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Field Investigation Methods
Published in Mark Edward Byrnes, Field Sampling Methods for Remedial Investigations, 2023
Magnetics is a geophysical survey method (Figure 4.4) that generally involves the measurement of the vertical gradient of the earth’s magnetic field or the earth’s magnetic field intensity. Anomalies in the earth’s magnetic field are caused by induced or remanent magnetism. Induced magnetic anomalies are the result of secondary magnetization induced in a ferrous body by the earth’s magnetic field (GeoVision 2007). The shape and amplitude of an induced magnetic anomaly is a function of the:Intensity and inclination of the earth’s magnetic field at the survey locationOrientation, geometry, size, depth, and magnetic susceptibility of the target
Low-Frequency Search Coil Magnetometers
Published in Krzysztof Iniewski, Smart Sensors for Industrial Applications, 2017
Low-frequency search coil magnetometers are widely used for geophysical prospecting, space research, magnetic anomaly detection [1–17], etc. Their advantages compared to other magnetometers are high resolution and low power consumption, defined only by the power consumption of the preamplifier. The inherent reduction of the search coils’ resolution with frequency can be compensated by increasing their size. Thus, large enough low-frequency search coils can compete with and even outperform fluxgates [9–11,15–17].
The Coupling of Atmospheric Electromagnetic Fields with Biological Systems
Published in Shoogo Ueno, Tsukasa Shigemitsu, Bioelectromagnetism, 2022
Tsukasa Shigemitsu, Shoogo Ueno
It has been hypothesized that migratory cetaceans use magnetic anomalies as indicators of direction determination, navigation, and course determination. Some studies have confirmed this hypothesis with erroneous landward and stranding behavior during seasonal long-distance migrations. The distribution of geomagnetic fields is greatly affected by local topographic changes and is observed as a magnetic anomaly. Conversely, the point where the magnetic anomaly becomes weak can also be considered a magnetic anomaly. Margaret Klinowska, biologist at the University of Cambridge, has compiled a record of 3,000 cases of stranding over past 70 years that are preserved in the British Museum. Klinowska analyzed all reports on passive stranding (dead body) and active stranding (live animal) along the British coastlines (1985, 1986). She found that the difference between passive stranding and active stranding. Live stranding is associated with geomagnetic disturbances. The pattern of magnetic disturbance, not the absolute level of disturbance is the key factor for live stranding at all latitudes investigated. Further, Kirschvink professor of California Institute of Technology and his co-workers tested the hypothesis that cetaceans use weak anomalies in the geomagnetic field as cues for orientation, navigation, and/or piloting (1986). Live stranding of whales has also been correlated with local geomagnetic anomalies. Kirschvink employed 212 stranding events of live animals (active stranding) recorded and preserved at the Smithsonian Institution and data on stranding locations along the US East Coast to examine the correspondence between magnetic topographic changes and stranding locations (1986). They found that there are highly significant tendencies for cetaceans to beach themselves near coastal locations with local magnetic minima. After confirming these significant effects by Monte-Carlo simulations, he suggested that cetaceans may be sensing local geomagnetic fluctuations. This suggested that cetaceans have a magnetic sensing system comparable to those of other migratory and homing animals, which suggests that magnetic topography and the magnetic lineation of the ocean play an important role in guiding long distance migration.
Implications of upper-mantle seismicity for deformation in the continental collision zone beneath the Alpine Fault, South Island, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2018
Carolin M. Boese, Tim A. Stern, Konstantinos Michailos, John Townend, Calum J. Chamberlain
Between Karangarua River and Fox Glacier basaltic rocks forming part of the Late Cretaceous Arnott Basalt are associated with a large positive magnetic anomaly (Rattenbury 2015, their Fig. 9). The modelled dip of the basalt layers is constrained from outcrops and they are inferred to be shallow, crustal features. Similar anomalies are seen in the lower Whataroa River area where no outcropping rocks can be associated with the magnetic anomalies. The epicentres of upper mantle earthquakes beneath the central Westland section of the Alpine Fault coincide with this magnetic anomaly. The outcropping basalts could be shallow representatives of mafic intrusions at greater depths.