled by the slope direction. Northwest-trending faults occur along the coast and reported earthquake mechanism solutions show right-lateral first motions. These faults and related folds affect Mesozoic rocks and parallel the San Andreas fault system which lies to the south, most probably sharing its origin—that of shear interaction between the Pacific and North American lithospheric plates.

Late Cenozoic Underthrusting of the Continental Margin off Northernmost California

The presence of magnetic anomaly 3, age 5 million years, beneath the continental slope off northernmost California, is evidence for underthrusting of the continental margin during the late Cenozoic. Folded and faulted strata near the base of the slope attest to deformation of the eastern edge of the turbidite sedimzents in the Gorda Basin; the deformation observed is exactly that expected from underthrusting. The relative motions of three crustal plates also suggest underthrusting, possibly with a major component of right-lateral slip.