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1

Seafloor spreading magnetic anomalies south off Sri Lanka  

Microsoft Academic Search

Results obtained from compilation and reinterpretation of about 21,200 line km of bathymetry, magnetic and satellite gravity data between 10°S to 10°N latitudes and 75 to 90°E longitudes south off Sri Lanka are presented here. Magnetic data and the synthetic seafloor spreading model reveal the presence of Mesozoic anomaly sequence M11 through M0 south of Sri Lanka. The oldest magnetic anomaly

M. Desa; M. V. Ramana; T. Ramprasad

2006-01-01

2

Numerical investigations of the spreading-rate dependence of anomalous skewness of marine magnetic anomalies due to seafloor spreading  

NASA Astrophysics Data System (ADS)

An improved understanding of the spreading-rate dependence of anomalous skewness from magnetic anomalies due to seafloor spreading will allow for better constraints on apparent polar wander paths, plate reconstructions, and the magnetic and thermal structure of oceanic lithosphere. Anomalous skewness, which is the difference between experimentally determined skewness and skewness expected from simple magnetization models with vertical reversal boundaries, has been observed to vary as a function of spreading rate, decreasing with increasing spreading rate and becoming negligible at spreading half-rates exceeding about 55 mm/a [Roest et al. 1992; Dyment et al. 1994]. In our analysis, we determine model-based estimates of anomalous skewness as a function of spreading rate for each anomaly. We do so by creating many synthetic profiles using the model of Dyment and Arkani-Hamed (1995), which was specifically constructed to produce anomalies with anomalous skewness consistent with observed anomalies. We experimentally determine the phase shift that causes the resulting synthetic magnetic anomaly to best match a profile produced from a "standard" model for anomalies due to seafloor spreading that assumes simple vertical reversal boundaries. We present results for those anomalies between 12r and 33r from which reliable paleomagnetic poles may potentially be determined. Differences in anomalous skewness for different anomalies determined at the same spreading rate can be attributed to the sequence effect, that is, the effect on the shape of a magnetic anomaly above seafloor of a single polarity chron of the magnetization of neighboring blocks of lithosphere magnetized during other chrons. We find that the sequence effect is smaller than we expected with the largest difference being between the results for anomaly 25r and those for anomaly 33r, for which the difference is 14 degrees at a 10 mm/a half-rate. Results for other anomalies lie between these two. We also infer a small outward displacement of the magnetic anomalies, which-like anomalous skewness-decreases with increasing spreading rate and vanishes at half rates exceeding 55 mm/a. We find that results obtained trying to find the best match to the synthetic magnetic anomaly profile are generally similar to results obtained when using the balanced-shoulder criterion for when an anomaly has been successfully deskewed. The values of chron-specific (or anomaly-specific) anomalous skewness that we have determined can be used to reduce the number of adjustable parameters in the determination of paleomagnetic poles from skewness data from three to two, to simply the latitude and longitude of the paleomagnetic pole. Implications for the northward motion of the Pacific Plate will be discussed.

Boswell, S. M.; Zheng, L.; Gordon, R. G.; Dyment, J.

2011-12-01

3

Toward Quantifying the Spreading-Rate Dependence of Anomalous Skewness of Marine Magnetic Anomalies due to Seafloor Spreading  

NASA Astrophysics Data System (ADS)

In past work, reliable paleomagnetic poles have been determined from skewness data by solving for a single additional adjustable parameter, anomalous skewness, assumed to be independent of spreading rate [Petronotis et al. 1992, 1994; Petronotis & Gordon 1999]. Nonetheless, analysis of anomalies in several ocean basins indicate that anomalous skewness depends on spreading rate for spreading half rates less than ?50 mm/yr [Roest et al., 1992; Dyment et al. 1994]. To facilitate investigation of the influence of spreading-rate dependent anomalous skewness on the determination of paleomagnetic poles determined from skewness, we build on the model for marine magnetic anomalies due to seafloor spreading of Dyment and Arkani-Hamed [1995]. We use this model to estimate anomalous skewness as a function of spreading rate for many anomalies. Synthetic magnetic anomaly profiles for oceanic lithosphere with sloping curving reversal boundaries were produced by forward modeling. Anomalous skewness values for chrons 25n to 33r were visually determined at various spreading rates using two approaches: balancing the shoulders of an anomaly corresponding to a single chron and best matching an anomaly corresponding to a single chron to a synthetic anomaly determined assuming vertical reversal boundaries. The new results may facilitate the determination of paleomagnetic poles from less widely distributed crossings of a magnetic anomaly than were used before. Further implications for determination of paleomagnetic poles for the Pacific plate will be discussed.

Boswell, S. M.; Zheng, L.; Gordon, R. G.; Dyment, J.

2010-12-01

4

Seafloor spreading magnetic anomalies in the Enderby Basin, East Antarctica  

Microsoft Academic Search

The timing of the early separation of India from the contiguous Antarctica–Australia is still an unresolved problem although it is well established that Antarctica and India formed a single Indo-Antarctic platform prior to the fragmentation of eastern Gondwanaland. Inadequate age information either in the form of magnetic anomaly isochrons or dating of oceanic rocks from the conjugate margins of Antarctica

M. V. Ramana; T. Ramprasad; Maria Desa

2001-01-01

5

Seafloor spreading in the eastern Gulf of Mexico: New evidence for marine magnetic anomalies  

NASA Astrophysics Data System (ADS)

Possible sea-floor spreading anomalies are indentified in marine magnetic surveys conducted in the eastern Gulf of Mexico. A symmetric pattern of lineated anomalies can be correlated with the geomagnetic time scale using previously proposed opening histories for the Gulf of Mexico basin. Lineated magnetic anomalies are characterized by amplitudes of up to 30 nT and wavelengths of 45-55 km, and are correlatable across 12 different ship tracks spanning a combined distance of 6,712 km. The magnetic lineations are orientated in a NW-SE direction with 3 distinct positive lineations on either side of the inferred spreading ridge anomalies. The magnetic anomalies were forward modeled with a 2 km thick magnetic crust composed of vertically bounded blocks of normal and reverse polarity at a model source depth of 10 km. Remnant magnetization intensity and inclination are 1.6 A m-1 and 0.2° respectively, chosen to best fit the magnetic observed amplitudes and, for inclination, in accord with the nearly equatorial position of the Gulf of Mexico during Jurassic seafloor spreading. The current magnetic field is modeled with declination and inclination of and 0.65° and 20° respectively. Using a full seafloor spreading rate of 1.7 cm/yr, the anomalies correlate with magnetic chrons M21 to M10. The inferred spreading direction is consistent with previous suggestions of a North-East to South-West direction of sea-floor spreading off the west coast of Florida beginning 149 Ma (M21) and ending 134 Ma (M10). The opening direction is also consistent with the counter-clockwise rotation of Yucatan proposed in past models.

Eskamani, Philip K.

6

Satellite magnetic anomalies related to seafloor spreading in the South Atlantic Ocean  

Microsoft Academic Search

Oceanic magnetic anomalies have been observed from satellite. The strongest anomalies are the long-wavelength components of the sea-floor spreading signature. Unfortunately, because of technical issues involving the treatment of satellite magnetic data, these signals are obscured in the South Atlantic Ocean because they trend north-south. However, a map does exist in which such features are observed, essentially because of a

Michael E. Purucker; Jerome Dyment

2000-01-01

7

Contribution of oceanic gabbros to sea-floor spreading magnetic anomalies.  

PubMed

The contribution of oceanic gabbros, representative rocks for layer 3 of the oceanic crust, to sea-floor spreading magnetic anomalies has been controversial because of the large variation in magnetic properties. Ocean Drilling Program (ODP) Leg 118 contains a continuous 500.7-meter section of oceanic gabbro that allows the relations between magnetization and petrologic characteristics, such as the degree of metamorphism and the magmatic evolution, to be clarified. The data suggest that oceanic gabbros, together with the effects of metamorphism and of magmatic evolution, account for a significant part of the marine magnetic anomalies. PMID:17777035

Kikawa, E; Ozawa, K

1992-10-30

8

Review of seafloor spreading around Australia. II. Marine magnetic anomaly modelling  

Microsoft Academic Search

This paper updates the models of seafloor spreading magnetic anomalies in the oceanic lithosphere of the Indo?Australian Plate and adjacent plates around Australia. The regions are the eastern Indian Ocean (Argo, Gascoyne, Cuvier and Perth Abyssal Plains), the southeast Indian Ocean (off the southern margin of Australia and the conjugate Wilkes Land margin of Antarctica), the southwest Pacific Ocean (Tasman

J. J. Veevers; Z. X. Li

1991-01-01

9

Early India-Australia Spreading History Revealed by Newly Detected Magnetic Anomalies  

NASA Astrophysics Data System (ADS)

The seafloor within the Perth Abyssal Plain (PAP), offshore Western Australia, is the only section of crust that directly records the early spreading history between India and Australia during the Mesozoic breakup of Gondwana. However, this early spreading has been poorly constrained due to an absence of data, including marine magnetic anomalies and data constraining the crustal nature of key tectonic features. Here, we present new magnetic anomaly data from the PAP that shows that the crust in the western part of the basin was part of the Indian Plate - the conjugate flank to the oceanic crust immediately offshore the Perth margin, Australia. We identify a sequence of M2 and older anomalies in the west PAP within crust that initially moved with the Indian Plate, formed at intermediate half-spreading rates (35 mm/yr) consistent with the conjugate sequence on the Australian Plate. More speculatively, we reinterpret the youngest anomalies in the east PAP, finding that the M0-age crust initially formed on the Indian Plate was transferred to the Australian Plate by a westward jump or propagation of the spreading ridge shortly after M0 time. Samples dredged from the Gulden Draak and Batavia Knolls (at the western edge of the PAP) reveal that these bathymetric features are continental fragments rather than igneous plateaus related to Broken Ridge. These microcontinents rifted away from Australia with Greater India during initial breakup at ~130 Ma, then rifted from India following the cessation of spreading in the PAP (~101-103 Ma).

Williams, S.; Whittaker, J. M.; Granot, R.; Müller, D.

2013-12-01

10

Early India-Australia spreading history revealed by newly detected Mesozoic magnetic anomalies in the Perth Abyssal Plain  

E-print Network

region of preserved seafloor that directly records the history of Early Cretaceous seafloor spreading between India and Australia. However, despite the clear importance of the seafloor spreading historyEarly India-Australia spreading history revealed by newly detected Mesozoic magnetic anomalies

Granot, Roi

11

Investigation of spreading center ecolution by joint inversion of seafloor magnetic anomaly and tectonic fabric data  

NASA Technical Reports Server (NTRS)

Spreading center segments that have experienced a complex tectonic history including rift propagation may have a complicated signature in bathymetric and magnetic anomaly data. To gain insight into the history of such regions, we have developed techniques in which both the magnetic anomaly patterns and seafloor fabric trends are predicted theoretically, and the combined predictions are compared numerically with the data to estimate best fitting parameters for the propagation history. Fitting functions are constructed to help determine which model best matches the digitized fabric and magnetic anomaly data. Such functions offer statistical criteria for choosing the best fit model. We use this approach to resolve the propagation history of the Cobb Offset along the Juan de Fuca ridge. In this example, the magnetic anomaly data prove more useful in defining the geometry of the propagation events, while the fabric, with its greater temporal resolution, is more useful for constraining the rate of propagation. It thus appears that joint inversion of magnetic and seafloor fabric data can be valuable in tectonic analyses.

Shoberg, Tom; Stein, Seth

1994-01-01

12

Early Tertiary seafloor spreading magnetic anomalies and paleo-propagators in the northern Arabian Sea  

Microsoft Academic Search

Study of closely spaced new marine magnetic profiles, in conjunction with published magnetic data, provide an updated identification of linear magnetic anomalies in the northern Arabian Sea from the Owen Fracture Zone in the west to the Laxmi and Chagos–Laccadive Ridges in the east. For the first time the entire magnetic anomaly sequence 28 through 20 is mapped eastwards from

A. K. Chaubey; G. C. Bhattacharya; G. P. S. Murty; K. Srinivas; T. Ramprasad; D. Gopala Rao

1998-01-01

13

Mesozoic magnetic anomaly lineations and seafloor spreading history of the northwestern Pacific  

Microsoft Academic Search

We have identified Late Jurassic to Early Cretaceous magnetic anomaly lineations (M0 to M35 of the Japanese and Hawaiian lineation sets) and fracture zones in the northwestern Pacific more comprehensively than previous investigators. We fixed 3500 positions of magnetic anomalies identified from magnetic data collected along cruise tracks as well as 151 positions of fracture zones from bathymetric and seismic

Masao Nakanishi; Kensaku Tamaki; Kazuo Kobayashi

1989-01-01

14

Early India-Australia spreading history revealed by newly detected Mesozoic magnetic anomalies in the Perth Abyssal Plain  

NASA Astrophysics Data System (ADS)

seafloor within the Perth Abyssal Plain (PAP), offshore Western Australia, is the only section of crust that directly records the early spreading history between India and Australia during the Mesozoic breakup of Gondwana. However, this early spreading has been poorly constrained due to an absence of data, including marine magnetic anomalies and data constraining the crustal nature of key tectonic features. Here, we present new magnetic anomaly data from the PAP that shows that the crust in the western part of the basin was part of the Indian Plate—the conjugate flank to the oceanic crust immediately offshore the Perth margin, Australia. We identify a sequence of M2 and older anomalies in the west PAP within crust that initially moved with the Indian Plate, formed at intermediate half-spreading rates (35 mm/yr) consistent with the conjugate sequence on the Australian Plate. More speculatively, we reinterpret the youngest anomalies in the east PAP, finding that the M0-age crust initially formed on the Indian Plate was transferred to the Australian Plate by a westward jump or propagation of the spreading ridge shortly after M0 time. Samples dredged from the Gulden Draak and Batavia Knolls (at the western edge of the PAP) reveal that these bathymetric features are continental fragments rather than igneous plateaus related to Broken Ridge. These microcontinents rifted away from Australia with Greater India during initial breakup at ~130 Ma, then rifted from India following the cessation of spreading in the PAP (~101-103 Ma).

Williams, Simon E.; Whittaker, Joanne M.; Granot, Roi; Müller, Dietmar R.

2013-07-01

15

Magnetic anomalies and seafloor spreading rates in the northern South Atlantic.  

PubMed

A geomagnetic profile across the northern South Atlantic yields spreading rates for the last 70 m.y. which vary from 1.6 to 2.0 cm/year. There is evidence for three regional discontinuities in the spreading history of the South Atlantic. PMID:16057239

van Andel, T H; Moore, T C

1970-04-25

16

Opening of the Gulf of Mexico and the Nature of the Crust in the Deep Gulf: New Evidence from Seafloor Spreading Magnetic Anomalies  

NASA Astrophysics Data System (ADS)

The seafloor spreading history in the Gulf of Mexico is poorly constrained due to a lack of recognized seafloor spreading magnetic anomalies, a paucity of deep penetrating seismic data, and absence of drilling to constrain crystalline ocean floor composition and ages. We have identified lineated magnetic anomalies in the eastern Gulf on profiles collected during the Woods Hole R/V Farnella FRNL85-2 cruise that correlate with magnetic chrons M21R to M10. Forward modeling shows that these anomalies formed during creation of weakly magnetized new seafloor in the eastern Gulf between 149-134 Ma at an average half-spreading rate of 3.2 cm/yr. The oldest anomalies are located against stretched continental crust beneath the western Florida shelf on the east and the Yucatan shelf on the west. The youngest anomalies form a juxtaposed conjugate pair that mark the location of an extinct spreading ridge between Yucatan and Florida. Seismic velocities of the crust in the eastern Gulf and the amplitude of the magnetic anomalies are similar to the Iberian and Newfoundland rifted margins, where the early stages of continental breakup were accommodated by exhumation of subcontinental lithosphere rather than creation of new basaltic oceanic crust. We infer that the eastern Gulf of Mexico is underlain by exhumed sub-continental peridotitic mantle intruded by lesser volumes of basaltic igneous rocks generated by decompression melting of the asthenosphere during the late stages of opening of the Gulf. The long wavelength characteristics of the magnetic and gravity fields in the eastern Gulf, as well as the seismic velocity structure of the crust, differ from those in the central and western Gulf, which are more similar to typical magmatic rifted margins. This suggests that the character of the Gulf changes along strike, from a magmatic western portion to an amagmatic eastern portion. Paleogeographic restoration of the lineated magnetic anomaly pattern suggests a 4-phase model for opening of the Gulf. During phase 1 (Early Permian-Late Triassic), Yucatan and associated tectonic blocks that now comprise eastern Mexico were translated eastward from the Pacific realm into positions near the modern western Gulf. During phase 2 (Late Triassic-ca. 160 Ma) Yucatan and the South Florida block were translated southeastward relative to North America, rotating 6.7? counterclockwise about a pole located at 34?N, 74?W. This resulted in ca. 430 km of southeastward extension on the North American coastal plain, 120 km of southward extension on the northern Yucatan shelf, and displacement of the South Florida Block from a pre-rift position on the northwest Florida shelf to its modern position. During phase 3 (ca. 160-149 Ma), Yucatan rotated counterclockwise 46? relative to North America about a pole located at 27.6?N, 84.0?W. Phase 3 may have coincided with seafloor spreading in the central and western Gulf, but predated seafloor spreading in the eastern Gulf. During phase 4 (149-134 Ma), Yucatan moved southwestward relative to North America, rotating counterclockwise 2.2? about a pole located at 17.6?N, 74.2?W and completing opening of the Gulf.

Harry, D. L.; Eskamani, P. K.

2013-12-01

17

Updated interpretation of magnetic anomalies and seafloor spreading stages in the South China Sea - Implications for the Tertiary tectonics of Southeast Asia  

Microsoft Academic Search

An updated interpretation of the magnetic data of the South China Sea is presented, and its implications for the evolution of the South China Sea spreading ridge are discussed. A new identification of magnetic lineations in the basin is described. The kinematic parameters of spreading are then computed from the fit of the magnetic isochrons, and the characteristics of the

Anne Briais; Philippe Patriat; Paul Tapponnier

1993-01-01

18

Pacific plate apparent polar wander between 67 Ma and 44 Ma determined from the analysis of the skewness of both vector and scalar magnetic anomalies due to seafloor spreading  

NASA Astrophysics Data System (ADS)

Pacific plate apparent polar wander between 67 Ma and 44 Ma determined from the analysis of the skewness of both vector and scalar magnetic anomalies due to seafloor spreading The apparent polar wander (APW) path for the Pacific plate is important to the study of Pacific plate motions and their relation to circum-Pacific tectonics. It can be used to discriminate between alternative plate motion circuits, determine the motion of Pacific hotspots relative to the paleomagnetic axis, and test the fixed hotspot hypothesis. The pioneering investigations of Jean Francheteau and his colleagues of Pacific plate APW through the analysis of magnetic anomalies over seamounts helped to demonstrate that the Pacific plate has had substantial northward motion relative to the spin axis since Cretaceous time. We also investigate the APW of the Pacific plate through analysis of magnetic anomalies. Instead of anomalies over seamounts, however, we investigate the skewness (asymmetry) of magnetic anomalies due to seafloor spreading. In prior work, skewness analysis of shipboard magnetic profiles has been used to determine Pacific paleomagnetic poles for chron 25r (57 Ma B.P.; Petronotis et al., 1994), chron 27r to 31n (62 to 69 Ma B.P.; Acton and Gordon, 1991) and chron 32n (72 Ma B.P.; Petronotis and Gordon, 1999). Recently, vector aeromagnetic data from low paleolatitudes, combined with shipboard profiles from low paleolatitudes, were used to determine a paleomagnetic pole with compact confidence limits for anomaly 12r (32 Ma B.P.; Horner-Johnson and Gordon, 2010). Here we use the low-paleolatitude shipboard- and vector aero-magnetic profiles to determine new paleomagnetic poles for the Pacific plate. A new feature of our analysis is a correction for the spreading-rate dependence of anomalous skewness (Koivisto et al. 2011). We estimate anomalous skewness as a function of spreading rate for each anomaly by creating many synthetic profiles using the model of Dyment and Arkani-Hamed (1995) and by experimentally determining the phase shift that causes the resulting synthetic magnetic anomaly to best match a profile produced from a "standard" model for anomalies due to seafloor spreading that assumes simple vertical reversal boundaries (Boswell et al., 2011). Thus, we solve for only two adjustable parameters, the latitude and the longitude of the paleomagnetic pole. We focus on preliminary results from the skewness of crossings of magnetic anomalies 20r (44 Ma B.P.), 24r (55 Ma B.P.) and 30n/31n (67 Ma B.P.) between the Galapagos and Murray fracture zones on the Pacific plate. We choose this region of the Pacific plate because numerical experiments, similar to those conducted by Acton and Gordon (1991), show that these data contribute much more information about the location of paleomagnetic poles than do those from any other region of similar size. Implications for Pacific plate tectonics, motion between hotspots, and true polar wander will be discussed.

Zheng, L.; Gordon, R. G.; Horner-Johnson, B. C.

2011-12-01

19

Magnetic Anomaly Lineations in the Gulf of Aden  

NASA Astrophysics Data System (ADS)

We present the magnetic anomaly lineations in the Gulf of Aden to expose the seafloor spreading history. The Gulf of Aden is a young ocean basin formed by the rifting of Arabia Plate away from Somalia Plate. The Arabian plate moves away from Somalia Plate in an NE direction, at a rate of about 2 cm/yr. The rifting started from Oligocene (Bosworth et al., 2005). Seafloor spreading started at about 20 Ma in the eastern part of the Gulf of Aden (Fournier et al., 2010) and propagated westward into the Arabia-Africa continent (Manighetti et al., 1997). It reached the Afar hotspot area about 10 Ma (Audin et al., 2001). The spreading system continues to interact with the hotspot up to the present. Tamsett and Searle (1988) exposed that strike of segmentations of the spreading centers in the Gulf of Aden is NW-SE, although the trend of the spreading system is ENE. We examined magnetic anomaly data collected in the cruises by R/V L'Atalante in 1995 and R/V Hakuho-maru from 2000 to 2001 as well as those collected in other cruises. Elongated negative magnetic anomalies, which amplitude are more than 500 nT, are observed over the spreading centers. Most of the elongated anomalies are parallel with the spreading centers. The elongated magnetic anomalies west of 46 30'E have an E-W trend around the spreading centers. Several discontinuities in the magnetic anomaly contour map illustrate the position of the fracture zones concealed by sediments. Most of magnetic anomaly lineations east of 46 30'E have an N60-65 W strike. Our identification of magnetic anomaly lineations indicates a symmetric seafloor spreading with a spreading rate of about 1.0 cm/yr, although Leroy et al. (2004) showed an asymmetric seafloor spreading of the Sheba Ridge, east of our study area. The kinematics of the Arabia plate changed about 5 Ma, but our results did not show any coeval change in spreading rates of the spreading system in the Gulf of Aden.

Noguchi, Y.; Nakanishi, M.; Tamaki, K.; Fujimoto, H.; Huchon, P.; Leroy, S.; Styles, P.

2012-12-01

20

Spreading rate dependence of gravity anomalies along oceanic transform faults.  

PubMed

Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis. Here we present a systematic study of the residual mantle Bouguer gravity anomaly of 19 oceanic transform faults that reveals a strong correlation between gravity signature and spreading rate. Previous studies have shown that slow-slipping transform faults are marked by more positive gravity anomalies than their adjacent ridge segments, but our analysis reveals that intermediate and fast-slipping transform faults exhibit more negative gravity anomalies than their adjacent ridge segments. This finding indicates that there is a mass deficit at intermediate- and fast-slipping transform faults, which could reflect increased rock porosity, serpentinization of mantle peridotite, and/or crustal thickening. The most negative anomalies correspond to topographic highs flanking the transform faults, rather than to transform troughs (where deformation is probably focused and porosity and alteration are expected to be greatest), indicating that crustal thickening could be an important contributor to the negative gravity anomalies observed. This finding in turn suggests that three-dimensional magma accretion may occur near intermediate- and fast-slipping transform faults. PMID:17625563

Gregg, Patricia M; Lin, Jian; Behn, Mark D; Montési, Laurent G J

2007-07-12

21

Modelling Mars' Magnetic Anomalies  

Microsoft Academic Search

An internal potential function was derived up to n=90 to improve upon an ongoing study of the crustal structure of the Martian magnetic field. The data included MGS magnetic observations below 200 km altitude taken during the two aerobraking phases (AB1 and AB2), the Science Phase Orbits (SPO), as well as higher altitude (370--440 km) data taken on the nightside

B. B. Ferguson; J. C. Cain; D. T. Mozzoni

2001-01-01

22

Equatorial Pacific magnetic anomalies identified from vector aeromagnetic data  

NASA Astrophysics Data System (ADS)

It has long been challenging to identify magnetic anomalies due to seafloor spreading in the equatorial Pacific. Here we show that Project Magnet vector aeromagnetic profiles from the equatorial Pacific record magnetic anomalies due to seafloor spreading much more clearly than do shipboard total intensity profiles. The anomalies are reliably recorded at wavelengths between ~20 and ~150 km in the vertical and east components, which have high coherence, differ in phase by ~90°, and resemble synthetic magnetic anomaly profiles. From an analysis of a single near-equatorial vector aeromagnetic profile we infer that the magnetic lineations strike ~8°-10° counter-clockwise of north and that magnetic anomaly 7 is located ~400 km further east than previously estimated. The newly estimated location of anomaly 6 is consistent with a tentative estimate by Wilson from a low-amplitude shipboard magnetic profile. Because the skewness of profiles over the seafloor formed near the paleoequator changes rapidly with paleolatitude and paleostrike, a skewness analysis of these data may provide useful bounds on the location of Pacific Plate paleomagnetic poles, and indicate that this seafloor has had little, if any, northward motion relative to the spin axis since it formed.

Horner-Johnson, Benjamin C.; Gordon, Richard G.

2003-11-01

23

Interpretation of magnetic anomalies over the Grenada Basin  

NASA Astrophysics Data System (ADS)

The Grenada Basin is a back arc basin located near the eastern border of the Caribbean Plate. The basin is bounded on the west by the north-south trending Aves Ridge (a remnant island arc) and on the east by the active Lesser Antilles island arc. Although this physiography suggests that east-west extension formed the basin, magnetic anomalies over the basin exhibit predominantly east-west trends. If the observed magnetic anomalies over the basin are produced by seafloor spreading, then the orientation of extension is complex. Extension in back arc basins is roughly normal to the trench, although some basins exhibit oblique extension. Present models for the formation of the Grenada Basin vary from north-south extension through northeast-southwest extension to east-west extension. An interpretation of magnetic anomalies over the Grenada Basin supports basin development by nearly east-west extension. Low amplitude magnetic anomaly trends subparallel to the island arc magnetic anomaly trends over the southern part of the basin and the results of forward three-dimensional (3-D) magnetic modeling are consistent with this conclusion. Late Cenozoic tectonic movements may have been responsible for disrupting the magnetic signature over the northern part of the basin. On the basis of our 3-D analysis, we attribute the prominent east-west trending anomalies of the Grenada Basin to fracture zones formed during seafloor spreading at low latitude. This east-west trend is not interpreted as indicating north-south extension of the basin.

Bird, Dale E.; Hall, Stuart A.; Casey, John F.; Millegan, Patrick S.

1993-10-01

24

Northern east Pacific rise: Magnetic anomaly and bathymetric framework  

SciTech Connect

The oceanic crust in the eastern Pacific between 7/sup 0/N and 30/sup 0/N and east of 127/sup 0/W contains a fairly complete history of the spreading centers associated with the East Pacific Rise since 25 m.y. B.P. (late Oligocene). In this paper, we have summarized the seafloor spreading magnetic-anomaly data and the bathymetric data that reflect the record of this technique history. The well-defined magnetic lineations north of the Clarion fracture zone, in the mouth of the Gulf of California, and on the east flank of the East Pacific Rise (EPR) are carefully examined and used to provide a guide for interpreting the spreading pattern between the Clarion and Clipperton fracture zones, southward of the Rivera fracture zone over the Mathematician Ridge, and over the entire EPR east of the Mathematician Ridge between the Rivera and Siqueiros fracture zones. The bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas. The fracture zone bathymetry and the seafloor spreading magnetc lineations on the EPR south of the Rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations. All these data provide a good record of the plate reorganizations in the middle Miocene at magnetic anomaly 5A time (12.5 to 11 m.y. B.P.), in the late Miocene at a magnetic anomaly 3'--4 time (6.5 m.y. B.P.), and in the Pliocene at magnetic anomaly 2'--3 time (3.5 m.y.B.P.). Several abandoned spreading centers, including the Mathematician Ridge, were left behind as a result of these reorganizations. The Mathematician Ridge is shown to be a set of ridges and trough whose origin is related to the tectonics activity associated with each of the above mentioned reorganizations since anomaly 5A.

Klitgord, K.D.; Mammerickx, J.

1982-08-10

25

An impactor origin for lunar magnetic anomalies.  

PubMed

The Moon possesses strong magnetic anomalies that are enigmatic given the weak magnetism of lunar rocks. We show that the most prominent grouping of anomalies can be explained by highly magnetic extralunar materials from the projectile that formed the largest and oldest impact crater on the Moon: the South Pole-Aitken basin. The distribution of projectile materials from a model oblique impact coincides with the distribution of magnetic anomalies surrounding this basin, and the magnetic properties of these materials can account for the intensity of the observed anomalies if they were magnetized in a core dynamo field. Distal ejecta from this event can explain the origin of isolated magnetic anomalies far from this basin. PMID:22403388

Wieczorek, Mark A; Weiss, Benjamin P; Stewart, Sarah T

2012-03-01

26

An Impactor Origin for Lunar Magnetic Anomalies  

NASA Astrophysics Data System (ADS)

The Moon possesses strong magnetic anomalies that are enigmatic given the weak magnetism of lunar rocks. We show that the most prominent grouping of anomalies can be explained by highly magnetic extralunar materials from the projectile that formed the largest and oldest impact crater on the Moon: the South Pole-Aitken basin. The distribution of projectile materials from a model oblique impact coincides with the distribution of magnetic anomalies surrounding this basin, and the magnetic properties of these materials can account for the intensity of the observed anomalies if they were magnetized in a core dynamo field. Distal ejecta from this event can explain the origin of isolated magnetic anomalies far from this basin.

Wieczorek, Mark A.; Weiss, Benjamin P.; Stewart, Sarah T.

2012-03-01

27

Regional magnetic anomaly constraints on continental rifting  

NASA Technical Reports Server (NTRS)

Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.

Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

1985-01-01

28

The magnetic anomaly of the Ivreazone  

NASA Technical Reports Server (NTRS)

A magnetic field survey was made in the Ivreazone in 1969/70. The results were: significant anomaly of the vertical intensity is found. It follows the basic main part of the Ivrea-Verbano zone and continues to the south. The width of the anomaly is about 10 km, the maximum measures about +800 gamma. The model interpretation shows that possibly the anomaly belongs to an amphibolitic body, which in connection with the Ivrea-body was found by deep seismic sounding. Therefore, the magnetic anomaly provides further evidence for the conception that the Ivrea-body has to be regarded as a chip of earthmantle material pushed upward by tectonic processes.

Albert, G.

1979-01-01

29

Gulf of Aden axial magnetic anomaly and the Curie temperature isotherm  

Microsoft Academic Search

The main features of magnetic anomalies over ocean ridges have been explained1 as a corollary of seafloor spreading and geomagnetic reversals. Oceanic crust is formed in a narrow region, becoming magnetized in the direction of the Earth's magnetic field as its temperature falls through the Curie point of the magnetic minerals present. The Gulf of Aden was one of the

D. Tamsett; R. W. Girdler

1982-01-01

30

Reduction of satellite magnetic anomaly data  

NASA Technical Reports Server (NTRS)

Analysis of global magnetic anomaly maps derived from satellite data is facilitated by inversion to the equivalent magnetization in a constant thickness magnetic crust or, equivalently, by reduction to the pole. Previous inversions have proven unstable near the geomagnetic equator. The instability results from magnetic moment distributions which are admissible in the inversion solution but which make only small contribution to the computed values of anomaly field. Their admissibility in the solution could result from noisy or incomplete data or from small poorly resolved anomalies. The resulting magnetic moments are unrealistically large and oscillatory. Application of the method of principal components (e.g. eigenvalue decomposition and selective elimination of less significant eigenvectors) is proposed as a way of overcoming the instability and the method is demonstrated by applying it to the region around the Bangui anomaly in Central Africa.

Slud, E. V.; Smith, P. J.; Langel, R. A.

1984-01-01

31

Sources of Near Side Lunar Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

Lunar Prospector magnetometer data has been used to identify a number of nearside magnetic anomalies. Some of the features identified appear to correlate with impact ejecta, supporting a basin ejecta origin to the nearside anomalies. Additional information is contained in the original extended abstract.

Richmond, Nicola C.; Hood, Lon L.; Halekas, J. S.; Mitchell, D. L.; Lin, R. P.; Acuna, M. H.; Binder, A.B.

2002-01-01

32

Understanding Magnetic Anomalies and Their Significance.  

ERIC Educational Resources Information Center

Describes a laboratory exercise testing the Vine-Matthews-Morley hypothesis of plate tectonics. Includes 14 questions with explanations using graphs and charts. Provides a historical account of the current plate tectonic and magnetic anomaly theory. (MVL)

Shea, James H.

1988-01-01

33

Interpretation of satellite elevation magnetic anomalies  

NASA Technical Reports Server (NTRS)

The present discussion is based on a study of the magnetic field data obtained with the aid of the magnetic field satellite Magsat, deployed in October 1979, over most of the earth during a 7.5-month mission. Inversions using spherical harmonic coefficients are considered along with the inversion of residual fields. In order to perform the correct operation, it is necessary to add on to the source function produced by the inversion process a magnetization function which has no external field. Such a function is known as an annihilator. The use of the annihilator for Pacific Ocean anomalies is discussed. Attention is given to models of oceanic crustal magnetization, and continental long-wavelength anomalies. It is found that in continental regions the annihilator is also useful if induced magnetizations are thought to be responsible for the long-wavelength anomaly.

Harrison, C. G. A.; Carle, H. M.; Hayling, K. L.

1986-01-01

34

The mineralogy of global magnetic anomalies  

NASA Technical Reports Server (NTRS)

Experimental and analytical data on magnetic mineralogy was provided as an aid to the interpretation of magnetic anomaly maps. An integrated program, ranging from the chemistry of materials from 100 or more km depth within the Earth, to an examination of the MAGSAT anomaly maps at about 400 km above the Earth's surface, was undertaken. Within this framework, a detailed picture of the pertinent mineralogical and magnetic relationships for the region of West Africa was provided. Efforts were directed toward: (1) examining the geochemistry, mineralogy, magnetic properties, and phases relations of magnetic oxides and metal alloys in rocks demonstrated to have originated in the lower crust of upper mantle, (2) examining the assumption that these rocks portray the nature of their source regions; and (3) examining the regional geology, tectonics, gravity field and the MAGSAT anomaly maps for West Africa.

Haggerty, S. E. (principal investigator)

1984-01-01

35

Continental magnetic anomaly constraints on continental reconstruction  

NASA Technical Reports Server (NTRS)

Crustal magnetic anomalies mapped by the MAGSAT satellite for North and South America, Europe, Africa, India, Australia and Antarctica and adjacent marine areas were adjusted to a common elevation of 400 km and differentially reduced to the radial pole of intensity 60,000 nT. These radially polarized anomalies are normalized for differential inclination, declination and intensity effects of the geomagnetic field, so that in principle they directly reflected the geometric and magnetic polarization attributes of sources which include regional petrologic variations of the crust and upper mantle, and crustal thickness and thermal perturbations. Continental anomalies demonstrate remarkably detailed correlation of regional magnetic sources across rifted margins when plotted on a reconstruction of Pangea. Accordingly, they suggest further fundamental constraints on the geologic evolution of the continents and their reconstructions.

Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

1985-01-01

36

Paleomagnetic Poles From the Skewness of Marine Magnetic Anomalies  

NASA Astrophysics Data System (ADS)

The skewness of marine magnetic anomalies due to seafloor spreading depends strongly on the direction of the paleomagnetic field as oceanic lithosphere is created and cooled. Thus, anomaly skewness can be used to estimate paleoomagnetic poles and is attractive, in part, because the ages of the poles can easily be related to the geomagnetic polarity time scale. Here we review methods for determining paleomagnetic poles from anomaly skewness and examine the accuracy of the poles. A concern has been the influence of ``anomalous" skewness, recognized in pioneering studies of anomaly skewness (Cande 1976). Anomalous skewness can be thought of as a systematic difference between observed skewness and that expected from simple models of the marine magnetic source that assume vertical boundaries between reversals. Anomalous skewness is now understood to be the consequence of non-vertical curving reversal boundaries expected from the thermal and magmatic evolution of oceanic lithosphere (Dyment & Arkani-Hamed 1995). Anomalous skewness depends on spreading rate if spreading is slow, but is independent of spreading rate if spreading is fast (Dyment & Arkani-Hamed 1995). The profiles we examine for paleomagnetic analysis dominantly record fast spreading and thus we are able to approximate anomalous skewness as being independent of spreading rate. We can therefore treat anomalous skewness as a third adjustable parameter, along with pole latitude and pole longitude, when determining paleomagnetic poles from skewness estimates. At any one crossing of a magnetic anomaly, local effects could cause the estimate of the paleomagnetic direction to be in error. Aside from anomalous skewness, however, errors in skewness estimates are expected to be uncorrelated from site to site except at exceptionally closely spaced sites. Thus we can treat misfits as independent random errors and reduce the statistical error in the pole position by obtaining many estimates of skewness from widely separated sites. The plate geometry of the Pacific plate throughout much of Late Cretaceous and Tertiary time, in particular the long north-south-striking paleo-East Pacific Rise, provides a nearly ideal geometry for recording critical information on the location of Pacific plate paleomagnetic poles. Moreover, a large skewness gradient with paleolatitude is expected, which helps to limit the location and, to a lesser degree, the strike of the paleoequator and thus strongly constrains the pole. If the accuracy of all skewness estimates is uniform, estimates of skewness near the paleo-equator can be shown to contain much more information than those from higher paleo-latitudes. On total-intensity magnetic profiles the amplitudes of anomalies near the paleo-equator are very low and likely have higher than average uncertainties. On vector aeromagnetic profiles, however, clear anomalies are recorded near the paleo-equator and provide strong constraints on the pole position. The assumptions made in determining paleomagnetic poles from skewness are subject to several critical tests including comparisons of anomalous skewness estimated from the single-plate method with those determined from cross-ridge analysis, comparisons with other skewness poles of similar age, and comparisons with poles determined from other types of paleomagnetic data. We present several such tests and show that the skewness results pass all these tests of consistency. Thus, there are many reasons to believe that poles determined from skewness give unbiased and accurate paleomagnetic poles.

Horner-Johnson, B. C.; Gordon, R. G.

2005-12-01

37

New magnetic anomaly map of the East Antarctic continental margin  

NASA Astrophysics Data System (ADS)

Marine magnetic survey coverage of the southern part of Indian Ocean is to a certain extent limited for defining the magnetic pattern of the continental margin of East Antarctica. The USA research vessels collected the bulk of the marine magnetic data in the beginning of 1960's. During the succeeding years Australian, German, Japanese, Russian and other international scientific programs made major contributions to the network of marine magnetic data. Since the beginning of new century only two nations (Russian and Australian) have acquired the marine magnetic data in the southern part of Indian Ocean. The marine surveys in the Cosmonaut Sea, the western part of the Cooperation Sea in the Davis and Mawson Seas were accomplished by the PMGRE in 2000-2009 field seasons. The marine magnetic data collected during two seasons (2001-2002) within the AASOPP Project which was established in early 2000 to define the outer limits of the continental shelf offshore of the Australian Antarctic Territory (AAT) covered the full length of the AAT from 40OE to 160OE. The new magnetic anomaly map of the East Antarctic continental margin incorporates all available data acquired by the international community since the IGY 1957-58 through to 2009. Results of the compilation do not radically alter recent models describing first-order motions between the Antarctic, Australian and Indian plates, but they help to resolve uncertainties in early break-up history of opening between these plates. The timing and direction of early seafloor spreading in the area off the Antarctic margin, once conjugate to part of the Southern Greater Indian margin and to Australian margin, along the largely unknown region of the Enderby Basin, Davis Sea and Mawson Sea has been analyzed by many authors using different data sets. It is highly likely that spreading in the Enderby Basin occurred around the same time as the well documented M-sequence (anomalies M10 to M0) off the Perth Basin, Western Australia (Powell et al. 1988). The history of the early spreading is complicated further by the likelihood of one or several ridge jumps in which most early seafloor crust was transferred to the Antarctic plate and the Elan Bank micro-continent was isolated from the Indian continent (Muller et al. 2001). Additionally, a large amount of the seafloor crust is now probably overprinted by igneous activity associated with the Kerguelen Plume, which began forming the Kerguelen LIP from about 120-110 Ma. However all available results of interpretations do not match to the magnetic anomaly pattern which can be distinguished by the newly compiled map. Our observations suggest that this is especially correct to the Enderby Basin and to lesser degree for the region that was conjugate to Australia. The prominent magnetic anomaly boundary signal and sharp basement step correlated with the MacRobertson Coast Anomaly or the Enderby Basin Anomaly (Golynsky et al., 2007) is not observed elsewhere in the Enderby Basin, Princess Elizabeth Trough or Davis Sea. In the central Enderby Basin there some evidences for an abandoned ‘fossil' spreading centre that might continue to the west of the Kerguelen Plateau, east of Gunnerus Ridge. The estimated timing of its extinction corresponding to the early surface expression of the Kerguelen Plume at the Southern Kerguelen Plateau around 120 Ma and the subsequent formation of the Elan Bank microcontinent. Alternatively, the ridge jump occurred only in the central Enderby basin, due to the proximity of the Kerguelen plateau, whereas seafloor spreading continued in the western Enderby basin and conjugate south of Sri Lanka basin.

Golynsky, Alexander; Ivanov, Sergey; Kazankov, Andrey

2010-05-01

38

Magnetic signatures for satellite anomalies  

NASA Astrophysics Data System (ADS)

A study of the electrostatic discharge event records of a geosynchronous communications satellite from April 1983 to December 1987 has uncovered similarities with the yearly trends of magnetic activity in the declining portion of the 11-year solar cycle, with maxima around the equinoxes and minima during solstitial months. Detailed comparisons with magnetograms obtained near the satellite's footprint, at Yellowknife, Canada, indicate that magnetic storms, substorms, and bays offer magnetic signatures for the discharge events; substorms are noted to play a dominant role. The occurrences of electrostatic discharge relative to the magnetic perturbations implies a variable time delay in the occurrence after initiation of the magnetic disturbance.

Lam, Hing-Lan; Hruska, Jaroslava

1991-02-01

39

Geological reasons for change in intensity of linear magnetic anomalies of the Kursk magnetic anomaly  

NASA Technical Reports Server (NTRS)

The geological reasons for fluctuations in the anomalous field intensity along the polar axes were examined. The Kursk magnetic anomaly is used as the basis for the study. A geological-geophysical section was constructed which used the results of the interpretation of gravimagnetic anomalies.

Zhavoronkin, I. A.; Kopayev, V. V.

1985-01-01

40

Explanation of the nature of stripe magnetic anomalies without inversions  

NASA Astrophysics Data System (ADS)

Several scientists of different branches express doubts on the validity of the Earth's geomagnetic field inversions hypothesis [Vine F.J., Matthews D.H, 1963]. Presently a lot of information allows to link the appearance of stripe magnetic anomalies of both signs with the spreading fracture structure (horizontal segmentation of intrusions and sills, breaks in the strong crust, vertical movements of blocks), remagnetization near the borders of the blocks, hydrothermal activity. Non-inversion mechanism of origin of linear stripe magnetic anomalies in the oceans could be explained as follows. Ascending asthenospheric flows have been enrich with volatile components, become thinner, pressure on the walls of the lithospheric plates grows and part them. When it approaches the surface: - horizontal tensile pressure grows, - lithostatic pressure in the vertical column of rocks decreases, - crust strong upper layer flakes away and begins to move horizontally. It is important that thin magmatic and magnetic layers (further layers) of the newly formed strong upper crust move away from the ridge axis. The structure of such layers forms by horizontal stresses and so consist of the hills and depressions sequences or updiped and downdiped blocks heaped each other. This layer is the main source of the magnetic field and cannot be approximated by a horizontal homogeneous plate as it proved before. In the mid-ocean ridges (MOR) the folding periods of layer depend on its thickness and rigidity and horizontal velocity of spreading. The higher velocity - the longer periods of roughness are and contrary. Same pattern is observed for the stripe magnetic anomalies distribution. The magnetic field of the MOR forms there due to young lava flows which get thermoremanent magnetization according the current direction of geomagnetic field. Partial destruction of the relief, overlaying and creation of the new shapes occur when new magma penetrates the moved magnetic layer. The process entails partial flux reversal of rocks with the decrease of total magnetic field amplitude. The complicated magnetic field with alternating-sign linear anomalies appears. Taking into account limited vertical thickness of the oceanic magnetic layer, the false effect of negative magnetization would appear even with short shifts of the blocks. Conclusions. Theoretical calculations and analysis 'in situ' data prove that observation of magnetic anomalies of both signs in MOR areas are connected with fracturing tectonics, horizontal segmentation of sills, faults in the crust, vertical movements of blocks, self remagnetization near its margins. At the present time geological and geophysical facts lead to revision of some facts of tectonic theory and rejection of the old hypothesis connected with simplified ideas of the magnetic layer regularity and cyclical nature of magma flows. The main task of this work is to return scientists to the initial point of stripe magnetic anomalies discovery and general revision of the oceanic crust's structure without the limitations of Vine-Matthews-Morley hypothesis. Please fill in your abstract text.

Melikhov, Vjacheslav; Lygin, Ivan; Sokolova, Tatiana

2014-05-01

41

Equivalent magnetization over the World's Ocean and the World Digital Magnetic Anomaly Map  

NASA Astrophysics Data System (ADS)

As a by-product of our recent work to build a candidate model over the oceans for the second version of the World Digital Magnetic Anomaly Map (WDMAM), we derived global distributions of the equivalent magnetization in oceanic domains. In a first step, we use classic point source forward modeling on a spherical Earth to build a forward model of the marine magnetic anomalies at sea-surface. We estimate magnetization vectors using the age map of the ocean floor, the relative plate motions, the apparent polar wander path for Africa, and a geomagnetic reversal time scale. We assume two possible magnetized source geometry, involving both a 1 km-thick layer bearing a 10 A/m magnetization either on a regular spherical shell with a constant, 5 km-deep, bathymetry (simple geometry) or following the topography of the oceanic basement as defined by the bathymetry and sedimentary thickness (realistic geometry). Adding a present-day geomagnetic field model allows the computation of our initial magnetic anomaly model. In a second step, we adjust this model to the existing marine magnetic anomaly data, in order to make it consistent with these data. To do so, we extract synthetic magnetic along the ship tracks for which real data are available and we compare quantitatively the measured and computed anomalies on 100, 200 or 400 km-long sliding windows (depending the spreading rate). Among the possible comparison criteria, we discard the maximal range - too dependent on local values - and the correlation and coherency - the geographical adjustment between model and data being not accurate enough - to favor the standard deviation around the mean value. The ratio between the standard deviations of data and model on each sliding window represent an estimate of the magnetization ratio causing the anomalies, which we interpolate to adjust the initial magnetic anomaly model to the data and therefore compute a final model to be included in our WDMAM candidate over the oceanic regions lacking data. The above ratio, after division by the magnetization of 10 A/m used in the model, represents an estimate of the equivalent magnetization under the considered magnetized source geometry. The resulting distributions of equivalent magnetization are further discussed in terms of mid-ocean ridges, presence of hotspots and oceanic plateaus, and the age of the oceanic lithosphere. Global marine magnetic data sets and models represent a useful tool to assess first order magnetic properties of the oceanic lithosphere.

Dyment, Jerome; Choi, Yujin; Hamoudi, Mohamed; Thébault, Erwan; Quesnel, Yoann; Roest, Walter; Lesur, Vincent

2014-05-01

42

Magnetic anomalies northeast of Cape Adare, northern Victoria Land (Antarctica), and their relation to onshore structures  

USGS Publications Warehouse

An aeromagnetic survey was flown over the offshore region northeast of Cape Adare and the magnetic anomalies compared to onshore structures between Pennell Coast and Tucker Glacier. The magnetic anomalies show two nearly orthogonal major trends. NNW-SSE trending anomalies northeast of Cape Adare represent seafloor spreading within the Adare Trough. A connection of these anomalies to the Northern Basin of the Ross Sea is not clear. Onshore faults are closely aligned to offshore anomalies. Main trends are NW-SE to NNW-SSE and NE-SW to NNESSW. NNW-SSE oriented dextral-transtensional to extensional faults parallel the Adare Peninsula and Adare Trough anomalies. NE-SW trending normal faults appear to segment the main Hallett volcanic bodies.

Damaske, D.; Läufer, A.L.; Goldmann, F.; Möller, H.-D.; Lisker, F.

2007-01-01

43

Paleo-Pole Positions from Martian Magnetic Anomaly Data  

NASA Technical Reports Server (NTRS)

Magnetic component anomaly maps were made from five mapping cycles of the Mars Global Surveyor s magnetometer data. Our goal was to find and isolate positive and negative anomaly pairs which would indicate magnetization of a single source body. From these anomalies we could compute the direction of the magnetizing vector and subsequently the location of the magnetic pole existing at the time of magnetization. We found nine suitable anomaly pairs and from these we computed four North and 3 South poles with two at approximately 60 degrees north latitude. These results suggest that during the existence of the Martian main magnetic field it experienced several reversals.

Taylor, Patrick T.; Frawley, James J.

2003-01-01

44

Crustal Magnetic Field Anomalies and Global Tectonics  

NASA Astrophysics Data System (ADS)

A wide variety of evidence suggests that the ruling isochron (geomagnetic polarity versus age) hypothesis of marine magnetic lineations has no merit - undermining therefore one of the central tenets of plate tectonics. Instead, variable induction by the ambient geomagnetic field is likely to be the principal agent for mega-scale crustal magnetic features - in both oceanic and continental settings. This revitalizes the fault-controlled susceptibility-contrast model of marine magnetic lineations, originally proposed in the late 1960s. Thus, the marine magnetic 'striping' may be ascribed to tectonic shearing and related, but variable, disintegration of the original iron-oxide mineralogy, having developed primarily along one of the two pan-global sets of orthogonal fractures and faults. In this way, fault zones (having the more advanced mineral alteration) would be characterized by relatively low susceptibility, while more moderately affected crustal sections (located between principal fault zones) would be likely to have less altered oxide mineralogy and therefore higher magnetic susceptibility. On this basis, induction by the present geomagnetic field is likely to produce oscillating magnetic field anomalies with axis along the principal shear grain. The modus operandi of the alternative magneto-tectonic interpretation is inertia-driven wrenching of the global Alpine age palaeo-lithosphere - triggered by changes in Earth's rotation. Increasing sub-crustal loss to the upper mantle during the Upper Mesozoic had left the ensuing Alpine Earth in a tectonically unstable state. Thus, sub-crustal eclogitization and associated gravity-driven delamination to the upper mantle led to a certain degree of planetary acceleration which in turn gave rise to latitude-dependent, westward inertial wrenching of the global palaeo-lithosphere. During this process, 1) the thin and mechanically fragile oceanic crust were deformed into a new type of broad fold belts, and 2) the continents were subjected to relative 'in situ' rotations (mostly moderate). Examples of marine magnetic lineations with landward continuation along prominent transcurrent fault zones, and the fact that striped marine magnetic anomalies may display orthogonal networks - concordant with the ubiquitous system of rectilinear fractures, faults and joints - corroborate the wrench tectonic interpretation of crustal field anomalies.

Storetvedt, Karsten

2014-05-01

45

Charge particle deflection by lunar magnetic anomalies  

NASA Astrophysics Data System (ADS)

Ever since the Apollo era, a question has remained as to the origin of the lunar swirls (high albedo regions coincident with the regions of surface magnetization). Different processes have been proposed for their origin. In this work we test the idea that the lunar swirls have a higher albedo relative to surrounding regions because they deflect incoming solar wind particles that can darken, or weather, the surface. Particle tracking is used to estimate the influence of four lunar magnetic anomalies on incoming solar wind. The regions investigated include Mare Ingenii, Gerasimovich, Renier Gamma and Northwest of Apollo. Both ions and electrons are tracked as they interact with the anomalous magnetic field and impact maps are calculated. The impact maps are then compared to optical observations and comparisons are made between the maxima and minima in surface fluxes and the high and low albedo regions.

Harnett, E. M.; Kramer, G. Y.

2013-12-01

46

Rock magnetic investigation of possible sources of the Bangui magnetic anomaly1 , M., Quesnel2*  

E-print Network

Rock magnetic investigation of possible sources of the Bangui magnetic anomaly1 2 Ouabego1,2 , M 44297159514 Email: quesnel@cerege.fr15 16 Abstract17 The Bangui Magnetic Anomaly (BMA) is the largest lithospheric magnetic field anomaly on18 Earth at low latitudes. Previous studies investigated its geological

Boyer, Edmond

47

Magnetic and Bathymetrie Data Bearing on Sea-Floor Spreading North of Iceland  

Microsoft Academic Search

rates of 1.0 cm\\/yr normal to the ridge crests between Iceland and the Jan Mayen fracture zone and on Mohns ridge. The trans-Arctic extension of the ridge is characterized by anomalously great water depths and spreading rates probably I cm\\/yr or less. The magnetic anomaly signatures reveal exceptionally low amplitudes compared to other ridges, even when these factors are taken

Peter R. Vogt; Ned A. Ostenso; G. Leonard Johnson

1970-01-01

48

Improving the geological interpretation of magnetic and gravity satellite anomalies  

NASA Technical Reports Server (NTRS)

Current limitations in the quantitative interpretation of satellite-elevation geopotential field data and magnetic anomaly data were investigated along with techniques to overcome them. A major result was the preparation of an improved scalar magnetic anomaly map of South America and adjacent marine areas directly from the original MAGSAT data. In addition, comparisons of South American and Euro-African data show a strong correlation of anomalies along the Atlantic rifted margins of the continents.

Hinze, W. J.; Braile, L. W. (principal investigators); Vonfrese, R. R. B.

1985-01-01

49

Anomalies and Transport Coefficients: The Chiral Gravito-Magnetic Effect  

E-print Network

Axial anomalies give rise to interesting new transport phenomena such as the "chiral magnetic effect". We discuss how the associated transport coefficients can be studied via Kubo formulas at weak and strong coupling, the latter via gauge gravity duality. We argue for a new "chiral gravito-magnetic" (or vortical) effect sensitive to the presence of mixed gauge-gravitational anomalies.

Karl Landsteiner; Eugenio Megias; Francisco Pena-Benitez

2011-10-17

50

Anomalies and Transport Coefficients: The Chiral Gravito-Magnetic Effect  

E-print Network

Axial anomalies give rise to interesting new transport phenomena such as the "chiral magnetic effect". We discuss how the associated transport coefficients can be studied via Kubo formulas at weak and strong coupling, the latter via gauge gravity duality. We argue for a new "chiral gravito-magnetic" (or vortical) effect sensitive to the presence of mixed gauge-gravitational anomalies.

Landsteiner, Karl; Pena-Benitez, Francisco

2011-01-01

51

A 65 Ma palaeomagnetic pole for the Pacific plate from the skewness of magnetic anomalies 27r-31.  

NASA Astrophysics Data System (ADS)

The authors use the skewness of seafloor-spreading magnetic anomalies 27r-31 to determine a revised Late Maastrichtian - early Palaeocene palaeomagnetic pole for the Pacific plate. They used numerical experiments to estimate the potential information in magnetic profiles that had not been previously analysed for skeweness information.

Acton, G. D.; Gordon, R. G.

1991-08-01

52

The mineralogy of global magnetic anomalies  

NASA Technical Reports Server (NTRS)

Progress is reported in developing predictive abilities to evaluate the potential stabilities of magnetic minerals in the Earth crust and mantle by: (1) computing oxidation state profiling as a function of temperature and pressure; (2) compiling data on basalts to establish validity of the oxidation state profiles; (3) determining Fe-Ni alloys in association with magnetitie as a function of temperature and oxidation state; and (4) acquiring large chemical data banks on the mineral ilmenite which decomposes to mineral spinel in the presence of high sulfur or carbonate environments in the lower crust upper mantle. In addition to acquiring these data which are related to constraining Curie isotherm depths, an excellent correlation was found between MAGSAT anomaly data and the geology of West Africa.

Haggerty, S. E. (principal investigator)

1981-01-01

53

An alternative interpretation of the Cayman trough evolution from a reidentification of magnetic anomalies  

NASA Astrophysics Data System (ADS)

Magnetic data were collected during the Wilkes (1973) and Seacarib II (1987) cruises to the Cayman trough. A new interpretation of magnetic data is carried out. An isochron pattern is drawn up from our anomaly identifications. An early Eocene age (49Ma, Ypresian) for Cayman trough opening is proposed instead of the late Oligocene or middle Eocene ages suggested by previous studies. Our plate tectonic reconstruction is simpler and fits the on-land geology (Jamaica and Cuba) and the tectonics. Our reconstruction shows a southward propagation of the spreading centre between magnetic anomalies 8 and 6 (26 and 20Ma). The trough width increases by 30km in this period. The southward propagation of the Cayman spreading centre from the Middle Oligocene to the Early Miocene induced the development of the restraining bend of the Swan Islands, the formation of a 1km high scarp on the eastern trace of the Cayman trough transform fault (Walton fault) and the formation of a pull-apart basin (Hendrix pull-apart). Magnetic anomalies and magnetization maps give information about the deformation and the rocks. The proposed evolutionary model of the Cayman trough from the inception of seafloor spreading to the present configuration is presented in relation to the tectonic escape of the northern boundary of the Caribbean plate from the Maastrichtian to the Present.

Leroy, S.; Mauffret, A.; Patriat, P.; Mercier de Lépinay, B.

2000-06-01

54

Magnetic anomalies and tectonic fabric of marginal basins North of New Zealand  

SciTech Connect

Detailed airborne magnetic studies conducted over the region of the S. W. Pacific marginal basins extending from the Solomon Islands to New Zealand suggest that three major phases of basin formation and island arc development have occurred in this region. Development of the Tasman Sea took place during the Late Cretaceous-Paleocene. Development of the basins to the east of the Tasman Sea occurred predominantly during the Oligocene as well as during the Upper Miocene to Recent. The South Fuji Basin, consisting of the Kupe and Minerva Abyssal Plains, is marked by the presence of possibly two RRR triple junction spreading centers that were active between the times of anomalies 13 to 7 (36--25.5 m.y.). The Kupe Abyssal Plain shows the presence of residual magnetic anomalies 7 to 13 of the eastern limb of the proposed spreading center. The western limb appears to have been subducted beneath the present site of the Three Kings Rise. This seafloor spreading phase (calculated half-spreading rate of 35 mm/yr) was coincident with the overthrusting phase of the New Caledonia ultramafic rocks. During that period, active volcanism along the then continuous Solomons-New Hebrides-Fiji-Lau Island arc was taking place. Magnetic anomalies from 1 to 4 (0--8 m.y. B. P.) are seen to extend along a clearly defined lineation pattern over the North Fuji Basin.

Malahoff, A.; Feden, R.H.; Fleming, H.S.

1982-05-10

55

World Digital Magnetic Anomaly Map (WDMAM) rev.2: Oceanic Domains  

NASA Astrophysics Data System (ADS)

A large amount of aeromagnetic and marine magnetic data, complemented by satellite magnetic data, have been compiled and processed to produce the first World Digital Magnetic Anomaly Map (WDMAM; [1]). In oceanic areas, the data coverage is, however, very sparse over remote parts of the Pacific, Indian, and Southern oceans. Two attempts have been proposed to fill the gaps in these areas. Model WDMAM1-B [1] do so by superimposing synthetic magnetic anomalies computed from the age map of [2] - derived from a self-consistent plate tectonic model (and indirectly from the marine magnetic data), but the result is dominated by the synthetic anomalies which amplitudes poorly fit that of the observations. Model EMAG-2 [3] interpolates between sparse marine magnetic data using directional gridding and extrapolation based on the age map of [4], but the result displays many artificially elongated features due to the improper interpolation of non linear anomaly (caused, for instance, by a seamount). We propose a new map based on the following steps: (a) more realistic forward modeling of the marine magnetic anomalies including remanent magnetization vectors which take into account the age and motion of the oceanic lithosphere, as proposed by [5] for satellite anomalies; (b) evaluation of the equivalent magnetization by comparison of the synthetic and observed anomalies along the ship tracks; and (c) adjustment of the synthetic anomaly maps using this equivalent magnetization prior merging with the observed anomalies. [1] Korhonen et al., map published by CCGM/CGMW (http://ccgm.free.fr/), 2007 [2] Müller et al., JGR, 1997 [3] Maus et al., G3, 2009 [4] Müller et al., G3, 2008 [5] Dyment and Arkani-Hamed, JGR, 1998

Hamoudi, M.; Dyment, J.; Choi, Y.; Thebault, E.; Quesnel, Y.; Roest, W. R.; Lesur, V.

2012-12-01

56

Study of gravity and magnetic anomalies using MAGSAT data  

NASA Technical Reports Server (NTRS)

The results of modeling satellite-elevation magnetic and gravity data using the constraints imposed by near surface data and seismic evidence shows that the magnetic minimum can be accounted for by either an intracrustal lithologic variation or by an upwarp of the Curie point isotherm. The long wavelength anomalies of the NOO's-vector magnetic survey of the conterminous U.S. were contoured and processed by various frequency filters to enhance particular characteristics. A preliminary inversion of the data was completed and the anomaly field calculated at 450 km from the equivalent magnet sources to compare with the POGO satellite data. Considerable progress was made in studing the satellite magnetic data of South America and adjacent marine areas. Preliminary versions of the 1 deg free-air gravity anomaly map (20 m gal contour interval) and the high cut (lambda approximately 8 deg) filtered anomaly maps are included.

Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (principal investigators)

1981-01-01

57

Uncertainty in magnetization directions derived from planetary magnetic anomalies in view of numerical experiments with coalesced anomalies from Earth  

Microsoft Academic Search

Martian magnetization vectors and paleopole locations determined by different investigators using different methodologies are contradictory. I suggest that one of the reasons for this is that the anomalies that are assumed to be caused by a homogeneously magnetized source may actually be due to coalescence of multiple crustal sources that may be magnetically coherently or incoherently magnetized and whose coalescence

D. Ravat

2006-01-01

58

Alternative explanation for intermediate--wavelength magnetic anomalies  

SciTech Connect

Harrison and Carle and others have examined very long profiles of the magnetic field and have calculated one-dimensional power spectra. In these they expect to see, but do not find, a minimum in power at intermediate wavelengths, between 65 and 150 km. Conventional one-dimensional models of the field predict very little power in this band, which lies between the spectral peaks arising from sources in the crust and the core. Mantle sources or high-intensity, long-wavelength magnetizations have been proposed to account for the observations. An alternative, more plausible explanation is that one-dimensional spectra of two-dimensional fields contain contributions from wavenumbers in the perpendicular (i.e., nonsampled) direction. Unless the seafloor spreading anomalies are perfectly lineated at right angles to the profile, some low-wavenumber energy must be attributed to this effect; we propose that such directional aliasing is a major factor in the power spectra. To support this idea we discuss theoretical models and analyze a large-scale marine survey.

Shure, L.; Parker, R.L.

1981-12-10

59

Magnetic structure of a slow spreading ridge segment: Insights from near-bottom magnetic measurements  

E-print Network

intensity of the seafloor. In the vicinity of the spreading axis a considerable number of magnetizationMagnetic structure of a slow spreading ridge segment: Insights from near-bottom magnetic represents laterally averaged seafloor magnetization, whereas the NRM has variations at the scale

Paris-Sud XI, Université de

60

A triple junction trace beneath Reunion Island? Insight from marine magnetic anomalies  

NASA Astrophysics Data System (ADS)

Reunion Island is the most recent expression of a hotspot which formed the Deccan Trap flood basalt, the Chagos-Laccadives Ridge, the southern part of the Mascarene Plateau, Mauritius and Reunion Islands. Both Mauritius and Reunion islands are isolated structures which have formed on the pre-existing oceanic lithosphere of the Mascarene Basin, an oceanic basin created by seafloor spreading between anomalies 34 and 27 (83-60 Ma). The location of Mauritius and Reunion islands may reflect either a preferential rise of hotspot material through pre-existing structures of the oceanic lithosphere or the discontinuous activity of a weakening hotspot. We address this question using bathymetric and magnetic data collected by R/V L'Atalante in 2006 as part of cruise FOREVER (FORmation and Evolution of the Volcanic Edifice of Reunion), complemented by other data in the area. We apply crossover error analysis to correct data from different cruises for time variations not considered by the IGRF model and build a magnetic anomaly map. This map displays coherent magnetic anomalies over most of the area. Anomalies 28 to 20 are identified in the Madagascar Basin, east of the Mascarene Islands. Conjugate sequences of anomalies 31 to 27 (on the northern flank) and 34 to 27 (on the southern flank) are recognized west of the Mascarene Islands, on the conjugate flanks of the Mascarene fossil spreading centre. In the Mascarene Island compartment, the seafloor spreading anomalies can be deciphered under most of the Reunion Island edifice (radius 100 km) with only an inner zone of radius 50 km showing shorter wavelength anomalies related to the volcanic structures of the island. The seafloor spreading lineations show two orientations, N120°E-N140°E and N90°E-N110°E in the central and eastern part of the compartment, respectively. We interpret these different orientations as reflecting the presence of the trace of the Indian Ocean Triple Junction (IOTJ, between India, Africa, and Antarctica) in the area. Magnetic anomaly identifications in the Central Indian Basin clearly show that the IOTJ trace has been located in this basin since anomaly 29 (65 Ma). Before this time, the trace was most likely located in the Mascarene Basin. The observed chevron-shaped anomalies in the Reunion - Mauritius area are likely to be anomalies 29r, 30, and 31 on the northern flank of the Mascarene and Southeast Indian Ridges, i.e. on the Indian plate at the time of their formation. Two offset sequences of anomalies 32 and 33 are observed further north, NW of Mauritius Island. This evolving offset and a complex propagator-like structure observed SE of Reunion Island may reflect the different spreading rates on two different ridges at a triple junction. The conjugate anomalies are locally identified east of the northern Madagascar Plateau, although the data are sparse in this area. If confirmed by plate reconstructions of the Mascarene, Madagascar, Crozet and Central Indian basins, this model would imply that Reunion Island was formed on a specific location, the complex trace of the Indian Ocean Triple Junction on the Indian plate.

Bissessur, D.; Dyment, J.; Deplus, C.; Yatheesh, V.

2009-04-01

61

Sources of Magnetic Anomalies on Mars and Their Implications  

NASA Technical Reports Server (NTRS)

The sources of intense magnetic anomalies on Mars are investigated with models including constraints from geology, gravity and topography. Implications of the derived sources for the early evolution of Mars are examined.

Raymond, C. A.; Smrekar, S. E.; Stofan, E. R.

2000-01-01

62

Ionospheric characteristics above Martian crustal magnetic anomalies Paul Withers,1  

E-print Network

- sphere of Mars, (b) to correlate the spatial distribution of these profiles with magnetic field strength. To date, numerical models of the effects of the magnetic field on the space environment at Mars haveIonospheric characteristics above Martian crustal magnetic anomalies Paul Withers,1 M. Mendillo,1 H

Mendillo, Michael

63

Magnetic resonance images of neuronal migration anomalies.  

PubMed

Neuronal migration anomalies are a spectrum of brain malformations caused by insults to migrating neuroblasts during the sixth week to fifth month of gestation. To study the characteristics of MRI findings in migration anomalies, MR images of 36 patients (28 children and 8 adults) with migration anomalies were evaluated. Five patients had lissencephaly, eight had pachygyria, twelve had schizencephaly, six had heterotopias of gray matter, three had hemimegalencephaly, and two had polymicrogyria. The frequency of migration anomalies was 0.51% of all cranial MRI studies and 1.21% of pediatric cranial MRI studies at our hospital. The major clinical presentations of these patients were seizure (64%), development delay (42%), motor deficits (42%) and mental retardation (25%). Twenty-five patients (69%) associated with other brain anomalies, including: other migration anomalies in 12 cases (33%), absence of the septum pellucidum in 10 cases (28%), Dandy-Walker malformation/variant in 5 cases, arachnoid cyst in 4 cases, agenesis of the corpus callosum in 3 cases, holoprosencephaly in 2 cases, mega cisterna magna in 1 case and cephalocele in 1 case. Some of them presented with multiple complicated anomalies. As MR imaging provides superb gray-white matter distinction, details of cortical anatomy and multiplanar capability, it can clearly delineate the detail morphologic changes of the brain caused by neuronal migration disorders as well as the associated anomalies. PMID:9780601

Jaw, T S; Sheu, R S; Liu, G C; Chou, M S

1998-08-01

64

Deflection of solar wind protons from the Lunar magnetic anomalies  

NASA Astrophysics Data System (ADS)

The first measurements, which was made on the lunar orbits, has shown that Moon has no its intrinsic dipolar magnetic field. However the residual magnetization in returned lunar samples and also the anomalous magnetization of lunar surface (till several hundred nT) was found even in Apollo missions. Observations of Kaguya and Chandrayaan reveal the significant solar wind protons deflection from the lunar surface in particular from the magnetic anomalies regions. Such deflection implies that the magnetic anomalies may act as magnetosphere-like obstacles (mini-magnetospheres), modifying the upstream plasma. We examined the conditions in solar wind and estimated plasma parameters in solar wind and in crustal magnetic field. Then we made the estimation of the possibility of mini-magnetosphere and shock-like structure formation. Also we applied our calculations to the case of big anomaly.

Sadovski, Andrei; Skalsky, Alexander

65

Deflection of solar wind protons from the Lunar magnetic anomalies  

NASA Astrophysics Data System (ADS)

The first measurements, which was made on the lunar orbits, has shown that Moon has no its intrinsic dipolar magnetic field. However the residual magnetization in returned lunar samples and also the anomalous magnetization of lunar surface (till several hundred nT) was found even in Apollo missions. Observations of Kaguya and Chandrayaan reveal the significant solar wind protons deflection from the lunar surface in particular from the magnetic anomalies regions. Such deflection implies that the magnetic anomalies may act as magnetosphere-like obstacles (mini-magnetospheres), modifying the upstream plasma. We examined the conditions in solar wind and estimated plasma parameters in solar wind and in crustal magnetic field. Then we made the estimation of the possibility of mini-magnetosphere and shock-like structure formation. Also we applied our calculations to the case of big anomaly.

Sadovski, Andrei M.; Skalsky, Alexander A.

2014-05-01

66

The south-central United States magnetic anomaly  

NASA Technical Reports Server (NTRS)

A positive magnetic anomaly, which dominates the MAGSAT scalar field over the south-central United States, results from the superposition of magnetic effects from several geologic sources and tectonic structures in the crust. The highly magnetic basement rocks of this region show good correlation with increased crustal thickness, above average crustal velocity and predominantly negative free-air gravity anomalies, all of which are useful constraints for modeling the magnetic sources. The positive anomaly is composed of two primary elements. The western-most segment is related to middle Proterozoic granite intrusions, rhyolite flows and interspersed metamorphic basement rocks in the Texas panhandle and eastern New Mexico. The anomaly and the magnetic crust are bounded to the west by the north-south striking Rio Grande Rift. The anomaly extends eastward over the Grenville age basement rocks of central Texas, and is terminated to the south and east by the buried extension of the Ouachita System. The northern segment of the anomaly extends eastward across Oklahoma and Arkansas to the Mississippi Embayment. It corresponds to a general positive magnetic region associated with the Wichita Mountains igneous complex in south-central Oklahoma and 1.2 to 1.5 Ga. felsic terrane to the north.

Starich, P. J.; Hinze, W. J.; Braile, L. W.

1985-01-01

67

ARTEMIS spacecraft observations of lunar magnetic anomalies at low altitude  

NASA Astrophysics Data System (ADS)

ARTEMIS is the first spacecraft mission to make dual-spacecraft measurements of particles and fields from orbit around the Moon. The spacecraft is well-suited to investigate the interaction of lunar magnetic anomalies with the solar wind and terrestrial magnetospheric plasma, with frequent periapsis passes within 50 km of the surface, and occasional passes lower than 30 km. In the second half of 2011 ARTEMIS passes within a few tens of km from the surface, in the vicinity of an anomaly. We will present ARTEMIS observations from one (or possibly more) of these low altitude passes near magnetic anomalies, and offer interpretation of the observations of magnetic (FGM) and electric (EFI) field as well as suprathermal charged particles (ESA). We will place the ARTEMIS observations in context with previous observational and theoretical work dealing with the influence of anomalies on their local plasma environment.

Brain, D. A.; Ames, W. F.; Poppe, A.; Halekas, J. S.; Bonnell, J. W.; Glassmeier, K.; McFadden, J. P.; Angelopoulos, V.

2011-12-01

68

The Origin of the Jurassic Quiet Zone -new insights from Hawaiian Jurassic magnetic anomalies (Invited)  

NASA Astrophysics Data System (ADS)

Marine magnetic anomalies recorded in oceanic crust, have played a central role in documenting Earth's magnetic field history as compiled in the geomagnetic polarity timescale (GPTS). The oldest part of the marine record is the Jurassic Quiet Zone (JQZ) (pre-M29 chrons) which is known to be a period when field intensity was low, while reversal rate was high. The origin and character of the JQZ has been the subject of marine magnetic studies over past 20 years in the western Pacific where the oldest and arguably best preserved Jurassic magnetic anomalies create three Jurassic lineation sets (Japanese, Hawaiian, and Phoenix). The Japanese JQZ sequence was extensively investigated by an aeromagnetic and 2 deeptow magnetometer surveys, revealing (i) the presence of lineated anomalies older than M29; (ii) a GPTS record extending from M29 to M44 with a tie to ODP Hole 801C and (iii) remarkably fast reversals that decrease in intensity back in time until M38. Prior to M38 there is a low amplitude zone (LAZ) in anomalies lasting until M42, when both anomaly amplitude and a lineated character reappears around Hole 801C. Recently collected (2011) high quality seasurface marine magnetic anomaly data from the Hawaiian lineations show changes in magnetic anomaly shape and amplitude that are similar in to the Japanese lineations, suggesting that the anomalies record globally coherent geomagnetic field behavior for the Jurassic. Specifically, the strong similarity of anomaly patterns between the Japanese and Hawaiian sequences from M19 to M38 supports the remarkably dynamic geomagnetic field behavior of fast reversals and changing intensity, confirming a proposed record of the GPTS sequence for M29 to M38. While the LAZ in the Hawaiian sequence is not as clear as in the Japanese lineations, we believe we can correlate the earlier M42-M44 sequence between the two sets of lineations. The slower spreading rate in the Hawaiian lineations may contribute to this lack of resolution of the LAZ and result in a less clear recording of anomalies. We present models to investigate if this is simply a lack of spatial resolution or if there are indeed different processes active within the Hawaiian sequence such as seamount/plateau formation and crustal construction.

Tominaga, M.; Tivey, M.; Sager, W. W.

2013-12-01

69

Correlated Magnetic and Gravity Anomalies West of the Isidis Basin, Mars and Implications for Plains Magnetism  

Microsoft Academic Search

The magnetic field of Mars reflects strong crustal magnetism resulting from an ancient internal field. The crustal anomaly pattern parallels the geologic dichotomy in that most of the anomalies detected by the Mars Global Surveyor are located within the persumably older southern highlands while the northern lowlands has weak or no magnetic signature at satellite atltiudes. We have analyzed a

C. A. Raymond; S. E. Smrekar; G. E. McGill; A. M. Dimitriou

2004-01-01

70

Polar Wander of Mars: Evidence from Magnetic Anomalies  

Microsoft Academic Search

The pole positions determined from 16 magnetic anomalies indicate that the dipole core field axis was at 25 N. If the dipole core field coincided with the rotation axis of Mars at the time of magnetization the pole positions suggest that the axis of rotation of Mars has wandered by 65°.

J. Arkani-Hamed; D. Boutin

2003-01-01

71

First high-resolution near-seafloor survey of magnetic anomalies of the South China Sea  

NASA Astrophysics Data System (ADS)

We successfully conducted the first high-resolution near-seafloor magnetic survey of the Central, Southwest, and Northern Central Basins of the South China Sea (SCS) during two cruises on board Chinese R/V HaiYangLiuHao in October-November 2012 and March-April 2013, respectively. Measurements of magnetic field were made along four long survey lines, including (1) a NW-SE across-isochron profile transecting the Southwest Basin and covering all ages of the oceanic crust (Line CD); (2) a N-S across-isochron profile transecting the Central Basin (Line AB); and (3) two sub-parallel NE-SW across-isochron profiles transecting the Northern Central Basin of the SCS (Lines D and E). A three-axis magnetometer was mounted on a deep-tow vehicle, flying within 0.6 km above the seafloor. The position of the tow vehicle was provided by an ultra-short baseline navigation system along Lines D and E, while was estimated using shipboard GPS along Lines AB and CD. To investigate crustal magnetization, we first removed the International Geomagnetic Reference Field (IGRF) of 2010 from the measured magnetic data, and then downward continued the resultant magnetic field data to a horizontal plane at a water depth of 4.5 km to correct for variation due to the fishing depth of the deep-tow vehicle. Finally, we calculated magnetic anomalies at various water depths after reduction-to-the-pole corrections. We also constructed polarity reversal block (PRB) models of crustal magnetization by matching peaks and troughs of the observed magnetic field anomaly. Our analysis yielded the following results: (1) The near-bottom magnetic anomaly showed peak-to-trough amplitudes of more than 2,500 nT, which are several times of the anomaly amplitudes at the sea surface, illustrating that deep-tow measurements acquired much higher spatial resolutions. (2) The deep-tow data revealed several distinctive magnetic anomalies with wavelengths of 5-15 km and amplitudes of several hundred nT. These short-wavelength anomalies were unrecognized in sea surface measurements. (3) Preliminary results showed that the study regions might have experienced several episodes of magnetic reversal events that were not recognized in existing models. (4) We are currently investigating the geomagnetic timing of these relatively short-duration events to determine the detailed spreading history of the sub-basins of the SCS. These high-resolution near-seafloor magnetic survey lines are located close to the planned drilling sites of IODP Expedition 349 scheduled for January-March 2014.

Lin, J.; Xu, X.; Li, C.; Sun, Z.; Zhu, J.; Zhou, Z.; Qiu, N.

2013-12-01

72

Correlations of Lunar Magnetic Anomalies with Geologic Age and Material  

NASA Astrophysics Data System (ADS)

While the moon has is no present-day internally generated magnetic field, widespread coherently magnetized geologic units were observed with Apollo era surface and sub-satellite measurements and more recently with Lunar Prospector. However, unlike at Mars, magnetized lunar units show no clear-cut correlation with age: a few, but not all, basins of Nectarian age (3.92-3.85 Ga) exhibit magnetic anomalies within the basin; some, but not all, basins exhibit magnetic anomalies associated with their ejecta; and most of the crustal magnetization is in a spatially extensive region to the NW of South Pole Aitken. Recent paleomagnetic analyses have been performed on a range of sample types and ages including absolute and relative paleointensity and directional measurements. Collectively, these paleomagnetic results have been used to suggest the existence of a lunar dynamo during the period ~ 3.6 - 4.2 Ga. Various mechanisms that could have produced a dynamo spanning all or part of this time interval are being investigated, such as precession, nutation, and thermally or compositionally-driven core convection. It is also apparent that shock plays an important, although still poorly-understood, role in the magnetic history of the Moon: concentrations of magnetic anomalies correlate with the antipodes of four major impact basins; strong fields at Apollo 16 site those associated with the Reiner Gamma formation are attributed to basin ejecta; experiments have shown shock can demagnetize or remagnetize a material in the absence of a permanent magnetic field. Thus, despite significant recent work, no single data set, experiment, or model provides an unambiguous record of lunar magnetic evolution. A clear understanding regarding the timing of either a permanent global field or the existence of intermittent transient fields is not apparent. Here we focus on the issue of the correlation of crustal magnetic anomalies with geologic age (Copernican, Eratosthenian, Imbrian, Nectarian or Pre-Nectarian) and geologic unit (basin, crater, mare or dark, and terra materials) in an effort to place constraints on the source of magnetizations and the timing of acquisition of remanence. Previous studies have investigated the correlation of magnetization with individual basin age or particular formation units (e.g. Caley Formation) but this has not been extended to the global scale, covered all lunar ages, or expanded beyond correlation with basin materials. Statistical analyses using Lunar Prospector Magnetometer and Electron Reflectometer data quantify the correlation of geologic ages and units with magnetic anomalies. The majority of observable magnetic anomalies are associated with visible surface units having ages that are Imbrian or Nectarian. Magnetic anomalies are statistically more likely to occur in association with crater ejecta and highland material than with basin materials. We discuss whether this global interpretation is representative of magnetic anomalies found NW of South Pole Aitken (SPA) basin, to help determine whether the sources of circum-SPA magnetic anomalies are fundamentally different from those of magnetic anomalies elsewhere on the moon.

Lawrence, K. P.; Johnson, C. L.

2011-12-01

73

The mineralogy of global magnetic anomalies  

NASA Technical Reports Server (NTRS)

The Curie Balance was brought to operational stage and is producing data of a preliminary nature. Substantial problems experienced in the assembly and initial operation of the instrument were, for the most part, rectified, but certain problems still exist. Relationships between the geology and the gravity and MAGSAT anomalies of West Africa are reexamined in the context of a partial reconstruction of Gondwanaland.

Haggerty, S. E. (principal investigator)

1982-01-01

74

Low energy spread ion source with a coaxial magnetic filter  

DOEpatents

Multicusp ion sources are capable of producing ions with low axial energy spread which are necessary in applications such as ion projection lithography (IPL) and radioactive ion beam production. The addition of a radially extending magnetic filter consisting of a pair of permanent magnets to the multicusp source reduces the energy spread considerably due to the improvement in the uniformity of the axial plasma potential distribution in the discharge region. A coaxial multicusp ion source designed to further reduce the energy spread utilizes a cylindrical magnetic filter to achieve a more uniform axial plasma potential distribution. The coaxial magnetic filter divides the source chamber into an outer annular discharge region in which the plasma is produced and a coaxial inner ion extraction region into which the ions radially diffuse but from which ionizing electrons are excluded. The energy spread in the coaxial source has been measured to be 0.6 eV. Unlike other ion sources, the coaxial source has the capability of adjusting the radial plasma potential distribution and therefore the transverse ion temperature (or beam emittance).

Leung, Ka-Ngo (Hercules, CA); Lee, Yung-Hee Yvette (Berkeley, CA)

2000-01-01

75

Improved determination of vector lithospheric magnetic anomalies from MAGSAT data  

NASA Technical Reports Server (NTRS)

Scientific contributions made in developing new methods to isolate and map vector magnetic anomalies from measurements made by Magsat are described. In addition to the objective of the proposal, the isolation and mapping of equatorial vector lithospheric Magsat anomalies, isolation of polar ionospheric fields during the period were also studied. Significant progress was also made in isolation of polar delta(Z) component and scalar anomalies as well as integration and synthesis of various techniques of removing equatorial and polar ionospheric effects. The significant contributions of this research are: (1) development of empirical/analytical techniques in modeling ionospheric fields in Magsat data and their removal from uncorrected anomalies to obtain better estimates of lithospheric anomalies (this task was accomplished for equatorial delta(X), delta(Z), and delta(B) component and polar delta(Z) and delta(B) component measurements; (2) integration of important processing techniques developed during the last decade with the newly developed technologies of ionospheric field modeling into an optimum processing scheme; and (3) implementation of the above processing scheme to map the most robust magnetic anomalies of the lithosphere (components as well as scalar).

Ravat, Dhananjay

1993-01-01

76

Approximating edges of source bodies from magnetic or gravity anomalies.  

USGS Publications Warehouse

Cordell and Grauch (1982, 1985) discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks. The final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes. Attempts to automate their final step. The method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources. The method applies to both local surveys and to continent-wide compilations of magnetic and gravity data.-from Authors

Blakely, R.J.; Simpson, R.W.

1986-01-01

77

Rotational dynamics of Mars: Using magnetic anomalies modeling to estimate  

Microsoft Academic Search

The possible polar wandering of the planet Mars is investigated by modeling some of the many surface magnetic anomalies discovered by Mars Global Surveyor (MGS). First I describe the physics of polar wandering by exposing the theory developed by Ricard et al. [1993] and Spada et al. [1996]. I derive the linear form of the equation of polar motion in

Daniel Mars Polar Motion Boutin

2005-01-01

78

Macquarie island and the cause of oceanic linear magnetic anomalies.  

PubMed

Macquarie Islands is formed of probably Pliocene oceanic crust. Intruded into pillow lavas is a belt of harzburgite and layered gabbro mnasses cut by dike swarms. Similar belt-like structures may cause the linear magnetic anomalies of the ocean. PMID:17731490

Varne, R; Gee, R D; Quilty, P G

1969-10-10

79

Manifestation of the petrogeneration zones of Northern and the Bering seas in ground magnetic anomalies and anomalies of satellite Champ  

NASA Astrophysics Data System (ADS)

The purpose of this paper are showed results of studying of specificity of a deep structure of zones of petrogeneration Northern and the Bering seas on aeromagnetic and satellite magnetometric datas. Research lateral and vertical heterogeneitys an earth's crust of Northern sea is carried out on the basis of the analysis of measurements of satellite Champ at height of 100 km and the digital database created on materials of sea shooting of a geomagnetic field, executed on non-magnetic schooner "Zarya". On sea measurements in Northern sea through large oil fields and gas ( Frigg, Ekofisk, Forties trough, Leman, etc.). Geomagnetic sections for an interval of depths from 1 up to 30 km are constructed. It has allowed to study character of distribution of magnetization of breeds of a cover, horizontal lamination intracore layers of an earth's crust and to allocate in zones petrogeneration synvertical fluidoconduct zones the channels described by alternation of not magnetic and low-magnetic layers. They were showed on geomagnetic sections as permeable zones quasi- laminated structures with the lowered magnetic properties in an interval of depths from 8 up to 28 km. Comparison to a map of the magnetic anomalies measured at height of 100 km by satellite Champ, has shown, that areas of the greatest petrocongestions North Sea ????? at height of 100 km are dated for a zone of gradients and a minimum of northeast displacement of regional anomalies of western and east blocks of Northern sea. It corresponds to representations about an orientation of a fissuring zone and the increased size of a geothermal gradient North Sea rift and is corresponded position allocated on hydromagnetic structures deep fluidoconduct channels. Thus, distribution to water areas of deposits of deposits is emphasized not only low-magnetic areas in a thickness of a sedimentary cover where they are directly located, but also by not magnetic lenses in breeds of the base spreading it in intervals of depths of 8-11 km and 15-18 km. The oil-gas-bearing province of the Bering Sea occupies uniform sedimentary megabasin. On aeromagnetic measurements at height of 300 m are constructed geomagnetic sections in an interval of depths from 0.5 km up to 25 km crossing the basic zones possible petrocongestions with traps structural and of structural - stratigraphic types. Distribution of magnetization in an interval of development of potentially productive sandy layers on depths from 1 up to 5 km is received. The most perspective zones possible petrocongestions are allocated in Ilpinsky, Olutorsky and Olutorsko-Komandorsky sedimentary basins. The deep permeable zone with system of low-magnetic lenses in intervals of depths 8-10, 12, 18-20 km, dated to Pilgin zone possible petrocongestions was most brightly showed. Comparison of ground supervision to the data received by results of measurements from satellite Champ at height of 100 km, shows, that large oil-gas-bearing Vertuhovskaya, Karaginskaya, Pahachiskaya and Pilginskaya zones are dated for a minimum isometric satellite magnetic anomaly. At height of 400 km this minimum keeps the form that speaks about stability of a condition of the permeable zones supervising oil-gas-bearing.

Litvinova, Tamara; Krasinsky, Egor; Petrova, Alevtina; Demina, Irina

2010-05-01

80

Deep-sea Vector Magnetic Anomalies over the Bayonnaise Knoll Caldera (Izu-Ogasawara Arc) (Invited)  

NASA Astrophysics Data System (ADS)

The Bayonnaise Knoll caldera is located on the eastern margin of the backarc rift zone of the Izu-Ogasawara island arc. The caldera rim is ~3 km in diameter and 100-200 m high from the caldera floor 840-920 m deep. A large active hydrothermal field associated with sulfide deposit, called the Hakurei site, has been found at the foot of the southeastern caldera wall. We conducted deep-sea magnetic measurements using autonomous underwater vehicles to map ~75 % of an area 3 km by 4 km in the caldera. The magnetic vector field data were collected at 40-150 m altitude along the survey lines spaced 80-200 m apart. We improved the conventional correction method applied for removing the effect of vehicle magnetization, which greatly enhanced the precision of the resulting vector anomalies and allowed us to use the vector anomaly instead of the total intensity anomaly for inversion analysis. The magnetization distribution obtained using the vector anomaly was significantly different from the one obtained using the total intensity anomaly, especially in areas where the survey tracks were widely spaced. The aliasing effect appears in areas of sparse data distribution, and the magnetic field is more correctly calculated from the vector anomaly than the total intensity anomaly. The magnetization distribution in the caldera has two major features: a ~1.5-km wide belt of high magnetization, trending NNW-SSE through the caldera, and a clear low magnetization zone, ~300 m x ~500 m wide, extending over the Hakurei site. The high magnetization belt is considered to reflect basaltic volcanism associated with the backarc rifting that occurred after the formation of the Bayonnaise Knoll. The low magnetization zone is interpreted as the alteration zone resulting from the hydrothermal activity. Several zones of localized high magnetization are recognized within the high magnetization belt, some of them in the caldera wall adjacent to the low magnetization zone of the Hakurei site. We speculate that intensive magma intrusion occurred beneath the caldera wall and has provided the heat to generate hydrothermal fluid, which has been spouting out through the caldera wall faults. The surface expression of the vent field extends beyond the alteration zone inferred from the magnetization distribution, spreading upwards in the caldera wall. High-resolution topography around the Hakurei site indicates that the hydrothermal vents are generally distributed over a landform of slope failure. These observations would imply that hydrothermal fluid rising up in the up-flow zone moves laterally as well when it comes near the seafloor, probably along numerous fractures and fissures in the caldera wall. The distribution of pre-existing faults and fractures may rather control the fluid flow pathways in the shallow part and condition the surface extent of the vent field.

Honsho, C.; Ura, T.; Kim, K.

2013-12-01

81

Variations of the magnetic field near Mars caused by magnetic crustal anomalies  

Microsoft Academic Search

The possible avenues for photoelectron transport were determined during southern hemisphere winter at Mars by using a mapping analysis of the theoretical magnetic field. Magnetic field line tracing was performed by superposing two magnetic field models: (1) magnetic field derived from a three-dimensional (3D) self-consistent quasi-neutral hybrid model which does not contain the Martian crustal magnetic anomalies and (2) a

R. A. Frahm; E. Kallio; Y. Futaana; A. Fedorov; P. Janhunen

2008-01-01

82

The composite magnetic anomaly map of the East Antarctic  

NASA Astrophysics Data System (ADS)

Airborne and marine magnetic observations in East Antarctica and adjacent seas of the Indian Ocean were compiled for a magnetic anomaly map of the Antarctic. For East Antarctica, over 260,000 line km of Russian reconnaissance magnetic data were used that had been collected since 1955 mainly at line spacings of about 5, 20 and 50 km. For the offshore areas, magnetic data from American, Australian, German, Japanese, and Russian marine expeditions were incorporated. Digitally recorded data and data digitized from published and unpublished maps and profiles were included in the compilation. Local grids of these data were developed and merged into a regional grid at an interval of 5 km. The prime product of this compilation is a shaded-relief map that shows the most complete and coherent perspective to date of the region's magnetic character. In combination with other types of data, the compilation provides new insight on the tectonic features and history of this largely inaccessible region of the world. It maps out approximately 4300 km of the Antarctic Continental Margin Magnetic Anomaly (ACMMA) related to Gondwana breakup, new cratons and mobile belts, and large submarine igneous provinces.

Golynsky, A. V.; Alyavdin, S. V.; Masolov, V. N.; Tscherinov, A. S.; Volnukhin, V. S.

2002-03-01

83

Seafloor spreading in the Weddell Sea from magnetic and gravity data  

Microsoft Academic Search

A re-compilation of magnetic data in the Weddell Sea is presented and compared with the gravity field recently derived from retracked satellite altimetry. The previously informally named ‘Anomaly-T,’ an east–west trending linear positive magnetic and gravity anomaly lying at about 69°S, forms the southern boundary of the well-known Weddell Sea gravity herringbone. North of Anomaly-T, three major E–W linear magnetic

L. C Kovacs; P Morris; J Brozena; A Tikku

2002-01-01

84

A magnetic anomaly of possible economic significance in southeastern Minnesota  

USGS Publications Warehouse

An aeromagnetic survey in southeastern Minnesota by the U. S. Geological Survey in cooperation with the State of Minnesota has revealed a high-amplitude, linear, and narrow magnetic feature that suggests a possible source of Precambrian iron-formation of economic value. For the past few years the U. S. Geological Survey has been conducting detailed geophysical studies of the midcontinent gravity anomaly--a broad, high-amplitude feature that extends from Lake Superior through the States of Minnesota, Iowa, Nebraska, and part of Kansas. As part of this study an aeromagnetic survey of the southern part of the State was made in cooperation with the State of Minnesota during the summer of 1963, in which a linear high-amplitude anomaly of the order of 4,000 gammas was discovered. Because of the high amplitude, the linearity, and the narrowness of the magnetic feature, it is believed the source may be Precambrian iron-formation of possible economic value. The anomalous area is in Fillmore County, approximately between the towns of Lanesboro and Peterson in the extreme southeastern part of the State. (See figures 1 and 2.) At the site of the anomaly, Cambrian sedimentary rocks occur in the valley of the Root River, and Ordovician rocks (nearly flat lying) mantle the upland areas. The uplands are largely covered by glacial deposits, which are relatively thin (Paul K. Sims, written communication, 1964). Depths to the Precambrian are estimated to range from 500 feet to 1,000 feet below the surface. The aeromagnetic map shown in figure 2 was compiled from continuous magnetic profiles made along east-west flight lines 1,000 feet above ground, and spaced approximately 1 mile apart. Contour intervals of 20, 100, and 500 gammas were used depending on the intensity. The instrument for the survey was a flux-gate type magnetometer (AN/ASQ-3A) which measures total-field variations. The contour map displays variations in magnetic pattern which are typical of shallow Precambrian rocks. Anomalies of the order of 1,000 gammas are shown along the east and west edges of the map. The outstanding feature is the previously mentioned linear positive anomaly that trends northeast and reaches a peak of 3,960 gammas. The positive anomaly is contoured from data on four consecutive profiles, but only two show high amplitudes. The high-amplitude anomalies along traverses 1 and 2 are shown in figure 3. Depth calculations suggest that the source of the anomaly lies about 1,000 feet below the surface. Assuming a dikelike source and magnetization resulting entirely from induction in the earth's field, several calculations were made in an attempt to fit the magnetic profile taken along the line AA' (see figs. 2 and 4), considered to be a typical cross-section of the magnetic anomaly. Comparisons are shown between observed and computed profiles. The fixed parameters used were (a) distance from detector to source of 2,000 ft; width of dike of 5,000 ft; dip of dike of 75?, 90?, 105? , and 120? , as shown. The best fit occurs when the dike is vertical or dips 75? to the southwest. For these cases, the susceptibility, k, is computed to be 0.016 c.g.s, units, and is comparable to k = 0.02+ calculated by Bath (1962) for the relatively unmetamorphosed iron-formation of the Main Megabi district in Minnesota where the induced magnetization was most likely the dominant magnetization. If the dominant magnetization for the anomaly in Fillmore County were remanent rather than induced, the economic importance of the anomaly would be greatly reduced. This anomaly seems sufficiently promising to warrant further geologic and geophysical investigation. Detailed ground magnetic and electrical studies would be useful to delineate the feature. In the final analysis, however, the presence of iron-formation can be determined only by the drill.

Zietz, Isidore

1964-01-01

85

Anomalies.  

ERIC Educational Resources Information Center

This theme issue on anomalies includes Web sites, CD-ROMs and software, videos, books, and additional resources for elementary and junior high school students. Pertinent activities are suggested, and sidebars discuss UFOs, animal anomalies, and anomalies from nature; and resources covering unexplained phenonmenas like crop circles, Easter Island,…

Online-Offline, 1999

1999-01-01

86

Preliminary interpretation of satellite gravity and magnetic anomalies in the region of the Philippine Sea Plate  

NASA Astrophysics Data System (ADS)

The Philippine Sea, situated in the northwestern Pacific, is one of the largest marginal seas on the Earth. Analysis of the Philippine Sea's intraplate fault tectonic systems and lithosphere's density and magnetism structures has a significant contribution to understanding not only the dynamic principles of subduction and convergence zones but also effect of plate subduction on back-arc area. It is also important to have cognizance for structure evolution of the ocean crust, the tension and extending progress of marginal sea basins and the mechanisms of geodynamics. Meanwhile, it can be a significant approach for researching the evolution of the East China Sea and the South China Sea. Using high-precision gravity forwarding method based on spatial domain in spherical coordinate, we have calculated the Bouguer gravity disturbance (BGD) in the Philippine Sea based on the ETOPO1 1 arc-minute topography & bathymetry data and the gravity field model EIGEN-6C. After removing the gravity effect of the sediments and deep abnormal materials, we make spherical cap harmonic analysis of the residual anomaly and obtain the topography of Moho and apparent-density's distribution of our study area by alternate iteration inversion method. Then, we calculate the distributions of the study area's magnetic anomalies based on the Earth magnetic model NGDC720, reduce to the pole of the study area's magnetic anomalies by the equivalent source method based on spherical prism magnetic forwarding, inverse the processed magnetic anomalies with spherical cap harmonic analysis to obtain the topography of Curie surface and the apparent magnetic susceptibility distribution. Finally, we divide the Philippine Sea block into tectonic units and derive the faults distributions through the analysis of gravity magnetic anomalies' linear characteristics. The results show that West Philippine Basin is divided by Central Basin Ridge into two block units, the tectonic trend of the north block is south-east, but there is a trend migration to the south for the south tectonic block which may be related to the southeast rift of the Eurasian plate and the northwest spread of the Pacific plate. We find that there are faults of about south-north direction between the north block of West Philippine Basin and Urdaneta Plateau. Moreover, the tectonic is complicated in the south block of West Philippine Basin and there are no apparent tectonic trends. The Shikoku Basin and Parece Vela Basin have lower Bouguer gravity than in West Philippine Basin indicating that the West Philippine Basin has lower thickness crust and becomes thicker from north to south. The density distribution of Philippine plate is not homogeneous, which presents that it is higher in the west plate than the east and shows a low density and low magnetism at Central Basin Ridge. And there are many clear and strong striped magnetic anomalies in the West Philippine Basin having the direction of NWW-SEE, but in Shikoku Basin and Parece Vela Basin the magnetic anomaly is very weak. This study is supported by the National Science Foundation of China (Grant No.: 40730317 and 40774060 ) and International Cooperation Projection in Science and Technology (Grant No.: 2010DFA24580).

Chen, C.; Hu, Z.; Du, J.; Wang, Q.

2011-12-01

87

Numerical Simulations on Origin of Galilean Moons' Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

Galileo mission detected the magnetic anomalies originated from Galilean moons. These anomalies are likely generated in the moons interiors, under the influence of a strong ambient Jovian field. Among various possible generation mechanisms of the anomalies, we focus on magneto-convection and dynamos in the interiors via numerical simulation. To mimic the electromagnetic environment of the moons, we introduce in our numerical model an external uniform magnetic field B(sub 0) with a fixed orientation but varying field strength. Our results show that a finite B(sub 0) can substantially alter the dynamo processes inside the core. When the ambient field strength B(sub 0) increases to approximately 40% of the field generated by the pure dynamo action, the convective state in the core changes significantly: the convective flow decreases by 80% in magnitude, but the differential rotation becomes stronger in much of the fluid layer, leading to a stronger field generated in the core. The field morphologies inside the core tend to align with the ambient field, while the flow patterns show the symmetry-breaking effect under the influence of B(sub 0). Furthermore, the generated field tends to be temporally more stable.

Jiao, LiQuo; Kuang, WeiJia; Ma, ShiZhuang

2011-01-01

88

Improving the geological interpretation of magnetic and gravity satellite anomalies  

NASA Technical Reports Server (NTRS)

Quantitative analysis of the geologic component of observed satellite magnetic and gravity fields requires accurate isolation of the geologic component of the observations, theoretically sound and viable inversion techniques, and integration of collateral, constraining geologic and geophysical data. A number of significant contributions were made which make quantitative analysis more accurate. These include procedures for: screening and processing orbital data for lithospheric signals based on signal repeatability and wavelength analysis; producing accurate gridded anomaly values at constant elevations from the orbital data by three-dimensional least squares collocation; increasing the stability of equivalent point source inversion and criteria for the selection of the optimum damping parameter; enhancing inversion techniques through an iterative procedure based on the superposition theorem of potential fields; and modeling efficiently regional-scale lithospheric sources of satellite magnetic anomalies. In addition, these techniques were utilized to investigate regional anomaly sources of North and South America and India and to provide constraints to continental reconstruction. Since the inception of this research study, eleven papers were presented with associated published abstracts, three theses were completed, four papers were published or accepted for publication, and an additional manuscript was submitted for publication.

Hinze, William J.; Braile, Lawrence W.; Vonfrese, Ralph R. B.

1987-01-01

89

Marine Magnetic Anomaly Compilations in the Indian Ocean for Plate Tectonics and Beyond (Invited)  

NASA Astrophysics Data System (ADS)

The French territories in the western and southern parts of the Indian Ocean (i.e. Reunion and Mayotte islands, islands in the Mozambique Channel, Kerguelen and Crozet archipelagos, Saint Paul and Amsterdam islands…) have triggered significant scientific activities, including marine geophysics, by French scientists in this area. French marine magnetic data in this ocean span more than four decades, with records as old as 1966 and as recent as early 2009. Similarly, Indian scientists have collected a large amount of geophysical data in the northern Indian Ocean, with a focus on the Arabian Sea, the Bay of Bengal, the Central Indian Basin, and surrounding areas. To take advantage of the obvious complementarity of the French and Indian data sets for plate tectonics studies, we have conducted two projects funded by the Indo-French Centre for the Promotion of Advanced Research, the first one regarding the Arabian and eastern Somali basins, the second one the Central Indian, Madagascar and Crozet basins. These projects have been complemented by more localized work over the Mascarene Basin and Wharton basins, both characterized by an abandoned spreading centre. The purpose of this presentation is to show how such a compilation is being used to conduct plate tectonic studies, from the identification of the magnetic anomalies to their unambiguous picking using the analytic signal, the construction of isochrons and tectonic chart, and the paleogeographic reconstructions. Beyond this classical use, the compiled data can be used to produce magnetic anomaly grids and maps in areas with sufficient data coverage: such grids may help to improve and/or complement future versions of the World Digital Magnetic Anomaly Map (WDMAM).

Dyment, J.; Bhattacharya, G. C.; Vadakkeyakath, Y.; Bissessur, D.; Jacob, J.; Kattoju, K. R.; Ramprasad, T.; Royer, J.; Patriat, P.; Chaubey, A. K.; Srinivas, K.; Choi, Y.

2009-12-01

90

Current disruption and its spreading in collisionless magnetic reconnection  

SciTech Connect

Recent magnetic reconnection experiments (MRX) [Dorfman et al., Geophys. Res. Lett. 40, 233 (2013)] have disclosed current disruption in the absence of an externally imposed guide field. During current disruption in MRX, both the current density and the total observed out-of-reconnection-plane current drop simultaneous with a rise in out-of-reconnection-plane electric field. Here, we show that current disruption is an intrinsic property of the dynamic formation of an X-point configuration of magnetic field in magnetic reconnection, independent of the model used for plasma description and of the dimensionality (2D or 3D) of reconnection. An analytic expression for the current drop is derived from Ampere's Law. Its predictions are verified by 2D and 3D electron-magnetohydrodynamic (EMHD) simulations. Three dimensional EMHD simulations show that the current disruption due to localized magnetic reconnection spreads along the direction of the electron drift velocity with a speed which depends on the wave number of the perturbation. The implications of these results for MRX are discussed.

Jain, Neeraj; Büchner, Jörg [Max-Planck/Princeton Center for Plasma Physics, Max Planck Institute for Solar System Research, 37191 Katlenburg-Lindau (Germany)] [Max-Planck/Princeton Center for Plasma Physics, Max Planck Institute for Solar System Research, 37191 Katlenburg-Lindau (Germany); Dorfman, Seth [University of California Los Angeles, Los Angeles, California 90095 (United States)] [University of California Los Angeles, Los Angeles, California 90095 (United States); Ji, Hantao [Max-Planck/Princeton Center for Plasma Physics, Deparment of Astrophysica Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08540 (United States)] [Max-Planck/Princeton Center for Plasma Physics, Deparment of Astrophysica Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08540 (United States); Surjalal Sharma, A. [Department of Astronomy, University of Maryland, College Park, Maryland 20742 (United States)] [Department of Astronomy, University of Maryland, College Park, Maryland 20742 (United States)

2013-11-15

91

Absolute Magnetization Distribution on Back-arc Spreading Axis Hosting Hydrothermal Vents; Insight from Shinkai 6500 Magnetic Survey  

NASA Astrophysics Data System (ADS)

Near-bottom magnetic profiling using submersible, deep-tow, Remotely Operated Vehicle (ROV) and Autonomous Underwater Vehicle (AUV) make possible to conduct high-resolution surveys and depict detailed magnetic features reflecting, for instance, the presence of fresh lavas or hydrothermal alteration, or geomagnetic paleo-intensity variations. We conducted near-bottom three component magnetic measurements onboard submersible Shinkai 6500 in the Southern Mariana Trough, where five active hydrothermal vent fields (Snail, Yamanaka, Archean, Pica, and Urashima sites) have been found in both on- and off-axis areas of the active back-arc spreading center, to detect signals from hydrothermally altered rock and to distinguish old and new submarine lava flows. Fourteen dives were carried out at an altitude of 1-40 m during the R/V Yokosuka YK10-10 and YK10-11 cruises in 2010. We carefully corrected the effect of the induced and permanent magnetizations of the submersible by applying the correction method for the shipboard three-component magnetometer measurement modified for deep-sea measurement, and subtracted the IGRF values from the corrected data to obtain geomagnetic vector anomalies along the dive tracks. We then calculated the synthetic magnetic vector field produced by seafloor, assumed to be uniformly magnetized, using three dimensional forward modeling. Finally, values of the absolute magnetizations were estimated by using a linear transfer function in the Fourier domain from the observed and synthetic magnetic anomalies. The distribution of estimated absolute magnetization generally shows low values around the five hydrothermal vent sites. This result is consistent with the equivalent magnetization distribution obtained from previous AUV survey data. The areas of low magnetization are also consistent with hydrothermal deposits identified in video records. These results suggest that low magnetic signals are due to hydrothermal alteration zones where host rocks are demagnetized by hydrothermal circulation. The low magnetization zones around the off-axis vent sites are about ten times wider than those surrounding the on-axis sites, possibly reflecting the longer duration of hydrothermal circulation at these sites. Another interesting result is that the absolute magnetization shows extremely high intensities (>80 A/m) at the neo volcanic zones (NVZ) and relatively low intensities (<10 A/m) two to five kilometers away from the NVZ. These variations are quite consistent with those of the Natural Remanent Magnetization measured on basalt samples, suggesting that the low-temperature oxidation of host rock due to the reaction with seawater has completed within a few kilometers distance from the spreading axis. We conclude that the magnetization of the uppermost oceanic crust decreases with age due to the combination of the both hydrothermal rapid alteration and the low-temperature gradual alteration processes.

Fujii, M.; Okino, K.; Honsho, C.; Mochizuki, N.; Szitkar, F.; Dyment, J.

2013-12-01

92

Local inversion of magnetic anomalies: Implication for Mars' crustal evolution Yoann Quesnel, Benoit Langlais, Christophe Sotin  

E-print Network

Local inversion of magnetic anomalies: Implication for Mars' crustal evolution Yoann Quesnel location by polar reorientation. Keywords: Mars; Magnetic field; Lithospheric sources; Local inversion detected strong and localized magnetic anomalies on Mars (Acuña et al., 1999). No Earth-like global

Paris-Sud XI, Université de

93

Two-dimensional MHD simulation of the solar wind interaction with magnetic field anomalies on the  

E-print Network

of typical solar wind conditions and the surface magnetic field strengths measured by Lunar ProspectorTwo-dimensional MHD simulation of the solar wind interaction with magnetic field anomalies on the Moon when the magnetic anomaly field strength is above 10 nT at 100 km above the surface (for a surface

Harnett , Erika

94

First scalar magnetic anomaly map from CHAMP satellite data indicates weak lithospheric field  

Microsoft Academic Search

Satellite magnetic anomaly maps derived by different techniques from Magsat\\/POGO data vary by more than a factor of 2 in the deduced strength of the lithospheric magnetic field. Here, we present a first anomaly map from new CHAMP scalar magnetic field data. After subtracting a recent Ørsted main and external field model, we remove remaining unmodeled large-scale external contributions from

S. Maus; M. Rother; R. Holme; H. Lühr; N. Olsen; V. Haak

2002-01-01

95

Initial mapping and interpretation of lunar crustal magnetic anomalies using Lunar Prospector magnetometer data  

Microsoft Academic Search

Maps of relatively strong crustal magnetic field anomalies detected at low altitudes with the magnetometer instrument on Lunar Prospector are presented. On the lunar nearside, relatively strong anomalies are mapped over the Reiner Gamma Formation on western Oceanus Procellarum and over the Rima Sirsalis rille on the southwestern border of Oceanus Procellarum. The main Rima Sirsalis anomaly does not correlate

L. L. Hood; A. Zakharian; J. Halekas; D. L. Mitchell; R. P. Lin; M. H. Acuña; A. B. Binder

2001-01-01

96

Magnetic Structure of Backarc Spreading Axis with Hydrothermal Vents; the Southern Mariana Trough  

NASA Astrophysics Data System (ADS)

Seafloor hydrothermal systems are important in relation to global heat and chemical fluxes as well as habitat of microbial communities. The substantial variation of hydrothermal systems in various tectonic settings has important implications for the magnetic structure of oceanic crust. It has been very difficult to detect the geophysical signature of hydrothermal systems from sea-surface data because the small scale of hydrothermal systems is below the limit of resolution. The advance of near-bottom survey methods using a submersible, deep-tow, ROV and AUV has made possible high-resolution geophysical mapping around hydrothermal areas. Near-bottom magnetic surveys can provide direct information on the magnetization of the shallower oceanic crust, implying hydrothermal alteration both in active and fossil vent sites. Near-bottom three component magnetic measurements on submersible Shinkai 6500 were carried out at hydrothermal fields in the Southern Mariana Trough, a slow spreading backarc basin. Fourteen dive surveys were conducted during cruises YK11-10 and YK10-11. We investigated the magnetic structure of four hydrothermal systems located at on- and off-axis to clarify how the geophysical and geological setting controls the fluid circulation at small scale. Recent researches at slow spreading ridges showed a relationship between crustal magnetic structure and host rock around hydrothermal vents (e.g. Tivey and Dyment, 2010), but no observation at backarc spreading axis has been reported so far. We carefully corrected the effects of induced and permanent magnetizations of the submersible by applying the method of Isezaki [1986] with dumped least-square method (Honsho et al., 2009). After subtracting the IGRF from the corrected observed data, we obtained geomagnetic vector anomalies in geographical coordinate. For three transects of the axis, we applied three methods; 2D inversion technique (Parker and Huestis, 1972), 2D forward modeling technique (Honsho et al, 2009) and 2D direct inversion technique (Hussenoeder et al., 1995). Transect 1 (T1) and transect 2 (T2) are parallel and very closely located, crossing the neo-volcanic zone near an on-axis hydrothermal site (Snail Site) at different altitude, 2m and 30m. Transect 3 (T3) also crosses a large on-axis volcanic mound on which another hydrothermal site (Yamanaka Site) is located. The equivalent magnetization calculated on T1 and T2 are similar although their resolutions are different. The one along T3 shows high values around the large volcanic mound and an area of low magnetization near a hydrothermal field recognized from high-resolution bathymetry (Yoshikawa et al., 2012). A similar reduction of magnetization above hydrothermal fields was also reported in basalt-hosted sites along the Mid Atlantic Ridge. The detailed bathymetry (2m grid) collected by AUV Urashima in the study area allows us to investigate the effect of three dimensional structure. We estimate magnetization using a new technique based on 3D forward modeling (Szitkar et al, this meeting). A preliminary result shows a similar but more detailed magnetic structure around the Yamanaka Site compared to results of the 2D methods.

Fujii, M.; Okino, K.; Mochizuki, N.; Honsho, C.; Szitkar, F.; Dyment, J.; Nakamura, K.

2012-12-01

97

Flare-related Magnetic Anomaly with a Sign Reversal  

NASA Astrophysics Data System (ADS)

In this paper we report a significant magnetic anomaly, specifically an apparent sign reversal of magnetic polarities in small areas of Michelson Doppler Imager (MDI) magnetograms during the impulsive phase of an X5.6 flare on 2001 April 6. Three flare kernels were observed to emit >=50 keV hard X-rays, which are located in strong magnetic fields of order +/-1000-1500 G. We find that the apparent sign reversal began and persisted for a few minutes in all three kernels, in precise temporal and spatial correspondence with the hard X-ray sources. We search for a combination of instrumental and flare-induced line profile effects that can account for this behavior. Our studies provide a viable scenario that the observed transient sign reversal is likely to be produced by distorted measurements when the Ni I 6768 Å line comes into emission or strong central reversal as a result of nonthermal beam impact on the atmosphere in regions of strong magnetic fields.

Qiu, Jiong; Gary, Dale E.

2003-12-01

98

Deep-tow study of magnetic anomalies in the Pacific Jurassic Quiet Zone  

E-print Network

The Jurassic Quiet Zone (JQZ) is a region of low amplitude, difficult-to-correlate magnetic anomalies located over Jurassic oceanic crust. We collected 1200 km of new deep-tow magnetic anomaly profiles over the Pacific JQZ that complement 2 deep...

Tominaga, Masako

2006-10-30

99

ANOMALIES MAGNETIQUES ET DATATION DES FONDS OCEANIQUES : QUARANTE ANS APRES VINE ET MATTHEWS  

E-print Network

By interpreting the marine magnetic anomalies as resulting from seafloor spreading, Vine and Matthews (1963) gave@ipgp.jussieu.fr) Extended English Abstract MAGNETIC ANOMALIES AND AGE OF THE SEAFLOOR: FORTY YEARS AFTER VINE AND MATTHEWS, dating the seafloor using scalar sea-surface magnetic anomalies requires a magnetisation vector non

Déverchère, Jacques

100

Exploring the strength of newly formed oceanic lithosphere and its correlation with spreading rate and ridge depth anomalies  

NASA Astrophysics Data System (ADS)

We have developed a moving window admittance technique to determine the relationship between free-air gravity anomaly and bathymetry as a function of wavelength over the world's ocean basins and their margins. Preliminary results from the Western Pacific Ocean show that the technique resolves the effective elastic thickness (Te), a proxy for long-term (>106 yr) strength, of the oceanic lithosphere to better than ±3 km for Te<20 km over horizontal distances of a few tens of km. In this paper we explore Te results over the global mid-ocean ridge system, show that Te at newly formed lithosphere varies from essentially 0 km to almost 10 km, and explore the correlation between variations in Te, spreading rate, and ridge crest depth to investigate the origins of this variation. We show that for the zero age ridge depth most commonly used in cooling plate models, 2500 m, the median Te is 3.0 km with a median absolute deviation of 1.3 km. Overall, Te increases with increased depth and decreases as spreading rate increases, but back-arc basins and some sections of the Antarctic-Pacific ridge depart from this trend. We also examine the effect of using a theoretical admittance function customised for the ridge environment compared to the standard admittance function for oceanic lithosphere and test for a long wavelength admittance (>500 km), believed to originate in the mantle, and thus indicative of dynamic support through upwelling.

Kalnins, L. M.; Watts, A. B.

2010-12-01

101

Paleomagnetic and rock magnetic characterization of magnetic anomalies in the Central Iberian Arc (Iberian Peninsula)  

NASA Astrophysics Data System (ADS)

The Central Iberian Arc is one of the four oroclines delineated by the European Variscan Belt. It is located in NW and Central Iberia and characterized by a conspicuous magnetic response. The most intense magnetic anomaly within this arc is the so called Eastern Galicia Magnetic Anomaly (EGMA; Aller et al., 1994), located in the northern part of Spain and associated to the Lugo-Sanabria dome, an extensional structure in the inner part of arc. The aeromagnetic map of the Iberian Peninsula (Ardizone et al., 1989; Miranda et al., 1989) shows that the EGMA continues to Central Spain and turns back to the Atlantic Ocean, as a broad positive anomaly, delineating a tight fold at the core of the Central Iberian Arc. The source of the EGMA seems to be magnetite-bearing migmatites and inhomogeneous granites formed during an extensive late Carboniferous thermal event triggered by Variscan crustal thickening. These rocks were modeled as a lens-shaped body up to 12 km thick with magnetic susceptibility values between 0.02and 0.03 SI units, that underlie the whole dome extension and continues toward the west of it (Ayarza and Martínez Catalán, 2007). However, this body crops out only in the deepest and northernmost part of the dome, in the Xistral Tectonic Window, and there, only its upper part is accessible. Migmatites and granitoids are abundant along the rest of the anomaly, but their magnetic susceptibility is low. Thus, the source of the magnetic anomaly should be buried there and its nature is unknown. Paleomagnetic and rock magnetic studies in the outcropping rocks responsible for the EGMA have been carried out, adding new constraints to the origin of this anomaly. Rock magnetic analysis as progressive acquisition of IRM, hysteresis loops, thermomagnetic experiments and X-ray indicate that the ferromagnetic fraction is dominated by multidomain magnetite and titanohematite. It is remarkable the unusual high anisotropy of magnetic susceptibility of these rocks, showing degree of anisotropy values 1.2magnetic fabric shows Variscan affinity, related to an extensional ductile detachment that bounds the Lugo-Sanabria dome to the west. The paleomagnetic analysis consisting in thermal and alternating field demagnetization allows isolating a stable paleomagnetic component with high coercivity and maximum unblocking temperatures of about 630°C, that systematically shows reversed polarity. This component has been interpreted as a remagnetization because its mean direction match those of the Iberian Peninsula after anticlockwise rotation related to the opening of the Bay of Biscay during the Early Cretaceous. All these data must be included in the models in order to place new constraints on the origin, position, and shape of the source and to asses whether all the broad magnetic anomaly at the core of the Central Iberian Arc has the same origin as the EGMA, or a deeper source contributes to it and to the rest of the anomaly.

Villalain, J.; Ayarza, P.; Martinez-Catalan, J. R.; Álvarez-Lobato, F.; Gómez-Barreiro, J.; Suárez Barrios, M.; Torres-López, S.

2013-12-01

102

Airborne detection of magnetic anomalies associated with soils on the Oak Ridge Reservation, Tennessee  

SciTech Connect

Reconnaissance airborne geophysical data acquired over the 35,000-acre Oak Ridge Reservation (ORR), TN, show several magnetic anomalies over undisturbed areas mapped as Copper Ridge Dolomite (CRD). The anomalies of interest are most apparent in magnetic gradient maps where they exceed 0.06 nT/m and in some cases exceed 0.5 nT/m. Anomalies as large as 25nT are seen on maps. Some of the anomalies correlate with known or suspected karst, or with apparent conductivity anomalies calculated from electromagnetic data acquired contemporaneously with the magnetic data. Some of the anomalies have a strong correlation with topographic lows or closed depressions. Surface magnetic data have been acquired over some of these sites and have confirmed the existence of the anomalies. Ground inspections in the vicinity of several of the anomalies has not led to any discoveries of manmade surface materials of sufficient size to generate the observed anomalies. One would expect an anomaly of approximately 1 nT for a pickup truck from 200 ft altitude. Typical residual magnetic anomalies have magnitudes of 5--10 nT, and some are as large as 25nT. The absence of roads or other indications of culture (past or present) near the anomalies and the modeling of anomalies in data acquired with surface instruments indicate that man-made metallic objects are unlikely to be responsible for the anomaly. The authors show that observed anomalies in the CRD can reasonably be associated with thickening of the soil layer. The occurrence of the anomalies in areas where evidences of karstification are seen would follow because sediment deposition would occur in topographic lows. Linear groups of anomalies on the maps may be associated with fracture zones which were eroded more than adjacent rocks and were subsequently covered with a thicker blanket of sediment. This study indicates that airborne magnetic data may be of use in other sites where fracture zones or buried collapse structures are of interest.

Doll, W.E.; Beard, L.P. [Oak Ridge National Lab., TN (United States). Environmental Sciences Div.; Helm, J.M. [Univ. of Utah, Salt Lake City, UT (United States). Dept. of Geology and Geophysics

1995-04-01

103

Solar wind interaction with a lunar magnetic anomaly: Hybrid modelling results  

NASA Astrophysics Data System (ADS)

New in situ plasma, neutral atom and magnetic field observations done by recent lunar missions have revealed that the solar wind interaction with the Moon is more complex and scientifically more interesting than anticipated before. Especially, an unexpectedly high fraction of the incident solar wind protons is reflected from the surface, and an even larger fraction by the lunar magnetic anomalies. Such reflection has been observed both by measuring deviated solar wind ion flow near the magnetic anomalies and by observing decreased flux of energetic neutral hydrogen atoms, H-ENAs, from the surface region of strong magnetic anomalies. These processes affect the properties of plasma near the lunar surface. In this work we study the solar wind interaction with a lunar magnetic anomaly by a 3D hybrid model (HYB-Anomaly). In the hybrid model, ions are modelled as particles while electrons form a charge neutralizing massless fluid. The HYB-Anomaly model can also simulate H-ENA productions when the solar wind protons hit against the surface. The magnetic anomaly has a surface strength of the order of 100nT, producing an interaction region with length scales at or below proton inertial length scales. We find an upward electric field responsible for the deceleration of precipitating protons, which is consistent with observed H-ENA features. In this presentation, we further discuss the dependence of H-ENA emissions on the direction of the interplanetary magnetic field.

Alho, Markku; Jarvinen, Riku; Kallio, Esa; Wurz, Peter; Barabash, Stas; Futaana, Yoshifumi

2014-05-01

104

Contributions of cretaceus quiet zone natural remanent magnetization to Magsat anomalies in the Southwest Indian Ocean  

NASA Technical Reports Server (NTRS)

The Magsat magnetic anomalies over the Southwest Indian Ocean are modeled using a combination of induced plus viscous remanent magnetization (IM/VRM) and natural remanent magnetization (NRM). Two broad, roughly parallel, SW to NE trending triple-peaked positive anomalies dominate the region, one lying south of Africa and the other north of Antarctica. Although these anomaly peaks generally correspond with the Agulhas Plateau/Maud Rise, Mozambique Plateau/Astrid Ridge, and Madagascar Ridge/Conrad Rise conjugate pairs, the IM/VRM contribution from structural characteristics (i.e., crustal thickness) accounts for only about 20% of the anomaly amplitudes. A spatially variable but observationally constrained NRM contribution in Cretaceous Quiet Zone (KQZ) crust is required to account for the location, shape, and amplitude contrast of these anomalies. Many crustal features in the Southwest Indian Ocean near Antarctica have little geophysical data to constrain their structure but do hagve tectonic conjugates near Africa for which much more geophysical data are generally available. Using geophysical and geological constraints from one member to model the magnetization structure of its conjugate reproduces the observed Magsat reduced-to-pole anomalies over both structures very well. This suggests that no significant alteration in their magnetization structure has occurred since the features split. Models of these conjugate structures show that IM/VRM reproduces the Magsat anomalies associated with non-KQZ crust but that both IM/VRM and a dominant NRM component are required to explain the anomalies associated with KQZ crust.

Fullerton, Lawrence G.; Frey, Herbert V.; Roark, James H.; Thomas, Herman H.

1994-01-01

105

Rock-magnetic and remanence properties of synthetic Fe-rich basalts: Implications for Mars crustal anomalies  

E-print Network

Rock-magnetic and remanence properties of synthetic Fe-rich basalts: Implications for Mars crustal sample set can easily account for the observed 1000-nT Mars magnetic anomalies, even in a magnetized magnetism; TRM; titanomagnetite; Mars; magnetic anomalies; Mars Global Surveyor Earth and Planetary Science

Hammer, Julia Eve

106

Magnetic Anomalies of the Fennoscandian Shield on a 2km resolution grid  

NASA Astrophysics Data System (ADS)

Joint magnetic anomaly grid of the Fennoscandian Shield was released 2002, smoothed and used as data for the WDMAM2007. In comparison with MF5 this grid showed superior characteristics to other sets. The data will be released as a 2 km resolution grid for the WDMAM2011 with eventual updates of anomaly levels.

Korhonen, Juha V.; Aaro, Sven; Reidar Skilbrei, Jan; All, Tarmo

2010-05-01

107

Long-wavelength Magnetic and Gravity Anomaly Correlations of Africa and Europe  

NASA Technical Reports Server (NTRS)

Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic Shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.

Vonfrese, R. R. B.; Hinze, W. J. (principal investigators); Olivier, R.

1984-01-01

108

Long-wavelength magnetic and gravity anomaly correlations on Africa and Europe  

NASA Technical Reports Server (NTRS)

Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.

Vonfrese, R. R. B.; Olivier, R.; Hinze, W. J.

1985-01-01

109

Estimating Antarctic near-surface magnetic anomalies from Oersted and CHAMP satellite magnetometer observations  

Microsoft Academic Search

Significant improvement in predicting near-surface magnetic anomalies can result from the highly accurate magnetic observations of the CHAMP satellite that is orbiting at about 400 km altitude. In general, regional magnetic signals of the crust are strongly masked by the core field and its secular variations due to wavelength coupling in the spherical harmonic representation and thus are difficult to

R. R. von Frese; H. Kim; L. R. Gaya-Pique; P. T. Taylor; A. V. Golynsky; J. Kim

2004-01-01

110

Study on velocity spread for axis-encircling electron beams generated by single magnetic cusp  

NASA Astrophysics Data System (ADS)

The physical characteristics of an annular Pierce-type electron gun are investigated analytically. The electron gun is used in conjunction with a nonadiabatic magnetic reversal and adiabatic compression region to produce an axis-encircling beam. Typical magnetic field profiles that can generate zero velocity spreads are obtained from the analytical calculation, taking into account initial canonical angular momentum spreads at the cathode and the crossing of the beam trajectory and magnetic flux line before the magnetic cusp. Using this magnetic fields, a fairly low axial velocity spread of less than 1% is achieved by an electron trajectory program [W. B. Hermannsfeldt, Electron Trajectory Program (Stanford Linear Acceleration Center, Stanford, CA, 1979)], which agrees well with that by analytical estimation.

Jeon, S. G.; Baik, C. W.; Kim, D. H.; Park, G. S.; Sato, N.; Yokoo, K.

2002-05-01

111

High-altitude structure of the magnetic anomalies using the gradient measurements in stratosphere  

NASA Astrophysics Data System (ADS)

HIGH-ALTITUDE STRUCTURE OF THE MAGNETIC ANOMALIES USING THE GRADIENT MEASUREMENTS IN STRATOSPHERE Yu. Tsvetkov, N. ROTANOVA, M. Belikova Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAS, Troitsk, Moscow Region, 142190, Russia rotanova@izmiran.rssi.ru/FAX: +7-095-3340124 Method of the recalculation of the anomaly magnetic field over the range of the altitudes of 20-40 km is suggested. Technique is based on the experimental data of the anomaly magnetic field, its vertical gradient and the gradient increment along vertical line, obtained from the aerostat gradient magnetic surveys in stratosphere. The high-altitude structure of the magnetic anomalies, obtained for the Baikal region has been constructed. These results were used to obtain the estimations of the deep magnetic sources. The numerous values of the low boundary of the sources are 30-35 km. These estimations of the depth coincide with the ones, obtained from the results of the spectral analysis of the same magnetic anomalies.

Tsvetkov, Yu.; Rotanova, N.; Belikova, M.

2003-04-01

112

Magnetic Anomalies Within Lunar Impact Basins: Constraints on the History of the Lunar Dynamo  

NASA Astrophysics Data System (ADS)

Previous work has shown that lunar crustal magnetization has a combination of origins including shock remanent magnetization in transient magnetic fields and thermoremanent magnetization in a steady core dynamo magnetic field (e.g., Hood and Artemieva, Icarus, 2008; Richmond and Hood, JGR, 2008; Garrick-Bethell et al., Science, 2009; Hood, Icarus, 2011). In particular, magnetic anomalies within the interiors of lunar impact basins and large craters provide a potentially valuable means of constraining the history of the former dynamo (Halekas et al., MAPS, 2003; Hood, 2011). These anomalies likely have a thermoremanent origin owing to high subsurface temperatures reached at the time of impact and therefore require a long-lived, steady magnetic field to explain their magnetization. Central anomalies have previously been confirmed to be present using Lunar Prospector magnetometer (LP MAG) data within several Nectarian-aged basins (Moscoviense, Mendel-Rydberg, Crisium, and Humboldtianum), implying that a dynamo existed during this lunar epoch (Hood, 2011). Here, we further analyze low altitude LP MAG data for several additional basins, ranging in age from Nectarian to Imbrian. Results indicate that magnetic anomalies with a probable basin-related origin are present within at least two additional Nectarian-aged basins (Serenitatis and Humorum) and one Imbrian-aged basin (Schrodinger). No discernible anomalies are present within the largest Imbrian-aged basins, Imbrium and Orientale. While there is uncertainty regarding the age of the Schrodinger basin, it has been reported to be slightly more recent than Imbrium (Wilhelms, 1984). Our initial interpretation is therefore that a dynamo likely existed during the Imbrian epoch. The absence of anomalies within Imbrium and Orientale can be explained by insufficient conditions for acquisition of strong magnetization (e.g., inadequate concentrations of efficient remanence carriers) following these relatively large impacts.

Richmond, N. C.; Hood, L. L.

2011-12-01

113

Evidence for seafloor spreading in the Laxmi Basin, northeastern Arabian Sea  

Microsoft Academic Search

Main magnetic anomaly data from the Laxmi Basin for the first time reveal the presence of fairly correlatable NNW-trending magnetic lineations. These magnetic lineations are symmetric about a central negative magnetic anomaly and the axis of symmetry coincides with a characteristic short-wavelength free-air gravity low. The anomalies are interpreted as representing a two-limbed seafloor spreading sequence which can be equated

G. C. Bhattacharya; A. K. Chaubey; G. P. S. Murty; K. Srinivas; V. Subrahmanyam; K. S. Krishna

1994-01-01

114

Reduced to Pole Long-wavelength Magnetic Anomalies of Africa and Europe  

NASA Technical Reports Server (NTRS)

To facilitate analysis of the tectonic framework for Africa, Europe and adjacent marine areas, MAGSAT scalar anomaly data are differentially reduced to the pole and compared to regional geologic information and geophysical data including surface free-air gravity anomaly data upward continued to satellite elevation (350 km) on a spherical Earth. Comparative analysis shows magnetic anomalies correspond with both ancient as well as more recent Cenozoic structural features. Anomalies associated with ancient structures are primarily caused by intra-crustal lithologic variations such as the crustal disturbance associated with the Bangui anomaly in west-central Africa. Anomalies correlative with Cenozoic tectonic elements appear to be related to Curie isotherm perturbations. A possible example of the latter is the well-defined trend of magnetic minima that characterize the Alpine orogenic belt from the Atlas mountains to Eurasia. In contrast, a well-defined magnetic satellite minimum extends across the stable craton from Finland to the Ural mountains. Prominent magnetic maxima characterize the Arabian plate, Iceland, the Kursk region of the central Russian uplift, and generally the Precambrian shields of Africa.

Hinze, W. J.; Vonfrese, R. R. B. (principal investigators); Olivier, R.

1984-01-01

115

Reduced to pole long-wavelength magnetic anomalies of Africa and Europe  

NASA Technical Reports Server (NTRS)

To facilitate analysis of the tectonic framework for Africa, Europe and adjacent marine areas, MAGSAT scalar anomaly data are differentially reduced to the pole and compared to regional geologic information and geophysical data including surface free-air gravity anomaly data upward continued to satellite elevation (350 km) on a spherical Earth. Comparative analysis shows magnetic anomalies correspond with both ancient as well as more recent Cenozoic structural features. Anomalies associated with ancient structures are primarily caused by intra-crustal lithologic variations such as the crustal disturbance associated with the Bangui anomaly in west-central Africa. Anomalies correlative with Cenozoic tectonic elements appear to be related to Curie isotherm perturbations. A possible example of the latter is the well-defined trend of magnetic minima that characterize the Alphine orogenic belt from the Atlas mountains to Eurasia. In contrast, a well-defined magnetic satellite minimum extends across the stable craton from Finland to the Ural mountains. Prominent magnetic maxima characterize the Arabian plate, Iceland, the Kursk region of the central Russian uplift, and generally the Precambrian shields of Africa.

Olivier, R.; Hinze, W. J.; Vonfrese, R. R. B.

1985-01-01

116

Satellite-Altitude Geopotential Study of the Kursk Magnetic Anomaly (KMA)  

NASA Technical Reports Server (NTRS)

With the successful launch of the Orsted, SAC-C and CHAMP satellites we are able to make both magnetic and gravity anomaly maps of the Earth's crust; magnetic from all three missions and gravity with CHAMP. We have used these data to study the KMA area of Russia. This is an important region for several reasons: (1) we have already made satellite magnetic anomaly maps of this region and they can be integrated with the gravity data from CHAMP for a comprehensive interpretation; (2) KMA contains the largest know reserves of iron-ore in the world; and (3) there are significant ground truth data available for this region from aeromagnetic, balloon surveys and geophysical mapping, including extensive rock magnetic/paleo-magnetic and geologic studies. Utilizing the gravity observations, collocated with the magnetic data enabled us to make a joint interpretation. While there is a high amplitude magnetic anomaly recorded over the KMA the gravity anomaly at satellite altitude revealed by CHAMP is only around 3-6 mGal but is not centered on the magnetic high. This would indicate that despite the fact that in the region of the KMA the rocks have a higher percentage of iron than in the surrounding formations the entire area is Archean-Proterozoic in age and therefore very dense.

Taylor, Patrick T.; Kim, Hyung Rae; vonFrese, Ralph R. B.; Potts, Laramie V.; Frawley, James J.

2003-01-01

117

Marine Magnetic Anomalies, Geomagnetic Field Reversals, and Motions of the Ocean Floor and Continents  

Microsoft Academic Search

This paper summarizes the results of the three previous papers in this series, which have shown the presence of a pattern of magnetic anomalies, bilaterally symmetric about the crest of the ridge in the Pacific, Atlantic, and Indian oceans. By assuming that the pattern is caused by a sequence of normally and reversely magnetized blocks that have been produced by

J. R. Heirtzler; G. O. Dickson; E. M. Herron; W. C. Pitman; X. Le Pichon

1968-01-01

118

An overview of new methods for deriving and interpreting satellite magnetic anomaly maps  

Microsoft Academic Search

Since July 2000, the low orbiting CHAMP satellite is measuring the magnetic field in unprecedented resolution and accuracy. After 2009, the Swarm constellation of satellites will provide even more accurate measurements, including the east-west vector gradients of the field. Even with the exceptional data quality, compiling high resolution magnetic anomaly maps remains a formidable task. Due to attenuation with altitude,

S. Maus; K. Hemant

2005-01-01

119

Enhanced Electron Precipitation in Brazilian Magnetic Anomaly in association with Sudden Commencement  

NASA Astrophysics Data System (ADS)

Following the first satellite observations of enhanced particle flux in the region of the Brazilian Magnetic Anomaly1,2, various attempts have been made to detect effects associated with the precipitation of radiation belt particles over the region of this anomaly at balloon altitudes3. Since 1968 balloon observations of charged particles and X-rays have been made periodically at the Instituto de Pesquisas Espaciais at São José dos Campos, Brazil. During one of the flights on December 17, 1971, a moderate geomagnetic storm occurred when the balloon was floating at a ceiling altitude of ~3 mbar. Marked changes in the measured particle flux were observed in association with the changes in the magnetic field. As well as pointing out this correspondence we discuss the observational results in relation to observations made on April 6, 1972, during a magnetically quiet period. To our knowledge this is the first direct detection of particle precipitation in the magnetic anomaly at balloon altitudes.

Martin, I. M.; Rai, D. B.; da Costa, J. M.; Palmeira, R.; Trivedi, N. B.

1972-11-01

120

Observations of magnetic anomaly signatures in Mars Express ASPERA-3 ELS data  

NASA Astrophysics Data System (ADS)

Mars Express (MEX) Analyser of Space Plasmas and Energetic Atoms (ASPERA-3) data is providing insights into atmospheric loss on Mars via the solar wind interaction. This process is influenced by both the interplanetary magnetic field (IMF) in the solar wind and by the magnetic 'anomaly' regions of the martian crust. We analyse observations from the ASPERA-3 Electron Spectrometer near to such crustal anomalies. We find that the electrons near remanent magnetic fields either increase in flux to form intensified signatures or significantly reduce in flux to form plasma voids. We suggest that cusps intervening neighbouring magnetic anomalies may provide a location for enhanced escape of planetary plasma. Initial statistical analysis shows that intensified signatures are mainly a dayside phenomenon whereas voids are a feature of the night hemisphere.

Soobiah, Y.; Coates, A. J.; Linder, D. R.; Kataria, D. O.; Winningham, J. D.; Frahm, R. A.; Sharber, J. R.; Scherrer, J. R.; Barabash, S.; Lundin, R.; Holmström, M.; Andersson, H.; Yamauchi, M.; Grigoriev, A.; Kallio, E.; Koskinen, H.; Säles, T.; Riihelä, P.; Schmidt, W.; Kozyra, J.; Luhmann, J.; Roelof, E.; Williams, D.; Livi, S.; Curtis, C. C.; Hsieh, K. C.; Sandel, B. R.; Grande, M.; Carter, M.; Sauvaud, J.-A.; Fedorov, A.; Thocaven, J.-J.; McKenna-Lawler, S.; Orsini, S.; Cerulli-Irelli, R.; Maggi, M.; Wurz, P.; Bochsler, P.; Krupp, N.; Woch, J.; Fränz, M.; Asamura, K.; Dierker, C.

2006-06-01

121

Weak extremely-low-frequency magnetic field-induced regeneration anomalies in the planarian, Dugesia tigrina  

SciTech Connect

The authors recently reported that cephalic regeneration in the planarian Dugesia tigrina was significantly delayed in populations exposed continuously to combined parallel DC and AC magnetic fields. This effect was consistent with hypotheses suggesting an underlying resonance phenomenon. The authors report here, in a parallel series of investigations on the same model system, that the incidence of regeneration anomalies presenting as tumor-like protuberances also increases significantly (P < .001) in association with exposure to weak 60 Hz magnetic fields, with peak intensities ranging between 1.0 and 80.0 {micro}T. These anomalies often culminate in the complete disaggregation of the organism. Similar to regeneration rate effects, the incidence of regeneration anomalies is specifically dependent upon the planaria possessing a fixed orientation with respect to the applied magnetic field vectors. However, unlike the regeneration rate effects, the AC magnetic field alone, in the absence of any measurable DC field, is capable of producing these anomalies. Moreover, the incidence of regeneration anomalies follows a clear dose-response relationship as a function of AC magnetic field intensity, with the threshold for induced electric field intensity estimated at 5 {micro} V/m. The addition of either 51.1 or 78.4 {micro}T DC magnetic fields, applied in parallel combination with the AC field, enhances the appearance of anomalies relative to the 60 Hz AC field alone, but only at certain AC field intensities. Thus, whereas the previous study of regeneration rate effects appeared to involve exclusively resonance interactions, the regeneration anomalies reported here appear to result primarily from Faraday induction coupling.

Jenrow, K.A.; Smith, C.H.; Liboff, A.R. [Oakland Univ., Rochester, MI (United States). Dept. of Physics] [Oakland Univ., Rochester, MI (United States). Dept. of Physics

1996-12-31

122

The intermediate wavelength magnetic anomaly field of the north Pacific and possible source distributions  

NASA Technical Reports Server (NTRS)

A technique that eliminates external field sources and the effects of strike aliasing was used to extract from marine survey data the intermediate wavelength magnetic anomaly field for (B) in the North Pacific. A strong correlation exists between this field and the MAGSAT field although a directional sensitivity in the MAGSAT field can be detected. The intermediate wavelength field is correlated to tectonic features. Island arcs appear as positive anomalies of induced origin likely due to variations in crustal thickness. Seamount chains and oceanic plateaus also are manifested by strong anomalies. The primary contribution to many of these anomalies appears to be due to a remanent magnetization. The source parameters for the remainder of these features are presently unidentified ambiguous. Results indicate that the sea surface field is a valuable source of information for secular variation analysis and the resolution of intermediate wavelength source parameters.

Labrecque, J. L.; Cande, S. C.; Jarrard, R. D. (principal investigators)

1983-01-01

123

The mineralogy of global magnetic anomalies. [rock magnetic signatures and MAGSAT geological, and gravity correlations in West Africa  

NASA Technical Reports Server (NTRS)

Problems with the Curie balance, which severely hindered the acquisition of data, were rectified. Chemical analytical activities are proceeding satisfactorily. The magnetization characteristics of metamorphic suites were analyzed and susceptibility data for a wide range of metamorphic and igneous rocks. These rock magnetic signatures are discussed as well as the relationships between geology, gravity and MAGSAT anomalies of West Africa.

Haggerty, S. E. (principal investigator)

1982-01-01

124

The Smoking Gun: Remanent Magnetic Anomalies on Mars and the Formation of the Crustal Dichotomy via Giant Impact  

NASA Astrophysics Data System (ADS)

The formation of large-scale crustal magnetic anomalies in the Southern Highlands of Mars is equivocal. Though some are indeed elongated primarily in the east-west direction, initial map projections exacerbated their linear nature, leading to the hypothesis that the anomalies are equivalent to magnetic stripes due to spreading of Earth's sea floor and hence to the proposal of plate tectonics on Mars. This interpretation, however, is inconsistent with Martian geology. For instance, a plate-tectonics model predicts the anomalies should be formed in thin, oceanic crust at low elevation, but instead they are found in the thick crust of the Highlands, not in the thin crust of the Northern Lowlands. Indeed, the formation of this Crustal Dichotomy is also equivocal, with models ranging from a giant impact (or multiple smaller impacts) near either the current north or south poles, to plate tectonics-like processes, to mantle convection, either eroding the crust in the northern hemisphere or thickening the crust in the south. Recently, the idea of a giant impact in the north has been resurrected, with the proposal that the Dichotomy results from the formation of an elliptical basin by a giant impact very early in Martian history. While it may be tempting to suggest that the current, generally demagnetized state of the Northern Lowlands may be related to this impact, this linkage makes implicit assumptions about the timing of dynamo shut-off on Mars, and it neglects other demagnetization mechanisms possibly operating in the Lowlands after such an impact (e.g., later hydrothermal processing). More direct magnetic evidence for the giant impact hypothesis would come if the remanent magnetism in Southern Highlands were relatable in a unique way to the putative impact. Here, we show that the positions of many of the dominant elongated magnetic anomalies on Mars are consistent with the first ring of a multi-ring basin. The best match comes from an ellipse ~2200 km wider than the inferred boundary of the basin. This distance is the square root of 2 minus 1 of the long axis, and root-2 spacing is characteristic of the inward dipping normal faults in multi-ring basins. The constant distance of our predicted ring, as opposed to variable spacing due to the elliptical nature of the basin, is also consistent with the idea that multi-ring basins form from stress release during inward collapse of the transient crater. Because of the size of the basin, the second ring would be found in the antipodal region, where its formation is dubious and where seismic focusing from the impact has been proposed to explain the generally absent magnetic anomalies in the south polar region. The observation that the elongated magnetic anomalies on Mars mark the first ring around a basin both provides an explanation for the formation of many of the anomalies, and supports the hypothesis that the Crustal Dichotomy of Mars is the product of a giant impact that formed an elliptical basin.

Dombard, A. J.; Johnson, C. L.

2011-12-01

125

Lunar Magnetic Field Observation and Initial Global Mapping of Lunar Magnetic Anomalies by MAP-LMAG Onboard SELENE (Kaguya)  

NASA Astrophysics Data System (ADS)

The magnetic field around the Moon has been successfully observed at a nominal altitude of ˜100 km by the lunar magnetometer (LMAG) on the SELENE (Kaguya) spacecraft in a polar orbit since October 29, 2007. The LMAG mission has three main objectives: (1) mapping the magnetic anomaly of the Moon, (2) measuring the electromagnetic and plasma environment around the Moon and (3) estimating the electrical conductivity structure of the Moon. Here we review the instrumentation and calibration of LMAG and report the initial global mapping of the lunar magnetic anomaly at the nominal altitude. We have applied a new de-trending technique of the Bayesian procedure to multiple-orbit datasets observed in the tail lobe and in the lunar wake. Based on the nominal observation of 14 months, global maps of lunar magnetic anomalies are obtained with 95% coverage of the lunar surface. After altitude normalization and interpolation of the magnetic anomaly field by an inverse boundary value problem, we obtained full-coverage maps of the vector magnetic field at 100 km altitude and the radial component distribution on the surface. Relatively strong anomalies are identified in several basin-antipode regions and several near-basin and near-crater regions, while the youngest basin on the Moon, the Orientale basin, has no magnetic anomaly. These features well agree with characteristics of previous maps based on the Lunar Prospector observation. Relatively weak anomalies are distributed over most of the lunar surface. The surface radial-component distribution estimated from the inverse boundary value problem in the present study shows a good correlation with the radial component distribution at 30 km altitude by Lunar Prospector. Thus these weak anomalies over the lunar surface are not artifacts but likely to be originated from the lunar crustal magnetism, suggesting possible existence of an ancient global magnetic field such as a dynamo field of the early Moon. The possibility of the early lunar dynamo and the mechanism of magnetization acquisition will be investigated by a further study using the low-altitude data of the magnetic field by Kaguya.

Tsunakawa, Hideo; Shibuya, Hidetoshi; Takahashi, Futoshi; Shimizu, Hisayoshi; Matsushima, Masaki; Matsuoka, Ayako; Nakazawa, Satoru; Otake, Hisashi; Iijima, Yuichi

2010-07-01

126

Study on crustal magnetic anomalies and Curie surface in Southeast Tibet  

NASA Astrophysics Data System (ADS)

In this paper, the Potsdam model POMME-6.2 is used to investigate the distributions of crustal magnetic anomalies and Curie surface in Southeast Tibet. The Curie surface is compared with the regional heat flow, Bouguer anomaly, Moho depth, and seismicity. The results show that the magnetic anomalies and Curie surface are both consistent with the geological structure. Sichuan Basin exhibits a high positive anomaly, while orogenic belts such as the Longmenshan, northwestern Sichuan, and western Yunnan, exhibit weak positive or negative anomalies. The distribution of magnetic anomaly confirms that escape flow from east Tibet branches into northeastward part and southward part on west Sichuan Basin, due to resistance by the rigid basin. The depth of Curie surface ranges from 20 to 34 km. The Curie surface beneath the Longmenshan, Xiaojiang and Lijiang-Xiaojinhe faults is shallow, with the uplift strike consistent with the faults. The Curie surface beneath Sichuan Basin and the central Bayan Har massif is deep, with sheet-like depressions. Strong earthquakes primarily occurred in the areas with the uplift of Curie surface. The heat flow values near Tengchong, Lijiang, Dali and Kunming are high and the Curie surface there is shallow.

Gao, Guoming; Kang, Guofa; Bai, Chunhua; Wen, Limin

2015-01-01

127

Interpretations of gravity and magnetic anomalies in the Songliao Basin with Wavelet Multi-scale Decomposition  

NASA Astrophysics Data System (ADS)

In this paper, we introduce the method of Wavelet Multi-scale Decomposition (WMD) combined with Power Spectrum Analysis (PSA) for the separation of regional gravity and magnetic anomalies. The Songliao Basin is situated between the Siberian Plate and the North China Plate, and its main structural trend of gravity and magnetic anomaly fields is NNE. The study area shows a significant feature of deep collage-type construction. According to the feature of gravity field, the region was divided into five sub-regions. The gravity and magnetic fields of the Songliao Basin were separated using WMD with a 4th order separation. The apparent depth of anomalies in each order was determined by Logarithmic PSA. Then, the shallow high-frequency anomalies were removed and the 2nd-4th order wavelet detail anomalies were used to study the basin's major faults. Twenty-six faults within the basement were recognized. The 4th order wavelet approximate anomalies were used for the inversion of the Moho discontinuity and the Curie isothermal surface.

Li, Changbo; Wang, Liangshu; Sun, Bin; Feng, Runhai; Wu, Yongjing

2015-01-01

128

Why are There So Few Magnetic Anomalies in Martian Lowlands and Basins?  

NASA Technical Reports Server (NTRS)

The discovery of large areas of strongly magnetized crust on Mars [1,2] provides important information on the timing of both crustal and deeper interior processes on that planet. Critical to an understanding of that timing, as well as to the processes that have contributed to the magnetization and demagnetization of crustal materials, is the geographical distribution of magnetic anomalies discernible from spacecraft orbit. The paucity of resolved magnetic anomalies in the northern lowlands and within and surrounding the best-preserved major impact basins has been noted since the crustal field was first globally mapped [1], but no straightforward explanation of that full pattern has yet been offered. Here we suggest that ancient hydrothermal alteration of magnetic carriers in Martian lowlands and basins may have contributed to the magnetization distribution observed today.

Solomon, Sean C.; Aharonson, Oded; Banerdt, W. Bruce; Dombard, Andrew J.; Frey, Herbert V.; Golombek, Matthew P.; Hauck, Steven A., II; Head, James W., III; Johnson, Catherine L.; McGovern, Patrick J.

2003-01-01

129

Soil Magnetism and Magnetic Anomalies at the Marshall's Pen Archaeological Site, Mandeville, Jamaica  

NASA Astrophysics Data System (ADS)

Marshall's Pen, a 1000-acre parcel of land in Mandeville, Jamaica, underlain by limestone bedrock and bauxite soils, served as a coffee plantation in the early 19th century. Two to three hundred slaves of African descent worked the plantation from AD 1802 until slavery was abolished in Jamaica in 1838. The goal of the archaeological program at Marshall's Pen is to complement what little is known about Jamaican slave society from the historical record. Geophysical prospection was conducted at Marshall's Pen by ten undergraduate students as part of a Keck Geology Consortium project in the summer of 1999. In the slaves' village consisting of living and domestic labor areas, G858 cesium vapor magnetometer readings were taken every 0.1 seconds along 49 profiles, each 50 m long and spaced 1 meter apart, and magnetic susceptibility readings were taken at 1-meter intervals. Seven significant magnetic anomalies (up to 100 nT peak-to-peak) were detected in the village. Two of these were found to be caused by a buried machete and an iron woodworking tool. Three anomalies were associated with a large area of black, burned soil. Archaeological testing in this area produced partially carbonized seeds, charcoal, ceramics that were smudged after manufacture, and cutlery; this evidence suggests a domestic kitchen area. In situ susceptibility readings were zero on bedrock and low on the bauxite soils. Susceptibility readings generally correlated with the magnetics, to values as high as 50 (x 10-6, volume specific SI) in the ``kitchen'' area, suggesting a source in the susceptibility contrast for these magnetic anomalies. Soil samples were collected from the bauxite outside the village, and from the village area in the summer of 2001; ten village sites were sampled away from the kitchen area, and four from the kitchen area. Five samples from each site were boxed, weighed, and measured for laboratory susceptibility measurements. Eleven samples outide the village had a geometric mean susceptibility of 144 (x 10-8, mass-specific SI); forty-nine samples from the ten village off-kitchen sites had a mean susceptibility of 105; twenty samples from the four village on-kitchen sites had a mean susceptibility of 821. One sample from a village off-kitchen site had a susceptibility of 1894 due to the head of a roofing nail included in the sample. Isothermal remanent magnetization experiments were carried out on one sample from most sites. Three samples from outside the village had ratios of IRM(0.1T)/IRM(1.0T) of 0.76, 0.5, and 0.74; ratios for ten samples from the village away from the kitchen were between 0.72-0.77; ratios for two samples from the village in the kitchen were more easily saturated with values of 0.90 and 1.0. The susceptibility and IRM results are consistent with reduction of hematite from sites outside the kitchen to magnetite or maghemite at sites within the kitchen area. The resulting higher susceptibilities could generate the magnetic anomalies in this area.

Figueroa, E.; Sternberg, R. S.; Delle, J. A.; Lawrence, N. D.; McAdoo, B. G.; Savina, M. E.

2002-05-01

130

A Maastrichtian palaeomagnetic pole for the Pacific plate from a skewness analysis of marine magnetic anomaly 32  

NASA Astrophysics Data System (ADS)

The asymmetry (skewness) of marine magnetic anomaly 32 (72.1-73.3 Ma) on the Pacific plate has been analysed in order to estimate a new palaeomagnetic pole. Apparent effective remanent inclinations of the seafloor magnetization were calculated from skewness estimates of 108 crossings of anomaly 32 distributed over the entire Pacific plate and spanning a great-circle distance of ~12 000 km. The data were inverted to obtain a palaeomagnetic pole at 72.1 degN, 26.8 degE with a 95 per cent confidence ellipse having a 4.0 deg major semi-axis oriented 98 deg clockwise of north and a 1.8 deg minor semi-axis; the anomalous skewness is 14.2 deg+/-3.7 deg. The possible dependence of anomalous skewness on spreading rate was investigated with two empirical models and found to have a negligible effect on our palaeopole analysis over the range of relevant spreading half-rates, ~25 to ~90 mm yr^-1. The new pole is consistent with the northward motion for the Pacific plate indicated by coeval palaeocolatitude and palaeoequatorial data, but differs significantly from, and lies to the northeast of, coeval seamount poles. We attribute the difference to unmodelled errors in the seamount poles, mainly in the declinations. Comparison with the northward motion inferred from dated volcanoes along the Hawaiian-Emperor seamount chain indicates 13 deg of southward motion of the Hawaiian hotspot since 73 Ma. When the pole is reconstructed with the Pacific plate relative to the Pacific hotspots, it differs by 14 deg-18 deg from the position of the pole relative to the Indo-Atlantic hotspots. This has several possible explanations including bias in one or more of the palaeomagnetic poles, motion between the Pacific and Indo-Atlantic hotspots, and errors in plate reconstructions relative to the hotspots.

Petronotis, Katerina E.; Gordon, Richard G.

1999-10-01

131

Craton vs. rift uppermost mantle contributions to magnetic anomalies in the United States interior  

NASA Astrophysics Data System (ADS)

The interpretation of satellite magnetic information (Magsat, Oersted, CHAMP, Swarm) requires the understanding of the mineralogy of crustal and mantle sources. Also, spectral analysis of magnetic data over forearcs and cratons calls for upper mantle contribution. The prospect of such a contribution contradicts the view that the mantle is too hot and its magnetism is too weak to influence magnetic anomalies. Here we examine the rock magnetic properties of fresh mantle xenoliths from four settings across the United States: phlogopite-spinel dunites from the Bearpaw Mountains, Montana, and lherzolites/harzburgites from San Carlos, Arizona; Kilbourne Hole, New Mexico; and Knippa, Texas. Paleomagnetic results show single-component natural remanent magnetizations (NRMs), which, combined with optical and secondary electron microscopy support the lack of post-eruption alteration and absence of host-rock contamination. The NRM carriers include magnetite at Bearpaw Mountain and San Carlos, and pyrrhotite at Kilbourne Hole and Knippa. These four areas show continental crust of distinct thicknesses and various geotherms. The potential mantle contribution to magnetic anomalies is forward modeled using crustal thickness, current geotherm and average magnetic properties of xenoliths. The San Carlos and Kilbourne Hole mantle, situated near the Rio Grande Rift is too hot and its magnetism is too weak to contribute to anomalies. The sulfide-dominated assemblage at Knippa does not support magnetization at mantle depths. In contrast, the Bearpaw Mountains combine a relatively cold geotherm (craton) and abundance of magnetite formed at mantle depth. This cratonic mantle, metasomatized by fluids from the Farallon plate, may contribute to long wavelength magnetic anomalies.

Friedman, S. A.; Feinberg, J. M.; Ferré, E. C.; Demory, F.; Martín-Hernández, F.; Conder, J. A.; Rochette, P.

2014-06-01

132

Magnetic anomalies in east Pacific using MAGSAT data  

NASA Technical Reports Server (NTRS)

Methods for solving problems encountered in separating the core field from the crustal field are summarized as well as those methods developed for inverting total magnetic field data to obtain source functions for oceanic areas. Accounting for magnetization contrasts and the magnetization values measured in rocks of marine origin are also discussed.

Harrison, C. G. A. (principal investigator)

1983-01-01

133

Contrast-enhanced portal magnetic resonance angiography in dogs with suspected congenital portal vascular anomalies.  

PubMed

Contrast-enhanced multiphase magnetic resonance angiography (CE-MRA) was used in 17 dogs with a suspected congenital portal vascular anomaly. Portal vascular anomalies were identified in 16 of the 17 dogs. Eleven had a single intrahepatic portocaval shunt (two central divisional, three right divisional, and six left divisional), one dog had a double intrahepatic portocaval shunt, one dog had a hepatic arteriovenous malformation, one dog had a complex intrahepatic porto-caval shunt. Two dogs had an extrahepatic portosystemic shunt and no shunt was identified in one dog. Total imaging time was <10?min and image quality was good to excellent in all dogs. Portal CE-MRA is a feasible, fast and non invasive technique to diagnose portal vascular anomalies in dogs, with a large field-of-view and good anatomic depiction of the abnormal vessels. Based on these results, CE-MRA is an efficient imaging technique for the diagnosis of portal vascular anomalies in dogs. PMID:21554476

Mai, Wilfried; Weisse, Chick

2011-01-01

134

Influence of Martian crustal magnetic anomalies on the emission of energetic neutral hydrogen atoms  

NASA Astrophysics Data System (ADS)

We analyze the data on hydrogen energetic neutral atoms (ENAs) emissions from the dayside of Mars, recorded by a Neutral Particle Detector of the Analyzer of Space Plasmas and Energetic Atoms aboard Mars Express from 14 March to 9 July 2004. We first identify and analyze events of the ENA flux enhancement coinciding with the presence of the crustal magnetic anomalies on the dayside of Mars. We then backtrace the ENA emissions to the lower altitudes (source region) and build up an average map of the flux intensities in the geographic coordinates with all the available data. The map shows a peak-to-valley ENA flux enhancement of 40%-90% close to the crustal magnetic anomaly regions. These results suggest the influence of the magnetic anomalies on the ENA emission from the dayside of Mars. The enhancement may result from the deviation of the highly directional plasma flow above anomalies toward the detectors such that more charge exchange ENAs would be recorded. Alternatively, higher exospheric densities above the anomalies would also result in an increase of the charge exchange ENA flux.

Wang, X.-D.; Barabash, S.; Futaana, Y.; Grigoriev, A.; Wurz, P.

2014-10-01

135

Plasma-surface interaction in magnetic dipole fields: Understanding the near surface electrical environment in magnetic anomaly regions  

NASA Astrophysics Data System (ADS)

The Moon has no global magnetic field, only localized crustal magnetic anomalies. In-situ measurements have shown evidence for complex solar wind plasma interaction with these local magnetic fields, and indicated a strong correlation with the high-albedo markers on the lunar surface, so-called the lunar swirls. Due to the limitations of existing in-orbit and surface measurements, laboratory studies and computer simulations play important roles in understanding the near-surface/surface electric field environment in the magnetic anomaly regions. In laboratory experiments, we investigate plasma-surface interaction in a magnetic dipole field with magnetized electrons but unmagnetized ions to emulate the interaction of the solar wind with the lunar surface in moderate magnetic anomalies. We have studied the electric potential distributions above an insulating surface in a dipole field with the dipole axis parallel (0 degree) to the surface in plasma [Wang et al., 2012]. Here, we report on a complementary new study with the dipole field axes at 90 and 45 degrees to the surface. The dipole field is created with a cylindrical permanent magnet. When the dipole axis is normal to the surface, the surface potential in the central cusp region rises to more positive values than outside the field, and a bump-like potential structure emerges in the sheath above the surface. These results indicate a significant population of reflected electrons due to the magnetic mirror effect in the cusp region. The potential-bump structure diminishes when the plasma density and neutral pressure increase. A different vertical dipole field is created with a smaller-sized cylindrical magnet, which has a similar strength peaked at the central surface but decreases faster with the height. Our data shows that the potential bump moves closer to the surface and the rise in surface potential in the central cusp region is less than that above the larger-sized magnet. Two-dimensional potential contours above the surface with the 45 degrees dipole field are measured as well. The results from different field configurations show self-consistency. The implications of the laboratory results for the electric environment in lunar magnetic anomaly regions will be discussed. Wang, X., M. Horányi, S. Robertson, "Characteristics of a plasma sheath in a magnetic dipole field: Implications to the solar wind interaction with the lunar magnetic anomalies", J. Geophys. Res., 117, A06226 (2012).

Wang, X.; Howes, C.; Horanyi, M.; Robertson, S. H.

2012-12-01

136

Remanent and induced magnetic anomalies over a layered intrusion: Effects from crystal fractionation and magma recharge  

NASA Astrophysics Data System (ADS)

The Bjerkreim-Sokndal (BKS) norite - quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~ 930 Ma. The BKS is exposed over an area of 230 km 2 with a thickness of ~ 7000 m and is of economic interest for ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe 3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the measured magnetic properties of NRM, susceptibility, and hysteresis presented here, and in terms of mineralogy. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRMs associated either with hemo-ilmenite, or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~ 3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20 km by ground-magnetic measurements. The highly varied magnetic properties of this intrusion, caused by varied magmatic crystallization of combinations of opaque minerals, illustrate some of the possibilities to be considered in evaluating crustal magnetic anomalies.

McEnroe, Suzanne A.; Brown, Laurie L.; Robinson, Peter

2009-12-01

137

Single crystal growth, magnetic properties and Schottky anomaly of HoFeO3 orthoferrite  

NASA Astrophysics Data System (ADS)

The HoFeO3 single crystal was successfully grown by the floating zone technique using a four-mirror-image-furnace under flowing air. Magnetic properties of HoFeO3 single crystal were studied over a wide temperature range. Magnetic measurements under different magnetic fields found that the spin reorientation transition in the crystal is well described by the earlier proposed theory with no fitting parameters. Specific heat of HoFeO3 single crystal was measured from 2 to 300 K under zero magnetic field. Schottky anomaly appeared between 2 and 5 K due to the Ho3+ spin ordering, and the anomaly of specific heat due to Fe3+ spin reorientation between 50 and 58 K was observed.

Shao, Mingjie; Cao, Shixun; Wang, Yabin; Yuan, Shujuan; Kang, Baojuan; Zhang, Jincang; Wu, Anhua; Xu, Jun

2011-03-01

138

Paleogene seafloor spreading in the southeast Tasman Sea  

Microsoft Academic Search

Magnetic anomalies 11-18 have been identified in the southeast Tasman Sea, the area of ocean crust southwest of Fiordland, New Zealand, west of the Puysegur Trench (the present plate boundary) and southwest of the older (80-58 Ma) ocean crust of the Tasman Sea basin. Structures associated with two changes in spreading direction are preserved in the area. Spreading between the

R. Wood; G. Lamarche; R. Herzer; J. Delteil; B. Davy

1996-01-01

139

Controls on Martian hydrothermal systems: Application to valley network and magnetic anomaly formation  

E-print Network

vents. There is also evidence for the past existence of hydrothermal systems on Mars (see Farmer [1996Controls on Martian hydrothermal systems: Application to valley network and magnetic anomaly December 2001; accepted 3 January 2002; published 3 May 2002. [1] Models of hydrothermal groundwater

Harrison, Keith

140

Using Magnetic Flux Density To Identify Anomalies In Pipe Wall Thickness  

Microsoft Academic Search

In making seamless pipe, there are certain inherent wall thickness anomalies and defects associated with the manufacturing processes. Similarly, both seamless and welded pipe that has been in use for a period of time develop areas of reduced wall thickness during their in-service life. By taking advantage of continued improvement in technology and relying on the basic principles of magnetism,

William Walters; David Steely

141

Gravity and magnetic anomalies and the deep structure of the Parnaiba cratonic basin, Brazil  

E-print Network

Gravity and magnetic anomalies and the deep structure of the Parnaiba cratonic basin, Brazil A. B profile across the Parnaiba cratonic basin in NorthEast Brazil. The purpose of this project is to acquire margin of Parnaíba Basin, Brazil. Geophysics 64: 337-356. Ussami N, Cogo de Sa N, Molina EC. 1993

Watts, A. B. "Tony"

142

Hydrology in the Durius Valles Region: Evaluation of Possible Correlation with Volcanism and Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

We envision the contribution of subglacial flows, hydrothermalism and sapping in the Durius Valles system and the consequences in term of climate on Mars in recent geological times. We evaluate the possible correlation of the hydrology with volcanism and magnetic anomalies.

Cabrol, Natalie A.; Marinangeli, Lucia; Grin, Edmond A.

2000-01-01

143

Unusual ionospheric absorption characterizing energetic electron precipitation into the South Atlantic Magnetic Anomaly  

Microsoft Academic Search

An imaging riometer (IRIS) was installed newly in the southern area of Brazil in order to investigate precipitation of energetic electrons into the South Atlantic Magnetic Anomaly (SAMA). An unusual ionospheric absorption event was observed in the nighttime (~20 h LT) near the maximum depression (Dst ~ -164 nT) and the following positive excursion during the strong geomagnetic storm on

Masanori Nishino; Kazuo Makita; Kiyofumi Yumoto; N. J. Schuch; M. A. Abdu

2002-01-01

144

Lunar Ion Transport Near Magnetic Anomalies: Possible Implications for Swirl Formation  

NASA Technical Reports Server (NTRS)

The bright swirling features on the lunar surface in areas around the Moon but most prominently at Reiner Gamma, have intrigued scientists for many years. After Apollo and later Lunar Prospector (LP} mapped the Lunar magnetic fields from orbit, it was observed that these features are generally associated with crustal magnetic anomalies. This led researchers to propose a number of explanations for the swirls that invoke these fields. Prominent among these include magnetic shielding in the form of a mini-magnetosphere which impedes space weathering by the solar wind, magnetically controlled dust transport, and cometary or asteroidal impacts that would result in shock magnetization with concomitant formation ofthe swirls. In this presentation, we will consider another possibility, that the ambient magnetic and electric fields can transport and channel secondary ions produced by micrometeorite or solar wind ion impacts. In this scenario, ions that are created in these impacts are under the influence of these fields and can drift for significant distances before encountering the magnetic anomalies when their trajectories are disrupted and concentrated onto nearby areas. These ions may then be responsible for chemical alteration of the surface leading either to a brightening effect or a disruption of space weathering processes. To test this hypothesis we have run ion trajectory simulations that show ions from regions about the magnetic anomalies can be channeled into very small areas near the anomalies and although questions remain as to nature of the mechanisms that could lead to brightening of the surface it appears that the channeling effect is consistent with the existence of the swirls.

Keller, J. W.; Killen, R. M.; Stubbs, T. J.; Farrell, W. M.; Halekas, J. S.

2011-01-01

145

Auroral evidence of a localized magnetic anomaly in Jupiter's northern hemisphere  

NASA Astrophysics Data System (ADS)

We analyze more than 1000 HST/Advanced Camera for Survey images of the ultraviolet auroral emissions appearing in the northern hemisphere of Jupiter. The auroral footprints of Io, Europa, and Ganymede form individual footpaths, which are fitted with three reference contours. The satellite footprints provide a convenient mapping between the northern Jovian ionosphere and the equatorial plane in the middle magnetosphere, independent of any magnetic field model. The VIP4 magnetic field model is in relatively good agreement with the observed footprint of Io. However, in the auroral kink sector, between the 80° and 150° System III meridians, the model significantly departs from the observation. One possible way to improve the agreement between the VIP4 model and the observed footprints is to include a magnetic anomaly. We suggest that this anomaly is characterized by a weakening of the surface magnetic field in the kink sector and by an added localized tilted dipole field. This dipole rotates with the planet at a depth of 0.245 RJ below the surface, and its magnitude is set to ˜1% of Jupiter's dipole moment. The anomaly has a very limited influence on the magnetic field intensity in the equatorial plane between the orbits of Io and Ganymede. However, it is sufficient to bend the field lines near the high-latitude atmosphere and to reproduce the observed satellite ultraviolet footpaths. JUNO's in situ measurements will determine the structure of Jupiter's magnetic field in detail to expand on these results.

Grodent, Denis; Bonfond, Bertrand; GéRard, Jean-Claude; Radioti, Aikaterini; Gustin, Jacques; Clarke, John T.; Nichols, Jonathan; Connerney, John E. P.

2008-09-01

146

Thermal evolution of the North Atlantic lithosphere: New constraints from magnetic anomaly inversion with a fractal magnetization model  

NASA Astrophysics Data System (ADS)

Using recently published global magnetic models, we present the first independent constraint on North Atlantic geothermal state and mantle dynamics from magnetic anomaly inversion with a fractal magnetization model. Two theoretical models of radial amplitude spectrum of magnetic anomalies are found almost identical, and both are applicable to detecting Curie depths in using the centroid method based on spectral linearization at certain wave number bands. Theoretical and numerical studies confirm the robustness of this inversion scheme. A fractal exponent of 3.0 in the magnetic susceptibility is found suitable, and Curie depths are well constrained by their known depths near the mid-Atlantic ridge. While generally increasing with growing ages, North Atlantic Curie depths show large oscillating and heterogeneous patterns related most likely to small-scale sublithospheric convections, which are found to have an onset time around 40 Ma and a scale of about 500 km, and are in preferred transverse rolls. Hotspots in North Atlantic also contribute to large geothermal and Curie-depth variations, but they appear to connect more closely to geochemical anomalies or small-scale convection than to mantle plumes. Curie depths can be correlated to heat flow gridded in a constant 1° interval, which reveals decreasing effective thermal conductivity with depths within the magnetic layer. North Atlantic Curie points are mostly beneath the Moho, suggesting that the uppermost mantle is magnetized from serpentinization and induces long-wavelength magnetic anomalies. Small-scale convection and serpentinization together may cause apparent flattening and deviations in heat flow and bathymetry from theoretical cooling models in old oceanic lithosphere.

Li, Chun-Feng; Wang, Jian; Lin, Jian; Wang, Tingting

2013-12-01

147

Magnetic Signatures of Impact Fractured Rocks from Sierra Madera, Texas, USA - Implications to Magnetic Anomalies on Mars  

NASA Astrophysics Data System (ADS)

Mars Express Orbiter (sounding radar data) revealed that craters of ancient origin had been covered by thick sediments in northern hemisphere. Mars MOLA topography mission identified many crater on Mars surface. Thus despite the Mars dichotomy, both northern and southern hemisphere have been covered by impacts to similar density. Mars currently has no global magnetic field of internal origin. In southern hemisphere, magnetic field intensities due to anomalies of remanent origin are much lower over the gigantic impact craters (e.g. Hellas, Prometheus, and Argyre). Low magnetic field may not relate to the absence of internal dynamo but due to impacts. For example, the aerial survey over a two billion year old, largest crater on Earth, Vredefort in South Africa observed much lower magnetic intensity over the crater, despite of the strongly magnetized simgle domain (SD) magnetite in shocked granites. Randomized magnetic vector orientations caused by impact may be the origin of the lower magnetic field observed on both Vredefort and Mars. We conducted magnetic analysis for a suite of Sierra Madera Impact deformed rock sites with complete shatter cone structures and multiple striated joint set (MSJS), and the initial results were intriguing. NRM vector orientations, REM ratios, and AF demagnetization curves showed contrasted magnetic signatures between the sites as well as within the samples. The NRM signatures in small scale shatter cones and larger scale shatter cones indicated shock demagnetization (SDM). The peculiar signatures of the site with MSJS may be both SDM and shock magnetization (SRM). We characterized the complexity and distinct magnetic signatures of impact fractured rocks. The results suggest that the size of the shatter cones and structures may reflect the magnetic signatures of both intensity and directions. Also, the dimensional scale of shatter cones is indicative parameters for randomization of the magnetic vector orientations. Such variations may influence on overall magnetic intensity observed from a distance, which relates to magnetic anomalies on Mars and Moons.

Adachi, T.; Kletetschka, G.; Wasilewski, P. J.; Mikula, V.

2007-05-01

148

Contribution of multidomain titanomagnetite to the intensity and stability of Mars crustal magnetic anomalies  

NASA Astrophysics Data System (ADS)

basalts with compositions relevant to the crusts of Mars and Earth were synthesized at igneous temperatures and held at 650°C for 21 to 257 days under quartz-fayalite-magnetite fO2 buffer conditions. The run products are germane to slowly cooled igneous intrusions, which might be a significant volumetric fraction of the Martian crust and carriers of magnetic anomalies in the Southern Highlands. Both basalts acquired intense thermoremanent magnetizations and intense but easily demagnetized anhysteretic remanent magnetizations carried by homogeneous multidomain titanomagnetite. Hypothetical intrusions on Mars composed of these materials would be capable of acquiring intense remanences sufficient to generate the observed anomalies. However, the remanence would be easily demagnetized by impact events after the cessation of the Mars geodynamo. Coercivity enhancement by pressure or formation of single domain regions via exsolution within the multidomain grains is necessary for long-term retention of a remanence carried exclusively by multidomain titanomagnetite grains.

Brachfeld, Stefanie; Cuomo, David; Tatsumi-Petrochilos, Lisa; Bowles, Julie A.; Shah, Deepa; Hammer, Julia

2014-11-01

149

Marine Magnetic Anomalies of the Northern Part of the Gulf of Aqaba, Dead Sea Rift  

NASA Astrophysics Data System (ADS)

MARINE MAGNETIC ANOMALIES OF THE NORTHERN PART OF THE GULF OF AQABA, DEAD SEA RIFT Al-Zoubi (1), Z. Ben-Avraham (2), T. M. Niemi (3), E. Akawi (1), G. Tibor (4), R. Al-Rzouq (1), J.K. Hall (5), A. Abueladas (1), G. Hartman (2) (1) Surveying & Geomatics Department, Al-Balqa' Applied University, Salt, Jordan (2) Department of Geophysics & Planetary Sciences, Tel-Aviv University, Tel-Aviv, Israel (3) University of Missouri-Kansas City, USA. (4) Israel Oceanographic and Limnological Research, Haifa, Israel (5) Geological Survey of Israel, Jerusalem, Israel A high-resolution marine magnetic survey in the northern part of the Gulf of Aqaba, Dead Sea Rift was carried out during October and November 2006. The survey led by an international research group (Israel, Jordan, and USA) funded by MERC, USA and aims to provide the municipalities of Aqaba and Elat a base map of active faults for seismic hazard assessment. The total magnetic intensity at sea surface was measured by a proton precession magnetometer. Diurnal magnetic variation was corrected from the data by using the observation located in southern part of Israel during the survey period. The correction of the external field variation was carried out based on the continuous magnetic observations at a reference magnetic observatory close to the survey area. For calculations of the total intensity of magnetic anomaly, the IGRF model was used as the core field model in accordance with the recommendation of the IAGA. Geomagnetic total intensity anomaly map of the study area has been produced. The magnetic anomaly map shows that there are two major magnetic trends appear in the study area. These are the magnetic high across the northwest section of the Gulf and a magnetic low across the southeast section. These two general trends are divided by a northeast-trending boundary. The magnetic map reveals a complex faults system between the deep part of the Gulf as a pull-apart basin and the on land transform fault in the Araba valley.

Al-Zoubi, A.

2009-04-01

150

Investigation of vehicle induced magnetic anomaly by triple-axis magnetoelectric sensors  

NASA Astrophysics Data System (ADS)

This paper investigates magnetoelectric (ME) sensors for vehicle detection. We propose a novel triple-axis ME magnetic sensor system consisting of tri-layers of Metglas/ Pb(Zr, Ti)O3/Metglas laminates together with its fabrication and installation methods. This non-intrusive ME sensor system with a larger sensing range is viable for detection and recognition of vehicle induced magnetic signatures in an outdoor (open) environment. We also show a finite element simulation method capable predicting the magnetic anomaly projection in the geomagnetic field.

Shen, Ying; Gao, Junqi; Hasanyan, Davresh; Wang, Yaojin; Li, Menghui; Li, Jiefang; Viehland, D.

2012-11-01

151

The satellite magnetic anomaly of Ahaggar - Evidence for African Plate motion  

NASA Technical Reports Server (NTRS)

The Ahaggar volcanic province of North Central Africa is considered a region of excess heat flow (hot spot) and hence elevated Curie isotherm. Using a modified version of the Parker FFT potential field representation, magnetic signals were calculated at Magsat altitudes for models in which the African Plate is both fixed and moving. The moving-plate model extends the Curie isotherm anomaly in the direction of plate motion and provides a satisfactory match to vertical component anomaly data when the magnitude of plate velocity is 0.75 cm/yr. Although the signal levels are marginal for the scalar component anomalies of this region, the same model provides an adequate match to this data set and is clearly preferable to a fixed-plate model.

Phillips, R. J.; Brown, C. R.

1985-01-01

152

Modeling of the Central Magnetic Anomaly at Haughton Impact Structure, Canada  

NASA Astrophysics Data System (ADS)

Located on Devon Island, Nunavut, Canada, the 23-km diameter Haughton impact structure is one of the best-preserved medium-size complex impact structures on Earth. The impact occurred ~39 Ma ago into a target formation composed of an ~2-km thick sequence of Lower Paleozoic sedimentary rocks of the Arctic Platform overlying Precambrian metamorphic basement of the Canadian Shield (Osinski et al., 2005). Clast-rich impact melt rocks line the crater and impact-induced hydrothermal activity took place, but since then no significant geological event has affected the area. In the 1980s, ground magnetic and gravity measurements were carried out within the central part of the crater (Pohl et al., 1988). A significant anomaly was discovered and coarsely modeled by a source body of simple geometry. More recently, an airborne magnetic survey delivered additional data that covered the whole crater but no modeling was done (Glass et al., 2002). Here, we present the results of a new ground magnetic survey accompanied by rock magnetic property measurements made on all samples of the crater. This has provided additional constraints to investigate the origin of this central magnetic anomaly. By conducting modeling, we have been able to reveal the geometry and volume of the source body as well as its magnetization properties. Our results suggest that the necessary magnetization intensity to account for this anomaly is too large to be associated with uplifted pre-impact target rocks. Therefore, we suggest that hydrothermal alteration could have enhanced the magnetization of the central part of this crater. References : Osinski, G. R. et al. 2005. MPS, 40:1759-1776 ; Pohl, J. et al. 1988. Meteoritics, 23:235-238 ; Glass, B. J. et al. 2002, Abstract #2008. 33th LPSC

Quesnel, Y.; Gattacceca, J.; Osinski, G. R.; Rochette, P.

2011-12-01

153

Dielectric anomalies and spiral magnetic order in CoCr2O4  

NASA Astrophysics Data System (ADS)

We have investigated the structural, magnetic, thermodynamic, and dielectric properties of polycrystalline CoCr2O4 , an insulating spinel exhibiting both ferrimagnetic and spiral magnetic structures. Below Tc=94K the sample develops long-range ferrimagnetic order, and we attribute a sharp phase transition at TS?27K to the onset of long-range spiral magnetic order. Neutron measurements confirm that the structure remains cubic at 80K and at 11K ; the magnetic ordering by 11K is seen to be rather complex. Density functional theory supports the view of a ferrimagnetic semiconductor with magnetic interactions consistent with noncollinear ordering. Capacitance measurements on CoCr2O4 show a sharp decrease in the dielectric constant at TS , but also an anomaly showing thermal hysteresis falling between approximately T=50 and 57K . We tentatively attribute the appearance of this higher-temperature dielectric anomaly to the development of short-range spiral magnetic order, and discuss these results in the context of utilizing dielectric spectroscopy to investigate noncollinear short-range magnetic structures.

Lawes, G.; Melot, B.; Page, K.; Ederer, C.; Hayward, M. A.; Proffen, Th.; Seshadri, R.

2006-07-01

154

True Polar Wander and Hotspot Fixity: A Paleomagnetic Investigation of the Skewness of Magnetic Anomaly 12r (32 Ma B.P.) on the Pacific Plate  

NASA Astrophysics Data System (ADS)

Prior studies have shown that Pacific hotspots and Indo-Atlantic hotspots have moved in approximate unison relative to the spin axis since 65 Ma B.P. [Morgan, 1981; Gordon and Cape, 1981; Gordon, 1982] and since 56 Ma B.P. [Petronotis et al., 1994], which is most simply interpreted as true polar wander. In contrast, Pacific hotspots and Indo-Atlantic hotspots give conflicting results for 72 Ma B.P. and for 81 Ma B.P., which may indicate motion between Pacific hotspots and Indo-Atlantic hotspots [Tarduno and Cottrell, 1997; Petronotis et al., 1999; Tarduno et al., 2003]. Thus it is important to estimate Pacific plate apparent polar wander (APW) for more time intervals. From such estimates the APW of Pacific hotspots can be inferred and compared with that of Indo-Atlantic hotspots [e.g., Besse and Courtillot 2002]. Here we present a study of the skewness of anomaly 12r between the Galapagos and Clipperton and between the Clipperton and Clarion fracture zones. We chose this region for several reasons: First, numerical experiments, like those conducted by Acton and Gordon [1991], indicate that magnetic profiles between the Galapagos and Clarion fracture zones should contain the most information about the Pacific plate paleomagnetic pole for chron C12r (32 Ma B.P.). Second, in these two spreading rate corridors, spreading half rates range from 72 to 86 mm/a and therefore have negligible anomalous skewness, given that they exceed ?50 mm/a [Roest et al., 1992; Dyment et al. 1994]. Third, vector aeromagnetic profiles are available for analysis. One of the challenges to interpreting magnetic anomalies in low latitudes where the anomalies strike nearly north-south is the very low amplitude of the signal relative to the noise, the latter of which can be especially intense near the present magnetic equator due to the amplification of diurnal variation by the equatorial electrojet. Previously we showed that vector aeromagnetic profiles record low-latitude Pacific plate magnetic anomalies due to seafloor spreading with much greater clarity than do shipboard profiles in the same region [Horner-Johnson and Gordon, 2003]. The pole that we obtain has compact 95% confidence limits. We reduce the profiles to this pole and show that the appearance of the reduced-to-the-pole profiles is sensitive to the assumed pole position. The new pole shows that Pacific hotspots have moved significantly relative to the spin axis during the formation of the Hawaiian island and seamount chain, and is consistent with Pacific hotspots having moved in approximate unison with Indo-Atlantic hotspots relative to the spin axis since 32 Ma B.P.

Gordon, R. G.; Horner-Johnson, B. C.

2010-12-01

155

Bangui Anomaly  

NASA Technical Reports Server (NTRS)

Bangui anomaly is the name given to one of the Earth s largest crustal magnetic anomalies and the largest over the African continent. It covers two-thirds of the Central African Republic and therefore the name derives from the capitol city-Bangui that is also near the center of this feature. From surface magnetic survey data Godivier and Le Donche (1962) were the first to describe this anomaly. Subsequently high-altitude world magnetic surveying by the U.S. Naval Oceanographic Office (Project Magnet) recorded a greater than 1000 nT dipolar, peak-to-trough anomaly with the major portion being negative (figure 1). Satellite observations (Cosmos 49) were first reported in 1964, these revealed a 40nT anomaly at 350 km altitude. Subsequently the higher altitude (417-499km) POGO (Polar Orbiting Geomagnetic Observatory) satellite data recorded peak-to-trough anomalies of 20 nT these data were added to Cosmos 49 measurements by Regan et al. (1975) for a regional satellite altitude map. In October 1979, with the launch of Magsat, a satellite designed to measure crustal magnetic anomalies, a more uniform satellite altitude magnetic map was obtained. These data, computed at 375 km altitude recorded a -22 nT anomaly (figure 2). This elliptically shaped anomaly is approximately 760 by 1000 km and is centered at 6%, 18%. The Bangui anomaly is composed of three segments; there are two positive anomalies lobes north and south of a large central negative field. This displays the classic pattern of a magnetic anomalous body being magnetized by induction in a zero inclination field. This is not surprising since the magnetic equator passes near the center of this body.

Taylor, Patrick T.

2004-01-01

156

Circum-Arctic mapping project: new magnetic anomaly map of the Arctic (to 60 degrees N)  

NASA Astrophysics Data System (ADS)

An international effort to compile Circum-Arctic geophysical and bedrock data has been conducted by several national agencies (Russia-VSEGEI and VNIIO, Sweden-SGU, Finland-GTK, Denmark-GEUS, USA-USGS, Canada-GSC, Germany-BGR and Norway-NGU) since 2005. This project aims to produce an atlas that will comprise geological and geophysical digital maps at a scale of 1: 5 million scale for the Arctic region limited by the 60 degree North latitude. New published and classified magnetic anomaly gridded data from each participant group were gathered and converted to a common datum (WGS84) and format. The Greenland region magnetic anomaly grid (Verhoef et al., 1996) has been updated with new aeromagnetic surveys performed in West Greenland between 1992-2001 (Rasmussen, 2002), and in the Nares Strait area (Damaske & Oakey, 2006; Oakey & Damaske, 2006). The oceanic area east of Greenland (NE Atlantic) contains most of the aeromagnetic data used in the Verhoef et al., (1996)'s compilation (pre-1990) plus new aeromagnetic surveys over offshore Norway collected up to 2007 (Olesen et al., 1997; Olesen et al., 2007; Gernigon et al., 2008). The gridded data has been upward continued to 1 km above ground or sea-level and trimmed around the areas of major overlaps. The Alaska USGS aeromagnetic compilation has been used as the "master grid" for merging the major gridded data sets together and the downward continued lithospheric magnetic field model MF6 derived from satellite data (Maus et al., 2008) has been used as a regional reference surface. We have used a blending function over the area of overlap in order to smooth the transition from one grid to the other (GridKnit, GEOSOFT). The resulting grid has been re-sampled to a 2 km grid cell. In order to construct the final Circum-Arctic magnetic anomaly grid (CAMP-M) we have adopted the approach used by several research groups for compiling the World Digital Magnetic Anomaly Map (WDMAM) and used near-surface magnetic data for the short wavelength component of the compilation and the satellite derived magnetic anomalies for the long wavelength (Hemant et al., 2007; Maus et al., 2007). MF6 extends to spherical harmonics degree 120 (333 km wavelength) and therefore it is able to provide consistent long wavelength information between 300 and 400 km. This information is mainly related to regional deeper and/or thicker portions of the magnetic sources within the crust. We have prepared two versions for the CAMP-M magnetic anomaly grid. The first one combines short wavelength components of regional grids (less than 400 km) with long wavelengths (400 km) of the MF6 model. The second one combines short wavelengths of regional datasets (obtained by filtering with a cosine squared taper to remove the wavelengths in the waveband between 307 and 333 km and larger, with the MF6 model (to degree 120). We have selected Model 1 as the new Circum-Arctic Magnetic Anomaly Map.

Gaina, Carmen

2010-05-01

157

LIMAT: a computer program for least-squares inversion of magnetic anomalies over long tabular bodies  

NASA Astrophysics Data System (ADS)

A popular method for the inversion of magnetic anomalies in total vertical or horizontal field over thin sheet thick dike and vertical fault is presented. The magnetic anomaly over thin sheet may be expressed as a polynomial of the form FX2+ C1FX+ C2F+ C3X3+ C4X2+ C5X+ C6 The initial parameters of the source are obtained from the coefficients C1,C2,…, C6 by inverting a 6×6 matrix. The thick dike and the vertical fault are an ensemble of thin sheets. So the same initial solution obtained for the thin sheet model can be used for the thick dike and the vertical fault. Besides, in this method the computer calculates the initial solution by using all the discrete magnetic anomaly values and the corresponding distances as an input. The initial solution thus obtained is modified in an iterative process using non-linear least-squares regression by employing Marquardt's algorithm. The regional value that is subjective in manual interpretation is also adjusted in this method to obtain a close fit. A computer program in FORTRAN 77 is presented and used to interpret synthetic and practical data and the efficacy of the results are discussed.

Raju, D. Ch. Venkata

2003-02-01

158

Remanent magnetization and 3-dimensional density model of the Kentucky anomaly region  

NASA Technical Reports Server (NTRS)

A three-dimensional model of the Kentucky body was developed to fit surface gravity and long wavelength aeromagnetic data. Magnetization and density parameters for the model are much like those of Mayhew et al (1982). The magnetic anomaly due to the model at satellite altitude is shown to be much too small by itself to account for the anomaly measured by Magsat. It is demonstrated that the source region for the satellite anomaly is considerably more extensive than the Kentucky body sensu stricto. The extended source region is modeled first using prismatic model sources and then using dipole array sources. Magnetization directions for the source region found by inversion of various combinations of scalar and vector data are found to be close to the main field direction, implying the lack of a strong remanent component. It is shown by simulation that in a case (such as this) where the geometry of the source is known, if a strong remanent component is present its direction is readily detectable, but by scalar data as readily as vector data.

Mayhew, M. A.; Estes, R. H.; Myers, D. M.

1984-01-01

159

Preliminary global mapping of lunar magnetic anomalies at nominal and low altitudes by MAP-LMAG onboard SELENE (KAGUYA)  

NASA Astrophysics Data System (ADS)

The magnetic field around the Moon has been successfully observed at nominal and lower altitudes by the lunar magnetometer (LMAG) on the SELENE (KAGUYA) spacecraft in a polar orbit from October 29, 2007 to June 10, 2009. Since the solar activity has been very low during the observation, relatively weak anomalies can be observed even at a nominal altitude of about 100 km. In this paper we report preliminary results of the global mapping in the constancy and optional phases and compare the results with previous global maps (e.g. Richmond and Hood, 2008; Mitchell et al., 2008). The nominal altitude was 70-120 km (mostly 100 +/- 10 km) in the constancy phase (November, 2007 to December, 2008). Based on dataset in the tail lobe and in the lunar wake, magnetic anomaly fields without altitude correction were mapped on 1 x 1 degree bins with 95 % coverage of the lunar surface. We also obtained full-coverage maps of the vector magnetic field at a constant altitude of 100 km after altitude normalization and interpolation of the magnetic anomaly field by the inverse boundary value problem, the EPR method by Toyoshima et al. (2008). After the constancy phase, we subsequently conducted the optional phase in 2009 to observe the magnetic field and plasma at lower altitudes. The altitude was mostly 50-70 km during January to March, and then further lowered by 20-50 km with a pericenter above the South-Pole Aitken basin. We obtained global maps of 1 x 1 degree bins at the low altitudes with 84 % coverage. We also applied our detrending method to the low-altitude dataset of the lunar magnetic field by the Lunar Prospector (LP). and compared them with our maps. As a result, characteristic features in the lunar magnetic anomaly distribution are consistent with each other. The results in the present study indicate that statistically significant magnetic anomalies are distributed over almost the whole lunar surface. Relatively strong anomalies are identified in several basin, basin-antipode and near-crater regions, while the youngest basin on the Moon, the Orientale basin, has no magnetic anomaly. The basin-forming impact model can explain formation of the basin-antipode anomaly in the amplified interplanetary magnetic field (e.g. Mitchell et al., 2008). However, some basins and their antipode regions show magnetic anomalies, and thus it seems difficult to induce significant magnetization due to the interplanetary magnetic field in both regions. These suggest that the early lunar dynamo or the early geodynamo before the Orientale basin formation is preferable as a magnetic field source of the lunar crustal magnetism to the interplanetary magnetic field.

Tsunakawa, H.; Shibuya, H.; Takahashi, F.; Shimizu, H.; Matsushima, M.; Matsuoka, A.; Nakazawa, S.; Otake, H.; Iijima, Y.

2009-12-01

160

Spherical Earth analysis and modeling of lithospheric gravity and magnetic anomalies. Ph.D. Thesis - Purdue Univ.  

NASA Technical Reports Server (NTRS)

A comprehensive approach to the lithospheric analysis of potential field anomalies in the spherical domain is provided. It has widespread application in the analysis and design of satellite gravity and magnetic surveys for geological investigation.

Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.

1980-01-01

161

The magnetic-anomaly model of the Jovian magnetosphere - A post-Voyager assessment  

NASA Technical Reports Server (NTRS)

Predictions previously put forth (Dessler and Vasyliunas, 1979) as tests for the magnetic-anomaly model (in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes) are reexamined in the light of Voyager and other recent observations. With regard to the prediction of a restricted longitude range of enhanced interaction between Io and Jupiter's ionosphere, the longitudinal asymmetries seen both in ground-based observations of sulfur emissions from the Io torus and in Voyager observations of Jovian auroral emissions are found to agree well with the predicted asymmetries.

Vasyliunas, V. M.; Dessler, A. J.

1981-01-01

162

Insights into magmatic processes and hydrothermal alteration of in situ superfast spreading ocean crust at ODP/IODP site 1256 from a cluster analysis of rock magnetic properties  

NASA Astrophysics Data System (ADS)

analyze magnetic properties from Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6°44.1' N, 91°56.1' W) on the Cocos Plate in ˜15.2 Ma oceanic crust generated by superfast seafloor spreading, the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Fuzzy c-means cluster analysis and nonlinear mapping are utilized to study down-hole trends in the ratio of the saturation remanent magnetization and the saturation magnetization, the coercive force, the ratio of the remanent coercive force and coercive force, the low-field magnetic susceptibility, and the Curie temperature, to evaluate the effects of magmatic and hydrothermal processes on magnetic properties. A statistically robust five cluster solution separates the data predominantly into three clusters that express increasing hydrothermal alteration of the lavas, which differ from two distinct clusters mainly representing the dikes and gabbros. Extensive alteration can obliterate magnetic property differences between lavas, dikes, and gabbros. The imprint of thermochemical alteration on the iron-titanium oxides is only partially related to the porosity of the rocks. Thus, the analysis complements interpretation based on electrofacies analysis. All clusters display rock magnetic characteristics compatible with an ability to retain a stable natural remanent magnetization suggesting that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Paleointensity determination is difficult because of the propensity of oxyexsolution during laboratory heating and/or the presence of intergrowths. The upper part of the extrusive sequence, the granoblastic dikes, and moderately altered gabbros may contain a comparatively uncontaminated thermoremanent magnetization.

Dekkers, Mark J.; Heslop, David; Herrero-Bervera, Emilio; Acton, Gary; Krasa, David

2014-08-01

163

Chapter 3: Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic  

USGS Publications Warehouse

New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain. ?? 2011 The Geological Society of London.

Gaina, C.; Werner, S.C.; Saltus, R.; Maus, S.; Aaro, S.; Damaske, D.; Forsberg, R.; Glebovsky, V.; Johnson, K.; Jonberger, J.; Koren, T.; Korhonen, J.; Litvinova, T.; Oakey, G.; Olesen, O.; Petrov, O.; Pilkington, M.; Rasmussen, T.; Schreckenberger, B.; Smelror, M.

2011-01-01

164

Origin of Strong Lunar Magnetic Anomalies: More Detailed Mapping in Regions Antipodal to Young Large Basins  

NASA Astrophysics Data System (ADS)

Previous work has found evidence that the largest concentrations of strong lunar crustal magnetic fields are in regions antipodal to four young large lunar basins: Orientale, Imbrium, Crisium, and Serenitatis (Mitchell et al., Icarus, 2008; and references therein). A preliminary model for the production of lunar basin antipodal magnetic signatures has been developed (Hood and Artemieva, Icarus, 2008; Gattacceca et al., EPSL, 2010). The model involves shock magnetization of crustal materials in the presence of a transient magnetic field amplified by the expanding ionized vapor-melt cloud as it converges in the antipodal region. The model does not exclude a core dynamo; any ambient magnetic field (external solar wind or internal core dynamo) can be amplified in the antipodal zone. In this paper, we report further efforts to map in more detail Lunar Prospector magnetometer data in regions antipodal to young lunar basins. In addition to the four basins identified above, we also consider the polar Schrodinger basin, which is one of the three youngest lunar basins and which has not been previously considered in this context. We apply a direct mapping method (see Hood, Icarus, 2011 for details) to produce more complete maps of lunar magnetic anomalies at low altitudes over the central far side and over the north polar region. We also consider geologic data and spacecraft imagery to identify unusual modified terrain, which may be indicative of shock modification in the same basin antipodal zones. Previous work indicates the existence of such terrain antipodal to Imbrium, Orientale, and Serenitatis, as well as antipodal to the Caloris basin on Mercury. Results first confirm the concentrations of anomalies antipodal to Orientale, Imbrium, Crisium, and Orientale, and the occurrence of modified terrain in three of the four basin antipode zones (see, e.g., Richmond et al., JGR, 2005). In addition, we report here evidence for a large concentration of anomalies that is centered within 5 to 8 degrees of the Schrodinger antipode; this is the largest concentration of strong anomalies in the north polar region (60N to the pole). Examinations of LROC imagery suggest the possible presence of modified terrain in the same area. If these provisional results are confirmed by later detailed studies, this would represent the fifth young lunar basin with an antipodal magnetic signature.

Hood, L. L.; Richmond, N.; Spudis, P.

2012-12-01

165

An attempt to obtain a detailed declination chart from the United States magnetic anomaly map  

USGS Publications Warehouse

Modern declination charts of the United States show almost no details. It was hoped that declination details could be derived from the information contained in the existing magnetic anomaly map of the United States. This could be realized only if all of the survey data were corrected to a common epoch, at which time a main-field vector model was known, before the anomaly values were computed. Because this was not done, accurate declination values cannot be determined. In spite of this conclusion, declination values were computed using a common main-field model for the entire United States to see how well they compared with observed values. The computed detailed declination values were found to compare less favourably with observed values of declination than declination values computed from the IGRF 1985 model itself. -from Author

Alldredge, L.R.

1989-01-01

166

Magnetic anomaly map of North America south of 50 degrees north from Pogo data  

NASA Technical Reports Server (NTRS)

A magnetic anomaly map produced from Pogo data for North America and adjacent ocean areas is presented. At satellite elevations anomalies have wavelengths measured in hundreds of kilometers, and reflect regional structures on a large scale. Prominent features of the map are: (1) a large east-west high through the mid-continent, breached at the Mississippi Embayment; (2) a broad low over the Gulf of Mexico; (3) a strong gradient separating these features, which follows the Southern Appalachian-Ouachita curvature; and (4) a high over the Antilles-Bahamas Platform which extends to northern Florida. A possible relationship between the high of the mid-continent and the 38th parallel lineament is noted.

Mayhew, M. A.

1976-01-01

167

Magnetic anomalies in Bahia Esperanza: A window of magmatic arc intrusions and glacier erosion over the northeastern Antarctic Peninsula  

NASA Astrophysics Data System (ADS)

Bahia Esperanza, constituting the NE tip of the Antarctic Peninsula, is made up of Paleozoic clastic sedimentary rocks overlain by a Jurassic volcano-sedimentary series and intruded by Cretaceous gabbros and diorites. The area is located along the southern part of the Pacific Margin magnetic anomaly belt. Field magnetic researches during February 2010 contribute to determining the deep geometry of the intermediate and basic intrusive rocks. Moreover, the new field data help constrain the regional Pacific Margin Anomaly, characterized up to now only by aeromagnetic and marine data. Field magnetic susceptibility measurements of intrusive intermediate and basic rocks, responsible for magnetic anomalies, ranges from 0.5 × 10- 3 SI in diorites to values between 0.75 × 10- 3 SI and 1.3 × 10- 3 SI in gabbros. In addition, a significant remanent magnetism should also have contributed to the anomalies. The regional magnetic anomaly is characterized by a westward increase from 100 nT up to 750 nT, associated with large intrusive diorite bodies. They probably underlie most of the western slopes of Mount Flora. Gabbros in the Nobby Nunatak determine local residual rough anomalies that extend northwards and westwards, pointing to the irregular geometry of the top of the basic rocks bodies below the Pirámide Peak Glacier. However, the southern and eastern boundaries with the Buenos Aires Glacier are sharp related to deep glacier incision. As a result of the glacier dynamics, magnetic anomalies are also detected north of the Nobby Nunatak due to the extension of the anomalous body and the presence of gabbro blocks in the moraines. The Bahia Esperanza region is a key area where onshore field geological and magnetic research allows us to constrain the shape of the crustal igneous intrusions and the basement glacier geometry, providing accurate data that complete regional aeromagnetic research.

Galindo-Zaldívar, Jesús; Ruiz-Constán, Ana; Pedrera, Antonio; Ghidella, Marta; Montes, Manuel; Nozal, Francisco; Rodríguez-Fernandez, Luis Roberto

2013-02-01

168

Investigations of medium wavelength magnetic anomalies in the eastern Pacific using Magsat data  

NASA Technical Reports Server (NTRS)

The author has identified the following significant results. Three long total magnetic field profiles taken over ocean basins were analyzed. It is found that there is a significant signal in the wavelength range of 1500 to 150 km. This is too short a wavelength to be caused by the core field, which becomes insignificant at about a wavelength of 1500 km; this intermediate wavelength signal is not caused by a typical sea floor spreading process, which should give maximum power in the wavelength region about 50 km. It is shown that the external magnetic field contributes very little to this intermediate wavelength signal. Efforts to explain the cause of this signal have failed.

Harrison, C. G. A. (principal investigator)

1980-01-01

169

Three-dimensional correlation imaging for total amplitude magnetic anomaly and normalized source strength in the presence of strong remanent magnetization  

NASA Astrophysics Data System (ADS)

We present the 3D correlation imaging approach for the total magnitude magnetic anomaly and the normalized source strength data for reducing effects of strong remanent magnetization. We divide the subsurface space into a 3D regular grid and then calculate the cross correlation between the observed total magnitude magnetic anomaly or normalized source strength and the theoretical total magnitude magnetic anomaly or normalized source strength at each grid node due to a magnetic dipole. The resultant correlation coefficients are used to describe the equivalent magnetic dipole distribution underground in a probabilistic sense. The two approaches were tested both on the synthetic magnetic data and the real magnetic data from a metallic deposit area in the middle-lower reaches of the Yangtze River, China. The results show that the two approaches can considerably reduce effects of remanent magnetization and delineate magnetic sources in the subsurface, and that the approach for the normalized source strength is less sensitive to strong remanent magnetization than that of the total magnitude magnetic anomaly.

Guo, Lianghui; Meng, Xiaohong; Zhang, Guoli

2014-12-01

170

Kursk Magnetic Anomaly at Satellite Altitude: Revisited with the Orsted Satellite  

NASA Technical Reports Server (NTRS)

The Kursk Magnetic Anomaly (KMA) of Russia (51 deg north, 37 deg east) has long been recognized as one of the largest magnetic anomalies on Earth. It is associated with the massive iron-ore formations of this region, however, model studies have revealed that the relationship between the two is not obvious. In an early effort to demonstrate the validity of Magsat data for crustal research a detailed study of the KMA, at an average altitude of 350 km and the surrounding region was made. They recorded a 27 nT high and a -9 nT low giving a 37 nT peak-to-trough anomaly over the immediate area of the KMA. Despite the much higher altitude of Orsted (620 to 850 km) we revisited the KMA to determine if this mission would also be able to record an associated anomalous crustal signature. The Orsted profiles we selected were from April to August 1999. From these data we chose those with an altitude range of 644 to 700 km and they were subsequently gridded, by least-squares collocation, to a mean elevation of 660 km. Both ascending and descending data were examined and signals common to both were extracted and averaged. A correlation coefficient between these two orbit orientations of 0.82 was computed. The quadrant-swapping method of Kim et al. was applied. Removal of the main geomagnetic field was accomplished with a polynomial fitting procedure. A positive anomaly of >2.5 nT with ari associated negative of <-0.5 nT for a >3 nT peak-to-trough range were computed. These Magsat and Orsted results are consistent with the decay of a dipole field over the studied altitude range. Significant differences between these two anomaly fields are due to the greater number of orbit profiles and therefore greater number of intersecting orbits (ascending and descending) available in the Orsted compilation. Of the four largest amplitude anomalies in the Orsted field three are present in the Magsat map. The fourth (>2.5 nT), however, is associated with the Belorussian-Lithuanian anteclise. This sugaests that additional geologic information may be apparent in the new Orsted field.

Taylor, Patrick T.; VonFrese, Ralph R. B.; Kim, Hyung Rae

2000-01-01

171

The magnetic anomaly model of the Jovian magnetosphere - Predictions for Voyager  

NASA Technical Reports Server (NTRS)

The magnetic anomaly model, in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes, has been put forth to account for the various observed Jovian magnetospheric phenomena that show evidence of Jovian longitudinal asymmetry or planetary spin periodicity. From this model, normalized by empirical fitting to Pioneer 10 and 11 flyby data and to ground-based radio data, a series of predictions are made that are subject to test by the forthcoming flybys of Jupiter by Voyagers 1 and 2. These predictions cover: (1) the longitude range and time intervals of enhanced interaction between Io (and possibly Europa) and Jupiter's ionosphere, (2) plasma, energetic particle, and magnetic field periodicities in the outer magnetosphere, and (3) the sub-spacecraft System III longitude and the time, modulo 10 hours, of the first and subsequent magnetopause crossings.

Dessler, A. J.; Vasyliunas, V. M.

1979-01-01

172

Adaptive cancellation of geomagnetic background noise for magnetic anomaly detection using coherence  

NASA Astrophysics Data System (ADS)

Magnetic anomaly detection (MAD) is an effective method for the detection of ferromagnetic targets against background magnetic fields. Currently, the performance of MAD systems is mainly limited by the background geomagnetic noise. Several techniques have been developed to detect target signatures, such as the synchronous reference subtraction (SRS) method. In this paper, we propose an adaptive coherent noise suppression (ACNS) method. The proposed method is capable of evaluating and detecting weak anomaly signals buried in background geomagnetic noise. Tests with real-world recorded magnetic signals show that the ACNS method can excellently remove the background geomagnetic noise by about 21?dB or more in high background geomagnetic field environments. Additionally, as a general form of the SRS method, the ACNS method offers appreciable advantages over the existing algorithms. Compared to the SRS method, the ACNS algorithm can eliminate the false target signals and represents a noise suppressing capability improvement of 6.4?dB. The positive outcomes in terms of intelligibility make this method a potential candidate for application in MAD systems.

Liu, Dunge; Xu, Xin; Huang, Chao; Zhu, Wanhua; Liu, Xiaojun; Yu, Gang; Fang, Guangyou

2015-01-01

173

Monitoring the evolution of Deception Island volcano from magnetic anomaly data (South Shetland Islands, Antarctica)  

NASA Astrophysics Data System (ADS)

Deception Island is a young and active volcano located in the south-western part of Bransfield back-arc basin. During the last twenty years the Royal Observatory of the Spanish Navy has carried out geophysical surveys in the area. In addition, an unmanned aerial vehicle flight was conducted in 2011 at 800 m height on the northern half of Deception Island. Analysing and comparing magnetic grids obtained in different periods and tie point readings allow us to detect temporal changes and isolate signals of volcanic origin. Magnetic survey cruises performed in Deception Island's inner bay (1988, 1999 and 2008), and the study of its outer area's magnetic anomaly changes, point to a period of high variations concentrated between December 1989 and December 1999 that may be related to the two main recent periods of seismic activity (1992 and January 1999). From December 1999 to December 2008, there were no significant changes in seismic activity; nevertheless, our data show some magnetic alterations, which might signal the slow progress of a volcanic environment towards equilibrium. Interpreting these magnetic changes called for the construction of several forward models. Additionally, we put forth this kind of study as a suitable, economical and easy method for monitoring an active volcanic system whenever it is possible to measure the magnetic field with accurate positioning, and if the external field components are removed correctly.

Catalán, Manuel; Martos, Yasmina M.; Galindo-Zaldívar, Jesús; Funaki, Minoru

2014-12-01

174

Analysis and interpretation of Ibuji spring magnetic anomaly using the Mellin transform  

NASA Astrophysics Data System (ADS)

The Mellin transform is a mathematical tool which has been applied in many areas of Mathematics, Physics and Engineering. Its application in Geophysics is in the computation of solution of potential problems for the determination of the mass as well as the depth to the basement of some solid mineral deposits. In this study, the Mellin transform is used to determine the depth to the top ( h) and the depth to the bottom ( H) of the basement of a profile of an anomalous magnetic body. Ibuji, the study area is located in Ifedore Local Government area of Ondo state, Nigeria, underlain by Precambrian complex rocks and bounded by geographical co-ordinate of Easting 5°00t'00? to 5°4t'30? and Northing 7°24t'00? to 7°27t'36?. The magnetic anomaly profile due to a two- dimensional body(vertical thin sheet)over magnetic spring of the study area was digitised and the values of magnetic amplitude (nT) with respect to its horizontal distance (say interval of 5 m) obtained from the digitized profile was then used in the computation of Mellin transform using Matlab programs. In order to determine the depths H and h, the amplitudes were considered at three arbitrary point ( s = ¼, ½ and ¾) such that, (0 < s < 1), where s is a complex variable of real positive integer. The value obtained for H was 47.95 m, which compared favourably with the result obtained using other methods. Meanwhile, the value obtained for h has a convergence restriction, whereby, at lower values of s, there is divergence, while at higher values of s, (about 0.9), the result converges and h was obtained to be 32.56 m. The Ibuji magnetic anomaly was therefore analysed to have a depth to the bottom ( H) of 47.95 m and depth to the top of 32.56 m using this mathematical tool.

Ozebo, Vitalis C.; Ogunsanwo, Fidelis O.; Adebayo, Gboyega A.; Adeniran, Olusola J.

2013-03-01

175

Observation of an unusual magnetic anomaly in the superconducting mixed state of heavy-fermion compound UBe13 by precise dc magnetization measurements.  

PubMed

We have performed precise dc magnetization measurements for a single crystal of UBe(13) down to 0.14 K, up to 80 kOe. We observed a magnetic anomaly in the superconducting (SC) mixed state at a field, named H(Mag)(*) (~ 26 kOe, at 0.14 K), implying that UBe(13) has a magnetically unusual SC state. We studied the magnetization curves of UBe(13), assuming that the H(Mag)(*) anomaly originates from (1) and unusual SC diamagnetic response, or (2) a peculiarity of the normal-state magnetization due to vortices in the SC mixed state. The origin of the H(Mag)(*) anomaly is discussed. PMID:23215607

Shimizu, Yusei; Haga, Yoshinori; Ikeda, Yoichi; Yanagisawa, Tatsuya; Amitsuka, Hiroshi

2012-11-21

176

Reduction and treatment of magnetic anomalies of crustal origin in satellite data  

NASA Technical Reports Server (NTRS)

The problem of proper reduction and treatment of the residual total magnetic field observed on satellite orbits is studied. The reduction procedure used for Pogo satellite data is reviewed, and a procedure is presented for reducing the residual total field observed on satellite orbits to a spherical surface. Several examples based on selected models are provided to demonstrate the accuracy of the formulas developed for continuation of the satellite data from an irregular to a spherical surface. This procedure is tested on a set of Pogo data covering the area that contains the Bangui magnetic anomaly in central Africa. A technique is also given for determining the field components on a spherical surface and calculating the total field in any fixed direction of the geomagnetic field.

Bhattacharyya, B. K.

1977-01-01

177

Evidence of Saturn's magnetic field anomaly from Saturnian kilometric radiation high-frequency limit  

SciTech Connect

The detailed analysis of Voyager observations of Saturn kilometric radiation (SKR), taking into account the polarization response of the planetary radio astronomy experiment, has allowed the authors to study separately the high-frequency limit of SKR emitted from the northern and southern auroral regions of the planet. Interpretation of the variations of these high-frequency limits, in the frame of a model inspired by the cyclotron maser mechanism, has allowed them to demonstrate unambiguously the existence of a magnetic anomaly, postulated for years, in the near-surface Saturnian field. Its location and amplitude are estimated, and it is shown that, although it accounts for the observed SKR modulation, it could not be detected by the spacecraft-borne magnetometers which passed too far from the planetary surface. This demonstrates that the current degree of comprehension of planetary radio emissions makes them a unique and very pertinent tool for the fine study of planetary magnetic fields.

Galopeau, P.; Zarka, P. (Observatoire de Paris, Meudon (France)); Ortega-Molina, A.

1991-08-01

178

Magnetic anomalies in East Antarctica: a window on major tectonic provinces and their boundaries  

USGS Publications Warehouse

An analysis of aeromagnetic data compiled within the Antarctic Digital Magnetic Anomaly Project (ADMAP) yields significant new insight into major tectonic provinces of East Antarctica. Several previously unknown crustal blocks are imaged in the deep interior of the continent, which are interpreted as cratonic nuclei. These cratons are fringed by a large and continuous orogenic belt between Coats Land and Princess Elizabeth Land, with possible branches in the deeper interior of East Antarctica. Most of the crustal provinces and boundaries identified in this study are only in part exposed. More detailed analyses of these crustal provinces and their tectonic boundaries would require systematic acquisition of additional high-resolution magnetic data, because at present the ADMAP database is largely inadequate to address many remaining questions regarding Antarctica’s tectonic evolution.

Golynsky, A.V.

2007-01-01

179

Magnetic anomaly analysis of the Ionian Sea: Is it the oldest in-situ ocean fragment of the world?  

NASA Astrophysics Data System (ADS)

It is well known that the Ionian Sea is characterized by thin (8-11 km) crystalline crust, thick (5-7 km) sedimentary cover, and low heat flow, typical for a Mesozoic (at least) basin. Yet seismic data have not yielded univocal interpretations, and a debate has developed on the oceanic vs. 'thinned continental' nature of the Ionian basin. Here we analyze the magnetic anomaly pattern of the Ionian Sea, and compare it to synthetic fields produced by a geopotential field generator, considering realistic crust geometry. The Ionian basin is mostly characterized by slightly negative magnetic residuals, and by a prominent positive (150 nT at sea level) 'B' anomaly at the northwestern basin margin. We first test continental crust models, considering a homogeneous crystalline crust with K=1x10-3, then a 5 km thick deep crustal layer of serpentinite (K=1x10-1). First model yields insignificant anomalies, while the second gives an anomaly pattern anti-correlated with the observed residuals. We subsequently test oceanic crust models, considering a 2 km thick 2A basaltic layer with K=5x10-3, magnetic remanence of 5 A/m, and a unique magnetic polarity (no typical oceanic magnetic anomaly stripes are apparent in the observed data set). Magnetic remanence directions were derived from Pangean-African paleopoles in the 290-190 Ma age window. Only reverse-polarity models reproduce the B anomaly, and among them the 220-230 Ma models best approximate magnetic features observed on the abyssal plain and at the western basin boundary. The Ionian Sea turns out to be the oldest preserved oceanic floor known so far. Reference Speranza, F., L. Minelli, A. Pignatelli, and M. Chiappini (2012), The Ionian Sea: The oldest in situ ocean fragment of the world?, J. Geophys. Res., 117, B12101, doi:10.1029/2012JB009475.

Speranza, F.; Minelli, L.; Pignatelli, A.; Chiappini, M.

2013-12-01

180

Energy detection based on undecimated discrete wavelet transform and its application in magnetic anomaly detection.  

PubMed

Magnetic anomaly detection (MAD) is a passive approach for detection of a ferromagnetic target, and its performance is often limited by external noises. In consideration of one major noise source is the fractal noise (or called 1/f noise) with a power spectral density of 1/fa (0magnetic anomaly detection and UDWT are introduced in brief, while a possible detection system based on giant magneto-impedance (GMI) magnetic sensor is also given out. Then our proposed energy detection based on UDWT is described in detail, and the probabilities of false alarm and detection for given the detection threshold in theory are presented. It is noticeable that no a priori assumptions regarding the ferromagnetic target or the magnetic noise probability are necessary for our method, and different from the discrete wavelet transform (DWT), the UDWT is shift invariant. Finally, some simulations are performed and the results show that the detection performance of our proposed detector is better than that of the conventional energy detector even utilized in the Gaussian white noise, especially when the spectral parameter ? is less than 1.0. In addition, a real-world experiment was done to demonstrate the advantages of the proposed method. PMID:25343484

Nie, Xinhua; Pan, Zhongming; Zhang, Dasha; Zhou, Han; Chen, Min; Zhang, Wenna

2014-01-01

181

Energy Detection Based on Undecimated Discrete Wavelet Transform and Its Application in Magnetic Anomaly Detection  

PubMed Central

Magnetic anomaly detection (MAD) is a passive approach for detection of a ferromagnetic target, and its performance is often limited by external noises. In consideration of one major noise source is the fractal noise (or called 1/f noise) with a power spectral density of 1/fa (0magnetic anomaly detection and UDWT are introduced in brief, while a possible detection system based on giant magneto-impedance (GMI) magnetic sensor is also given out. Then our proposed energy detection based on UDWT is described in detail, and the probabilities of false alarm and detection for given the detection threshold in theory are presented. It is noticeable that no a priori assumptions regarding the ferromagnetic target or the magnetic noise probability are necessary for our method, and different from the discrete wavelet transform (DWT), the UDWT is shift invariant. Finally, some simulations are performed and the results show that the detection performance of our proposed detector is better than that of the conventional energy detector even utilized in the Gaussian white noise, especially when the spectral parameter ? is less than 1.0. In addition, a real-world experiment was done to demonstrate the advantages of the proposed method. PMID:25343484

Nie, Xinhua; Pan, Zhongming; Zhang, Dasha; Zhou, Han; Chen, Min; Zhang, Wenna

2014-01-01

182

Long-Wavelength Magnetic Anomalies and Tectonic Divisions of the Tasmanides, Eastern Australia.  

NASA Astrophysics Data System (ADS)

Aeromagnetic data over eastern Australia reveal a pattern of domains defined by systematic and uniform regional highs and lows, emphasised by low-pass filtering, over which are superimposed shorter (<20 km) wavelength anomalies whose disposition is clearly related to mappable geology and its inferred subsurface continuation. Long baseline levelling accomplished through Geoscience Australia's AWAGS program has served to clarify the definition of these magnetic domains, and to confirm that they are not an artefact of grid merging. Geothermal and teleseismic data indicate that neither variation in Curie depth nor upper mantle magnetisation can produce the pattern of long-wavelength magnetic domains. Hence, domain-wide variations in magnetisation at the middle crustal (> 10 km depth) level are presumably the cause of these long-wavelength features. Although reversed polarity remanence, possibly carried by laminar hematite, could contribute to deeply sourced negative magnetic anomalies, the correspondence of magnetic low domains with the Proterozoic Curnamona Craton and the Ordovician Macquarie Arc, and of a high domain with the western Lachlan Orogen floored by Cambrian ocean crust, suggests that the control may be simply stark contrasts in lower to middle crustal susceptibility. Implicit in this analysis is a division of the domains by middle crust type into two categories, continental versus oceanic, with implications for the tectonic evolution of the Tasmanides. Contrary to previous interpretations, the Macquarie Arc was apparently built on a sliver of continental crust, and the Thomson Orogen is a compound feature, in which oceanic crust was accreted to an arc likewise floored by continental material.

Musgrave, R. J.

2011-12-01

183

GEODVEL vs. MORVEL: Comparison of plate motion determined from space geodesy with that determined from magnetic anomalies and transform azimuths (Invited)  

NASA Astrophysics Data System (ADS)

To test whether plate velocities averaged over the past two decades equal those averaged over the past 1 to 3 million years, we compare the angular velocities in model GEODVEL against those in MORVEL. GEODVEL is determined from four space geodetic techniques, GPS, SLR, VLBI, and DORIS. In GEODVEL we assume Earth’s center to be (CE) the mass center of solid Earth, and we estimate the velocity of CE assuming that, beside plate motion, the parts of the plate interiors near the late Pleistocene ice sheets are not moving relative to CE. In GEODVEL the uncertainties in plate velocity account for uncertainty in the velocity of CE. GEODVEL differs from prior models of plate velocity from space geodesy partly because the velocity of Earth’s center differs between GEODVEL and the other models and partly because the assignment of sites to plates differs between GEODVEL and the other models. MORVEL is determined mainly from transform azimuths and spreading rates estimated from magnetic anomalies either 0.8 Ma (anomaly 1o) or 3.2 Ma (anomaly 2A). MORVEL differs from NUVEL-1A in that (1) it includes spreading rates and transform azimuths estimated using high-quality observations taken over the past two decades, (2) it excludes data from the Gulf of California and earthquake slip vectors along subduction zones, and (3) it includes distinct east (Nubian) and west (Somalian) plates. In MORVEL the velocity of the plates of the Pacific Ocean relative to the surrounding continental plates depend strongly on the plate circuit (Eurasia)-North America-Nubia-Antarctica-Pacific-(Nazca or Cocos). In MORVEL the uncertainties in plate velocity account for uncertainty in outward displacement of magnetic anomalies. We compare the angular velocities in three dimensions on a plate-by-plate basis. We are finding, for the nine largest plates, the median difference between the GEODVEL and MORVEL sets of angular velocities to be 0.046 °/Myr, which is up to 5.1 mm/yr along Earth’s surface.

Argus, D.; Demets, C.; Gordon, R. G.

2009-12-01

184

Circum-Arctic Magnetic Anomalies - Challenges of Compilation and the Value of Regional Interpretation in a Frontier Area  

NASA Astrophysics Data System (ADS)

Important societal issues are driving increased attention to polar regions. The arctic, in particular, is the focus of scientific studies relating to climate change as well as resource exploration and territorial claims. The news and entertainment media are picking up on polar themes and driving interest within popular culture. Part of the attraction and mystique of the ends of the Earth lies in their relative inaccessibility and harsh environment. These same attributes make it difficult to conduct even basic scientific investigation, and therefore, the arctic remains a scientific frontier in many respects. Delineation of a robust tectonic framework for the top of the world is an essential prerequisite to resource assessment. The difficulty of making direct geologic observations beneath ice and sea requires remote measurement. Regional magnetic anomaly mapping provides important constraining information for the development of tectonic models for this structurally complex region. In addition to the obvious logistical challenges to detailed magnetic field measurement in the high arctic, noise and instability in the magnetic field itself at high latitudes presents difficulties. Nevertheless, regional magnetic anomaly data have been collected over the past 50 years for much of the arctic. The available surveys are diverse in vintage and survey design; the amplitude and frequency content of measured anomalies are widely variable. Availability of metadata and other documentation are also inconsistent for these surveys. This leads to significant challenges in constructing accurate regional magnetic anomaly maps. Preliminary maps from a new international cooperation effort (CAMP-GM, under the direction of Carmen Gaina, Geological Survey of Norway) provide the most consistent view yet of magnetic anomalies for the tectonically complex arctic basins and surrounding continents. Careful attention to digital compilation details allows the new grids to be mathematically filtered to assist in the regional characterization of magnetic domains and boundaries. The frequency content, amplitudes, and patterns of regional magnetic anomalies provide a window into the tectonic character and structure of the crust. Continental, oceanic, and various types of transitional crust each have a distinctive magnetic anomaly signature that can be used to define a fundamental tectonic framework of the circum-arctic. Interpretation can be extended by including additional data such as regional bathymetry (an indicator of crustal buoyancy and isostatic equilibrium) and free air gravity (an independent indicator of crustal density balance and composition). Used together with magnetic domains these data reveal a composite geodynamic subdivision of the arctic. This subdivision provides a framework for investigations of mineral and energy resource potential, tectonic reconstruction, and long-term climate dynamics.

Saltus, R. W.; Gaina, C.; Brown, P. J.

2007-12-01

185

Magnetization anomaly of Nb3Al strands and instability of Nb3Al Rutherford cables  

SciTech Connect

Using a Cu stabilized Nb{sub 3}Al strand with Nb matrix, a 30 meter long Nb{sub 3}Al Rutherford cable was made by a collaboration of Fermilab and NIMS. Recently the strand and cable were tested. In both cases instability was observed at around 1.5 Tesla. The magnetization of this Nb{sub 3}Al strand was measured first using a balanced coil magnetometer at 4.2 K. Strands showed an anomalously large magnetization behavior around at 1.6 T, which is much higher than the usual B{sub c2} {approx} 0.5 Tesla (4.2 K) of Nb matrix. This result is compared with the magnetization data of short strand samples using a SQUID magnetometer, in which a flux-jump signal was observed at 0.5 Tesla, but not at higher field. As a possible explanation for this magnetization anomaly, the interfilament coupling through the thin Nb films in the strands is suggested. The instability problem observed in low field tests of the Nb{sub 3}Al Rutherford cables is attributed to this effect.

Yamada, Ryuji; /Fermilab; Kikuchi, Akihiro; /Tsukuba Magnet Lab; Wake, Masayoshi; /KEK, Tsukuba

2006-08-01

186

Investigation of the Crust of the Pannonian Basin, Hungary Using Low-Altitude CHAMP Horizontal Gradient Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

The Pannonian Basin is a deep intra-continental basin that formed as part of the Alpine orogeny. It is some 600 by 500 km in area and centered on Hungary. This area was chosen since it has one of the thinnest continental crusts in Europe and is the region of complex tectonic structures. In order to study the nature of the crustal basement we used the long-wavelength magnetic anomalies acquired by the CHAMP satellite. The SWARM constellation, scheduled to be launched next year, will have two lower altitude satellites flying abreast, with a separation of between ca. 150 to 200 km. to record the horizontal magnetic gradient. Since the CHAMP satellite has been in orbit for eight years and has obtained an extensive range of data, both vertically and horizontally there is a large enough data base to compute the horizontal magnetic gradients over the Pannonian Basin region using these many CHAMP orbits. We recomputed a satellite magnetic anomaly map, using the spherical-cap method of Haines (1985), the technique of Alsdorf et al. (1994) and from spherical harmonic coefficients of MF6 (Maus et aI., 2008) employing the latest and lowest altitude CHAMP data. We then computed the horizontal magnetic anomaly gradients (Kis and Puszta, 2006) in order to determine how these component data will improve our interpretation and to preview what the SW ARM mission will reveal with reference to the horizontal gradient anomalies. The gradient amplitude of an 1000 km northeast-southwest profile through our horizontal component anomaly map varied from 0 to 0.025 nT/km with twin positive anomalies (0.025 and 0.023 nT/km) separated by a sharp anomaly negative at o nT/km. Horizontal gradient indicate major magnetization boundaries in the crust (Dole and Jordan, 1978 and Cordell and Grauch, 1985). Our gradient anomaly was modeled with a twodimensional body and the anomaly, of some 200 km, correlates with a 200 km area of crustal thinning in the southwestern Pannonian Basin.

Taylor, Patrick T.; Kis, Karoly I.; Puszta, Sandor; Wittmann, Geza; Kim, Hyung Rae; Toronyi, B.

2011-01-01

187

Investigation of the crust of the Pannonian Basin, Hungary using low-altitude CHAMP horizontal magnetic gradient anomalies  

NASA Astrophysics Data System (ADS)

The Pannonian Basin is a deep intracontinental basin that formed as part of the Alpine orogeny. It is some 600 by 500 km in area and centered on Hungary. This region was chosen since it has one of the thinnest continental crusts in Europe and is the location of complex tectonic structures. In order to study the nature of the crustal basement we used the long-wavelength magnetic anomalies acquired by the CHAMP satellite. The SWARM constellation, scheduled to be launched next year, will have two lower altitude satellites flying abreast, with a separation of between ca. 150 to 200 km. to record the horizontal magnetic gradient. Since the CHAMP satellite has been in orbit for eight years and has obtained an extensive range of data, both vertically and horizontally there is a large enough data base to compute the horizontal magnetic gradients over the Pannonian Basin region using these many CHAMP orbits. We computed a satellite magnetic anomaly map, using the spherical-cap method of Haines (1985), the technique of Alsdorf et al. (1994) and from spherical harmonic coefficients of MF6 (Maus et al., 2008) employing recent and lowest altitude CHAMP data. We then computed the horizontal magnetic anomaly gradients (Kis and Puszta, 2006) in order to determine how these component data will improve our interpretation and to preview what the SWARM mission will reveal with reference to the horizontal gradient anomalies. The gradient amplitude of an 1000 km northeast-southwest profile through our horizontal component anomaly map varied from 0 to 0.025 nT/km with twin positive anomalies (0.025 and 0.023 nT/km) separated by a sharp V-shaped anomaly gradient to 0 nT/km between the two highs. Horizontal gradients indicate major magnetization boundaries in the crust (Dole and Jordan, 1978 and Cordell and Grauch, 1985). Our gradient anomaly was modeled with a two-dimensional body and this anomaly indicates a lateral variation of some 200 km. The model correlates with a 200 km area of crustal thinning in the southwestern Pannonian Basin.

Taylor, P. T.; Kis, K. I.; Puszta, S.; Wittman, G.; Kim, H.; Toronyi, B.

2011-12-01

188

Deciphering tectonic phases of the Amundsen Sea Embayment shelf, West Antarctica, from a magnetic anomaly grid  

NASA Astrophysics Data System (ADS)

The Amundsen Sea Embayment (ASE), with Pine Island Bay (PIB) in the eastern embayment, is a key location to understanding tectonic processes of the Pacific margin of West Antarctica. PIB has for a long time been suggested to contain the crustal boundary between the Thurston Island block and the Marie Byrd Land block. Plate tectonic reconstructions have shown that the initial rifting and breakup of New Zealand from West Antarctica occurred between Chatham Rise and the eastern Marie Byrd Land at the ASE. Recent concepts have discussed the possibility of PIB being the site of one of the eastern branches of the West Antarctic Rift System (WARS). About 30,000 km of aeromagnetic data - collected opportunistically by ship-based helicopter flights - and tracks of ship-borne magnetics were recorded over the ASE shelf during two RV Polarstern expeditions in 2006 and 2010. Grid processing, Euler deconvolution and 2D modelling were applied for the analysis of magnetic anomaly patterns, identification of structural lineaments and characterisation of magnetic source bodies. The grid clearly outlines the boundary zone between the inner shelf with outcropping basement rocks and the sedimentary basins of the middle to outer shelf. Distinct zones of anomaly patterns and lineaments can be associated with at least three tectonic phases from (1) magmatic emplacement zones of Cretaceous rifting and breakup (100-85 Ma), to (2) a southern distributed plate boundary zone of the Bellingshausen Plate (80-61 Ma) and (3) activities of the WARS indicated by NNE-SSW trending lineaments (55-30 Ma?). The analysis and interpretation are also used for constraining the directions of some of the flow paths of past grounded ice streams across the shelf.

Gohl, Karsten; Denk, Astrid; Eagles, Graeme; Wobbe, Florian

2013-02-01

189

A Hybrid Positive-and-Negative Curvature Approach for Detection of the Edges of Magnetic Anomalies, and Its Application in the South China Sea  

NASA Astrophysics Data System (ADS)

In work discussed in this paper the characteristics of both the most positive and most negative curvatures of a magnetic anomaly were analyzed, and a new approach for detection of the edges of magnetic anomalies is proposed. The new approach, called the hybrid positive-and-negative curvature approach, combines the most positive and most negative curvatures into one curvature by formula adjustments and weighted summation, combining the advantages of the two curvatures to improve edge detection. This approach is suitable for vertically magnetized or reduction-to-pole anomalies, which avoids the complexity of magnetic anomalies caused by oblique magnetization. Testing on synthetic vertically magnetized magnetic anomalies data demonstrated that the hybrid approach traces the edges of magnetic source bodies effectively, discriminates between high and low magnetism intuitively, and is better than approaches based solely on use of the most positive or most negative curvature. Testing on reduced-to-pole magnetic anomalies data around the ocean basin of the South China Sea showed that the hybrid approach enables better edge detection than the most positive or most negative curvatures. On the basis of the features of the reduced-to-pole magnetic anomalies and their hybrid curvature, we suggest the tectonic boundary between the southwestern subbasin and the eastern subbasin of the South China Sea ranges from the northeastern edge of the Zhongsha Islands in the southeast direction to the northeastern edge of the Reed Bank.

Guo, Lianghui; Gao, Rui; Meng, Xiaohong; Zhang, Guoli

2014-11-01

190

Remanent and Induced Magnetic Anomalies over the Bjerkreim-Sokndal Layered Intrusion: Effects from Crystal Fractionation and Magma Recharge  

NASA Astrophysics Data System (ADS)

The Bjerkreim-Sokndal (BKS) norite-quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~930 Ma. The BKS is exposed over an area of 230 km2 with a thickness of ~7000m and is of economic interest for hemo-ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma containing hemo-ilmenite. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the magnetic properties of NRM, susceptibility, and hysteresis. Magnetic properties are correlated with the oxide mineralogy and mineral chemistry. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRM's associated either with hemo-ilmenite or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20 km by ground-magnetic measurements. The highly varied magnetic properties of this intrusion, caused by varied magmatic crystallization of combinations of oxide minerals illustrate some of the possibilities to be considered in evaluating crustal magnetic anomalies.

McEnroe, S. A.; Brown, L. L.; Robinson, P.

2013-12-01

191

Hot flow anomaly formation by magnetic deflection. [regions of hot plasma in earth magnetosphere  

NASA Technical Reports Server (NTRS)

Hot flow anomalies (HFAs) are localized plasma structures observed in the solar wind and magnetosheath near the earth's quasi-parallel bow shock. This paper presents one-dimensional hybrid computer simulations illustrating a formation mechanism for HFAs in which the single hot ion population results from a spatial separation of two counterstreaming ion beams. The higher-density cooler regions are dominated by the background (solar wind) ions, and the lower-density hotter internal regions are dominated by the beam ions. The spatial separation of the beam and background is caused by the deflection of the ions in large-amplitude magnetic fields which are generated by ion/ion streaming instabilities.

Onsager, T. G.; Thomsen, M. F.; Winske, D.

1990-01-01

192

Electromagnetic particle-in-cell simulations of the solar wind interaction with lunar magnetic anomalies.  

PubMed

We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier magnetohydrodynamics and hybrid simulations, the fully kinetic nature of iPic3D allows us to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe for the first time the interaction of a dipole model centered just below the lunar surface under plasma conditions such that only the electron population is magnetized. The fully kinetic treatment identifies electromagnetic modes that alter the magnetic field at scales determined by the electron physics. Driven by strong pressure anisotropies, the mini-magnetosphere is unstable over time, leading to only temporal shielding of the surface underneath. Future human exploration as well as lunar science in general therefore hinges on a better understanding of LMAs. PMID:24785022

Deca, J; Divin, A; Lapenta, G; Lembège, B; Markidis, S; Horányi, M

2014-04-18

193

Oxfordian magnetostratigraphy of Britain and its correlation to Tethyan regions and Pacific marine magnetic anomalies  

NASA Astrophysics Data System (ADS)

A suite of 11 sections through the Oxfordian (Upper Jurassic) strata in the Dorset and Yorkshire regions of England and the Isle of Skye in Scotland yielded magnetic polarity patterns directly calibrated to the ammonite biostratigraphy of the Boreal and the Subboreal faunal provinces. The sections include the leading candidate for the global stratotype (GSSP) for the Callovian-Oxfordian stage boundary. The mean Oxfordian paleomagnetic pole derived from the Dorset and Yorkshire sections is 71.3°N, 172.6°E ( ?p = 4.2°, ?m = 6.1°). The integrated magneto-biostratigraphic scale is consistent with results from the Sub-Mediterranean faunal province and extends the polarity pattern to the base of the Oxfordian. After adjusting for the estimated durations of ammonite subzones from cycle stratigraphy, the magnetostratigraphy confirms models for marine magnetic anomalies M30 through to M37, including some of the short-duration features recorded by deep-tow magnetic surveys in the western Pacific. The Callovian-Oxfordian boundary (base of Quenstedtoceras mariae Zone) occurs in a normal-polarity zone that is correlated to the youngest part of polarity chron M37n of this extension to the M-sequence.

Ogg, James G.; Coe, Angela L.; Przybylski, Piotr A.; Wright, John K.

2010-01-01

194

Electromagnetic Particle-in-Cell Simulations of the Solar Wind Interaction with Lunar Magnetic Anomalies  

NASA Astrophysics Data System (ADS)

We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier magnetohydrodynamics and hybrid simulations, the fully kinetic nature of iPic3D allows us to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe for the first time the interaction of a dipole model centered just below the lunar surface under plasma conditions such that only the electron population is magnetized. The fully kinetic treatment identifies electromagnetic modes that alter the magnetic field at scales determined by the electron physics. Driven by strong pressure anisotropies, the mini-magnetosphere is unstable over time, leading to only temporal shielding of the surface underneath. Future human exploration as well as lunar science in general therefore hinges on a better understanding of LMAs.

Deca, J.; Divin, A.; Lapenta, G.; Lembège, B.; Markidis, S.; Horányi, M.

2014-04-01

195

The role of magnetic resonance imaging in refining the diagnosis of suspected fetal renal anomalies  

PubMed Central

Objective: This prospective study was designed to detect the role of magnetic resonance imaging (MRI) in refining the diagnosis of suspected fetal renal anomalies detected during screening sonography. Material and Methods: 54 pregnant women, with suspected fetal renal anomalies detected during routine ultrasound screening, were rescanned by MRI to refine the diagnosis of the suspected renal anomalies. The pregnancy outcome was examined externally and by postnatal ultrasonography. Results: Fifty-four cases of suspected renal anomalies detected during screening sonography of 8400 pregnant women (0.6%), were res-canned by MRI in this study. The MRI gave a similar diagnosis to postnatal ultrasound in 46 cases (16 cases of hydronephrosis, 14 cases of Polycystic Kidney Disease (PCKD), 9 cases of Multicystic Kidney Disease (MCKD), 2 cases of Renal Agensis (RA), 3 cases of single renal cyst and 2 cases of megacystis+hydroureter), while it gave a different diagnosis (false positive) in 6 cases (4 cases of hydronephrosis diagnosed by MRI confirmed to be PCKD by postnatal ultrasound, also, 1 case of MCKD diagnosed by MRI confirmed to be hydronephrosis by postnatal ultrasound and 1 case of RA diagnosed by MRI confirmed to be normal by postnatal ultrasound). The prenatal ultrasound gave a similar diagnosis to postnatal ultrasound in 43 cases (14 cases of hydronephrosis, 13 case of PCKD, 9 cases of MCKD, 2 cases of RA, 3 cases of single renal cyst and 2 case of megacystis+hydroureter), while it gave a different diagnosis (false positive) in 9 cases; 4 cases of hydronephrosis diagnosed by prenatal sonography confirmed to be PCKD by postnatal ultrasound, one case of PCKD+one case of MCKD, and one case of megacystis+hydroureter confirmed to be hydronephrosis by postnatal ultrasound, while one case of MCKD diagnosed by prenatal sonography was confirmed to be PCKD by postnatal ultrasound and one case of RA diagnosed by prenatal ultrasound was confirmed to be normal by postnatal ultrasound. Conclusion: The MRI can be used as a complementary adjunctive modality with excellent tissue contrast, especially in equivocal cases or inconclusive sonographic findings. PMID:24592062

Abdelazim, Ibrahim Anwar; Belal, Maha Mohamed

2013-01-01

196

Geophysical Surveying of Shallow Magnetic Anomalies Using the iPhone Magnetometer  

NASA Astrophysics Data System (ADS)

This investigation examined whether the 3-axis Hall-effect magnetometer in the Apple iPhone 3GS can function as an effective shallow magnetic survey instrument. The xSensor Pro app from Crossbow Systems allows recoding of all three sensor components along with the GPS location, at a frequency of 1.0, 4.0, 16.0, and 32.0 Hz. If the iPhone proves successful in collecting useful magnetic data, then geophysicists and especially educators would have a new tool for high-density geophysical mapping. No-contract iPhones that can connect with WiFi can be obtained for about $400, allowing deployment of large numbers of instruments. iPhones with the xSensor Pro app surveyed in parallel with an Overhauser GEM system magnetometer (1 nT sensitivity) to test this idea. Anderson Bay, located on the Pyramid Lake Paiute Reservation, provided a rural survey location free from cultural interference. xSensor Pro, logged each component's intensity and the GPS location at a frequency of four measurements per second. Two Overhauser units functioned as a base unit and a roving unit. The roving unit collected total field at set points located with a handheld GPS. Comparing the total field computed from the iPhone components against that collected by the Overhauser establishes the level of anomalies that the iPhone can detect. iPhone total-field measurements commonly vary by 200 nT from point to point, so a spatial-temporal average over 25 seconds produces a smoothed signal for comparison. Preliminary analysis of the iPhone results show that the data do not accurately correlate to the total field collected by the Overhauser for any anomaly of less than 200 nT.

Opdyke, P.; Dudley, C.; Louie, J. N.

2012-12-01

197

Controls on Martian Hydrothermal Systems: Application to Valley Network and Magnetic Anomaly Formation  

NASA Technical Reports Server (NTRS)

Models of hydrothermal groundwater circulation can quantify limits to the role of hydrothermal activity in Martian crustal processes. We present here the results of numerical simulations of convection in a porous medium due to the presence of a hot intruded magma chamber. The parameter space includes magma chamber depth, volume, aspect ratio, and host rock permeability and porosity. A primary goal of the models is the computation of surface discharge. Discharge increases approximately linearly with chamber volume, decreases weakly with depth (at low geothermal gradients), and is maximized for equant-shaped chambers. Discharge increases linearly with permeability until limited by the energy available from the intrusion. Changes in the average porosity are balanced by changes in flow velocity and therefore have little effect. Water/rock ratios of approximately 0.1, obtained by other workers from models based on the mineralogy of the Shergotty meteorite, imply minimum permeabilities of 10(exp -16) sq m2 during hydrothermal alteration. If substantial vapor volumes are required for soil alteration, the permeability must exceed 10(exp -15) sq m. The principal application of our model is to test the viability of hydrothermal circulation as the primary process responsible for the broad spatial correlation of Martian valley networks with magnetic anomalies. For host rock permeabilities as low as 10(exp -17) sq m and intrusion volumes as low as 50 cu km, the total discharge due to intrusions building that part of the southern highlands crust associated with magnetic anomalies spans a comparable range as the inferred discharge from the overlying valley networks.

Harrison, Keith P.; Grimm, Robert E.

2002-01-01

198

Controls on Martian hydrothermal systems: Application to valley network and magnetic anomaly formation  

NASA Astrophysics Data System (ADS)

Models of hydrothermal groundwater circulation can quantify limits to the role of hydrothermal activity in Martian crustal processes. We present here the results of numerical simulations of convection in a porous medium due to the presence of a hot intruded magma chamber. The parameter space includes magma chamber depth, volume, aspect ratio, and host rock permeability and porosity. A primary goal of the models is the computation of surface discharge. Discharge increases approximately linearly with chamber volume, decreases weakly with depth (at low geothermal gradients), and is maximized for equant-shaped chambers. Discharge increases linearly with permeability until limited by the energy available from the intrusion. Changes in the average porosity are balanced by changes in flow velocity and therefore have little effect. Water/rock ratios of ~0.1, obtained by other workers from models based on the mineralogy of the Shergotty meteorite, imply minimum permeabilities of 10-16 m2 during hydrothermal alteration. If substantial vapor volumes are required for soil alteration, the permeability must exceed 10-15 m2. The principal application of our model is to test the viability of hydrothermal circulation as the primary process responsible for the broad spatial correlation of Martian valley networks with magnetic anomalies. For host rock permeabilities as low as 10-17 m2 and intrusion volumes as low as 50 km3, the total discharge due to intrusions building that part of the southern highlands crust associated with magnetic anomalies spans a comparable range as the inferred discharge from the overlying valley networks.

Harrison, Keith P.; Grimm, Robert E.

2002-05-01

199

Three-Dimensional Mapping of Magnetic Strata From Aeromagnetic Anomalies: The Deformed Neroly Formation South of Mt. Diablo, Northern California  

Microsoft Academic Search

We apply direct inversion of aeromagnetic anomalies to analyze the subsurface 3D shape of the highly magnetic Miocene Neroly Formation, which consists largely of medium to coarse-grained andesitic sandstones containing abundant magnetite. The Neroly Formation is widespread in the eastern San Francisco Bay region, and locally is tightly folded and disrupted by faulting in the compressional regime related to the

R. C. Jachens; R. W. Simpson; R. W. Graymer; C. M. Wentworth

2008-01-01

200

The history of Mars' dynamo as revealed by modeling magnetic anomalies near Tyrrhenus Mons and Syrtis Major  

NASA Astrophysics Data System (ADS)

The lack of magnetic anomalies within the major impact basins (Hellas, Argyre, and Isidis) has led many investigators to the conclusion that Mars' dynamo shut down prior to the time when these basins formed (˜4.0 Ga). We test this hypothesis by analyzing gravity and magnetic anomalies in the regions surrounding Tyrrhenus Mons and Syrtis Major, two volcanoes that were active during the late Noachian and Hesperian. We model magnetic anomalies that are associated with gravity anomalies and generally find that sources located below Noachian surface units tend to favor paleopoles near the equator and sources located below Hesperian surface features favor paleopoles near the geographical poles, suggesting polar wander during the Noachian-Hesperian. Both paleopole clusters have positive and negative polarities, indicating reversals of the field during the Noachian and Hesperian. Magnetization of sources below Hesperian surfaces is evidence that the dynamo persisted beyond the formation of the major impact basins. The demagnetization associated with the volcanic construct of Syrtis Major implies dynamo cessation occurred while it was geologically active approximately 3.6 billion years ago. Timing of dynamo activity is fundamentally linked to Mars' climate via the stability of its atmosphere, and is coupled to the extent and duration of surface geologic activity. Thus, the dynamo history is key for understanding both when Mars was most geologically active and when it may have been most hospitable to life.

Milbury, C.; Schubert, G.; Raymond, C. A.; Smrekar, S. E.; Langlais, B.

2012-10-01

201

Gulf Coast-East Coast magnetic anomaly I: Root of the main crustal decollement for the Appalachian-Ouachita orogen  

SciTech Connect

The Gulf Coast-East Coast magnetic anomaly extends for at least 4000 km from south-central Texas to offshore Newfoundland as one of the longest continuous tectonic features in North America and a major crustal element of the entire North Atlantic-Gulf Coast region. Analysis of 28 profiles spaced at 100km intervals and four computed models demonstrate that the anomaly may be explained by a thick zone of mafic and ultramafic rocks averaging 13-15 km in depth. The trend of the anomaly closely follows the trend of main Appalachian features: in the Gulf Coast of Louisiana, the anomaly is as far south of the Ouachita front as it is east of the western limit of deformation through the central Appalachians. Because the anomaly continues across well-known continental crust in northern Florida and onshore Texas, it cannot plausibly be ascribed to an edge effect at the boundary of oceanic with continental crustal compositions. The northwest-verging, deep-crustal events discovered in COCORP data from the Ouachitas and Appalachians suggest an analogy with the main suture of the Himalayan orogen in the Tibetan Plateau. In this paper the anomaly is identified with the late Paleozoic Alleghenian megasuture, in which the northwest-verging crustal-detachment surfaces ultimately root.

Hall, D.J. (Total Minatome Corporation, Houston, TX (USA))

1990-09-01

202

Inverse Dipolar Magnetic Anomaly Over the Volcanic Cone Linked to Reverse Polarity Magnetizations in Lavas and Tuffs - Implications for the Conduit System  

NASA Astrophysics Data System (ADS)

A combined magnetics and paleomagnetic study of Toluquilla monogenetic volcano and associated lavas and tuffs from Valsequillo basin in Central Mexico provides evidence on a magnetic link between lavas, ash tuffs and the underground volcanic conduit system. Paleomagnetic analyses show that lavas and ash tuffs carry reverse polarity magnetizations, which correlate with the inversely polarized dipolar magnetic anomaly over the volcano. The magnetizations in the lava and tuff show similar southward declinations and upward inclinations, supporting petrological inferences that the tuff was emplaced while still hot and indicating a temporal correlation for lava and tuff emplacement. Conduit geometry is one of the important controlling factors in eruptive dynamics of basaltic volcanoes. However volcanic conduits are often not, or only partly, exposed. Modeling of the dipolar anomaly gives a reverse polarity source magnetization associated with a vertical prismatic body with southward declination and upward inclination, which correlates with the reverse polarity magnetizations in the lava and tuff. The study documents a direct correlation of the paleomagnetic records with the underground magmatic conduit system of the monogenetic volcano. Time scale for cooling of the volcanic plumbing system involves a longer period than the one for the tuff and lava, suggesting that magnetization for the source of dipolar anomaly may represent a long time average as compared to the spot readings in the lava and tuff. The reverse polarity magnetizations in lava and tuff and in the underground source body for the magnetic anomaly are interpreted in terms of eruptive activity of Toluquilla volcano at about 1.3 Ma during the Matuyama reverse polarity C1r.2r chron.

Fucugauchi, J. U.; Perez-Cruz, L. L.; Trigo-Huesca, A.

2012-12-01

203

Characterization of Lunar Swirls at Mare Ingenii: A Model for Space Weathering at Magnetic Anomalies  

NASA Technical Reports Server (NTRS)

Analysis of spectra from the Clementine ultraviolet-visible and near-infrared cameras of small, immature craters and surface soils both on and adjacent to the lunar swirls at Marc Ingenii has yielded the following conclusions about space weathering at a magnetic anomaly. (l) Despite having spectral characteristics of immaturity, the lunar swirls arc not freshly exposed surfaces. (2) The swirl surfaces arc regions of retarded weathering, while immediately adjacent regions experience accelerated weathering, (3) Weathering in the off-swirl regions darkens and flattens the spectrum with little to no reddening, which suggests that the production of larger (greater than 40 nm) nanophase iron dominates in these locations as a result of charged particle sorting by the magnetic field. Preliminaty analysis of two other lunar swirl regions, Reiner Gamma and Mare Marginis, is consistent with our observations at Mare Ingenii. Our results indicate that sputtering/vapor deposition, implanted solar wind hydrogen, and agglutination share responsibility for creating the range in npFe(sup 0) particle sizes responsible for the spectral effects of space weathering.

Kramer, Georgianna Y.; Combe, Jean-Philippe; Harnett, Erika M.; Hawke, Bernard Ray; Noble, Sarah K.; Blewett, David T.; McCord, Thomas B.; Giguere, Thomas A.

2011-01-01

204

Modelling the gravity and magnetic field anomalies of the Chicxulub crater  

NASA Technical Reports Server (NTRS)

The approximately 180-km-diameter Chicxulub crater lies buried by approximately 1 km of sediment on the northwestern corner of the Yucatan Peninsula, Mexico. Geophysical, stratigraphic and petrologic evidence support an impact origin for the structure and biostratigraphy suggests that a K/T age is possible for the impact. The crater's location is in agreement with constraints derived from proximal K/T impact-wave and ejecta deposits and its melt-rock is similar in composition to the K/T tektites. Radiometric dating of the melt rock reveals an age identical to that of the K/T tektites. The impact which produced the Chicxulub crater probably produced the K/T extinctions and understanding the now-buried crater will provide constraints on the impact's lethal effects. The outstanding preservation of the crater, the availability of detailed gravity and magnetic data sets, and the two-component target of carbonate/evaporites overlying silicate basement allow application of geophysical modeling techniques to explore the crater under most favorable circumstances. We have found that the main features of the gravity and magnetic field anomalies may be produced by the crater lithologies.

Aleman, C. Ortiz; Pilkington, M.; Hildebrand, A. R.; Roest, W. R.; Grieve, R. A. F.; Keating, P.

1993-01-01

205

3D Electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies  

NASA Astrophysics Data System (ADS)

Unlike the Earth and Mercury, our Moon has no global magnetic field and is therefore not shielded from the impinging solar wind by a magnetosphere. However, lunar magnetic field measurements made by the Apollo missions provided direct evidence that the Moon has regions of small-scale crustal magnetic fields, ranging up to a few 100km in scale size with surface magnetic field strengths up to hundreds of nanoTeslas. More recently, the Lunar Prospector spacecraft has provided high-resolution observations allowing to construct magnetic field maps of the entire Moon, confirming the earlier results from Apollo, but also showing that the lunar plasma environment is much richer than earlier believed. Typically the small-scale magnetic fields are non-dipolar and rather tiny compared to the lunar radius and mainly clustered on the far side of the moon. Using iPic3D we present the first 3D fully kinetic and electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies. We study the behaviour of a dipole model with variable surface magnetic field strength under changing solar wind conditions and confirm that lunar crustal magnetic fields may indeed be strong enough to stand off the solar wind and form a mini-magnetosphere, as suggested by MHD and hybrid simulations and spacecraft observations. 3D-PIC simulations reveal to be very helpful to analyze the diversion/braking of the particle flux and the characteristics of the resulting particles accumulation. The particle flux to the surface is significantly reduced at the magnetic anomaly, surrounded by a region of enhanced density due to the magnetic mirror effect. Second, the ability of iPic3D to resolve all plasma components (heavy ions, protons and electrons) allows to discuss in detail the electron physics leading to the highly non-adiabatic interactions expected as well as the implications for solar wind shielding of the lunar surface, depending on the scale size (solar wind protons typically have gyroradii larger than the magnetic anomaly scale size) and magnetic field strength. The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement SWIFF (project 2633430, swiff.eu). Cut along the dipole axis of the lunar anomaly, showing the electron density structure.

Deca, J.; Lapenta, G.; Divin, A. V.; Lembege, B.; Markidis, S.

2013-12-01

206

Three-Dimensional Mapping of Magnetic Strata From Aeromagnetic Anomalies: The Deformed Neroly Formation South of Mt. Diablo, Northern California  

NASA Astrophysics Data System (ADS)

We apply direct inversion of aeromagnetic anomalies to analyze the subsurface 3D shape of the highly magnetic Miocene Neroly Formation, which consists largely of medium to coarse-grained andesitic sandstones containing abundant magnetite. The Neroly Formation is widespread in the eastern San Francisco Bay region, and locally is tightly folded and disrupted by faulting in the compressional regime related to the left-stepping (restraining) connection between the strike-slip Greenville and Concord Faults. The inversion technique is based on the conversion of the anomalies produced by a magnetic layer to their equivalent magnetic potential (psuedogravity) anomalies, manipulation of these anomalies to produce anomalies that would result from a half-space with a variable-depth top having the shape of the top surface of the layer, and then inverting these pseudogravity anomalies for the shape of that top surface. Assumptions include a constant layer thickness, uniform magnetization which implies a constant pseudodensity contrast, and a surface that is single-valued (no recumbent folds or strata repeated with depth). Constraints on 3D position are applied where the layer crops out or is at a depth known from well or other information. Application of this inversion technique to aeromagnetic anomalies over the Neroly Formation yields a complex top surface characterized by elongate overlapping troughs and structural highs, including the well-known Tassajara anticline and adjacent Sycamore Valley syncline. Troughs are true synclinal lows whereas the structural highs may be fold crests, steep truncated strata, and/or fault duplicated strata. The strongest deformation is confined to within ~7 km of the near-vertical overturned Neroly beds that crop out along the NE margin of the valley, and is characterized by four laterally overlapping, margin parallel structural highs and intervening troughs, each between 10 and 20 km in length. A fifth possible structural high lies farther SW. Separation between the highs increases southwestward across strike away from the valley margin. The gross structure implied by the inferred shape of the Neroly layer is that of a 7 km wide, NW oriented doubly- plunging synform with internal, high-amplitude 'wrinkles'. The technique shows promise for application to deformed magnetic layers in other regions. Elsewhere in California these include the Purisima Formation of the Hollister Valley and Santa Cruz Mountains, the Etchegoin Formation along the San Andreas Fault near Parkfield, and the Coastal Belt of the Franciscan Complex.

Jachens, R. C.; Simpson, R. W.; Graymer, R. W.; Wentworth, C. M.

2008-12-01

207

Magnetic anomaly in Ni51.5Fe21.5Ga27 single crystalline ferromagnetic shape memory alloy studied by ac impedance measurements  

NASA Astrophysics Data System (ADS)

A magnetic anomaly in the austenitic state of Ni51.5Fe21.5Ga27 single crystalline ferromagnetic shape memory alloy has been studied by means of ac impedance measurements. A much stronger effect of the degree of atomic order on the temperature of this anomaly (as compared to the temperature of the martensitic and para-ferromagnetic transitions) has been found. It has been shown that apart from the previously reported slight variation in the saturation magnetization, the magnetic anomaly results in a nearly one order of magnitude change in the value of initial magnetic permeability. The anomaly is not revealed in the resistive impedance at low frequencies, pointing likely to its purely magnetic origin.

Corró, M. L.; Kustov, S.; Cesari, E.; Chumlyakov, Y. I.

2009-04-01

208

Identification des anomalies magnétiques sur les dorsales à faible taux d'expansion: Méthode des taux fictifs  

NASA Astrophysics Data System (ADS)

The fit between calculated and observed magnetic anomalies from slow-spreading centers is improved when allowing for a transition zone between two inversely magnetized blocks. In this paper it is shown that these models are very easily computed by choosing a fictitious spreading rate which is slower than the real spreading rate and by changing the distance scale appropriately. With these slow fictitious spreading rates, the models are very sensitive to the relative position of the successive inversions and could be used to adjust these positions in the magnetic time scales.

Tisseau, J.; Patriat, Ph.

1981-02-01

209

Analysis of the Nuevo Leon magnetic anomaly and its possible relation to the Cerro Prieto magmatic-hydrothermal system  

SciTech Connect

The broad dipolar magnetic anomaly whose positive peak is centered near Ejido Nuevo Leon, some 5 km east of the Cerro Prieto I Power Plant, has long been suspected to have a genetic relationship to the thermal source of the Cerro Prieto geothermal system. This suspicion was reinforced after several deep geothermal wells, drilled to depths of 3 to 3.5 km over the anomaly, intersected an apparent dike-sill complex consisting mainly of diabase but with minor rhyodacite. A detailed fit of the observed magnetic field to a computer model indicates that the source may be approximated by a tabular block 4 by 6 km in area, 3.7 km in depth, 2.3 km thick, and dipping slightly to the north. Mafic dike chips from one well, NL-1, were analyzed by means of electron microprobe analyses which showed tham to contain a titanomagnetite that is paramagnetic at in-situ temperature conditions. As the dike mineralogy does not account for the magnetic anomaly, the magnetic source is believed to be a deeper, magnetite-rich assemblage of peridotite-gabbro plutons. the suite of igneous rocks was probably passively emplaced at a shallow depth in response to crustal extension and thinning brought on by strike-slip faulting. The bottom of the magnetic source body, at an estimated depth of 6 km, is presumed to be at or near that of the Curie isotherm (575/sup 0/C) for magnetite, the principal ferromagnetic mineral in peridotitic-gabbroic rocks. The geological model derived from the magnetic study is generally supported by other geophysical data. In particular, earthquake data suggest dike injection is occurring at depths of 6 to 11 km in an area beneath the magnetic source. Thus, it is possible that heat for the geothermal field is being maintained by continuing crustal extension and magmatic activity.

Goldstein, N.E.; Wilt, M.J.; Corrigan, D.J.

1982-10-01

210

Analysis of the Nuevo Leon Magnetic Anomaly and its possible relation to the Cerro Prieto magmatic-hydrothermal system  

SciTech Connect

The broad dipolar magnetic anomaly whose positive peak is centered near Ejido Nuevo Leon, some 5 km east of the Cerro Prieto I power plant, has long been suspected to have a genetic relationship to the thermal source of the Cerro Prieto geothermal system. This suspicion was reinforced after several deep geothermal wells, drilled to depths of 3-3.5 km over the anomaly, intersected an apparent dike-sill complex consisting mainly of diabase but with minor rhyodacite. A detailed fit of the observed magnetic field to a computer model indicates that the source may be approximated by a tabular block 4 x 6 km in area, 3.7 km in depth, 2.3 km thick, and dipping slightly to the north. Mafic dike chips from one well, NL-1, were analysed by means of electron microprobe analyses which showed them to contain a titanomagnetite that is paramagnetic at in situ temperature conditions. As the dike mineralogy does not account for the magnetic anomaly, the magnetic source is believed to be a deeper, magnetite-rich assemblage of peridotite-gabbro plutons. The suite of igneous rocks was probably emplaced at a shallow depth in response to crustal extension and thinning brought on by en echelon strike-slip faulting. The bottom of the magnetic source body, at an estimated depth of 6 km, is presumed to be at or near that of the Curie isotherm (575/sup 0/C) for magnetite, the principal ferromagnetic mineral in peridotiticgabbroic rocks. The geological model derived from the magnetic study is generally supported by other geophysical data. In particular, earthquake data suggest dike injection is occurring at depths of 6-11 km in an area beneath the magnetic source. Thus, it is possible that heat for the geothermal field is being maintained by continuing crustal extension and magmatic activity.

Goldstein, N.E.; Corrigan, D.J.; Wilt, M.J.

1984-01-01

211

Interplanetary medium condition effects in the South Atlantic Magnetic Anomaly: A case study  

NASA Astrophysics Data System (ADS)

One way to investigate the magnetosphere-ionosphere coupling is through the simultaneous observation of different parameters measured at different locations of the geospace environment and try to determine some relationships among them. The main objective of this work is to examine how the solar energetic particles and the interplanetary medium conditions may affect the space and time configuration of the ring current at low-latitudes and also to get a better understanding on how these particles interfere with the lower ionosphere in the South Atlantic Magnetic Anomaly region (SAMA). To accomplish this, the cosmic noise absorption (CNA) and the horizontal component of the Earth's magnetic field data measured from sites located in the SAMA region were compared with the proton and electron fluxes, interplanetary medium conditions (solar wind and the north-south component of the interplanetary magnetic field measured on board satellites), the SYM-H index and magnetometer data from Kakioka (KAK-Japan), located significantly outside the SAMA region. The time series analyzed correspond to the geomagnetic disturbance that occurred on August 25-30, 1998. The analysis was performed by implementing wavelet techniques, with particular attention to singularities detection, which highlights the presence of transient signals. The results are discussed in terms of the first three wavelet decomposition levels of the parameters. The magnitude of wavelet coefficients of the solar wind and proton flux at the two energy ranges analyzed is timely well correlated, indicating that these two signals are energetically linked. The larger wavelet coefficient amplitude of KAK and VSS magnetograms shows time delays that are compatible with an asymmetric configuration of the ring current, considering that at the storm time, VSS was at the dawn sector of the magnetosphere and KAK at the dusk side. The wavelet analysis of CNA signals reveals that the signal may be sensitive to the ionization produced by energetic electrons and protons as well. The time delays observed in wavelet coefficients may give an indication of the different accelerating process to which the particles are submitted when traveling along the magnetic field lines, from higher to lower latitudes, and the likely contribution of these particles to the ionization measured as an absorption of the cosmic noise in the lower ionosphere.

Mendes da Costa, Aracy; Oliveira Domingues, Margarete; Mendes, Odim; Marques Brum, Christiano Garnett

2011-07-01

212

Solar wind interaction with lunar crustal magnetic anomalies J.S. Halekas *, D.A. Brain, R.P. Lin, D.L. Mitchell  

E-print Network

Solar wind interaction with lunar crustal magnetic anomalies J.S. Halekas *, D.A. Brain, R.P. Lin Abstract Using Lunar Prospector data, we review the magnetic field and electron signatures of solar wind wind. To first order, solar wind magnetic fields pass relatively unim- peded through the Moon, while

California at Berkeley, University of

213

Anomalies in the evolution of global and large-scale solar magnetic fields as the precursors of several upcoming low solar cycles  

Microsoft Academic Search

Anomalies in the solar magnetic fields of various scales are studied. The polar magnetic field strength is shown to have decreased steadily during the last three solar cycles. This is because the increase in the dipole magnetic moment observed from 1915 to 1976 has changed into a decrease in the last three cycles. At the same time, the medium scale

V. N. Obridko; B. D. Shelting

2009-01-01

214

High-resolution Measurement Of Magnetic Anomalies With An Unmanned Airship  

NASA Astrophysics Data System (ADS)

High-resolution magnetic mapping of areas is a suitable way to determine location, geometry and physical parameters of disturbing objects that cause magnetic anomalies. Areas are often difficult to walk and handheld measurements can become costly. It can also be dangerous to enter areas where ordnance is suspected. In these cases it may be advantageous to use an aircraft to perform the measurement. We use a 6.5 m long unmanned airship. Compared to helicopters or gyrocopters, an advantage is that the damage in case of hazards is almost negligible. We made considerable efforts to construct a system that is easy to control without intense training under moderate wind conditions (up to 2 m/s wind speed). The airship has a mass of 10 kg and is powered by four electric motors with a maximum total power of 4.8 kW. Two of the rotors are used to control the altitude of the ship; the other two can be used to control direction and speed. The required energy is provided by four 4S1P Lithium-Polymer battery packs. Batteries are designed to provide a maximum of 125 A at 14.8 V. They have a capacity of 0.3 kWh and can be recharged in 20 minutes. The airship carries a differential GPS receiver that measures the position of the airship at 100 Hz with a precision of 10 cm. The distance to the ground is measured with ultrasonic sensors. A fluxgate magnetometer measures the magnetic field with an accuracy of 1 nT, also at 100 Hz. The flight path does not follow a rigid measuring grid but is a random walk, with roughly constant altitude to achieve a mean sensor position of 2 m above the ground. Thus, near-surface disturbing bodies are well resolved if their distance from each other is greater than 4 m. First measurements demonstrate the feasibility of the system. Future applications will be mid-scale measurements which are too large or too cumbersome for handheld measurements, and too small to justify the use of a manned helicopter.

Petzke, M.; Hofmeister, P.; Auster, H.; Hoerdt, A.; Glassmeier, K.

2011-12-01

215

The Effects of Crystal Fractionation and Magma Mixing on Remanent and Induced Magnetic Anomalies over a Layered Intrusion  

NASA Astrophysics Data System (ADS)

The Bjerkreim-Sokndal layered intrusion lies in the Rogaland Igneous Complex (~930 Ma) within the Baltic Shield in southern Norway. This 7 km-thick intrusion is divided into six Megacyclic units topped by mangerite and quartz-mangerite units. The course of crystal fractionation punctuated by the influx and mixing of more primitive magmas produces sequences of early plagioclase norites, intermediate hemo-ilmenite norites, and late magnetite-rich norites with subordinate ilmenite. Oriented samples were collected from 46 sites through the stratigraphy of the intrusion and subjected to petrophysical, paleomagnetic and rock magnetic measurements. Magnetic properties show a large range of values, with susceptibilities ranging from 1.47x10-4 to 2.15x10-1 SI, NRM intensities ranging from 0.104 to 58.8 A/m and corresponding Q values of 0.1 to 85. When induced and remanent magnetizations are averaged for each subdivided mega-unit a pattern of remanence-dominance at the base to induced-dominance at the top of each cycle is clear. Hysteresis properties indicate PSD to MD size magnetites with a continuous trend between them, indicative of the magnetite-rich rocks. Hysteresis properties falling outside the magnetite PSD-MD ranges are interpreted as hemo-ilmenite samples, in good agreement with the observed oxide mineralogy. Distinctive differences in the magnetic mineralogy also shows up in demagnetization behavior. Thermal plots show either a loss of magnetization at 580C, or above 600C. AF demagnetization plots show two separate populations - one with high coercivity (hemo-ilmenite) and one with low coercivity (magnetite). Magnetic anomalies over the body correspond directly to the magnetic properties, with positive (induced) anomalies over the magnetite-rich layers and magnetic lows (due to reversed magnetic signal) over layers with hemo-ilmenite present.

Brown, L. L.; McEnroe, S. A.; Robinson, P.

2005-05-01

216

Airborne gamma-ray and magnetic anomaly signatures of serpentinite in relation to soil geochemistry, northern California  

USGS Publications Warehouse

Serpentinized ultramafic rocks and associated soils in northern California are characterized by high concentrations of Cr and Ni, low levels of radioelements (K, Th, and U) and high amounts of ferrimagnetic minerals (primarily magnetite). Geophysical attributes over ultramafic rocks, which include airborne gamma-ray and magnetic anomaly data, are quantified and provide indirect measurements on the relative abundance of radioelements and magnetic minerals, respectively. Attributes are defined through a statistical modeling approach and the results are portrayed as probabilities in chart and map form. Two predictive models are presented, including one derived from the aeromagnetic anomaly data and one from a combination of the airborne K, Th and U gamma-ray data. Both models distinguish preferential values within the aerogeophysical data that coincide with mapped and potentially unmapped ultramafic rocks. The magnetic predictive model shows positive probabilities associated with magnetic anomaly highs and, to a lesser degree, anomaly lows, which accurately locate many known ultramafic outcrops, but more interestingly, locate potentially unmapped ultramafic rocks, possible extensions of ultramafic bodies that dip into the shallow subsurface, as well as prospective buried ultramafic rocks. The airborne radiometric model shows positive probabilities in association with anomalously low gamma radiation measurements over ultramafic rock, which is similar to that produced by gabbro, metavolcanic rock, and water bodies. All of these features share the characteristic of being depleted in K, Th and U. Gabbro is the only rock type in the study area that shares similar magnetic properties with the ultramafic rock. The aerogeophysical model results are compared to the distribution of ultramafic outcrops and to Cr, Ni, K, Th and U concentrations and magnetic susceptibility measurements from soil samples. Analysis of the soil data indicates high positive correlation between magnetic susceptibilities and concentration of Cr and Ni. Although the study focused on characterizing the geophysical properties of ultramafic rocks and associated soils, it has also yielded information on other rock types in addition to ultramafic rocks, which can also locally host naturally-occurring asbestos; specifically, gabbro and metavolcanic rocks.

McCafferty, A.E.; Van Gosen, B. S.

2009-01-01

217

Electromagnetic particle-in-cell simulations of the solar wind interaction with lunar magnetic anomalies  

NASA Astrophysics Data System (ADS)

We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier MHD and hybrid simulations, the fully kinetic nature of iPic3D allows to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe the general picture of the interaction of a dipole model centred just below the lunar surface under various solar wind and plasma conditions and focus on the kinetic effects. It is shown that the configuration is dominated by electron motion, because the LMA scale size is small with respect to the gyroradius of the solar wind ions. Driven by strong pressure anisotropies, the mini-magnetosphere is also unstable over time, leading to only temporal shielding of the surface underneath. Our work opens new frontiers of research toward a deeper understanding of LMAs and is ideally suited to be compared with field or particle observations from spacecraft such as Kaguya (SELENE), Lunar Prospector or ARTEMIS. The ability to evaluate the implications for future lunar exploration as well as lunar science in general hinges on a better understanding of LMAs. This research has received funding from the European Commission's FP7 Program with the grant agreement SWIFF (project 2633430, swiff.eu) and EHEROES (project 284461, www.eheroes.eu). The simulations were conducted on the computational resources provided by the PRACE Tier-0 project 2011050747 (Curie supercomputer). This research was supported by the Swedish National Space Board, Grant No. 136/11. JD has received support through the HPC-Europa2 visitor programme (project HPC08SSG85) and the KuLeuven Junior Mobility Programme Special Research Fund.

Deca, Jan; Divin, Andrey; Lapenta, Giovanni; Lembège, Bertrand; Markidis, Stefano; Horányi, Mihály

2014-05-01

218

An annular high-current electron beam with an energy spread in a coaxial magnetically insulated diode  

NASA Astrophysics Data System (ADS)

An elementary theory of an annular high-current electron beam in a uniform transport channel and a coaxial magnetically insulated diode is generalized to the case of counterpropagating electron beams with a spread over kinetic energies. Expressions for the sum of the absolute values of the forward and backward currents in a uniform transport channel and for the flux of the longitudinal component of the generalized momentum in a coaxial magnetically insulated diode as functions of the maximum electron kinetic energy are derived for different values of the relative width of the energy distribution function. It is shown that, in a diode with an expanding transport channel and a virtual cathode limiting the extracted current, counterpropagating particle flows are established between the cathode and the virtual cathode within a certain time interval after the beginning of electron emission. The accumulation of electrons in these flows is accompanied by an increase in their spread over kinetic energies and the simultaneous decrease in the maximum kinetic energy. The developed model agrees with the results of particle-in-cell simulations performed using the KARAT and OOPIC-Pro codes.

Grishkov, A. A.; Pegel, I. V.

2013-11-01

219

Deep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone and implications for the geomagnetic polarity reversal timescale and  

E-print Network

., 113, B07110, doi:10.1029/2007JB005527. 1. Introduction [2] The Jurassic period appears to be a time of the Jurassic magnetic field. It was once suggested that this Jurassic ``Quiet Zone'' (JQZ) reflects a periodDeep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone and implications

220

A systematic approach to the magnetic resonance imaging-based differential diagnosis of congenital Müllerian duct anomalies and their mimics.  

PubMed

Müllerian duct anomalies (MDAs) represent a wide spectrum of developmental abnormalities related to various gynecologic and obstetric complications, including primary amenorrhea, infertility, and endometriosis. The use of diverse imaging modalities, in conjunction with clinical information, provide important clues to the diagnosis of MDAs. Diagnostic imaging work-up for MDAs often begins with hysterosalpingography (HSG) and/or ultrasonography (US). Although HSG and/or US may suffice to detect the presence of a uterine abnormality, magnetic resonance (MR) imaging is generally needed to classify the abnormality into a specific MDA category. MR imaging has been gaining in popularity for use in evaluating MDAs, by virtue of its noninvasiveness, lack of ionizing radiation, and capability for multiplanar imaging and soft tissue characterization. Abnormalities in the external uterine fundal contour are readily recognized with MR imaging, allowing for clear differentiation between a fusion anomaly, such as a uterus didelphys or a bicornuate uterus, and a resorption anomaly, such as a septate uterus. Furthermore, MR imaging enables clear depiction of a rudimentary uterine horn in a unicornuate uterus. Accurate differential diagnosis of MDAs on the basis of their characteristic MR imaging findings is crucial, because the rates of gynecologic and obstetric complications vary considerably among MDAs. The diagnostic accuracy may be enhanced by adopting a systematic approach to MR imaging-based differential diagnosis. PMID:25070770

Yoo, Roh-Eul; Cho, Jeong Yeon; Kim, Sang Youn; Kim, Seung Hyup

2015-01-01

221

Breakup and early seafloor spreading between India and Antarctica  

Microsoft Academic Search

We present a tectonic interpretation of the breakup and early seafloor spreading between India and Antarctica based on improved coverage of potential field and seismic data off the east Antarctic margin between the Gunnerus Ridge and the Bruce Rise. We have identified a series of ENE trending Mesozoic magnetic anomalies from chron M9o (~130.2 Ma) to M2o (~124.1 Ma) in

Carmen Gaina; R. Dietmar Müller; Belinda Brown; Takemi Ishihara; Sergey Ivanov

2007-01-01

222

High-resolution near-bottom vector magnetic anomalies over Raven Hydrothermal Field, Endeavour Segment, Juan de Fuca Ridge  

NASA Astrophysics Data System (ADS)

near-bottom vector magnetic data were collected by remotely operated vehicle Jason over the Raven hydrothermal vent field (47°57.3'N 129°5.75'W) located north of Main Endeavour vent field on the Endeavour segment of the Juan de Fuca Ridge. The survey was part of a comprehensive heat flow study of the Raven site using innovative thermal blanket technology to map the heat flux and crustal fluid pathways around a solitary hydrothermal vent field. Raven hydrothermal activity is presently located along the western axial valley wall, while additional inactive hydrothermal deposits are found to the NW on the upper rift valley wall. Magnetic inversion results show discrete areas of reduced magnetization associated with both active and inactive hydrothermal vent deposits that also show high conductive heat flow. Higher spatial variability in the heat flow patterns compared to the magnetization is consistent with the heat flow reflecting the currently active but ephemeral thermal environment of fluid flow, while crustal magnetization is representative of the static time-averaged effect of hydrothermal alteration. A general NW to SE trend in reduced magnetization across the Raven area correlates closely with the distribution of hydrothermal deposits and heat flux patterns and suggests that the fluid circulation system at depth is likely controlled by local crustal structure and magma chamber geometry. Magnetic gradient tensor components computed from vector magnetic data improve the resolution of the magnetic anomaly source and indicate that the hydrothermally altered zone directly beneath the Raven site is approximately 15 × 106 m3 in volume.

Tivey, Maurice A.; Johnson, H. Paul; Salmi, Marie S.; Hutnak, Michael

2014-10-01

223

The Reykjanes Ridge: structure and tectonics of a hot-spot-influenced, slow-spreading ridge, from multibeam bathymetry, gravity and magnetic investigations  

Microsoft Academic Search

We report a comprehensive morphological, gravity and magnetic survey of the oblique- and slow-spreading Reykjanes Ridge near the Iceland mantle plume. The survey extends from 57.9°N to 62.1°N and from the spreading axis to between 30 km (3 Ma) and 100 km (10 Ma) off-axis; it includes 100 km of one arm of a diachronous `V-shaped' or `chevron' ridge. Observed

R. C. Searle; J. A. Keeton; R. B. Owens; R. S. White; R. Mecklenburgh; B. Parsons; S. M. Lee

1998-01-01

224

Magnetic Anomalies in the Terra Cimmeria\\/Sirenum Region of Mars: A Magnetization Model and Possible Sources  

Microsoft Academic Search

A new analysis of MGS aerobraking data indicates that anomaly sources in this region have a fairly random distribution and are not elongated by more than ~500 km in any direction. Sources most probably consist of magmatic (e.g., dike) intrusions.

L. L. Hood; N. C. Richmond; K. Harrison

2007-01-01

225

Aeromagnetic anomalies and discordant lineations beneath the Niger Delta: Implications for new fracture zones and multiple sea-floor spreading directions in the meso-Atlantic' Gulf of Guinea cul-de-sac  

SciTech Connect

An aeromagnetic contour map compiled over shallow water and onshore portions of the Nigerian continental margin, shows several elongate, long-wavelength anomaly closures with some alternating polarity, separated by steep gradient, NE lineations. The lineations are interpreted as new fracture zones or extensions of previously mapped ones. The NE trend in the western delta region is concordant with the fracture zone trends of the deeper Gulf of Guinea. Aeromagnetic lineations of the SE Niger Delta Basin however, discordantly trend ENE. Their termination against the former, is interpreted as evidence of early sea-floor spreading in a ENE-WSW direction in addition to the well documented NE-SW spreading of the Gulf of Guinea and the rest of the meso-Atlantic sea-floor; The geophysical crustal structure indicate the existence of two Early Cretaceous triple junctions beneath the Niger Delta Basin. The two triple-junctions further support the hypothesis that the African continent was a multi-plate system (in the Niger Delta region) during the early opening of the Atlantic.

Babalola, O.O.; Gipson, M. Jr. (Univ. of South Carolina, Columbia (United States))

1991-06-01

226

Anomalies in the evolution of global and large-scale solar magnetic fields as the precursors of several upcoming low solar cycles  

Microsoft Academic Search

Anomalies in the solar magnetic fields of various scales are studied. The polar magnetic field strength is shown to have decreased\\u000a steadily during the last three solar cycles. This is because the increase in the dipole magnetic moment observed from 1915\\u000a to 1976 has changed into a decrease in the last three cycles. At the same time, the medium scale

V. N. Obridko; B. D. Shelting

2009-01-01

227

Deep magnetic anomaly sources interpreted as Otanmäki type Iron ore reserves  

NASA Astrophysics Data System (ADS)

In Otanmäki ore province of Central Finland vertically integrated magnetization is estimated from two aeromagnetic coverages of different altitudes and by varying overall models of regional field. Petrophysically and geochemically determined magnetization of the mined deposits and correlation between it and ore concentration is used to evaluate iron ore reserves in the deeper part of known ore fields. Further, similar analysis is made to nearby magnetically anomalous areas covered by weakly magnetic metasediments, to estimate potential ore reserves at unexposed formations.

Korhonen, Juha; Kukkonen, Ilmo

2013-04-01

228

Spread-F during the magnetic storm of 22 January 2004 at low latitudes: Effect of IMF-Bz in relation to local sunset time  

NASA Astrophysics Data System (ADS)

The paper describes the results of spread-F at low latitude stations around the world during the magnetic storm starting at 0130 UT on 22 January 2004. The storm can be divided into two phases, first phase up to 1000 UT when interplanetary magnetic field IMF-Bz was highly fluctuating around a small positive value and the second phase after a sudden large southward turning of IMF-Bz at 1030 UT. The first phase produced strong spread-F at Jicamarca, Sao Luis, and Ascension Island and caused complete inhibition of spread-F at Thumba and Waltair in India. It generated weak spread-F at Ho Chi Minh City in Vietnam and strong spread-F at Hainan and Chung Li. The strong spread-F at Hainan and Chung Li were caused by the positive IMF-Bz during the first phase of the storm and not by the negative pulse of IMF-Bz at 1000 UT.

Rastogi, R. G.; Chandra, H.; Janardhan, P.; Hoang, Thai Lan; Condori, Louis; Pant, T. K.; Prasad, D. S. V. V. D.; Reinisch, B.

2014-08-01

229

True polar wander since 32 Ma B.P.: A paleomagnetic investigation of the skewness of magnetic anomaly 12r on the Pacific plate  

NASA Astrophysics Data System (ADS)

We test the fixed hot spot and fixed spin axis hypotheses through a paleomagnetic investigation of the skewness of crossings of magnetic anomaly 12r (32 Ma B.P.) between the Galapagos and Clarion fracture zones on the Pacific plate. We focus on this region for three reasons. First, numerical experiments show that these crossings, of all those available from the Pacific plate, should contain the most information about the location of the 32 Ma B.P. paleomagnetic pole for the Pacific plate. Second, many of the available crossings are from vector aeromagnetic profiles, which have superior signal-to-noise ratios. Third, the rate of seafloor spreading recorded in these crossings exceeds the threshold (half rate of 50 mm a-1) above which anomalous skewness is negligible. The new pole (83.5°N, 44.6°E) has compact 95% confidence limits (ellipse with major semiaxis length of 3.1° toward 84° clockwise from north and minor semiaxis length of 1.2°) and is not subject to the biases inherent in other methods for estimating Pacific plate paleomagnetic poles. The pole differs significantly by ?5° from the pole predicted if the Pacific hot spots have been fixed with respect to the spin axis, thus demonstrating, for the first time from paleomagnetic data, that Pacific hot spots have moved relative to the spin axis since the formation of the elbow in the Hawaiian-Emperor chain. The pole is consistent, however, with previously published paleomagnetic poles in a reference frame fixed relative to Indo-Atlantic hot spots. Thus, the new results require no motion between Pacific and Indo-Atlantic hot spots since 32 Ma B.P. Instead, superimposed on whatever motion occurs between hot spots, as expected for true polar wander.

Horner-Johnson, Benjamin C.; Gordon, Richard G.

2010-09-01

230

The point spread function of electrons in a magnetic field, and the decay of the free neutron  

NASA Astrophysics Data System (ADS)

Experiments in nuclear and particle physics often use magnetic fields to guide charged reaction products to a detector. Due to their gyration in the guide field, the particles hit the detector within an area that can be considerably larger than the diameter of the source where the particles are produced. This blurring of the image of the particle source on the detector surface is described by a suitable point spread function (PSF), which is defined as the image of a point source. We derive simple analytical expressions for such “magnetic” PSFs, valid for any angular distribution of the emitted particles that can be developed in Legendre polynomials. We investigate this rather general problem in the context of neutron ?-decay spectrometers and study the effect of limited detector size on measured neutron decay correlation parameters. To our surprise, insufficient detector size does not affect the accuracy of such measurements much, even for rather large radii of gyration. This finding can considerably simplify the layout of the respective spectrometers.

Dubbers, D.; Raffelt, L.; Märkisch, B.; Friedl, F.; Abele, H.

2014-11-01

231

Magnetic resonance imaging of cerebral anomalies in subjects with resistance to thyroid hormone  

SciTech Connect

Resistance to thyroid hormone (RTH) is an autosomal dominant disease caused by mutations in the human thyroid receptor beta gene on chromosome 3. Individuals with RTH have an increased incidence of attention deficit hyperactivity disorder (ADHD). The purpose of this study was to search for developmental brain malformations associated with RTH. Forty-three subjects (20 affected males [AM], 23 affected females [AF]) with resistance to thyroid hormone and 32 unaffected first degree relatives (18 unaffected males [UM], 14 unaffected females [UF]) underwent MRI brain scans with a volumetric acquisition that provided 90 contiguous 2 mm thick sagittal images. Films of six contiguous images beginning at a standard sagittal position lateral to the insula were analyzed by an investigator who was blind with respect to subject characteristics. The presence of extra or missing gyri in the parietal bank of the Sylvian fissure (multimodal association cortex) and multiple Heschl`s transverse gyri (primary auditory cortex) were noted. There was a significantly increased frequency of anomalous Sylvian fissures in the left hemisphere in males with RTH (AM: 70%; AF: 30%; UM: 28% UF: 28%). Also, there was an increased frequency of anomalous Sylvian fissures on the left combined with multiple Heschl`s gyri in either hemisphere in males with RTH (AM: 50%; AF: 9%; UM: 6%; UF: 0%). However, RTH subjects with anomalies did not have an increased frequency of ADHD as compared with RTH subjects with no anomalies. Abnormal thyroid hormone action in the male fetus early during brain development may be associated with grossly observable cerebral anomalies of the left hemisphere. The effects of mutations in the thyroid receptor beta gene provide a model system for studying the complex interaction of genetic and non-genetic factors on brain and behavioral development. 19 refs., 2 figs., 2 tabs.

Leonard, C.M. [Univ. of Florida Health Science Center, Gainesville, FL (United States); Hauser, P.; Weintraub, B.D. [National Institute of Mental Health, Bethesda, MD (United States)]|[Baltimore VA Medical Center, MD (United States)] [and others

1995-06-19

232

A test of the geocentric axial dipole hypothesis from an analysis of the skewness of the central marine magnetic anomaly  

NASA Astrophysics Data System (ADS)

A new, global set of palaeomagnetic observations was obtained from analysis of the symmetry of the shape of 203 crossings of the Central marine magnetic anomaly, the anomaly observed above seafloor, formed during the Brunhes normal polarity chron (0-0.78 Ma). The data indicate that the time-averaged field can be described best by a dominant geocentric axial dipole component, whose position differs insignificantly from the present spin axis, and by a small geocentric axial quadrupole component (6.0% -6.7%+5.7% the size of the dipole component). If we simply assume that the Brunhes palaeomagnetic axis has been aligned with the present spin axis, the quadrupole component is 6.2% ± 4.7%, which differs significatly from a purely dipolar field, and is in good agreement with estimates from other palaeomagnetic data. Besides expanding the spatial distribution of palaeomagnetic field observations, an important step in removing biases in prior field estimates caused by poor global coverage, these results illustrate that valuable geomagnetic information as well as accurate palaeomagnetic poles can be obtained from skewness data.

Acton, Gary D.; Petronotis, Katerina E.; Cape, Cheryl D.; Ilg, Sue Rotto; Gordon, Richard G.; Bryan, Phil C.

1996-11-01

233

Low-temperature anomalies in the magnetic and thermal properties of molecular cryocrystals doped with oxygen impurity  

NASA Astrophysics Data System (ADS)

The magnetic properties of oxygen pair clusters are investigated theoretically for different cluster geometries which can be realized by doping molecular cryomatrices with oxygen. Anomalous temperature and pressure behavior of the magnetic susceptibility, heat capacity, and entropy is predicted. It is proposed to use these anomalies for studying the parameters characterizing the oxygen clusters and the parameters of the host matrix: the effective spin-figure interaction constant D for the molecule in the matrix, the exchange parameter J, and the number of pair clusters Np, which can deviate markedly from the purely random value Np=6Nc2 (N is Avogadro's number, and c is the molar concentration of the impurity). The data on the magnetic susceptibility may be used to analyze the character of the positional and orientational short-range order in the solid solution. The value of D contains information about the orientational order parameter; the distance and angular dependence of the exchange interaction parameter are still subject to discussion in the literature. The temperature dependence of Np contains information about diffusion and clusterization processes in the system.

Freiman, Yu. A.; Tretyak, S. M.; Je?owski, A.

2000-09-01

234

The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies  

NASA Astrophysics Data System (ADS)

The Yakima fold and thrust belt (YFTB) in central Washington has accommodated regional, mostly north-directed, deformation of the Cascadia backarc since prior to emplacement of Miocene flood basalt of the Columbia River Basalt Group (CRBG). The YFTB consists of two structural domains. Northern folds of the YFTB strike eastward and terminate at the western margin of a 20-mGal negative gravity anomaly, the Pasco gravity low, straddling the North American continental margin. Southern folds of the YFTB strike southeastward, form part of the Olympic-Wallowa lineament (OWL), and pass south of the Pasco gravity low as the Wallula fault zone. An upper crustal model based on gravity and magnetic anomalies suggests that the Pasco gravity low is caused in part by an 8-km-deep Tertiary basin, the Pasco sub-basin, abutting the continental margin and concealed beneath CRBG. The Pasco sub-basin is crossed by north-northwest-striking magnetic anomalies caused by dikes of the 8.5 Ma Ice Harbor Member of the CRBG. At their northern end, dikes connect with the eastern terminus of the Saddle Mountains thrust of the YFTB. At their southern end, dikes are disrupted by the Wallula fault zone. The episode of NE-SW extension that promoted Ice Harbor dike injection apparently involved strike-slip displacement on the Saddle Mountains and Wallula faults. The amount of lateral shear on the OWL impacts the level of seismic hazard in the Cascadia region. Ice Harbor dikes, as mapped with aeromagnetic data, are dextrally offset by the Wallula fault zone a total of 6.9 km. Assuming that dike offsets are tectonic in origin, the Wallula fault zone has experienced an average dextral shear of 0.8 mm/y since dike emplacement 8.5 Ma, consistent with right-lateral stream offsets observed at other locations along the OWL. Southeastward, the Wallula fault transfers strain to the north-striking Hite fault, the possible location of the M 5.7 Milton-Freewater earthquake in 1936.

Blakely, Richard J.; Sherrod, Brian L.; Weaver, Craig S.; Wells, Ray E.; Rohay, Alan C.

2014-06-01

235

The Mackenzie River magnetic anomaly, Yukon and Northwest Territories, Canada-Evidence for Early Proterozoic magmatic arc crust at the edge of the North American craton  

USGS Publications Warehouse

We characterize the nature of the source of the high-amplitude, long-wavelength, Mackenzie River magnetic anomaly (MRA), Yukon and Northwest Territories, Canada, based on magnetic field data collected at three different altitudes: 300??m, 3.5??km and 400??km. The MRA is the largest amplitude (13??nT) satellite magnetic anomaly over Canada. Within the extent of the MRA, source depth estimates (8-12??km) from Euler deconvolution of low-altitude aeromagnetic data show coincidence with basement depths interpreted from reflection seismic data. Inversion of high-altitude (3.5??km) aeromagnetic data produces an average magnetization of 2.5??A/m within a 15- to 35-km deep layer, a value typical of magmatic arc complexes. Early Proterozoic magmatic arc rocks have been sampled to the southeast of the MRA, within the Fort Simpson magnetic anomaly. The MRA is one of several broad-scale magnetic highs that occur along the inboard margin of the Cordillera in Canada and Alaska, which are coincident with geometric changes in the thrust front transition from the mobile belt to stable cratonic North America. The inferred early Proterozoic magmatic arc complex along the western edge of the North American craton likely influenced later tectonic evolution, by acting as a buttress along the inboard margin of the Cordilleran fold-and-thrust belt. Crown Copyright ?? 2008.

Pilkington, M.; Saltus, R.W.

2009-01-01

236

Crystal structure and elastic-constant anomalies in the magnetic 3d transition metals  

Microsoft Academic Search

Assuming a saturated ferromagnet, the anomalous crystal structures of the magnetic 3d transition elements Fe, Co, and Ni are explained from simple band-filling arguments. The full-potential linear muffin-tin orbital (FP-LMTO) method is used to calculate the elastic constants (C11, C12, and C44) for the magnetic and cubic 3d transition metals Cr, Fe, and Ni. For Co calculations of the elastic

P. Soederlind; R. Ahuja; O. Eriksson; J. M. Wills; B. Johansson

1994-01-01

237

Seafloor magnetic lineation off the Otway\\/West Tasmania Basins: ridge jumps and the subsidence history of the southeast Australian margins  

Microsoft Academic Search

The seafloor off the Otway\\/West Tasmanian Basins has an east?west magnetic lineation attributable to seafloor spreading and notionally identified with the set of seafloor spreading anomalies A8?A20. Anomaly A20 (45 Ma) lies immediately south of a magnetic quiet zone that extends northward past the continent?ocean boundary (COB). The Southeast Indian Ocean has a constant angular width between the formerly conjugate

J. J. Veevers

1988-01-01

238

Surface plasmon assisted magnetic anomalies on room temperature gold films in high-intensity laser fields  

E-print Network

Supplementing our STM and electron emission studies, concluding in electron pairing in strong laser fields, further time-of-flight electron emission studies were carried out, changing the angle of polarization of incident light, exciting surface plasmon oscillations. It has been found, that those parts of the electron spectrum which have been attributed to electron pairing have a significantly different angular dependence around 80GW/cm2 where the pairing effect has been found than outside this region (e.g. 120 GW/cm2). These results have been interpreted as the stepping in of ideal or partly ideal diamagnetism on the one hand and as anomaly in the magneto-optical effect (rotation) on the other in the same laser intensity region where the pairing effect has been found.

Kroó, N; Varró, S

2014-01-01

239

Grain size dependent potential for self generation of magnetic anomalies on Mars via thermoremanent magnetic acquisition and magnetic interaction of hematite and magnetite  

Microsoft Academic Search

Early in the history of planetary evolution portions of Martian crust became magnetized by dynamo-generated magnetic field. A lateral distribution of the secondary magnetic field generated by crustal remanent sources containing magnetic carriers of certain grain size and mineralogy is able to produce an ambient magnetic field of larger intensity than preexisting dynamo. This ambient field is capable of magnetizing

Gunther Kletetschka; Norman F. Ness; J. E. P. Connerney; M. H. Acuna; P. J. Wasilewski

2005-01-01

240

EMAG2: A 2arc min resolution Earth Magnetic Anomaly Grid compiled from satellite, airborne, and marine magnetic  

E-print Network

, and marine magnetic measurements S. Maus CIRES, University of Colorado at Boulder, Boulder, Colorado 80309 (stefan.maus@noaa.gov) U. Barckhausen Federal Institute for Geosciences and Natural Resources, D-30655

Müller, Dietmar

241

Gravitational Anomaly and Transport  

E-print Network

Quantum anomalies give rise to new transport phenomena. In particular a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid.

Karl Landsteiner; Eugenio Megias; Francisco Pena-Benitez

2011-03-25

242

Gravitational Anomaly and Transport  

E-print Network

Quantum anomalies give rise to new transport phenomena. In particular a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid.

Landsteiner, Karl; Pena-Benitez, Francisco

2011-01-01

243

The Gop Basin - A Possible Imprint of Early Oceanic Spreading Between Greater Seychelles and India  

NASA Astrophysics Data System (ADS)

The Arabian and its conjugate Eastern Somali basins were formed by the seafloor spreading at the Carlsberg Ridge since Early Tertiary (anomaly 28n; ~62.5 Ma). The reconstruction model at anomaly 28n suggested existence of a wide swath of deep offshore region (Gop and Laxmi basins) between the Laxmi Ridge and the India-Pakistan continental shelf. In the present study we focus on the Gop Basin, where the important constraints about the early geodynamic evolution of the Arabian Sea appear to exist. The nature of the crust underlying this basin remains a matter of debate, with views varying from volcanics-intruded thinned continental crust to oceanic crust formed by a now extinct spreading centre. Our interpretation of an updated compilation of marine geophysical data supports the oceanic nature of the crust underlying the Gop Basin, where the Palitana Ridge represents the extinct spreading centre related to an episode of early oceanic spreading between Greater Seychelles (Seychelles-Laxmi Ridge block) and India. Our magnetic modelling shows that the well correlatable, prominent but short sequence of magnetic anomalies in the Gop Basin does not allow a unique identification; it can be reasonably explained either as A31r - A25r (~69 - 56 Ma) or as A29r - A25r (~65 - 56 Ma) sequence. Both the models suggest that spreading in the Gop Basin was significantly affected by the nearby onset of the Reunion hotspot at ~65 Ma, which formed the Deccan Traps on the adjacent western Indian mainland.

Bhattacharya, G. C.; Yatheesh, V.; Dyment, J.

2009-04-01

244

Spherical-earth Gravity and Magnetic Anomaly Modeling by Gauss-legendre Quadrature Integration  

NASA Technical Reports Server (NTRS)

The anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical Earth for an arbitrary body represented by an equivalent point source distribution of gravity poles or magnetic dipoles were calculated. The distribution of equivalent point sources was determined directly from the coordinate limits of the source volume. Variable integration limits for an arbitrarily shaped body are derived from interpolation of points which approximate the body's surface envelope. The versatility of the method is enhanced by the ability to treat physical property variations within the source volume and to consider variable magnetic fields over the source and observation surface. A number of examples verify and illustrate the capabilities of the technique, including preliminary modeling of potential field signatures for Mississippi embayment crustal structure at satellite elevations.

Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.; Luca, A. J. (principal investigators)

1981-01-01

245

Comparison of the dynamics and structure of Saturn and Jupiter magnetospheres: camshaft, magnetic anomalies and corotating convection models compared.  

NASA Astrophysics Data System (ADS)

Scenarios are presented for the overall flux and mass circulation in the jovian and saturnian magnetospheres It is argued that similar fundamanetal processes underly the dynamical processes at both planets However the differences in parameter regime for the two systems leads to substantial resulting differences in morphology Transport is accomplished from the inner magnetosphere by interchange motion which then feeds into the outer magnetosphere where ballooning driven by centrifugal stress leads to field reconnection and plasma loss It seems likely that Jupiter loses much more material per rotation cycle than Saturn and is possibly much more symmetrically loaded in respect of planetary longitude Material loss and flux return at Jupiter have fixed orientations in local time early evening and morning sector respectively and newly returned flux is probably responsible for the morningside cushion region in the outer magnetosphere At Jupiter the dawn-dusk asymmetry in the current sheet thin in morning thick in afternoon is also a dominant feature At Saturn there seems no evidence of a cushion region flux return is thought to take place sporadically over much of the nightside Although definitive statements about the dusk plasma sheet await the orbit evolution of Cassini a fundamental observational feature in the Saturnian context is a planetary rotation induced magnetic field asymmetry which argues against major dawn-dusk asymmetry We propose the rotational feature could originate from a localized ionospheric magnetic anomaly The

Southwood, D. J.; Kivelson, M. G.

246

Calculation of gravity and magnetic anomalies of finite-length right polygonal prisms.  

USGS Publications Warehouse

An equation is derived for the vertical gravity field due to a homogeneous body with polygonal cross?section and finite strike?length. The equation can be separated into the two?dimensional (2-D) terms of Talwani et al. (1959) and exact terms for the contributions of the ends of the prism. Equations for the magnetic field due to a similar body were derived by Shuey and Pasquale (1973), who coined the term “two?and?a?half dimensional” (2 1/2-D) to describe the geometry. Magnetic intensities are expressed as a vector sum, from which the common dot product formulation can be obtained by binomial expansion.

Cady, J.W.

1980-01-01

247

Spreading-rate-dependent anomalous skewness and the estimate of the chron 32 palaeomagnetic pole for the Pacific plate  

NASA Astrophysics Data System (ADS)

Palaeomagnetic poles can be determined from asymmetry (skewness) of marine magnetic anomalies. Early works applying the skewness method were limited by the discovery of an apparently systematic error known as anomalous skewness (Cande 1976). Anomalous skewness can be thought of as the systematic difference between the observed skewness and the skewness predicted by a simple magnetization model with rectangular 2-D layer 2A prisms of alternating polarity separated by vertical boundaries. In the early works, anomalous skewness could be isolated for anomalies with counterparts across a mid-ocean ridge, but was much harder to estimate for anomalies with subducted counterparts, as is mostly the case in the Pacific plate. Petronotis et al. (1992) presented a solution to this problem by simultaneously estimating anomalous skewness and a best-fitting palaeomagnetic pole from skewness data from a single plate. In their approach, anomalous skewness is assumed to be identical for different crossings of the same plate and any spreading-rate dependence of anomalous skewness is neglected. Nonetheless, anomalous skewness of marine magnetic anomalies is observed to decrease with increasing spreading rate and become negligible above spreading rates of about 50 mm yr-1 (e.g. Roest et al. 1992; Dyment et al. 1994). Dyment &Arkani-Hamed (1995) proposed a model in which the magnetic structure of the oceanic lithosphere is dependent on spreading rate with parameters adjusted to fit the observed spreading- rate dependence of anomalous skewness for some key anomalies. Here we apply their model to determine a new Maastrichtian palaeomagnetic pole for the Pacific plate from skewness estimates of magnetic anomaly 32. Previously Petronotis &Gordon (1999) obtained a palaeopole assuming spreading-rate independent anomalous skewness for the same data used here. They also investigated the possible dependence of anomalous skewness on spreading rate and found it to have negligible effect on their palaeopole. Using the anomalous skewness correction predicted by the model of Dyment &Arkani-Hamed, we find that the data require no additional anomalous skewness, thus providing some validation of their model. Moreover, it appears that the new pole position stays near the original pole position irrespective of what set of spreading rates is used to estimate anomalous skewness. The largest uncertainties in the anomalous-skewness correction are due to uncertainties in spreading rates, which are mainly due to uncertainties in the reversal time scale. The results support the assertion of Petronotis et al. that Pacific plate poles determined from low- palaeolatitude sites are insensitive to anomalous skewness.

Koivisto, E.; Gordon, R.; Dyment, J.; Arkani-Hamed, J.

2006-12-01

248

Particle-In-Cell Simulations of the Solar Wind Interaction with Lunar Crustal Magnetic Anomalies: Magnetic Cusp Regions  

NASA Technical Reports Server (NTRS)

As the solar wind is incident upon the lunar surface, it will occasionally encounter lunar crustal remanent magnetic fields. These magnetic fields are small-scale, highly non-dipolar, have strengths up to hundreds of nanotesla, and typically interact with the solar wind in a kinetic fashion. Simulations, theoretical analyses, and spacecraft observations have shown that crustal fields can reflect solar wind protons via a combination of magnetic and electrostatic reflection; however, analyses of surface properties have suggested that protons may still access the lunar surface in the cusp regions of crustal magnetic fields. In this first report from a planned series of studies, we use a 1 1/2-dimensional, electrostatic particle-in-cell code to model the self-consistent interaction between the solar wind, the cusp regions of lunar crustal remanent magnetic fields, and the lunar surface. We describe the self-consistent electrostatic environment within crustal cusp regions and discuss the implications of this work for the role that crustal fields may play regulating space weathering of the lunar surface via proton bombardment.

Poppe, A. R.; Halekas, J. S.; Delory, G. T.; Farrell, W. M.

2012-01-01

249

High-Accuracy Measurement of the Magnetic Moment Anomaly of the Electron Bound in Hydrogenlike Carbon  

Microsoft Academic Search

We present a new experimental value for the magnetic moment of the electron bound in hydrogenlike carbon \\\\( 12C 5+\\\\): gexp = 2.001 041 596 \\\\(5\\\\). This is the most precise determination of an atomic gJ factor so far. The experiment was carried out on a single 12C 5+ ion stored in a Penning trap. The high accuracy was made

H. Häffner; T. Beier; N. Hermanspahn; H.-J. Kluge; W. Quint; S. Stahl; J. Verdú; G. Werth

2000-01-01

250

Collapse of the magnetic ordering and structural anomalies in the U  

Microsoft Academic Search

:   We report specific heat and neutron diffraction measurements of seven samples in the solid solution system UxLa1-xS. All samples have the simple fcc NaCl crystal structure. Both specific heat and neutron diffraction confirm the suggestion\\u000a from the earlier magnetic measurements that the ferromagnetism disappears abruptly at 0.57. Near there is a doubling of the electronic contribution to the specific

F. Bourdarot; A. Bombardi; P. Burlet; R. Calemczuk; G. H. Lander; F. Lapierre; J. P. Sanchez; K. Mattenberger; O. Vogt

1969-01-01

251

Positive holes in magnesium oxide - Correlation between magnetic, electric, and dielectric anomalies  

NASA Technical Reports Server (NTRS)

The present magnetic susceptibility investigation of high purity MgO single crystals notes an anomally at 800 K which is associated with increasing electrical conductivity, a rise in static dielectric constant from 9 to 150, and the appearance of a pronounced positive surface charge. These phenomena can be accounted for in terms of peroxy defects which represent self-trapped, spin-paired positive holes at Mg(2+) vacancy sites. The holes begin to decouple their spins above 600 K.

Batllo, F.; Leroy, R. C.; Parvin, K.; Freund, F.; Freund, M. M.

1991-01-01

252

3D inversion and modeling of magnetic and gravimetric data characterizing the geophysical anomaly source in Pratinha I in the southeast of Brazil  

NASA Astrophysics Data System (ADS)

The Alto do Paranaíba Igneous Province (APIP) is known for its great mineral exploratory interest in phosphates, niobium, titanium, and diamonds, among others. In the years of 2005 and 2006, the Economic Development Company of Minas Gerais (CODEMIG — http://www.comig.com.br/) performed an airborne magnetic survey over the portion of this igneous province which belongs to Minas Gerais state, denominated Area 7. This survey revealed at the coordinates (19°45'S, 46°10'W) a tripolar anomaly here referred as Pratinha I. This anomaly does not present evidences of outcropping or topographic remodeling. So, boreholes or studies over its sources make the geophysical methods the best and less expensive solution for studying the body in its subsurface. Besides, two gravimetric ground surveys were performed in 2009 and 2010, confirming the existence of a density contrast over the region of the magnetic anomaly. Therefore, through the magnetometry and gravimetry processing, 3D modeling and inversions, it was possible to estimate the geometry, density and magnetic susceptibility, which when analyzed with the regional geology, enabled the proposition of an igneous intrusion of probable alkaline or kamafugitic composition to justify the gravimetric and magnetic response in the region.

Louro, Vinicius Hector Abud; Mantovani, Marta Silvia Maria

2012-05-01

253

Reconstructing Coherent Networks from Electroencephalography and Magnetoencephalography with Reduced Contamination from Volume Conduction or Magnetic Field Spread  

PubMed Central

Volume conduction (VC) and magnetic field spread (MFS) induce spurious correlations between EEG/MEG sensors, such that the estimation of functional networks from scalp recordings is inaccurate. Imaginary coherency [1] reduces VC/MFS artefacts between sensors by assuming that instantaneous interactions are caused predominantly by VC/MFS and do not contribute to the imaginary part of the cross-spectral densities (CSDs). We propose an adaptation of the dynamic imaging of coherent sources (DICS) [2] - a method for reconstructing the CSDs between sources, and subsequently inferring functional connectivity based on coherences between those sources. Firstly, we reformulate the principle of imaginary coherency by performing an eigenvector decomposition of the imaginary part of the CSD to estimate the power that only contributes to the non-zero phase-lagged (NZPL) interactions. Secondly, we construct an NZPL-optimised spatial filter with two a priori assumptions: (1) that only NZPL interactions exist at the source level and (2) the NZPL CSD at the sensor level is a good approximation of the projected source NZPL CSDs. We compare the performance of the NZPL method to the standard method by reconstructing a coherent network from simulated EEG/MEG recordings. We demonstrate that, as long as there are phase differences between the sources, the NZPL method reliably detects the underlying networks from EEG and MEG. We show that the method is also robust to very small phase lags, noise from phase jitter, and is less sensitive to regularisation parameters. The method is applied to a human dataset to infer parts of a coherent network underpinning face recognition. PMID:24349088

Drakesmith, Mark; El-Deredy, Wael; Welbourne, Stephen

2013-01-01

254

The South Atlantic Magnetic Field Anomaly and Its Effect on the Calculated Production of Atmospheric Neutrinos  

E-print Network

The theoretical calculations of the production of neutrinos via cosmic rays incident upon the earth's atmosphere (Barr et al., 1989; Becker-Szendy et al., 1992; Bugaev & Naumov, 1989; Gaisser et al, 1988; Honda et al., 1995) are examined. These calculations use a one-dimensional approximation in the production, transport, and decay of the produced particles. Examined are various additional effects of the earth's magnetic field and the three-dimensional nature of the problem which have the effect of decreasing the calulated ratio of muon neutrinos to electron neutrinos.

J. Poirier

2000-08-25

255

MAGSAT anomaly map and continental drift  

NASA Technical Reports Server (NTRS)

Anomaly maps of high quality are needed to display unambiguously the so called long wave length anomalies. The anomalies were analyzed in terms of continental drift and the nature of their sources is discussed. The map presented confirms the thinness of the oceanic magnetized layer. Continental magnetic anomalies are characterized by elongated structures generally of east-west trend. Paleomagnetic reconstruction shows that the anomalies found in India, Australia, and Antarctic exhibit a fair consistency with the African anomalies. It is also shown that anomalies are locked under the continents and have a fixed geometry.

Lemouel, J. L. (principal investigator); Galdeano, A.; Ducruix, J.

1981-01-01

256

Origin of the northern Indus Fan and Murray Ridge, Northern Arabian Sea: interpretation from seismic and magnetic imaging  

E-print Network

deposited during the drift phase after the break-up of India­ Seychelles­Africa. A predrift sequence, magnetic anomalies and gravity field modeling indicate to be of continental character. The continental anomalies. From this study, thinned continental crust spreads between the northern Murray Ridge System

Clift, Peter

257

Long periods (1 -10 mHz) geomagnetic pulsations variation with solar cycle in South Atlantic Magnetic Anomaly  

NASA Astrophysics Data System (ADS)

The occurrence and intensity of the geomagnetic pulsations Pc-5 (2-7 mHz) and its relationship with the solar cycle in the South Atlantic Magnetic Anomaly -SAMA is presented. The study of geomagnetic pulsations is important to help the understanding of the physical processes that occurs in the magnetosphere region and help to predict geomagnetic storms. The fluxgate mag-netometers H, D and Z, three axis geomagnetic field data from the Southern Space Observatory -SSO/CRS/INPE -MCT, São Martinho da Serra (29.42° S, 53.87° W, 480m a.s.l.), RS, Brasil, a were analyzed and correlated with the solar wind parameters (speed, density and temperature) from the ACE and SOHO satellites. A digital filtering to enhance the 2-7 mHz geomagnetic pulsations was used. Five quiet days and five perturbed days in the solar minimum and in the solar maximum were selected for this analysis. The days were chosen based on the IAGA definition and on the Bartels Musical Diagrams (Kp index) for 2001 (solar maximum) and 2008 (solar minimum). The biggest Pc-5 amplitude averages differences between the H-component is 78,35 nT for the perturbed days and 1,60nT for the quiet days during the solar maximum. For perturbed days the average amplitude during the solar minimum is 8,32 nT, confirming a direct solar cycle influence in the geomagnetic pulsations intensity for long periods.

Rigon Silva, Willian; Schuch, Nelson Jorge; Guimarães Dutra, Severino Luiz; Babulal Trivedi, Nalin; Claudir da Silva, Andirlei; Souza Savian, Fernando; Ronan Coelho Stekel, Tardelli; de Siqueira, Josemar; Espindola Antunes, Cassio

258

Geologic structure of the northern New Caledonia ridge, as inferred from magnetic and gravity anomalies  

USGS Publications Warehouse

Bathymetric, gravity, and magnetic data collected in the southwest Pacific Ocean over the northern New Caledonia ridge show that the main geological units known from the island of New Caledonia extend northward from this island, beneath the Grand Lagon Nord, the Grand Passage, and the d'Entrecasteaux reefs. These data support the model of tectonic evolution of the New Caledonia region proposed by Kroenke (1984). Differences in structure, geophysical signatures and morphology evident between areas north and those south of the Grand Passage, together with the nearness of the Le Noroit massif west of the Grand Passage, suggest that contemporaneously with Eocene to early Oligocene subduction along the western New Caledonia margin, an arc-ridge collision may have occurred near the northern termination of this subduction zone. -from Authors

Collot, J.-Y.; Rigolot, P.; Missegue, F.

1988-01-01

259

Concentration anomalies of the magnetization of HgSe:Fe crystals  

NASA Astrophysics Data System (ADS)

The field and temperature dependences of the magnetization of the semimagnetic semiconductor HgSe:Fe have been studied experimentally. The spin splitting of the Landau levels in the de Haas-van Alphen quantum oscillations has been recorded in the iron impurity concentration interval of 7 × 1018 cm-3 < N Fe < 2 × 1019 cm-3. The effective area of the extreme cross section of the Fermi surface has been determined from the obtained dependences of the oscillation period on the iron concentration, and the concentration of the collectivized electrons under conditions of the stabilization of the Fermi level on the iron donor level has been estimated. The critical impurity concentration at which the sharp increase in the Curie-Weiss temperature occurs owing to the spontaneous spin polarization of the system of hybridized electron states in iron-doped mercury selenide has been determined.

Popenko, N.; Bekirov, B.; Ivanchenko, I.; Bludov, A.; Pashchenko, V.

2014-10-01

260

Evaluation of seismo-electric anomalies using magnetic data in Taiwan  

NASA Astrophysics Data System (ADS)

The Parkinson vectors derived from 3-component geomagnetic data via the magnetic transfer function are discussed with respect to epicentre locations and hypocentre depths of 16 earthquakes (M ? 5.5) in Taiwan during a period of 2002-2005. To find out whether electric conductivity changes would happen particularly in the seismoactive depth ranges, i.e. in the vicinity of the earthquake foci, the frequency dependent penetration depth of the electromagnetic waves (skin effect) is taken into account. The background distributions involving the general conductivity structure and the coast effect at 20 particular depths are constructed using the Parkinson vectors during the entire study period. The background distributions are subtracted from the time-varying monitor distributions, which are computed using the Parkinson vectors within the 15-day moving window, to remove responses of the coast effect and underlying conductivity structure. Anomalous depth sections are identified by deviating distributions and agree with the hypocentre depths of 15 thrust and/or strike-slip earthquakes with only one exception of a normal fault event.

Chen, C. H.; Hsu, H. L.; Wen, S.; Yeh, T. K.; Chang, F. Y.; Wang, C. H.; Liu, J. Y.; Sun, Y. Y.; Hattori, K.; Yen, H. Y.; Han, P.

2013-03-01

261

New insights on the seafloor spreading patterns of the northern South China Sea (16° N-23° N)  

NASA Astrophysics Data System (ADS)

There are several models which attend to describe the spreading history of the South China Sea and its sea-floor spreading evolution. Based on the magnetic anomaly systematic study in the past, the South China Sea Basin can be divided into the southwestern and eastern parts by the several spreading orientation change stages. The eastern basin is revealed asymmetric between magnetic anomaly isochron 11 (about 32 Ma) and the ceased of the spreading of the South China Sea (magnetic anomaly isochron 5c) (Briais et al., 1993). Recent magnetic lineations showed the existence of magnetic anomaly 15-17 in the northernmost South China Sea area. However, the spreading features of the northern South China Sea (older then 32Ma) and their tectonic correlation with the whole South China Sea are still not well understood. To understand the rifting structures and their tectonic implications in the northern South China Sea, 9 multi-channel seismic profiles (ORI645, ORI654, ORI689, ORI693, ACT, EW9509, MLTW, 97304Aa and 97034Ab), the magnetic data collected off southwestern Taiwan (117° E~121° E longitude and 18.5° N - 23° N latitude), NGDC magnetic trackline data (National Geophysical Data Center from 1950 to present), CCOP magnetic data (Coordination Committee for Geoscience Programmes in East and Southeast Asia), satellite gravity anomaly data, the bathymetry (NGDC and swath bathymetry) are used. Based on the seismic data, the post-rift oldest sedimentary features were identified to be uplifted in the northeastern South China Sea (117.5° E-120.5° E and 19° N-22° N). The oldest features can be divided into a N45° trending part and a N90° trending part, separated by a possible N-S trending fracture zone. This feature is clearly absent at the north region of the LRTPB (Luzon Ryuku Transform Plate Boundary) and could be prolonged southward based on the geophysical data (gravity data , the swath bathymetric data and the magnetic data). Furthermore, in the whole northern South China Sea (112° E-121° E longitude, 16° N-23° N latitude), the orientation of the spreading has a major change between magnetic anomaly isochron 9 and 10. The orientation of the magnetic anomaly 11-17 area revealed E-W to ENE-SWS. However, the oldest sedimentation features in this area trend NE-SW. It is interesting that the anomaly 11 to 17 part of the oceanic crust is not existed at the south side of the South China Sea. There is no evidence which the northern anomaly 11-17 part was the extinct portion of the other spreading system(not belonged to South China Sea). Therefore, the anomaly 11-17 south part of the oceanic crust could be reasonably interpreted as subducted portion beneath the northwest Palawan.

Yeh, Y.; Sibuet, J.; Hsu, S.

2004-12-01

262

Gravity and magnetic anomalies of the western Arctic ocean and its margins provide an imperfect window to a complex, multi-stage tectonic history (Invited)  

NASA Astrophysics Data System (ADS)

Numerous scenarios are still in play for the tectonic development of the western Arctic. A wide range of kinematic models have been proposed for the opening of the Canadian basin. These models feature different combinations and geometries of extensional and transform motion and have informal descriptive names including the so-called ‘windshield wiper’, ‘railroad tracks’, ‘squeegee’, and ‘saloon door’ options. Another controversial issue is the timing and role of the gigantic Alpha-Mendeleev large igneous province relative to the tectonic stages. In our opinion, many current Arctic models have not adequately dealt with the mass and thermal fluxes implied by this huge province. Available data are extremely sparse for the circum-Arctic, although current political and economic interests are fueling accelerated data collection. Recent compilations of gravity and magnetic data are currently the best bets for synoptic imaging, however imprecise, of crustal composition and structure. Modeling and interpretation of regional geophysical anomalies provide some of the only available tests for scenario evaluation in the absence of more direct determinations of crustal structure and composition. Our goal in this talk is to review the key geophysical features of the western Arctic and relate these elements to the expectations of competing tectonic models. These key geophysical features include (1) contrasting Arctic domains of overall magnetic “thickness” and anomaly “fabric” (the domains correlate generally with broad tectonic categories); (2) cryptic sub-linear magnetic anomalies in the Canada basin (interpreted by some authors to be oceanic stripes); (3) a subtle but persistent gravity trough in the central Canada basin (inferred by some authors to represent an extensional trough); (4) spectacular “shelf edge” free-air gravity anomalies along the Canadian and Alaskan passive margins that show significant along-strike variation (which can be interpreted to reflect relative amount of magmatic activity); (5) complex and chaotic magnetic texture and fabric in the Alpha-Mendeleev large igneous province (perhaps reflecting pre-intrusive structural features and trends); and (6) large-amplitude, long-wavelength “deep magnetic highs” including well-studied examples in northern Alaska and north-western Canada (inferred to represent deep crustal elements that influence overall strength of the crust/upper mantle). The overall complexity of the Arctic geophysical anomaly fabric is indicative of significant variation in crustal composition and reflects a complicated, multi-stage tectonic development. It seems very likely that the best tectonic solutions for the circum-Arctic will include sub-elements of many current end-member models.

Saltus, R. W.; Miller, E. L.; Gaina, C.

2010-12-01

263

Correlation analysis between the occurrence of ionospheric scintillation at the magnetic equator and at the southern peak of the Equatorial Ionization Anomaly  

NASA Astrophysics Data System (ADS)

scintillation refers to amplitude and phase fluctuations in radio signals due to electron density irregularities associated to structures named ionospheric plasma bubbles. The phenomenon is more pronounced around the magnetic equator where, after sunset, plasma bubbles of varying sizes and density depletions are generated by plasma instability mechanisms. The bubble depletions are aligned along Earth's magnetic field lines, and they develop vertically upward over the magnetic equator so that their extremities extend in latitude to north and south of the dip equator. Over Brazil, developing bubbles can extend to the southern peak of the Equatorial Ionization Anomaly, where high levels of ionospheric scintillation are common. Scintillation may seriously affect satellite navigation systems, such as the Global Navigation Satellite Systems. However, its effects may be mitigated by using a predictive model derived from a collection of extended databases on scintillation and its associated variables. This work proposes the use of a classification and regression decision tree to perform a study on the correlation between the occurrence of scintillation at the magnetic equator and that at the southern peak of the equatorial anomaly. Due to limited size of the original database, a novel resampling heuristic was applied to generate new training instances from the original ones in order to improve the accuracy of the decision tree. The correlation analysis presented in this work may serve as a starting point for the eventual development of a predictive model suitable for operational use.

Lima, G. R. T.; Stephany, S.; Paula, E. R.; Batista, I. S.; Abdu, M. A.; Rezende, L. F. C.; Aquino, M. G. S.; Dutra, A. P. S.

2014-06-01

264

A source-depth separation filter: Using the Euler method on the derivatives of total intensity magnetic anomaly data  

USGS Publications Warehouse

An overview is given on the benefits of applying the Euler method on derivatives of anomalies to enhance the location of shallow and deep sources. Used properly, the method is suitable for characterizing sources from all potential-field data and/or their derivative, as long as the data can be regarded mathematically as "continuous". Furthermore, the reasons why the use of the Euler method on derivatives of anomalies is particularly helpful in the analysis and interpretation of shallow features are explained.

Ravat, D.; Kirkham, K.; Hildenbrand, T.G.

2002-01-01

265

Seafloor spreading and microcontinent formation during Mesozoic breakup between Australia and Greater India  

NASA Astrophysics Data System (ADS)

The Perth Abyssal Plain (PAP) formed at the nexus of rifting and breakup between three major continents within Gondwana - India, Australia and Antarctica. Oceanic crust within the PAP records the history of Mesozoic seafloor spreading as India moved away from Australia. However, despite the clear importance of the seafloor spreading history of the PAP in constraining the relative motions of these continents during the early stages of breakup, little attention has been paid to the PAP, and particularly its western flank largely due to a lack of new data in collected in this region. We present new observations to constrain the evolution of the PAP, collected during voyage ss2011/v06 of the Southern Surveyor in late 2011. The new data comprise magnetic anomaly profile data, swath bathymetry, and dredge samples collected from 7 sites. The most significant dredge results were obtained from the Batavia Knoll (BK) and Gulden Draak Knoll (GDK), two prominent bathymetric features located >1000 km west of the Australian continental margin. Previous tectonic reconstructions typically treat these bathymetric features as igneous plateaus emplaced on older oceanic crust. However, dredges carried out on the western flanks of each of these knolls recovered continental basement rocks, revealing that both knolls are continental fragments. Estimates of the depths to magnetic sources for shiptrack profiles across the knolls provide evidence for variations in sediment thickness within the knolls. We use forward modeling of shiptrack magnetic profiles combined with gravity anomalies derived from satellite altimetry to make first-order estimates of the extent and spatial variation in thickness of the continental crust. New magnetic anomaly profiles provide evidence for previously unidentified M-series anomalies in the western part of the Perth Abyssal Plain, east of the BK and GDK. These observations both support a reconstruction model in which the microcontinents rifted away from Australia as part of greater India during initial breakup at ~130 Ma. Seafloor spreading in the PAP continued during the early part of the Cretaceous Normal Superchron (until approximately 108 Ma assuming a constant spreading rate inferred from the M-series anomalies). A westward jump in the Australia-India plate boundary led to cessation of spreading in the PAP and the rifting of the BK and GDK from Greater India. Satellite-derived gravity anomalies and swath bathymetry profiles provide evidence for ridge propagation events within the PAP ocean crust, occurring during the Cretaceous Normal Superchron. This series of westwards jumps of the India-Australia plate boundary suggests a strong influence of the Kerguelen hotspot, located beneath eastern greater India at this time.

Williams, S.; Whittaker, J.; Müller, R.

2012-12-01

266

High-throughput screening of magnetic properties of quenched metallic-alloy thin-film composition spreads  

E-print Network

. silicon wafers. Scanning SQUID microscopy and magneto- optical Kerr effect measurements were used to map and characterizing high-temperature phases of metallic-alloys in thin-film composition spreads has been developed. A high-vacuum (10Ã?8 Torr) high-temperature annealing and quenching furnace system has been developed

Rubloff, Gary W.

267

Epitope spreading  

Microsoft Academic Search

Epitope (determinant) spreading is the development of immune responses to endogenous epitopes secondary to the release of self antigens during a chronic autoimmune or inflammatory response. The past year has seen considerable advances in our understanding of the contribution of epitope spreading to the chronic pathogenesis of experimental T-cell-mediated and antibody-mediated autoimmune diseases. Most significantly, conclusive functional evidence for a

Carol J Vanderlugt; Stephen D Miller

1996-01-01

268

Spill Spread  

NSDL National Science Digital Library

In this simulation, learners explore how ocean currents spread all kinds of pollutionâincluding oil spills, sewage, pesticides and factory wasteâfar beyond where the pollution originates. Learners create an experimental "ocean" (water in a tray) and "continents" (rocks), then add melting ice cubes to create temperature-driven currents in the water. Learners observe how "pollution," represented by food coloring, spreads through the model ocean affected by both "currents" and "continents." This activity can be used with lessons on ocean science or environmental hazards.

Science, Lawrence H.

2007-01-01

269

Earth analog for Martian magnetic anomalies: remanence properties of hemo-ilmenite norites in the Bjerkreim-Sokndal intrusion, Rogaland, Norway  

NASA Astrophysics Data System (ADS)

To explain the very large remanent magnetic anomalies on Mars, which no longer has a global magnetic field, it is important to evaluate rocks on Earth with the necessary properties of high natural remanent magnetization (NRM) and coercivity. Here, we describe a possible analog from the 230-km 2 930 Ma Bjerkreim-Sokndal layered intrusion (BKS) in Rogaland, Norway. In the layered series of the BKS, fractional crystallization of jotunitic magma was punctuated by influx and mixing of more primitive magmas, producing six megacyclic units, each typically with early plagioclase-rich norites, intermediate hemo-ilmenite-rich norites and late magnetite norites with subordinate near end-member ilmenite. Following each influx, the magma resumed normal crystallization and, following the last, near the base of Megacyclic Unit IV, crystallization continued until norites gave way to massive fayalite-magnetite mangerites and quartz mangerites in the upper part of the intrusion. The Megacycles are marked on a regional aeromagnetic map by remanent-controlled negative anomalies over ilmenite norites and induced positive anomalies over magnetite norites and mangerites. A prominent negative anomaly (with amplitude -13,000 nT in a high-resolution helicopter survey, down to -27,000 nT below background in ground magnetic profiles) occurs over the central part of Megacyclic Unit IV. The anomaly is centered on ilmenite norite Unit IVe and is most intense where cumulate layering is near vertical at the southeast edge of the Bjerkreim Lobe of the intrusion at Heskestad. Here, Unit IVe is flanked to the east by magnetite norite of Unit IVc and country-rock gneisses (group E) and to the west by Unit IVf magnetite norite and mangerites (group W). Magnetic properties were measured on 128 oriented samples. Susceptibilities are similar for all three sample groups at ˜8×10 -2, but Koenigsberger ratios are very different, with average values of 7.7 for IVe, and <1 for groups E and W. The IVe samples, with only a few percent of oxides, have the highest NRMs measured from the BKS, up to 74 A/m, with an average of 30.6 A/m, making them prime candidates for consideration as Mars analogs. The mean direction for IVe samples is D=17.6°, I=-79.9, a95=10°, almost opposite the present field. Evidence on origin of the strong NRM in IVe as compared to groups E and W, include greater abundance of hemo-ilmenite and of orthopyroxene with hemo-ilmenite exsolution, and the strong lattice-preferred orientation of both in a relationship favorable for "lamellar magnetism". Massive magnetite-free hemo-ilmenite ores in anorthosite from the same district also produce negative magnetic anomalies. They have a substantial but much lower NRM, suggesting that there are special oxide properties in the IVe rocks at Heskestad.

McEnroe, S. A.; Brown, L. L.; Robinson, Peter

2004-10-01

270

The Effects of Magnetic Anomalies Discovered at Mars on the Structure of the Martian Ionosphere and the Solar Wind Interaction as Follows from Radio Occultation Experiments  

NASA Technical Reports Server (NTRS)

The electron density distribution in the ionosphere of nonmagnetic (or weakly magnetized) planet depends not only on the solar ultraviolet intensity, but also on the nature of the SW interaction with this planet. Two scenarios previously have been developed based on the observations of the bow shock crossings and on the electron density distribution within the ionosphere. According to one of them Mars has an intrinsic magnetosphere produced by a dipole magnetic field and the Martian ionosphere is protected from the SW flow except during "overpressure conditions, when the planetary magnetic field can not balance the SW dynamic pressure. In the second scenario the Martian intrinsic magnetic dipole field is so weak that Mars has mainly an induced magnetosphere and a Venus-like SW/ionosphere interaction. Today the possible existence of a sufficiently strong global magnetic field that participates in the SW/Mars interaction can no longer be supported. The results obtained by the Mars-Global-Surveyor (MGS) space-craft show the existence of highly variable, but also very localized magnetic fields of crustal origin at Mars as high as 400-1500 nT. The absence of the large-scale global magnetic field at Mars makes it similar to Venus, except for possible effects of the magnetic anomalies associated with the remnant crustal magnetization. However the previous results on the Martian ionosphere obtained mainly by the radio occultation methods show that there appears to be a permanent existence of a global horizontal magnetic field in the Martian ionosphere. Moreover the global induced magnetic field in the Venus ionosphere is not typical at the solar zenith angles explored by the radio occultation methods. Additional information is contained in the original extended abstract.

Ness, N. F.; Acuna, M. H.; Connerney, J. E. P.; Cloutier, P.; Kliore, A. J.; Breus, T. K.; Krymskii, A. M.; Bauer, S. J.

1999-01-01

271

Infrared phonon anomaly and magnetic excitations in single-crystal Cu3Bi(SeO3)2O2Cl  

NASA Astrophysics Data System (ADS)

Infrared reflection as a function of temperature has been measured on the anisotropic single-crystal Cu3Bi(SeO3)2O2Cl. The complex dielectric function and optical properties along all three crystal axes of the orthorhombic cell were obtained via Kramers-Kronig analysis and by fits to a Drude-Lorentz model. Below 110 K drastic anomalies in the phonon spectrum (e.g., new modes and splitting of existing modes) are observed along all three crystal axes. Transmission in the terahertz region as a function of temperature has revealed magnetic excitations originating below the ferromagnetic ordering temperature, Tc=24 K. The origin of the excitations in the magnetic state will be discussed in terms of their polarization and externally-applied magnetic field dependence.

Miller, Kevin H.; Martin, C.; Xi, X.; Berger, H.; Carr, G. L.; Tanner, D. B.

2012-02-01

272

Effects of magnetic anomalies discovered at Mars on the structure of the Martian ionosphere and solar wind interaction as follows from radio occultation experiments  

NASA Astrophysics Data System (ADS)

The slopes of the electron density profiles obtained by radio occultation experiments at Mars revealed different variations with solar zenith angle in comparison with behavior of the electron density profiles in the magnetic field free ionosphere of Venus. The results obtained by the Mars-Global-Surveyor (MGS) spacecraft show the existence of highly variable and very localized magnetic fields of crustal origin at Mars. Addressing the difference between the ionosphere at Venus and Mars, the scale heights of electron density profiles obtained by radio occultation methods onboard Mariner 9 and Viking 1 are analyzed at altitudes higher than the topside boundary of the photoequilibrium region in the magnetic field-free ionosphere. The local increase of the mean scale height in the altitude region 180-250 km is assumed to be either an effect of a nonhorizontal magnetic field associated with the magnetic anomalies or diffusive equilibrium in the magnetic field free ionosphere. The areas where the scale height of electron density profile is increased in comparison with average one have been selected. The angle between the magnetic field measured by MGS MAG/ER at altitudes 120-250 km and local zenith direction is investigated throughout these selected areas.

Ness, N. F.; Acuña, M. H.; Connerney, J. E. P.; Kliore, A. J.; Breus, T. K.; Krymskii, A. M.; Cloutier, P.; Bauer, S. J.

2000-07-01

273

M3 spectral analysis of lunar swirls and the link between optical maturation and surface hydroxyl formation at magnetic anomalies  

NASA Astrophysics Data System (ADS)

We examined the lunar swirls using data from the Moon Mineralogy Mapper (M3). The improved spectral and spatial resolution of M3 over previous spectral imaging data facilitates distinction of subtle spectral differences, and provides new information about the nature of these enigmatic features. We characterized spectral features of the swirls, interswirl regions (dark lanes), and surrounding terrain for each of three focus regions: Reiner Gamma, Gerasimovich, and Mare Ingenii. We used Principle Component Analysis to identify spectrally distinct surfaces at each focus region, and characterize the spectral features that distinguish them. We compared spectra from small, recent impact craters with the mature soils into which they penetrated to examine differences in maturation trends on- and off-swirl. Fresh, on-swirl crater spectra are higher albedo, exhibit a wider range in albedos and have well-preserved mafic absorption features compared with fresh off-swirl craters. Albedoand mafic absorptions are still evident in undisturbed, on-swirl surface soils, suggesting the maturation process is retarded. The spectral continuum is more concave compared with off-swirl spectra; a result of the limited spectral reddening being mostly constrained to wavelengths less than ˜1500 nm. Off-swirl spectra show very little reddening or change in continuum shape across the entire M3 spectral range. Off-swirl spectra are dark, have attenuated absorption features, and the narrow range in off-swirl albedos suggests off-swirl regions mature rapidly. Spectral parameter maps depicting the relative OH surface abundance for each of our three swirl focus regions were created using the depth of the hydroxyl absorption feature at 2.82 ?m. For each of the studied regions, the 2.82 ?m absorption feature is significantly weaker on-swirl than off-swirl, indicating the swirls are depleted in OH relative to their surroundings. The spectral characteristics of the swirls and adjacent terrains from all three focus regions support the hypothesis that the magnetic anomalies deflect solar wind ions away from the swirls and onto off-swirl surfaces. Nanophase iron (npFe0) is largely responsible for the spectral characteristics we attribute to space weathering and maturation, and is created by vaporization/deposition by micrometeorite impacts and sputtering/reduction by solar wind ions. On the swirls, the decreased proton flux slows the spectral effects of space weathering (relative to nonswirl regions) by limiting the npFe0 production mechanism almost exclusively to micrometeoroid impact vaporization/deposition. Immediately adjacent to the swirls, maturation is accelerated by the increased flux of protons deflected from the swirls.

Kramer, Georgiana Y.; Besse, Sebastien; Dhingra, Deepak; Nettles, Jeffrey; Klima, Rachel; Garrick-Bethell, Ian; Clark, Roger N.; Combe, Jean-Philippe; Head, James W., III; Taylor, Lawrence A.; Pieters, Carlé M.; Boardman, Joseph; McCord, Thomas B.

2011-09-01

274

Resolvability of the interval between inversions using marine magnetic anomalies based on the Rao-Cramer inequality  

NASA Astrophysics Data System (ADS)

It has been indicated that the Rao-Cramer inequality can be used to estimate the resolvability of intervals with opposite geomagnetic field polarity based on marine anomalies and for measurement planning. Specifically, it has been elucidated that the width of a detected interval of one polarity is determined more exactly than its center.

Ivanov, S. A.; Merkur'ev, S. A.

2013-11-01

275

A Preliminary, Full Spectrum, Magnetic Anomaly Grid of the United States with Improved Long Wavelengths for Studying Continental Dynamics: A Website for Distribution of Data  

USGS Publications Warehouse

Under an initiative started by Thomas G. Hildenbrand of the U.S. Geological Survey, we have improved the long-wavelength (50-2,500 km) content of the regional magnetic anomaly compilation for the conterminous United States by utilizing a nearly homogeneous set of National Uranium Resource Evaluation (NURE) magnetic surveys flown from 1975 to 1981. The surveys were flown in quadrangles of 2 deg of longitude by 1 deg of latitude with east-west flight lines spaced 4.8 to 9.6 km apart, north-south tie lines variably spaced, and a nominal terrain clearance of 122 m. Many of the surveys used base-station magnetometers to remove external field variations.

Ravat, D.; Finn, C.; Hill, P.; Kucks, R.; Phillips, J.; Blakely, R.; Bouligand, C.; Sabaka, T.; Elshayat, A.; Aref, A.; Elawadi, E.

2009-01-01

276

Gravitational anomaly and transport phenomena.  

PubMed

Quantum anomalies give rise to new transport phenomena. In particular, a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid. PMID:21797593

Landsteiner, Karl; Megías, Eugenio; Pena-Benitez, Francisco

2011-07-01

277

Reliability of CHAMP Anomaly Continuations  

NASA Technical Reports Server (NTRS)

CHAMP is recording state-of-the-art magnetic and gravity field observations at altitudes ranging over roughly 300 - 550 km. However, anomaly continuation is severely limited by the non-uniqueness of the process and satellite anomaly errors. Indeed, our numerical anomaly simulations from satellite to airborne altitudes show that effective downward continuations of the CHAMP data are restricted to within approximately 50 km of the observation altitudes while upward continuations can be effective over a somewhat larger altitude range. The great unreliability of downward continuation requires that the satellite geopotential observations must be analyzed at satellite altitudes if the anomaly details are to be exploited most fully. Given current anomaly error levels, joint inversion of satellite and near- surface anomalies is the best approach for implementing satellite geopotential observations for subsurface studies. We demonstrate the power of this approach using a crustal model constrained by joint inversions of near-surface and satellite magnetic and gravity observations for Maude Rise, Antarctica, in the southwestern Indian Ocean. Our modeling suggests that the dominant satellite altitude magnetic anomalies are produced by crustal thickness variations and remanent magnetization of the normal polarity Cretaceous Quiet Zone.

vonFrese, Ralph R. B.; Kim, Hyung Rae; Taylor, Patrick T.; Asgharzadeh, Mohammad F.

2003-01-01

278

Anomaly Holography  

E-print Network

We consider, in the effective field theory context, anomalies of gauge field theories on a slice of a five-dimensional, Anti-de Sitter geometry and their four-dimensional, holographic duals. A consistent effective field theory description can always be found, notwithstanding the presence of the anomalies and without modifying the degrees of freedom of the theory. If anomalies do not vanish, the d=4 theory contains additional pseudoscalar states, which are either present in the low-energy theory as physical, light states, or are eaten by (would-be massless) gauge bosons. We show that the pseudoscalars ensure that global anomalies of the four-dimensional dual satisfy the 't Hooft matching condition and comment on the relevance for warped models of electroweak symmetry breaking.

Ben Gripaios; Stephen M. West

2007-04-30

279

Parametric study of a variable-magnetic-field-based energy-selection system for generating a spread-out Bragg peak with a laser-accelerated proton beam  

NASA Astrophysics Data System (ADS)

Laser-based proton beam acceleration, which produces broad energy spectra, is unsuitable for direct clinical use. Thus, employing an energy selection system is necessary. The purpose of the present study was to investigate a method whereby a variable magnetic field could be employed with an energy selection system to generate a spread-out Bragg peak (SOBP). For energy selection, particle transport and dosimetric property measurements, the Geant4 toolkit was implemented. The energy spectrum of the laser-accelerated proton beam was acquired using a particle-in-cell simulation. The hole size and the position of the energy selection collimator were varied in order to determine the effects of those parameters on the dosimetric properties. To generate an SOBP, we changed the magnetic field in the energy selection system for each beam weighting factor during beam irradiation. The overall results of this study suggest that the use of an energy selection system with a variable magnetic field can effectively generate an SOBP suitable for proton radiation therapy applications.

Kim, Dae-Hyun; Suh, Tae-Suk; Kang, Young Nam; Yoo, Seung Hoon; Pae, Ki-Hong; Shin, Dongho; Lee, Se Byeong

2013-01-01

280

Origin of anomalies and phase competitions around magnetic transition temperature in Pr0.7Ca0.3MnO3  

NASA Astrophysics Data System (ADS)

A polycrystalline sample of Pr0.7Ca0.3MnO3 is synthesized by the conventional solid-state reaction method and the phase formation is confirmed by x-ray diffraction. In this work, we addressed the phase competition issues in the vicinity of magnetic transition temperature and also established its correlation with oxygen contents of domains, disorder effects and heterogeneity in the material. The appearance and disappearance of anomaly in the vicinity of TC (128 K) with magnetic field is discussed in terms of establishment of short- and long-range networks between Mn3+ and Mn4+. Switching behaviour of two competing phases is analysed qualitatively and quantitatively, using an equivalent circuit model and magnetization analysis. The issue of coexisting phases is further substantiated using a simple depression angle approach of impedance plane plots. variable range hopping is found to be a better model than polaronic for explaining the transport properties of both competing phases below the magnetic transition temperature, 128 K.

Shah, Matiullah; Nadeem, M.; Atif, M.

2013-03-01

281

Evidence for True Polar Wander since mid-Cenozoic time: A Paleomagnetic Investigation of the Skewness of Magnetic Anomaly 12r (32 Ma) Between the Galapagos and Clarion Fracture Zones on the Pacific Plate  

NASA Astrophysics Data System (ADS)

In recent years, some researchers have asserted that there has been no motion of the Pacific hotspots relative to the spin axis since the age (ca. 47 Ma) of the elbow in the Hawaiian-Emperor chain (e.g., Tarduno et al. 2003). In contrast, the apparent polar wander of the Indo-Atlantic hotspots shows distinct motion of the hotspots relative to the spin axis over the same time interval (e.g., Morgan 1981; Besse and Courtillot 2002). If this latter shift is due to true polar wander, one would expect to see a similar shift of Pacific hotspots relative to the spin axis. Here we present critical new data and analyses to test these distinctly different hypotheses. Specifically, we present results of an investigation of the skewness of magnetic anomaly crossings of anomaly 12r between the Galapagos and Clipperton and between the Clipperton and Clarion fracture zones on the Pacific plate. We chose to focus on these adjacent regions for three reasons. First, numerical experiments showed that these crossings, of all those available from the Pacific plate, should contain the most information about the location of the 32 Ma paleomagnetic pole for the Pacific plate. Second, many of the available crossings are from vector aeromagnetic profiles, which have superior signal to noise ratios (Horner-Johnson and Gordon, 2003). Third, the rate of seafloor spreading recorded in these crossings exceeds the threshold (half rate of 50 mm/yr) above which no anomalous skewness occurs. Moreover, for the first time, we combine uncertainties in plate- hotspot rotations (Andrews et al. 2005) with paleomagnetic uncertainties to obtain the total uncertainties of our new paleomagnetic pole reconstructed into the Pacific hotspot frame of reference. The results show significant and unambiguous motion of Pacific hotspots relative to the spin axis since 32 Ma. Moreover, when the 32 Ma Pacific plate paleomagnetic pole is reconstructed into the Pacific hotspot reference frame, it is consistent with the paleomagnetic pole of the Indo-Atlantic hotspots. We conclude that the global set of hotspots have mainly moved in unison relative to the spin axis since 32 Ma, which is most simply interpreted as true polar wander.

Horner-Johnson, B. C.; Gordon, R. G.

2007-12-01

282

Low-Temperature anomalies of the Hall coefficient for a magnetic Kondo lattice of CeAl 2  

Microsoft Academic Search

The Hall coefficient R\\u000a H and magnetoresistance of a magnetic Kondo lattice of CeAl2 were investigated over a wide temperature range from 1.8 to 300 K in magnetic fields of up to 80 kOe. Analysis of the measured\\u000a angular dependences R\\u000a H(?, T, H) made it possible to separate the contributions of skew scattering and anomalous magnetic scattering to the

N. E. Sluchanko; A. V. Bogach; V. V. Glushkov; S. V. Demishev; N. A. Samarin; G. S. Burkhanov; O. D. Chistyakov

2002-01-01

283

Ages and magnetic structures of the South China Sea constrained by deep tow magnetic surveys and IODP Expedition 349  

NASA Astrophysics Data System (ADS)

analyses of deep tow magnetic anomalies and International Ocean Discovery Program Expedition 349 cores show that initial seafloor spreading started around 33 Ma in the northeastern South China Sea (SCS), but varied slightly by 1-2 Myr along the northern continent-ocean boundary (COB). A southward ridge jump of ˜20 km occurred around 23.6 Ma in the East Subbasin; this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the Southwest Subbasin, which propagated for about 400 km southwestward from ˜23.6 to ˜21.5 Ma. The terminal age of seafloor spreading is ˜15 Ma in the East Subbasin and ˜16 Ma in the Southwest Subbasin. The full spreading rate in the East Subbasin varied largely from ˜20 to ˜80 km/Myr, but mostly decreased with time except for the period between ˜26.0 Ma and the ridge jump (˜23.6 Ma), within which the rate was the fastest at ˜70 km/Myr on average. The spreading rates are not correlated, in most cases, to magnetic anomaly amplitudes that reflect basement magnetization contrasts. Shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers, in addition to large vertical intensity variations. These complexities are caused by late-stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion. Deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0.5, which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization. The primary contribution to magnetic anomalies of the SCS is not in the top 100 m of the igneous basement.

Li, Chun-Feng; Xu, Xing; Lin, Jian; Sun, Zhen; Zhu, Jian; Yao, Yongjian; Zhao, Xixi; Liu, Qingsong; Kulhanek, Denise K.; Wang, Jian; Song, Taoran; Zhao, Junfeng; Qiu, Ning; Guan, Yongxian; Zhou, Zhiyuan; Williams, Trevor; Bao, Rui; Briais, Anne; Brown, Elizabeth A.; Chen, Yifeng; Clift, Peter D.; Colwell, Frederick S.; Dadd, Kelsie A.; Ding, Weiwei; Almeida, Iván. Hernández; Huang, Xiao-Long; Hyun, Sangmin; Jiang, Tao; Koppers, Anthony A. P.; Li, Qianyu; Liu, Chuanlian; Liu, Zhifei; Nagai, Renata H.; Peleo-Alampay, Alyssa; Su, Xin; Tejada, Maria Luisa G.; Trinh, Hai Son; Yeh, Yi-Ching; Zhang, Chuanlun; Zhang, Fan; Zhang, Guo-Liang

2014-12-01

284

Gravitational Anomaly and Transport Phenomena  

Microsoft Academic Search

Quantum anomalies give rise to new transport phenomena. In particular, a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity

Karl Landsteiner; Eugenio Megías; Francisco Pena-Benitez

2011-01-01

285

Critical current of the ionization waves and anomaly of the positive column in an axial magnetic field  

Microsoft Academic Search

Influences of an axial magnetic field on the ionization wave and the positive column in rare gas discharges are studied experimentally. The upper critical current I(c) for the appearance of ionization waves in the magnetic field B is newly found. As B is gradually increased, the value of I(c) increases slightly from the Pupp's value, and after passing a prominent

M. Sato

1981-01-01

286

Antipodal Magnetic Anomalies on the Moon, Contributions from Impact Induced Currents Due to Positive Holes and Flexoelectric Phenomina and Dynamo  

NASA Technical Reports Server (NTRS)

Large impacts on the Moon generate large pressure pulses that penetrate the whole body. Several of these large impacts may have generated antipodal structure with anomalous magnetic intensity.These regions can be more than a thousand km across, with fields of the order of tens to hundreds of nT. This is the case of Orientale, Imbrium, Serenitatis, Crisium, and Nectaris impact basins. The production of large-scale magnetic fields and associated crustal magnetization due to lunar basin-forming impacts was hypothesized to have an origin in fields external to the impact plasma cloud that are produced by the magnetohydrodynamic interaction of the cloud with ambient magnetic fields and plasmas. During the period of compressed antipodal field amplification, seismic compressional waves from the impact converge at the antipode resulting in transient shock pressures that reach 2 GPa (20 kbar). This can produce conditions for shock magnetic acquisition of the crust antipodal to impact basins.

Kletetschka, G.; Freund, F.; Wasilewski, P. J.; Mikula, V.; Kohout, Tomas

2005-01-01

287

DOWN'S ANOMALY.  

ERIC Educational Resources Information Center

BOTH CLINICAL AND PATHOLOGICAL ASPECTS AND MATHEMATICAL ELABORATIONS OF DOWN'S ANOMALY, KNOWN ALSO AS MONGOLISM, ARE PRESENTED IN THIS REFERENCE MANUAL FOR PROFESSIONAL PERSONNEL. INFORMATION PROVIDED CONCERNS (1) HISTORICAL STUDIES, (2) PHYSICAL SIGNS, (3) BONES AND MUSCLES, (4) MENTAL DEVELOPMENT, (5) DERMATOGLYPHS, (6) HEMATOLOGY, (7)…

PENROSE, L.S.; SMITH, G.F.

288

Terrestrial spreading centers under Venus conditions - Evaluation of a crustal spreading model for Western Aphrodite Terra  

NASA Astrophysics Data System (ADS)

The model of Reid and Jackson (1981) for terrestrial spreading centers is applied to Venus conditions. On the basis of spreading rate, mantle temperature, and surface temperature, the model predicts both isostatic topography and crustal thickness. The model and Pioneer Venus altimetry and gravity data are used to test the hypothesis of Head and Crumpler (1987) that Western Aphrodite Terra is the location of crustal spreading on Venus. It is concluded that a spreading center model for Ovda Regio in Western Aphrodite Terra could account for the observed topography and line-of-sight gravity anomalies found in the Pioneer data.

Sotin, C.; Senske, D. A.; Head, J. W.; Parmentier, E. M.

1989-11-01

289

Episodic dike swarms inferred from near-bottom magnetic anomaly maps at the southern East Pacific Rise  

Microsoft Academic Search

Near-bottom, high-resolution magnetic field data gathered at the southern East Pacific Rise near 17°28'S, 18°14'S, and 18°37'S, using the autonomous underwater vehicle Autonomous Benthic Explorer (ABE) echo various geologic structures, including void space within lobate caverns, recent pillow mounds, and hydrothermal vent activity. This study is focused on a magnetic field low extending several kilometers along axis, coincident with a

Anjana K. Shah; Marie-Helene Cormier; William B. F. Ryan; Wen Jin; John Sinton; Eric Bergmanis; Julie Carlut; Al Bradley; Dana Yoerger

2003-01-01

290

Rates of continental breakup magmatism and seafloor spreading in the Norway Basin-Iceland plume interaction  

NASA Astrophysics Data System (ADS)

In year 2000, an ocean bottom seismometer (OBS) profile was acquired across the Møre margin to the Aegir Ridge, an extinct seafloor spreading axis. The margin is an early Eocene volcanic passive margin, located between the Faeroe-Iceland Ridge (FIR) and the East Jan Mayen Fracture Zone (EJMFZ). The P wave data were modeled by ray tracing to give a crustal transect showing a 10-11 km thick igneous crust created by breakup magmatism, tapering off to magma-starved seafloor spreading by C23 time (51.4 Ma). The location of the EJMFZ was reinterpreted from a satellite derived gravity map, and spreading direction in the Norway Basin reevaluated. No other fracture zones were confirmed, and both thin oceanic crust (4-5 km) and lack of fracture zones resemble ultraslow spreading on the Arctic Gakkel Ridge. Magnetic seafloor spreading anomalies were identified from the magnetic track recorded with the OBS profile, and half spreading rates were derived. Early seafloor spreading was slow (15-32 mm yr-1), approaching ultraslow (6-8 mm yr-1) by C20 time (42.7 Ma). A V-shaped pattern seen in the gravity field located only around the northern part of the Aegir Ridge corresponds to increased crustal thickness in the seismic model, recording northeast transport (3-6 mm yr-1) of more melt-fertile asthenosphere zones. The magma-starved character of the Norwegian Basin seen also during slow seafloor spreading may be the result of depletion of the asthenosphere when the Iceland plume constructed the FIR to the south, as the asthenosphere is subsequently transported into the Norway Basin.

Breivik, AsbjøRn Johan; Mjelde, Rolf; Faleide, Jan Inge; Murai, Yoshio

2006-07-01

291

Spreading process of the northern Mariana Trough: Rifting-spreading transition at 22N  

E-print Network

southward from incipient rifting to seafloor spreading within this region. This study aims to clarify of seafloor spreading after the transition. The new data set includes swath bathymetry with side- scan images is proved by seafloor-spreading fabric in the bathymetry, clear magnetic lineations, and the bull

Utrecht, Universiteit

292

The impact of the October-November 2003 intense solar storm events on the atmospheric circulation in the Pacific Southern Hemisphere Magnetic Anomaly region  

NASA Astrophysics Data System (ADS)

Evidences of the solar activity modulation of the Earth's climate have been observed on different time scales. The main solar activity mechanisms to control climate proposed to explain these observations are: (1) the variability of the total solar irradiance causing a change in the total energy input to the earth's atmosphere and consequent warming/cooling; (2) the variability of the solar ultraviolet emission and its effects on the stratospheric ozone and thermal structure; (3) the cosmic rays effects on the cloud coverage; and (4) high energy particle precipitation effects on mesospheric and stratospheric ozone in the auroral and/or southern hemisphere magnetic anomaly regions during solar storm events. It is conceivable that these mechanisms contribute to varying extends on different regions. However, the precise roles of each process during extreme solar events have not yet been investigated. Here we show that the unusual atmospheric circulation conditions over the southern Pacific and Atlantic oceans, and South America on late October and early November 2003 could be related to the large solar storm events, the Halloween events. We observed the development of anti-cyclones in the South Pacific after the onset of the main proton events. We observed also changes in the position and intensity of the Intertropical Convergence Zone and in the South Pacific Convergence zone. This result reveals that effects on the atmospheric conditions, including cloud coverage and radiative flux in the atmosphere, in the southern hemisphere magnetic anomaly region could be observed during extreme solar conditions. Previous studies suggested that the influence of solar activity on climate could be observed on decadal to millennia time scales. Our results demonstrate that the variability of the solar activity could have impact on southern hemisphere weather and climatic conditions. We anticipate our analysis to be a starting point for more sophisticated weather and climatic models. For example, the predictability of El Niño events could be tested, including its worldwide effects, based on space weather processes. Furthermore, the increase of the southern hemisphere temperature could be investigated based on changes of the Earth's magnetic field configuration.

Vieira, L. A.; da Silva, L. A.; Guarnieri, F.; Echer, E.; Prestes, A.; Dal Lago, A.; da Silva, M. R.; Schuch, N.; Wrasse, C. M.

2007-05-01

293

Effect of doping on the magnetic anomalies in Pr 1.5Ce 0.5Sr 2Cu 2NbO 10  

NASA Astrophysics Data System (ADS)

Pure Pr 1.5Ce 0.5Sr 2NbCu 2O 10 is not superconducting and magnetic susceptibility data reveal two magnetic anomalies at T(1)=11 and T N(2)=54 K. For the doped Pr 1.5Ce 0.5Sr 2Nb(Cu 1-xM x) 2O 10 where M= Fe, Zn, Cd, Ni and Ga, significant changes were observed only for the second peak which is extremely sensitive to the dopant concentration and shifted to higher temperatures. For a given M, T N(2) increases with the nominal dopant concentration. The largest shift is observed for M= Fe, e.g. for x(Fe)=0.05T N(2)=117 K. No specific correlation could be found between the temperature shift and the character of the dopant M. For substitutions made outside the CuO 2 planes no change in T N(2) occurs.

Asaf, U.; Felner, I.

1995-06-01

294

The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies  

SciTech Connect

Magnetic and gravity data, collected in south-central Washington near the Yakima Fold and Thrust Belt (YFTB) are used to model upper crustal structure, the extent of the late Columbia River Basalt flow named the Ice Harbor member, the vertical conduits (dikes) that the Ice Harbor erupted from, and whether the dikes are offset or affected by faulting on the Wallula Fault zone.

Blakely, Richard J.; Sherrod, Brian; Weaver, Craig; Wells, Ray E.; Rohay, Alan C.

2014-06-11

295

Aspects on the origin of the precursory magnetic anomalies of the Mw 6.4 Aquila earthquake  

NASA Astrophysics Data System (ADS)

An anomalous behaviour of the scaling exponent derived from the detrended fluctuation analysis (DFA) of the time series of low frequency variations of the horizontal and vertical magnetic field components has been recently reported as being observed 2 months prior to the Mw 6.3 earthquake on 6 April 2009, close to L'Aquila city, Italy. Here, we suggest a possible physical explanation of this effect based on the experience from similar measurements in Greece. In particular, for example, we compare these observations associated with Aquila earthquake with the ones of the Mw 6.6 earthquake on 13 May 1995 at Kozani-Grevena, Greece where both magnetic field variations and seismic electric signals (SES) were recorded. Almost 1 month before the latter earthquake, anomalous variations in both electric and magnetic field were detected, the time series of that were analysed by means of DFA and led to an exponent close to unity. Similarly, the calculated DFA exponent for the Aquila earthquake time series of the anomalous magnetic field variations 2 months before the main shock was also found close to unity. These results could imply that in the case of Aquila, according to the Maxwell's laws, one should expect to observe simultaneously with the magnetic signal an associated SES activity, provided that an appropriate station to monitoring the earth's electric field variations in the same area was available. Hence, it seems that similar underlying non-linear dynamic processes in mechanical and as well as electromagnetic sense, with features of criticality, dominated in both pre-focal areas.

Dologlou, Elizabeth

2014-03-01

296

An Atlas of K-Line Spectra for Cool Magnetic CP Stars: The Wing-Nib Anomaly (WNA)  

NASA Astrophysics Data System (ADS)

We present a short atlas illustrating the unusual Ca II K-line profiles in upper main-sequence stars with anomalous abundances. Slopes of the profiles for 10 cool, magnetic chemically peculiar (CP) stars change abruptly at the very core, forming a deep ``nib.'' The nibs show the same or nearly the same radial velocity as the other atomic lines. The near wings are generally more shallow than in normal stars. In three magnetic CP stars, the K lines are too weak to show this shape, although the nibs themselves are arguably present. The Ca II H lines also show deep nibs, but the profiles are complicated by the nearby, strong H? absorption. The K-line structure is nearly unchanged with phase in ? CrB and ? Cir. Calculations, including NLTE, show that other possibilities in addition to chemical stratification may yield niblike cores.

Cowley, C. R.; Hubrig, S.; Kamp, I.

2006-04-01

297

Ion-wake-induced anomaly of dust lattice mode in the presence of an external magnetic field.  

PubMed

We report a theoretical investigation of the dust lattice (DL) mode in two-dimensional Yukawa crystals in the presence of asymmetric ion flow and an external magnetic field perpendicular to the crystal plane. Two mutually perpendicular modes are found to be coupled due to Lorentz force. Interaction among the dust grains along the vertical direction of ion flow is strongly affected due to the formation of an ion wake. This causes anisotropy in interaction strength along two mutually perpendicular directions. Both hybrid modes are studied as characteristics of different ion flow speeds and magnetic field strengths. The study shows a fluctuation in DL mode frequency driven by the strength of the particle-wake interaction. The effect of ion flow on polarization of the hybrid wave amplitudes is discussed in detail. Results show a possible mechanism of anomalous phase transition in dusty plasma. PMID:24229292

Bhattacharjee, Saurav; Das, Nilakshi

2013-10-01

298

Ion-wake-induced anomaly of dust lattice mode in the presence of an external magnetic field  

NASA Astrophysics Data System (ADS)

We report a theoretical investigation of the dust lattice (DL) mode in two-dimensional Yukawa crystals in the presence of asymmetric ion flow and an external magnetic field perpendicular to the crystal plane. Two mutually perpendicular modes are found to be coupled due to Lorentz force. Interaction among the dust grains along the vertical direction of ion flow is strongly affected due to the formation of an ion wake. This causes anisotropy in interaction strength along two mutually perpendicular directions. Both hybrid modes are studied as characteristics of different ion flow speeds and magnetic field strengths. The study shows a fluctuation in DL mode frequency driven by the strength of the particle-wake interaction. The effect of ion flow on polarization of the hybrid wave amplitudes is discussed in detail. Results show a possible mechanism of anomalous phase transition in dusty plasma.

Bhattacharjee, Saurav; Das, Nilakshi

2013-10-01

299

Rock-magnetic and remanence properties of synthetic Fe-rich basalts: Implications for Mars crustal anomalies  

Microsoft Academic Search

We characterized the magnetic mineral assemblage and remanence properties of a set of synthetic samples patterned on the meteorite-derived basalt composition A?, which contains 18.9% total FeO. Basalts were synthesized at conditions that track 4 oxygen fugacity (fO2) buffer curves, from 3.4 log units below the quartz–fayalite–magnetite (QFM) buffer to 5 log units above QFM, and 6 cooling rates from 105 to

Stefanie A. Brachfeld; Julia Hammer

2006-01-01

300

6d, Coulomb branch anomaly matching  

NASA Astrophysics Data System (ADS)

6d QFTs are constrained by the analog of 't Hooft anomaly matching: all anomalies for global symmetries and metric backgrounds are constants of RG flows, and for all vacua in moduli spaces. We discuss an anomaly matching mechanism for 6d theories on their Coulomb branch. It is a global symmetry analog of Green-Schwarz-West-Sagnotti anomaly cancellation, and requires the apparent anomaly mismatch to be a perfect square, . Then ? I 8 is cancelled by making X 4 an electric/magnetic source for the tensor multiplet, so background gauge field instantons yield charged strings. This requires the coefficients in X 4 to be integrally quantized. We illustrate this for theories. We also consider the SCFTs from N small E8 instantons, verifying that the recent result for its anomaly polynomial fits with the anomaly matching mechanism.

Intriligator, Kenneth

2014-10-01

301

Octahedral distortion induced magnetic anomalies in LaMn0.5Co0.5O3 single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of LaMn0.5Co0.5O3 belonging to the ferromagnetic-insulator and distorted perovskite class were grown using a four-mirror optical float zone furnace. The as-grown crystal crystallizes into an orthorhombic Pbnm structure. The spatially resolved 2D Raman scan reveals a strain-induced distribution of transition metal (TM)-oxygen (O) octahedral deformation in the as-grown crystal. A rigorous annealing process releases the strain, thereby generating homogeneous octahedral distortion. The octahedra tilt by reducing the bond angle TM-O-TM, resulting in a decline of the exchange energy in the annealed crystal. The critical behavior is investigated from the bulk magnetization. It is found that the ground state magnetic behavior assigned to the strain-free LaMn0.5Co0.5O3 crystal is of the 3D Heisenberg kind. Strain induces mean field-like interaction in some sites, and consequently, the critical exponents deviate from the 3D Heisenberg class in the as-grown crystal. The temperature-dependent Raman scattering study reveals strong spin-phonon coupling and the existence of two magnetic ground states in the same crystal.

Manna, Kaustuv; Bhadram, Venkata Srinu; Elizabeth, Suja; Narayana, Chandrabhas; Anil Kumar, P. S.

2014-07-01

302

Spreading behaviour of the Pacific-Farallon ridge system since 83 Ma  

NASA Astrophysics Data System (ADS)

We present improved rotations, complete with uncertainties, for the Pacific-Farallon Ridge (PFR) between geomagnetic chrons 34y (83 Ma) and 10y (28.28 Ma). Despite substantial shortening since ˜55 Ma, this ridge system and its remnants (e.g. the East Pacific Rise) have produced as much as 45 per cent of all oceanic lithosphere created since the Late Cretaceous, but reconstructions face the twin challenges of extensive subduction of Farallon crust-which precludes reconstruction by fitting conjugate magnetic anomaly and fracture zone (FZ) traces-and asymmetric spreading behaviour for at least the past 51 Myr. We have calculated best-fit `half'-angle stage rotations between nine geomagnetic chron boundaries (34y, 33y, 29o, 24.3o, 20o, 18.2o, 17.1y, 13y and 10y) using combined anomaly and FZ data from both the northern and southern Pacific Plate. For rotations younger than chron 24.3o, estimates for spreading asymmetry, derived using anomaly picks from yet-to-be subducted Farallon/Nazca crust in the south Pacific, allow full stage rotations to be calculated. Between 50 and 83 Ma, where no direct constraints on spreading asymmetry are possible, a `best-fit' full stage rotation was calculated based on the net Nazca:Pacific spreading asymmetry (Pacific spreading fraction fPAC = 0.44) over the past 50 Myr, with conservative lower and upper bounds, based on variability in the degree of spreading asymmetry over periods of <15 Myr, assuming fPACs of 0.5 and 0.36, respectively. Synthetic flowlines generated from our new stage rotation produce a better match to Pacific FZ trends than previously published rotations. With the exception of the chron 18o-20o rotation, the six stage poles for rotations between chrons 33y and 13y (74-33 Ma) all cluster tightly at 60-75°E, 60-68°N, consistent with the relatively constant trend of the major Pacific FZs. This stability spans at least one episode of Farallon Plate fragmentation caused by subduction of PFR segments beneath the Americas, at 55-48 Ma, which appears to have greatly accelerated divergence on the surviving ridge without significantly affecting the location of the instantaneous rotation pole. Together with quasi-periodic 15-20 Myr variations in the degree of spreading asymmetry that also appear to correlate with changes in spreading rate, this indicates that forces other than slab pull may be a factor in determining Pacific-Farallon Plate motions.

Rowan, Christopher J.; Rowley, David B.

2014-06-01

303

Mexican-American Cooperative Program at the Cerro Prieto geothermal field: Analysis of the Nuevo Leon magnetic anomaly and its possible relation to the Cerro Prieto magmatic-hydrothermal system  

NASA Astrophysics Data System (ADS)

The broad dipolar magnetic anomaly whose positive peak is centered near Ejido Nuevo Leon, some 5 km east of the Cerro Prieto I Power Plant, has long been suspended to have a genetic relationship to the thermal source of the Cerro Prieto geothermal system. This suspicion was reinforced after several deep geothermal wells, drilled to depths of 3 to 3.5 km over the anomaly, intersected an apparent dike-sill complex consisting mainly of diabase but with minor rhyodacite. A detailed fit of the observed magnetic field to a computer model indicates that the source may be approximated by a tabular block 4 by 6 km in area, 3.7 km in depth, 2.3 km thick, and dipping slightly to the north. Mafic dike chips from one well, NL-1, were analyzed by means of electron microprobe analyses which showed them to contain a titanomagnetite that is paramagnetic at in-situ temperature conditions. As the dike mineralogy does not account for the magnetic anomaly, the magnetic source is believed to be a deeper, magnetite-rich assemblage of periodotite-gabbro plutons.

Goldstein, N. E.; Wilt, M. J.; Corrigan, D. J.

1982-10-01

304

Interpretation of CHAMP Magnetic Anomaly Data over the Pannonian Basin Region Using Lower Altitude Horizontal Gradient Data  

NASA Technical Reports Server (NTRS)

The ESA SWARM mission will have three earth orbiting magnetometer bearing satellites one in a high orbit and two side-by-side in lower orbits. These latter satellites will record a horizontal magnetic gradient. In order to determine how we can use these gradient measurements for interpretation of large geologic units we used ten years of CHAMP data to compute a horizontal gradient map over a section of southeastern Europe with our goal to interpret these data over the Pannonian Basin of Hungary.

Taylor, P. T.; Kis, K. I.; Wittmann, G.

2013-01-01

305

Curie-point depths estimated from fractal spectral analyses of magnetic anomalies in the western United States and northeast Pacific Oecan  

NASA Astrophysics Data System (ADS)

We estimate Curie-point depths (Zb) of the western United States and northeast Pacific Ocean by analyzing radially averaged amplitude spectra of magnetic anomalies based on a fractal magnetization model. The amplitude spectrum of source magnetization is proportional to the wavenumber (k) raised to a fractal exponent (-?). We first test whether long-wavelength components are captured appropriately by using variable overlapping windows ranging in sizes from 75 × 75 km2 to 200 × 200 km2. For each sliding window, the amplitude spectrum is pre-multiplied with the factor k-? prior to computation. We then use the centroid method (Tanaka et al., 1999) to calculate Zb. We find that when the window size approaches 200 × 200 km2 the resolution of estimated Zb is too low to reveal important geological features. For our study, fractal exponents larger than 0.6 will result in overcorrection. Considering the difficulty of simultaneous inversion of the depths to the top and centroid of magnetic sources (Zt and Z0 respectively) and ?, we fix ? = 0.5 for the whole study area. Note that ? here is defined for amplitude spectrum, which is equivalent to 1 for power spectrum of 2D magnetic sources. Our results show that the estimated Curie depths range from 4 km to 40 km. The average Zb in the northern part of the northeast Pacific Ocean is about 14 km below the sea level, and almost the same depths are found in the junction of the active and ancient Cascade arcs and remanent track of Yellowstone hotspot. Subduction beneath the North American plate and consequent magmatism can account for small Zb in the above mentioned volcanic arc regions. The Mendocino Triple Junction separates the northeast Pacific into northern (mainly consisting of the Explorer, Juan de Fuca and Gorda plates) and southern parts. Both the Zb and the thickness of magnetic layer in the southern part are larger than those in the northern part. This contrast is due to the fact that the Pacific plate to the south is older and colder, and has larger water depths, than the northern plates. It is noticed that a narrow E-W zone showing anomalous Zb and Zt around 44°N in Oregon might be associated with the rise of Yellowstone plume and tearing of Juan de Fuca Plate. The largest Curie depths up to about 40 km are mainly found in the southern parts of Colorado Plateaus and Middle Rocky Mountains, and these depths are well correlated to low surface heat flow. Based on the correlation curves between Curie depths and surface heat flow, we deduct that varying the fractal exponent ? from 0.5 down to 0 (in the case of random distribution of 2D magnetic sources) will increase the deducted effective average thermal conductivity of the magnetic layer from 2~3 W (m°C)-1 to 3~4 W (m°C)-1. These thermal conductivities are comparable to those measured from basalts and granites, also putting reasonable constraints on fractal exponent ? and Curie depths.

Wang, J.; Li, C.

2011-12-01

306

Unique Aeromagnetic-radar Ice-sounding Survey over the West Antarctic Ice Sheet Allows Three Dimensional Definition of Sources of Magnetic Anomalies Caused by Subglacial Volcanic Sources at the Bed of the Ice  

NASA Astrophysics Data System (ADS)

The West Antarctic Ice Sheet (WAIS) flows through the volcanically active West Antarctic Rift System (WARS). The aeromagnetic method has proven the most useful geophysical tool for studying subglacial volcanic rocks beneath the WAIS since early surveys in the 1950s. The Central West Antarctica (CWA) aerogeophysical survey covering ~354,000 km2 (about the area of Nevada and California combined) over the WAIS, consisting of a 5-km line-spaced, orthogonal set of aeromagnetic, radar ice-sounding and aerogravity measurements, is a unique Antarctic data set. This 1990-97 survey (CASERTZ and SOAR), still provides invaluable information on subglacial volcanic rocks, particularly when combined with widely spaced older aeromagnetic flight lines over a much greater area. These combined survey data indicate numerous high-amplitude (100->1000 nT), 5-50 km width, shallow-source, magnetic anomalies over a very extensive area (>1.2 x 106 km2) mostly resulting from subglacial volcanic eruptions. I interpreted the anomalies sampled in the CWA survey as defining ~1000 "volcanic centers" requiring high remanent normal magnetizations in the present field direction. About 400 of these anomaly sources (conservatively selected) are correlated with bed topography. The tops of >80% of these anomaly sources have <200 m relief at the bed of the WAIS. They appear modified by moving ice, requiring a younger age than the WAIS (~25 Ma). The 5 km by 5 km orthogonal flight line survey obviated aliasing of the magnetic and radar ice sounding data, because it is approximately equivalent to the flight elevation above the ice (1 km) surface plus the ice thickness (2-3 km); it reveals the magnetic anomalies and the tops of volcanic sources at its bed in three dimensions. Models (2 1/2 D) fit to a number of the magnetic anomalies, whose sources are at the bed of the ice sheet are constrained by topography measured by the radar ice sounding. Volcanoes in the WARS are <34 Ma, but at least four are active today. Most "volcanic centers" are buried beneath the WAIS; if a few are active today, subglacial volcanism may well have a significant effect on the WAIS regime. Aerogeophysical data (Blankenship et al., 1993, Mt. Casertz; Corr and Vaughan, 2008, near Hudson Mts.) indicated active subglacial volcanism, and suggested volcanic effects on WAIS dynamics. Future effects on the stability of the WAIS should not be ignored, as the present rapid changes resulting from global warming, could be accelerated by subglacial volcanism.

Behrendt, J. C.; Casertz; Soar Teams

2011-12-01

307

Spreading Rate versus Magma Supply in the Region of Mid-Atlantic Ridge at 16.5° N  

NASA Astrophysics Data System (ADS)

The region of Mid-Atlantic Ridge (MAR) at 16.5° N is a slow spreading center characterized by several detachment faults and oceanic core complexes. This area is ideal to study the relationship between the formation and the evolution of detachment faults, the role of magma supply during detachment faulting, and its effect on the magnetization of the crust at a slow-spreading center. In May-June 2013, during cruise KN210-05 on RV Knorr, we acquired multibeam bathymetry and sea surface magnetic anomaly data to understand the spreading history of a section of the MAR near 16.5° N. Multibeam data acquired using a SeaBeam 3012 system show that the ridge axis can be divided into a northern segment, characterized by a 4500-m deep axial valley, and a southern segment, which is characterized by a robust and continuous axial volcanic ridge which reaches to 3200 m water depth. Both segments are bordered to the west by active detachment faults. Magnetic data were acquired with a Marine Magnetics SeaSPY system, and inverted for crustal magnetization. The inversion assumes a constant thickness source layer of 0.5 km whose upper bound is bathymetry. Isochrons were identified from the magnetization map. We found that spreading rate is symmetric, and have calculated a total spreading rate in this area of ~24 km/Ma for the last 4 Ma. The central anomaly (Brunhes, 0-0.78 Ma) in the southern segment, however, has only half the predicted width of ~ 20 km and is located exclusively east of the axis. No Brunhes normal magnetization is recorded in the rift valley floor west of the axis, which is the hanging wall of the detachment. This observation confirms predictions from ';asymmetric' spreading at oceanic core complexes where slip along long-lived detachment faults take up extension on one (western) side and magmatic accretion occurs exclusively to the other (eastern) of the axis; the hanging wall, bounded by detachment fault and axis, should be as old as the core complex and its magnetization is therefore expected to be low due to its great age and likely pervasive hydrothermal alteration.

Palmiotto, C.; Schouten, H.; Smith, D. K.; Cann, J. R.; Dick, H. J.; Parnell-Turner, R. E.

2013-12-01

308

The Anatomy of the Pion Loop Hadronic Light by Light Scattering Contribution to the Muon Magnetic Anomaly  

E-print Network

This thesis investigates the Hadronic Light by Light (HLL) scattering contribution to the muon $g-2$, which is one of the most important low energy hadronic effects and consists mainly of the quark loop, the pion pole and the charged pion and kaon loops. In this work the charged pion loop has been investigated more closely. After reviewing the subject a preliminary introduction to Chiral Perturbation Theory (ChPT), Hidden Local Symmetry (HLS) model and the full Vector Meson Dominance (VMD) model is given, and they are used to calculate the pion loop HLL scattering contribution to the muon anomalous magnetic moment. The momentum regions where the contributions of the bare pion loop, the VMD model, and the HLS come from, have been studied, to understand why different models give very different results. The effects of pion polarizability and charge radius on the HLL scattering, which appear at order $p^4$ in ChPT, from $ L_9$ and $ L_{10}$ Lagrangian terms and their momentum regions have been studied.

Abyaneh, Mehran Zahiri

2012-01-01

309

The Anatomy of the Pion Loop Hadronic Light by Light Scattering Contribution to the Muon Magnetic Anomaly  

E-print Network

This thesis investigates the Hadronic Light by Light (HLL) scattering contribution to the muon $g-2$, which is one of the most important low energy hadronic effects and consists mainly of the quark loop, the pion pole and the charged pion and kaon loops. In this work the charged pion loop has been investigated more closely. After reviewing the subject a preliminary introduction to Chiral Perturbation Theory (ChPT), Hidden Local Symmetry (HLS) model and the full Vector Meson Dominance (VMD) model is given, and they are used to calculate the pion loop HLL scattering contribution to the muon anomalous magnetic moment. The momentum regions where the contributions of the bare pion loop, the VMD model, and the HLS come from, have been studied, to understand why different models give very different results. The effects of pion polarizability and charge radius on the HLL scattering, which appear at order $p^4$ in ChPT, from $ L_9$ and $ L_{10}$ Lagrangian terms and their momentum regions have been studied.

Mehran Zahiri Abyaneh

2012-08-13

310

M-sequence geomagnetic polarity time scale (MHTC12) that steadies global spreading rates and incorporates astrochronology constraints  

NASA Astrophysics Data System (ADS)

Geomagnetic polarity time scales (GPTSs) have been constructed by interpolating between dated marine magnetic anomalies assuming uniformly varying spreading rates. A strategy to obtain an optimal GPTS is to minimize spreading rate fluctuations in many ridge systems; however, this has been possible only for a few spreading centers. We describe here a Monte Carlo sampling method that overcomes this limitation and improves GPTS accuracy by incorporating information on polarity chron durations estimated from astrochronology. The sampling generates a large ensemble of GPTSs that simultaneously agree with radiometric age constraints, minimize the global variation in spreading rates, and fit polarity chron durations estimated by astrochronology. A key feature is the inclusion and propagation of data uncertainties, which weigh how each piece of information affects the resulting time scale. The average of the sampled ensemble gives a reference GPTS, and the variance of the ensemble measures the time scale uncertainty. We apply the method to construct MHTC12, an improved version of the M-sequence GPTS (Late Jurassic-Early Cretaceous, ˜160-120 Ma). This GPTS minimizes the variation in spreading rates in a global data set of magnetic lineations from the Western Pacific, North Atlantic, and Indian Ocean NW of Australia, and it also accounts for the duration of five polarity chrons established from astrochronology (CM0r through CM3r). This GPTS can be updated by repeating the Monte Carlo sampling with additional data that may become available in the future.

Malinverno, Alberto; Hildebrandt, Jordan; Tominaga, Masako; Channell, James E. T.

2012-06-01

311

High Occurrence of Aberrant Lymph Node Spread on Magnetic Resonance Lymphography in Prostate Cancer Patients With a Biochemical Recurrence After Radical Prostatectomy  

SciTech Connect

Purpose: To investigate the pattern of lymph node spread in prostate cancer patients with a biochemical recurrence after radical prostatectomy, eligible for salvage radiotherapy; and to determine whether the clinical target volume (CTV) for elective pelvic irradiation in the primary setting can be applied in the salvage setting for patients with (a high risk of) lymph node metastases. Methods and Materials: The charts of 47 prostate cancer patients with PSA recurrence after prostatectomy who had positive lymph nodes on magnetic resonance lymphography (MRL) were reviewed. Positive lymph nodes were assigned to a lymph node region according to the guidelines of the Radiation Therapy Oncology Group (RTOG) for delineation of the CTV for pelvic irradiation (RTOG-CTV). We defined four lymph node regions for positive nodes outside this RTOG-CTV: the para-aortal, proximal common iliac, pararectal, and paravesical regions. They were referred to as aberrant lymph node regions. For each patient, clinical and pathologic features were recorded, and their association with aberrant lymph drainage was investigated. The distribution of positive lymph nodes was analyzed separately for patients with a prostate-specific antigen (PSA) <1.0 ng/mL. Results: MRL detected positive aberrant lymph nodes in 37 patients (79%). In 20 patients (43%) a positive lymph node was found in the pararectal region. Higher PSA at the time of MRL was associated with the presence of positive lymph nodes in the para-aortic region (2.49 vs. 0.82 ng/mL; p = 0.007) and in the proximal common iliac region (1.95 vs. 0.59 ng/mL; p = 0.009). There were 18 patients with a PSA <1.0 ng/mL. Ten of these patients (61%) had at least one aberrant positive lymph node. Conclusion: Seventy-nine percent of the PSA-recurrent patients had at least one aberrant positive lymph node. Application of the standard RTOG-CTV for pelvic irradiation in the salvage setting therefore seems to be inappropriate.

Meijer, Hanneke J.M., E-mail: H.Meijer@rther.umcn.nl [Department of Radiation Oncology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Lin, Emile N. van [Department of Radiation Oncology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Debats, Oscar A. [Department of Radiology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Witjes, J. Alfred [Department of Urology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Span, Paul N.; Kaanders, Johannes H.A.M. [Department of Radiation Oncology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Barentsz, Jelle O. [Department of Radiology, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands)

2012-03-15

312

Chiral anomalies and differential geometry  

SciTech Connect

Some properties of chiral anomalies are described from a geometric point of view. Topics include chiral anomalies and differential forms, transformation properties of the anomalies, identification and use of the anomalies, and normalization of the anomalies. 22 references. (WHK)

Zumino, B.

1983-10-01

313

A statistical analysis of occurrence characteristics of Spread-F irregularities over Indian region  

NASA Astrophysics Data System (ADS)

We investigate the regularities of a change in Spread-F F probability during day-to-day, under varying solar variability, latitudinal behavior and their response to geomagnetic storm in equatorial and low-mid latitude stations. The occurrence characteristics of Spread-F irregularities, is obtained from daily hourly ionosonde data from a low-mid latitude station, Delhi (28.6°N, 77.2°E), for more than half a solar cycle (2001 to 2007). The latitudinal behavior of Spread-F is studied using ionosonde data from anomaly crest station, Ahmedabad (23.01°N, 72.36°E) and equatorial station, Kodaikanal (10.2°N, 77.5°E) for low, moderate and high solar activity periods. The maximum percentage occurrences of Spread-F were observed during the low solar activity year 2007, we believe, the low plasma and neutral density during 23/24 solar cycle minimum could be an important factor leading to the generation and propagation of TIDs and gravity waves. An anti-solar activity correlation to Spread-F occurrence is reported during all the seasons at different stations which are because of instability generated by the trans-equatorial meridional winds. There is a substantial variation during pre and post midnight hours in F region height from equatorial to low latitudes in response to magnetic disturbances. Concurrence was observed in the occurrence time of Spread-F to different storm events during different storm phases. The established irregularities and their behavior in Indian region are qualitatively interpreted and discussed.

Upadhayaya, A. K.; Gupta, Sumedha

2014-05-01

314

Magnetosheath Flow Anomalies in 3-D  

NASA Technical Reports Server (NTRS)

Measurements of the plasma and magnetic field with high temporal resolution on the Interball Tail probe reveal many flow anomalies in the magnetosheath. They are usually seen as flow direction and number density variations, accompanied by magnetic field discontinuities. Large flow anomalies with number density variations of factor of 2 or more and velocity variations of 100 km/s or more are seen with periodicity of about I per hour. The cases of flow anomalies following in succession are also observed, and suggest their decay while propagating through the magnetosheath. Some magnetospheric disturbances observed in the outer magnetosphere after the satellite has crossed the magnetopause on the inbound orbit suggest their association with magnetosheath flow anomalies observed in the magnetosheath prior to magnetopause crossing.

Vaisberg, O. L.; Burch, J. L.; Smirnov, V. N.; Avanov, L. A.; Moore, T. E.; Waite, J. H., Jr.; Skalsky, A. A.; Borodkova, N. L.; Coffey, V. N.; Gallagher, D. L.; Rose, M. Franklin (Technical Monitor)

2000-01-01

315

Pre-seismic geomagnetic anomaly and earthquake location  

NASA Astrophysics Data System (ADS)

Many researchers studied the relationships between appearances of geomagnetic anomalies and their distances to earthquake epicenters or faults. Yet, occasionally some magnetometer stations located nearby earthquake epicenters and/or faults do not observe geomagnetic anomalies. In this paper, a new hybrid system which simultaneously takes the hypocenter and fault plane solution into account is constructed to examine 38 earthquakes interpreted to be associated with geomagnetic anomalies during the period 1988-2001 in Taiwan. The Surface Magnetic Anomaly Reference Tip (SMART) of the new system is used instead of the epicenter or the fault to investigate statistically the distance relationship between the anomalies and the earthquake parameters. Results show that the anomalies gather along the fault and in the belt zone to the SMART. Possible mechanisms causing the anomalies in the two zones are proposed and discussed. Characteristics of the anomaly might shed some light on locations of faults before earthquake occurrences.

Chen, Chieh-Hung; Liu, Jann-Yenq; Lin, Pei-Ying; Yen, Horng-Yuan; Hattori, Katsumi; Liang, Wen-Tzong; Chen, Yuh-Ing; Yeh, Yih-Hsiung; Zeng, Xiaoping

2010-06-01

316

Conventional wisdom would say this vibration should spread out into the crystal, much the way water  

E-print Network

Conventional wisdom would say this vibration should spread out into the crystal, much the way water. The appearance of the mode coin- cides with an anomaly in the mechanical deformation behavior but has no effect

317

How Leaky Are Seafloor Spreading Center Axes?  

NASA Astrophysics Data System (ADS)

Some 500 active vent sites, both focused and diffuse, have now been located along spreading centers by either visual confirmation or instrumental detection of the discharging plume. Discovery of the large majority of these sites was made easier by high-volume discharge of particle-laden plumes. These observations led to estimates (as can be derived from the InterRidge Vents Database) of site frequency from ~0.5-5/100 km, generally increasing with spreading rate. Over the last decade, however, the increasing use of oxidation-reduction potential (ORP (mV)) (aka Eh) sensors capable of detecting minute concentrations of reduced hydrothermal chemicals (e.g., Fe+2, sulfides, Mn+2, H2, and others) suggests that these frequency estimates may be far too conservative. This hypothesis is consistent with earlier results from a few large-scale, high-resolution camera tows on some EPR segments. ORP data provide two important advantages for site identification not available with other commonly used continuously recording sensors: (1) detection of low-temperature, particle-scarce plumes, and (2) detection of reduced chemical species with very short residence times, thus increasing the location specificity of the discharge source. Here, we present high-resolution distributions of ORP anomalies observed in past plume surveys along the Eastern Lau Spreading Center (19.5°-22.5°S) in 2004 and 2008, the Galápagos Spreading Center (94.6°-86°W) in 2005/6 and 2011, as well as new data (2011) from the East Pacific Rise (9°-10°N). Except for the 2011 GSC data (a standard CTD tow-yo), all data were collected during continuous horizontal tows of ORP sensors at various depths <~120 m above the seafloor. We used two approaches to verify that ORP anomalies were authentic hydrothermal signals and not (especially in the case of small anomalies) produced by some other transient chemical anomaly. First, on the 2008 ELSC and 2011 EPR tows we compared temperature (?T) and ORP (?ORP) data from the two deepest sensors on each tow. Although temperature anomalies (?T°C) rarely exceeded 0.1°C, all sensors showed a positive correlation between ?ORP and ?T (ELSC, 1569 & 1493 mV/°C, r2~0.4; EPR, 1760 & 986 mV/°C, r2~0.6). Second, comparison of tows conducted days and years apart regularly detected anomalies at the same locations. While an exact enumeration of all sites is impossible from water column data alone, we estimate ~20 sites along 115 km of the EPR (17.5/100 km), ~40 sites along 425 km of the ELSC (9.4/100 km), and ~50 sites along 900 km of the GSC (5.5/100km). Anomalies <~1 km apart are considered as from the same source. For the EPR and ELSC surveys, these frequencies are considerably higher than expected for ridges of similar spreading rate. The higher frequencies reported here more closely match results from visual vent-mapping along 128 km of the EPR at 9°-10°N and 17°-18°S.The lower site frequency along the GSC is consistent with plume data on other ridges influenced by hotspot thermal anomalies. The aggregate mass flux of discharges from numerous small sites is unknown, and could be significant; in any case, these sites may be vital oases for hydrothermal biota.

Baker, E. T.; Resing, J. A.; Martinez, F.; Haymon, R. M.; Nakamura, K.; Walker, S. L.; Ferrini, V.

2013-12-01

318

Analysis of spacecraft anomalies  

NASA Technical Reports Server (NTRS)

The anomalies from 316 spacecraft covering the entire U.S. space program were analyzed to determine if there were any experimental or technological programs which could be implemented to remove the anomalies from future space activity. Thirty specific categories of anomalies were found to cover nearly 85 percent of all observed anomalies. Thirteen experiments were defined to deal with 17 of these categories; nine additional experiments were identified to deal with other classes of observed and anticipated anomalies. Preliminary analyses indicate that all 22 experimental programs are both technically feasible and economically viable.

Bloomquist, C. E.; Graham, W. C.

1976-01-01

319

North Cascades Geology: Sea-Floor Spreading  

NSDL National Science Digital Library

This site contains information about discoveries made after World War II when ocean-going geologists adapted sensitive magnetometers developed for antisubmarine warfare for use in seafloor research. This modern technology gave geologists their greatest boost in more than a century of field work and led to the idea of sea floor spreading. This site has animations showing sea-floor spreading and a magnetometer discovering magnetic strips. There are also diagrams showing the magnetic pattern on the ocean floor at the Juan de Fuca Ridge, Benioff-Wadati zones at continental margins, and an idealized representation of divergent plates with a resulting subduction zone.

320

Magnetic investigations  

SciTech Connect

Air and ground magnetic anomalies in the Climax stock area of the NTS help define the gross configuration of the stock and detailed configuration of magnetized rocks at the Boundary and Tippinip faults that border the stock. Magnetizations of geologic units were evaluated by measurements of magnetic properties of drill core, minimum estimates of magnetizations from ground magnetic anomalies for near surface rocks, and comparisons of measured anomalies with anomalies computed by a three-dimensional forward program. Alluvial deposits and most sedimentary rocks are nonmagnetic, but drill core measurements reveal large and irregular changes in magnetization for some quartzites and marbles. The magnetizations of quartz monzonite and granodiorite near the stock surface are weak, about 0.15 A/m, and increase at a rate of 0.00196 A/m/m to 1.55 A/m, at depths greater than 700 m (2300 ft). The volcanic rocks of the area are weakly magnetized. Aeromagnetic anomalies 850 m (2800 ft) above the stock are explained by a model consisting of five vertical prisms. Prisms 1, 2, and 3 represent the near surface outline of the stock, prism 4 is one of the models developed by Whitehill (1973), and prism 5 is modified from the model developed by Allingham and Zietz (1962). Most of the anomaly comes from unsampled and strongly-magnetized deep sources that could be either granite or metamorphosed sedimentary rocks. 48 refs., 23 figs., 3 tabs.

Bath, G.D.; Jahren, C.E.; Rosenbaum, J.G. [Geological Survey, Denver, CO (USA); Baldwin, M.J. [Fenix and Scisson, Inc., Mercury, NV (USA)

1983-12-31

321

Language-Spread Policy.  

ERIC Educational Resources Information Center

Language-spread policy (LSP) is policy promulgated by groups seeking to spread their languages to speakers or communicative domains. LSP can be internal or external, overt or disguised, and related in different ways to national policy. Intent may be to increase native-language advantage in international communication, disseminate ideology, create…

Ammon, Ulrich

1997-01-01

322

Tristan da Cunha Hotspot Tracks and the Seafloor Spreading History of the South Atlantic  

NASA Astrophysics Data System (ADS)

Careful mapping of more than 50 distinctive seafloor spreading magnetic anomalies between magnetochrons C5 and M4 has been used to develop a detailed spreading history for the South Atlantic between 15°S and 45°S and to investigate spreading axis interactions with the Tristan hotspot. Spreading appears to be roughly symmetrical with 3 separate phases identified: (1) steady spreading of ~30 mm/yr from 10 to ~45 Ma, (2) slower (15-18 mm/yr) and more variable spreading from 45 to ~70 Ma, and (3) an earlier faster spreading (45 mm/yr) from 70 to 84 Ma. C34-M0 distances provide an average value for pre-C34 spreading of ~27mm/yr. The noticeably larger C34-M0 distance on the S. American side near 32°S, 40°W is attributed to one or more eastward ridge jumps that occurred between 84 and 120 Ma. Residualized free air satellite gravity data have been used to delineate fracture zones (FZs) associated with the Early Cretaceous through Tertiary opening. More than 20 flow lines determined from these FZs intersect the magnetic lineations mapped between C5 and M4. The FZs and isochron data have been used to compute stage poles from 130 Ma to the present for both the South American and African sides, and the corresponding total reconstruction poles. Features attributed to hotspot activity on each plate have been rotated about these poles to determine when the hotspot was beneath the spreading axis. Coincident on-axis locations and the age of the underlying oceanic crust have then been used to document the history of the interaction of the Tristan hotspot with the spreading axis. In a fixed Africa reference frame the hotspot appears to move generally west-southwest. From 120 Ma to ~70 Ma, spreading was sufficiently rapid that the hotspot was maintained on or close to the ridge axis by eastward ridge jumps. From 70 to ~45 Ma the slower spreading allowed the hotspot to remain on the ridge without ridge jumps. At 45 Ma the hotspot crossed beneath the Meteor transform fault, was displaced from the ridge axis and became isolated beneath the African plate. The subsequent increase in spreading rate resulted in the hotspot remaining beneath the African plate where it has produced that part of the Walvis Ridge track between the Meteor FZ and Tristan from 45 Ma and the present. Comparison of paleolatitudes determined for Walvis Ridge features north of the Meteor FZ with the present location of Tristan suggests no significant latitudinal motion of the Tristan hotspot since ~ 80Ma. Between 130 Ma and 80Ma, however, the paleolatitude of hotspot features are roughly 10° more northerly that present day Tristan.

Hall, S. A.; Bird, D. E.

2007-12-01

323

Flame spread across liquids  

NASA Technical Reports Server (NTRS)

Recent reviews of our understanding of flame spread across liquids show that there are many unresolved issues regarding the phenomenology and causal mechanisms affecting ignition susceptibility, flame spread characteristics, and flame spread rates. One area of discrepancy is the effect of buoyancy in both the uniform and pulsating spread regimes. The approach we have taken to resolving the importance of buoyancy for these flames is: (1) normal gravity (1g) and microgravity (micro g) experiments; and (2) numerical modeling at different gravitational levels. Of special interest to this work, as discussed at the previous workshop, is the determination of whether, and under what conditions, pulsating spread occurs in micro g. Microgravity offers a unique ability to modify and control the gas-phase flow pattern by utilizing a forced air flow over the pool surface.

Ross, Howard D.; Miller, Fletcher; Schiller, David; Sirignano, William

1995-01-01

324

Deep crustal structure of the northeastern Gulf of Mexico: Implications for rift evolution and seafloor spreading  

NASA Astrophysics Data System (ADS)

image deep crustal structure using marine seismic refraction data recorded by a linear array of ocean-bottom seismometers in the Gulf of Mexico Basin Opening project (GUMBO Line 3) in order to provide new constraints on the nature of continental and oceanic crust in the northeastern Gulf of Mexico. GUMBO Line 3 extends ~524 km from the continental shelf offshore Pensacola, Florida, across the De Soto Canyon and into the central Gulf basin. Travel times from long offset, wide angle reflections and refractions resolve compressional seismic velocities and layer boundaries for sediment, crystalline crust, and upper mantle. We compare our results with coincident multichannel seismic reflection data. Our velocity model recovers shallow seismic velocities (~2.0-4.5 km/s) that we interpret as evaporites and clastic sediments. A Cretaceous carbonate platform is interpreted beneath the De Soto Canyon with seismic velocities >5.0 km/s. Crystalline continental crust thins seaward along GUMBO Line 3 from 23-10 km across the De Soto Canyon. High seismic velocity lower crust (>7.2 km/s) is interpreted as extensive syn-rift magmatism and possibly mafic underplating, common features at volcanic rift margins with high mantle potential temperatures. In the central Gulf basin we interpret thick oceanic crust (>8 km) emplaced at a slow full-spreading rate (~24 mm/yr). We suggest a sustained thermal anomaly during slow seafloor-spreading conditions led to voluminous basalt flows from a spreading ridge that overprinted seafloor magnetic anomalies in the northeastern Gulf of Mexico.

Eddy, Drew R.; Van Avendonk, Harm J. A.; Christeson, Gail L.; Norton, Ian O.; Karner, Garry D.; Johnson, Christopher A.; Snedden, John W.

2014-09-01

325

Interpretation of Mars southern highlands high amplitude magnetic field with total gradient and fractal source modeling: New insights into the magnetic mystery of Mars  

NASA Astrophysics Data System (ADS)

Using model studies, the total gradient (TG) of the Z-component magnetic field is shown to be a useful quantity for delineating sources of satellite-altitude magnetic anomalies; this field is used to constrain the location and lateral boundaries of sources of high amplitude magnetic anomalies of southern highlands of Mars. The TG field suggests two parallel linear and oppositely magnetized sources of 1000 and 1800 km length separated by 1000 km of region of intervening non-parallel sources. The simplest interpretation of the long, linear features is that they are zones of multitudinous crustal scale dikes formed in separate episodes of rifting, and not features associated with the mechanism of seafloor spreading. Forward modeling with uniformly magnetized sources suggests that magnetizations of the order of 10-50 A/m (40 km thickness) over ˜100 km width in the case of the southern source and of 12.5-27.5 A/m (40 km thickness) and ˜200 km width for the northern source are necessary to explain the Z-component amplitudes and features of the TG field. If the crustal magnetization on Mars were to be distributed fractally as on Earth, magnetizations matching the largest amplitude features on Mars may be spatially correlated from a 50-100 km distance range ( ? ˜ 3) to approaching nearly uniform magnetization ( ? ˜ 5) values. To keep magnetization intensity as small as possible, the higher end of ? values are preferred, whereas, small amplitude anomaly features could be generated from sources with ? ˜ 3. Many of the Mars anomaly features could be coalescence effects similar to the coalescence of anomaly features observed on http://icarus.cornell.edu/information/keywords.html.Earth.

Ravat, D.

2011-08-01

326

Was the Mid-Continent Rift part of a successful seafloor-spreading episode?  

NASA Astrophysics Data System (ADS)

The ~1.1 Ga Mid-Continent Rift (MCR), the 3000-km long largely-buried feature causing the largest gravity and magnetic anomaly within the North American craton, is traditionally considered a failed rift formed by isolated midplate volcanism and extension. We propose instead that the MCR formed as part of the rifting of Amazonia (Precambrian northeast South America) from Laurentia (Precambrian North America) and became inactive once seafloor spreading was established. A cusp in Laurentia's apparent polar wander path near the onset of MCR volcanism, recorded by the MCR's volcanic rocks, likely reflects the rifting. This scenario is suggested by analogy with younger rifts elsewhere and consistent with the geometry and timing of Precambrian rifting events including the MCR's extension to southwest Alabama along the East Continent Gravity High, southern Appalachian rocks having Amazonian affinities, and recent interpretation of large igneous provinces in Amazonia.

Stein, Carol; Stein, Seth; Merino, Miguel; Keller, G. Randy; Flesch, Lucy; Jurdy, Donna

2014-05-01

327

Was the Midcontinent Rift part of a successful seafloor-spreading episode?  

NASA Astrophysics Data System (ADS)

~1.1 Ga Midcontinent Rift (MCR), the 3000 km long largely buried feature causing the largest gravity and magnetic anomaly within the North American craton, is traditionally considered a failed rift formed by isolated midplate volcanism and extension. We propose instead that the MCR formed as part of the rifting of Amazonia (Precambrian northeast South America) from Laurentia (Precambrian North America) and became inactive once seafloor spreading was established. A cusp in Laurentia's apparent polar wander path near the onset of MCR volcanism, recorded by the MCR's volcanic rocks, likely reflects the rifting. This scenario is suggested by analogy with younger rifts elsewhere and consistent with the MCR's extension to northwest Alabama along the East Continent Gravity High, southern Appalachian rocks having Amazonian affinities, and recent identification of contemporaneous large igneous provinces in Amazonia.

Stein, Carol A.; Stein, Seth; Merino, Miguel; Randy Keller, G.; Flesch, Lucy M.; Jurdy, Donna M.

2014-03-01

328

Sea Floor Spreading I  

NSDL National Science Digital Library

In this introductory Excel tutorial (Activity I) students use Excel to explore the geodynamics model equation for ocean depth around a sea-floor spreading center. For students with no prior Excel experience.

Activity and Starting Point page by R.M. MacKay. Clark College, Physics and Meteorology.

329

Hot Flow Anomalies at Venus  

NASA Technical Reports Server (NTRS)

We present a multi-instrument study of a hot flow anomaly (HFA) observed by the Venus Express spacecraft in the Venusian foreshock, on 22 March 2008, incorporating both Venus Express Magnetometer and Analyzer of Space Plasmas and Energetic Atoms (ASPERA) plasma observations. Centered on an interplanetary magnetic field discontinuity with inward convective motional electric fields on both sides, with a decreased core field strength, ion observations consistent with a flow deflection, and bounded by compressive heated edges, the properties of this event are consistent with those of HFAs observed at other planets within the solar system.

Collinson, G. A.; Sibeck, David Gary; Boardsen, Scott A.; Moore, Tom; Barabash, S.; Masters, A.; Shane, N.; Slavin, J.A.; Coates, A.J.; Zhang, T. L.; Sarantos, M.

2012-01-01

330

Effects of magnetic anomalies discovered at Mars on the structure of the Martian ionosphere and solar wind interaction as follows from radio occultation experiments  

Microsoft Academic Search

The slopes of the electron density profiles obtained by radio occultation experiments at Mars revealed different variations with solar zenith angle in comparison with behavior of the electron density profiles in the magnetic field free ionosphere of Venus. The results obtained by the Mars-Global-Surveyor (MGS) spacecraft show the existence of highly variable and very localized magnetic fields of crustal origin

N. F. Ness; M. H. Acuña; J. E. P. Connerney; A. J. Kliore; T. K. Breus; A. M. Krymskii; P. Cloutier; S. J. Bauer

2000-01-01

331

The anomaly data base of screwworm information  

NASA Technical Reports Server (NTRS)

Standard statistical processing of anomaly data in the screwworm eradication data system is possible from data compiled on magnetic tapes with the Univac 1108 computer. The format and organization of the data in the data base, which is also available on dedicated disc storage, are described.

Giddings, L. E.

1976-01-01

332

Anomaly Detection for Internet Worms Yousof Al-Hammadi and Christopher Leckie  

E-print Network

Anomaly Detection for Internet Worms Yousof Al-Hammadi and Christopher Leckie ARC Special Research Victoria 3010, Australia Email: yaaa@ee.mu.oz.au, caleckie@cs.mu.oz.au Abstract Internet worms have become of worms and to reduce the worms' spread. Furthermore, existing approaches for anomaly detection of new

Aickelin, Uwe

333

Winter-to-winter recurrence of sea surface temperature, salinity and mixed layer depth anomalies  

Microsoft Academic Search

The mean seasonal cycle of mixed layer depth (MLD) in the extratropical oceans has the potential to influence temperature, salinity and mixed layer depth anomalies from one winter to the next. Temperature and salinity anomalies that form at the surface and spread throughout the deep winter mixed layer are sequestered beneath the mixed layer when it shoals in spring, and

Michael A Alexander; Michael S Timlin; James D Scott

2001-01-01

334

A Search for Anomalies  

Microsoft Academic Search

Since 1965 I have been culling systematically from the literature of science those observations that challenge reigning paradigms. The tangible result of the thousands of hours spent in libraries has been a series of Sourcebooks, Handbooks, and Catalogs that, at present, describe and evaluate roughly 2,000 anomalies— about one-half of my total collection. Some of these anomalies are truly profound

WILLIAM R. CORLISS

335

Magnetic surveys in equatorial oceanic regions: new methods, new data, and reprocessed old data (Invited)  

NASA Astrophysics Data System (ADS)

Magnetic anomalies in equatorial regions of the world’s oceans have low amplitudes in many places. This is because seafloor spreading anomalies in large parts of the Pacific and the Atlantic Ocean strike more or less north-south and thus almost parallel to the present geomagnetic field. In the near-horizontal geomagnetic field at the equator, these 2D source bodies generate only very small magnetic anomalies in the total field. To make things worse, the equatorial electrojet causes strong geomagnetic variations in the vicinity of the geomagnetic dip equator with amplitudes similar to those of the crustal field magnetic anomalies measured at the sea surface. This twofold challenge can be overcome by the use of total field gradiometers and vector magnetometers. (i) The use of gradiometers removes the temporal external variations. (ii) Vector data have the advantage of significantly higher amplitudes of magnetic anomalies in the vertical component compared to the total field. Examples of very long profiles form the central Pacific demonstrate the benefits of both methods. Since the equatorial areas with poor magnetic anomaly resolution in existing data compilations are vast and the progress in covering them with modern technology measurements is very slow, a method to improve the quality of exiting single sensor magnetic data from these regions is needed. It turns out that filtering can successfully redefine zero levels and remove trends and wavelengths from the data which are outside the wavenumber range of magnetic reversals in the crust. The reprocessing of old data is time consuming and requires individual treatment of each profile. However, it can significantly improve the data quality so that they can successfully be merged with the modern data.

Barckhausen, U.; Engels, M.

2009-12-01

336

Characterization of potential sources of magnetic anomalies within the crust in a tectonically active region: Amphibolites and migmatites from Potrillo Maar, New Mexico  

NASA Technical Reports Server (NTRS)

The purpose was to characterize the oxide mineralogy and petrology of samples collected from Potrillo Maar, New Mexico with the goal of explaining the magnetic anamoly that is observed over this region from remote sensing. Potrillo Maar is a diatreme that has brought rocks from all depths in the crust to the surface almost instantaneously. The samples are therefore thought to be representative of the crust as it exists today below this portion of the Rio Grande Rift. It is generally believed that oxide minerals (magnetite, hematite, etc.) are responsible for the magnetic signature of the crust. The samples from Portillo Maar therefore offer a unique opportunity to examine the magnetic mineralogy of the entire crust. The results indicate that the magnetic anamoly observed over Rio Grande Rift may be consequence of the tectonic activity that caused mylonitization of the rocks and allowed the infiltration of oxidizing fluids.

Spear, F. S.; Padovanni, E.

1985-01-01

337

Isotopic Anomalies in CP Stars: Helium, Mercury, Platinum, and Calcium  

E-print Network

We review the classical observational results for isotopic abundance variations for several elements in CP stars. We concentrate on the "newest" anomaly, in calcium. The cosmically very rare isotope, Ca-48 can rival and even dominate the more common, alpha nuclide, Ca-40. Relevant examples are found in the hot, non-magnetic HgMn stars, and the field horizontal-branch star, Feige 86. The calcium anomaly is also present in cool, magnetic stars, including the notorious HD 101065, Przybylski's star.

C. R. Cowley; S. Hubrig; F. Castelli

2007-11-15

338

Comparative analysis of spread-F signature and GPS scintillation occurrences at Tucumán, Argentina  

NASA Astrophysics Data System (ADS)

A deep understanding of the temporal and spatial evolution of the ionosphere can be achieved by using a multi-instrument approach which provides complementary information. Bearing this in mind, we analyze data recorded from October 2010 to September 2011, during the ascending phase of the 24th solar cycle, from an Advanced Ionospheric Sounder-Istituto Nazionale di Geofisica e Vulcanologia ionosonde and a GPS Ionospheric Scintillation and Total Electron Content (TEC) monitor receiver, located in the same site at low latitude in the Southern American longitudinal sector (Tucumán, 26.9°S, 294.6°E, magnetic latitude 15.5°S, Argentina). Such site offers the opportunity to perform combined spread-F and GPS scintillation statistics of occurrence under the southern crest of the equatorial ionospheric anomaly. Spread-F signatures, classified into four types (strong range spread-F (SSF), range spread-F, frequency spread-F (FSF), and mixed spread-F), the phase and amplitude scintillation index (?? and S4, respectively), the TEC, and the rate of TEC parameter, marker of the TEC gradients, that can cause scintillation, are considered. The seasonal behavior results as follows: the occurrence of all four types of spread-F is higher in summer and lower in winter, while the occurrence of scintillation peaks at equinoxes in the postsunset sector and shows a minimum in winter. The correspondence between SSF and scintillation seems to be systematic, and a possible correlation between S4 and FSF peaks is envisaged at the terminator. Evidence that scintillation, unlike ESF, is recorded all-day long, allows to speculate also on the relationship between the features of the sporadic E irregularities and scintillation patterns. Our results indicate that the daytime amplitude scintillation is in correspondence with the appearance of a dense Es layer, with critical frequency above 4 MHz. The investigation focused also on two particular periods, from 12 to 16 March 2011 and from 23 to 29 September 2011, both characterized by the simultaneous presence of SSF signatures and scintillation phenomena, allowing to discuss the role of traveling ionospheric disturbances as a strong candidate causing ionospheric irregularities.

Spogli, L.; Lucilla, A.; Pezzopane, M.; Romano, V.; Zuccheretti, E.; De Franceschi, G.; Cabrera, M.; Ezquer, R. G.

2013-12-01

339

9 CFR 319.762 - Ham spread, tongue spread, and similar products.  

Code of Federal Regulations, 2012 CFR

... 2012-01-01 2012-01-01 false Ham spread, tongue spread, and similar products...Meat Salads and Meat Spreads § 319.762 Ham spread, tongue spread, and similar products. “Ham Spread,” “Tongue Spread,”...

2012-01-01

340

9 CFR 319.762 - Ham spread, tongue spread, and similar products.  

... 2014-01-01 2014-01-01 false Ham spread, tongue spread, and similar products...Meat Salads and Meat Spreads § 319.762 Ham spread, tongue spread, and similar products. “Ham Spread,” “Tongue Spread,”...

2014-01-01

341

9 CFR 319.762 - Ham spread, tongue spread, and similar products.  

Code of Federal Regulations, 2010 CFR

... 2010-01-01 2010-01-01 false Ham spread, tongue spread, and similar products...Meat Salads and Meat Spreads § 319.762 Ham spread, tongue spread, and similar products. “Ham Spread,” “Tongue Spread,”...

2010-01-01

342

9 CFR 319.762 - Ham spread, tongue spread, and similar products.  

Code of Federal Regulations, 2011 CFR

... 2011-01-01 2011-01-01 false Ham spread, tongue spread, and similar products...Meat Salads and Meat Spreads § 319.762 Ham spread, tongue spread, and similar products. “Ham Spread,” “Tongue Spread,”...

2011-01-01

343

9 CFR 319.762 - Ham spread, tongue spread, and similar products.  

Code of Federal Regulations, 2013 CFR

... 2013-01-01 2013-01-01 false Ham spread, tongue spread, and similar products...Meat Salads and Meat Spreads § 319.762 Ham spread, tongue spread, and similar products. “Ham Spread,” “Tongue Spread,”...

2013-01-01

344

Infrared phonon anomaly and magnetic excitations in single-crystal Cu3Bi(SeO3)2O2Cl  

NASA Astrophysics Data System (ADS)

Infrared reflection and transmission as a function of temperature have been measured on single crystals of Cu3Bi(SeO3)2O2Cl. The complex dielectric function and optical properties along all three principal axes of the orthorhombic cell were obtained via Kramers-Kronig analysis and by fits to a Drude-Lorentz model. Below 115 K, 16 additional modes [8(E?â)+6(E?b?)+2(E??)] appear in the phonon spectra; however, powder x-ray diffraction measurements do not detect a new structure at 85 K. Potential explanations for the new phonon modes are discussed. Transmission in the far infrared as a function of temperature has revealed magnetic excitations originating below the magnetic ordering temperature (Tc˜24 K). The origin of the excitations in the magnetically ordered state will be discussed in terms of their response to different polarizations of incident light, behavior in externally applied magnetic fields, and the anisotropic magnetic properties of Cu3Bi(SeO3)2O2Cl as determined by dc susceptibility measurements.

Miller, K. H.; Stephens, P. W.; Martin, C.; Constable, E.; Lewis, R. A.; Berger, H.; Carr, G. L.; Tanner, D. B.

2012-11-01

345

Beam Spreading Devices  

NASA Astrophysics Data System (ADS)

Effective use of a particle beam for radiotherapy necessitates delivery of that beam in such a way that it covers the target volume with a prescribed dose distribution. The particle beam extracted from an accelerator normally has beam dimensions smaller than that of a typical target. Therefore, that beam has to be spread out to match the target volume. This chapter will discuss aspects of the transverse and longitudinal spreading techniques using scattering and scanning techniques and some of the devices used to implement these techniques.

Flanz, Jay

346

Equivalent magnetization over the World Ocean  

NASA Astrophysics Data System (ADS)

In another presentation (Hamoudi et al., this meeting), we present the construction of a new candidate for the World Digital Magnetic Anomaly Map (WDMAM) over oceanic areas. This map is based on: (a) a more realistic forward modeling of the marine magnetic anomalies which includes remanent magnetization vectors taking into account the age and motion of the oceanic lithosphere; (b) evaluation of the equivalent magnetization by comparison of the synthetic and observed anomalies along ship tracks; and (c) adjustment of the synthetic anomaly maps using this equivalent magnetization prior to merging with the observed anomalies. A by-product of this approach is a global distribution of equivalent magnetization over the World's Ocean. Note that, because no global basement map exists for the oceanic areas, we assume a uniform, 5 km-deep and 1 km-thick magnetized layer for the forward model. The resulting equivalent magnetization is therefore relative to this over-simplistic magnetic source. A first observation is that, within the hypotheses of the forward model, the average equivalent magnetization is about 3 A/m, a value which compares well with the Natural Remanent Magnetization (NRM) measured on ancient basalt samples. As expected, the mid-ocean ridges are marked by stronger equivalent magnetizations, an observation which reflects both the stronger NRM measured at ridge axes and their shallower bathymetry (not taken into account in our forward model). More interesting is the observation of significant along-axis variations. In the North Atlantic Ocean, the Kolbeinsey and Reykjanes ridges around Iceland are marked by a very strong equivalent magnetization and the Azores Plateau by a strong one as well.. Again this may reflect the combined effect of shallower seafloor, thicker and/or more magnetized basaltic layer at hotspots. In contrast, the areas between 45 and 55°N and between 0 and 10°N (Equatorial FZ) correspond to a weak equivalent magnetization. Further south, the Mid-Atlantic Ridge displays a more uniform signature, although off-axis variations seem associated to the Tristan and St Helena hotspots. In the Indian Ocean, a strong equivalent magnetization characterizes areas of hotspot-ridge interaction such as the Gulf of Aden, the Central Indian Ridge near Rodrigues Island, the Southwest Indian Ridge near Marion Island, and the Southeast Indian Ridge near St Paul and Amsterdam Islands. A weaker one is observed in colder area, at the Australian-Antarctic Discordance and around the Rodrigues Triple Junction. The Pacific Ocean is characterized by a generally stronger equivalent magnetization, both near ridges and in abyssal plains. Time variations, i.e. along seafloor spreading flowlines, are apparent across the Mid-Atlantic and Pacific-Antarctic ridges, with highs near the ridge axis (younger than 10 Ma) and between ~83 and 60 Ma, just after the Cretaceous Normal Superchron and lows between ~60 and 10 Ma. The Mesozoic basins of the Pacific and Atlantic oceans show a weaker equivalent magnetization before ~155 Ma and a stronger one after. Basins covered by thick sediments such as the Bengal Bay, Great Australian Bight, Nova Scotia Basin, and Western Somali Basin show a very weak equivalent magnetization, reflecting both a deeper basement and a possible thermal demagnetization. Some of these variations coincide with satellite magnetic anomalies.

Dyment, J.; Hamoudi, M.; Choi, Y.; Thebault, E.; Quesnel, Y.; Roest, W. R.; Lesur, V.

2012-12-01

347

Vascular anomalies in children.  

PubMed

The process of understanding and treating children with vascular anomalies has been hampered by confusing and occasionally incorrect terminology. The most important step when evaluating a maxillofacial vascular anomaly is to determine whether it is a tumor or a malformation. In most cases, this diagnosis can be made by history and physical examination. Selective radiographic imaging is helpful in differentiating vascular malformations or the extent of bony involvement and/or destruction. Children with vascular anomalies should be managed by an interdisciplinary team of trained providers who are committed to following, treating, and studying patients with these complex problems. PMID:22771277

Abramowicz, Shelly; Padwa, Bonnie L

2012-08-01

348

Insights about the structure and evolution of the Scotia Arc from a new magnetic data compilation  

NASA Astrophysics Data System (ADS)

Analysis of a new regional compilation of magnetic anomalies from marine, aeromagnetic and satellite data reveals the main structural/tectonic elements of the Scotia Arc. The most relevant magnetic anomaly in the continental crust, the Pacific Margin Anomaly (PMA), is related to composite magmatic arc batholiths. It was emplaced by subduction processes along the Pacific continental margin of the Antarctic Peninsula and can be followed within the continental blocks of the South Scotia Ridge and South America. Four representative magnetic profiles also show the structure in depth, and allow us to characterize the main crustal elements of the region. The new compilation and models improve our knowledge of the Scotia Arc's development. The PMA is seen to have a roughly W-E orientation, decreasing in intensity eastwards from the Pacific Margin of the Antarctic Peninsula, and extending towards the South Scotia Ridge to Discovery Bank and even to Herdman Bank. However, the identification of the PMA in the North Scotia Ridge is uncertain, since the magnetic anomalies and the modeled profiles do not support the presence of an important batholithic body. This setting can be attributed to the kinematics of subduction, almost orthogonal to the Pacific margin of the Antarctic Peninsula and oblique along the South American margin. Based on the new magnetic anomaly map, magnetic modeling, and the continuity of the PMA along the Antarctic Peninsula and South Scotia Ridge, we propose a reconstruction of the initial distribution of the main continental blocks in the initial stages during the Cretaceous. The anomalies identified in the northern Scotia Sea are probably related to local basic and/or intermediate igneous rocks intruded in pull-apart basins that developed in the South America-Antarctica plate boundary deformation zone during the initial stages of South Atlantic Ocean and Weddell Sea spreading.

Martos, Yasmina M.; Catalán, Manuel; Galindo-Zaldívar, Jesús; Maldonado, Andrés; Bohoyo, Fernando

2014-12-01

349

Long-wavelength aeromagnetic anomaly map of the conterminous United States  

NASA Astrophysics Data System (ADS)

Total intensity magnetic anomaly unflltered and low-pass filtered profile and contour maps of the conterminous United States have been prepared from data provided by the U.S. Naval Oceanographic Office's Project MAGNET Survey. The maps are useful for regional geological investigations because the anomalies, particularly on the filtered maps that emphasize long-wavelength anomalies, can be correlated with known major geologic features. The most intense positive, long-wavelength anomaly occurs over Precambrian mafic basement rocks in eastern Tennessee and Kentucky. Other examples of prominent positive anomalies occur over the Great Valley of California and the Colorado Plateau and along the Appalachian fold belt. In contrast, prominent negative long-wavelength magnetic anomalies occur over the Cascade Mountains, Mississippi Embayment, and southern Rocky Mountains and marginally to the positive anomaly related to the Mid-continent Rift.

Sexton, John L.; Hinze, William J.; von Frese, Ralph R. B.; Braile, Lawrence W.

1982-07-01

350

Salmon Spread Ingredients  

E-print Network

Salmon Spread Ingredients: 15 ounces salmon, canned 1 small onion 1 tablespoon lemon juice 1 salmon and place in a bowl. Use a fork to mash bones and remove skin. 2. Cut the ends off of the onion, and peel off the brown layers. Cut the onion in half lengthwise, and place the flat side on the cutting

Liskiewicz, Maciej

351

Systems and spread.  

PubMed

This is the fifth in a series of papers about the science of quality improvement. In this paper, we explore the issue of healthcare as a system and how this contributes to our understanding of how to spread improvement. PMID:24589145

Siriwardena, A Niroshan; Gillam, Steve

2014-01-01

352

Anomalies in vortex lattice dynamics driven by induced ac currents in superconducting films with magnetic arrays of two-fold symmetry  

NASA Astrophysics Data System (ADS)

We study the dynamics of the vortex lattice driven by ac induced currents in the critical state regime, for T > 0.70 TC. The samples are superconducting films grown on top of two-fold symmetry array of magnetic dots. In these heterostructures, the induced ac currents flow parallel to the short and to the long side of the pinning array in different areas of the samples simultaneously. This behavior produces remarkable effects in the vortex lattice dynamics. First of all, periodic features are observed in the ac susceptibility versus applied magnetic field measurements which are related to matching effects between the vortex lattices and the magnetic array. However, the vortex lattice reconfiguration observed in magnetotransport experiments is absent. Some of these features are revealed as maxima instead of being minima, indicating higher mobility at certain matching fields. Competing unstable vortex configurations could lead to increase vortex mobility precluding the reconfiguration transition. At high temperatures, where the matching effects show up, the magnetic permeability of the dots is the mechanism that governs the JC(T) behavior. Moreover, the temperature dependence of the pinning force FP(T) shows a temperature crossover related to an unexpected enhancement in vortex mobility. Vortex–vortex interaction and the interplay between trapped and interstitial vortices are a hint to explain these phenomena.

Moreno, A. J.; Chiliotte, C. E.; Pasquini, G.; Bekeris, V.; Gomez, A.; del Valle, J.; Gonzalez, E. M.; Prieto, J. L.; Vicent, J. L.

2015-01-01

353

Imaging of auriculotemporal nerve perineural spread  

PubMed Central

Importance: Adenoid cystic carcinomas (ACCs) are relatively rare tumours, notorious for wide local infiltration and perineural spread. Perineural extension commonly occurs along branches of the trigeminal and facial nerves, and its presence represents a poor prognostic factor with implications for treatment approach. Observations: We report the case of a 61-year-old female presenting with worsening left facial numbness and weakness. On magnetic resonance imaging, the patient was found to have perineural spread of a left parotid tumour along the auriculotemporal nerve. There was involvement of the V2 and V3 branches of the trigeminal nerve. An ultrasound-guided biopsy of the mass demonstrated ACC. Conclusions and relevance: The auriculotemporal nerve may serve as a route for tumour spread, particularly in the setting of head and neck malignancy. Moreover, this particular suspicion should be raised when patients with known malignancy experience concomitant trigeminal (V) and facial (VII) nerve dysfunctions. PMID:24282445

Chan, Michael; Dmytriw, Adam A.; Bartlett, Eric; Yu, Eugene

2013-01-01

354

Clinical Features and Associated Abnormalities in Children and Adolescents With Corpus Callosal Anomalies  

PubMed Central

Callosal anomalies are frequently associated with other central nervous system (CNS) and/or somatic anomalies. We retrospectively analyzed the clinical features of corpus callosal agenesis/hypoplasia accompanying other CNS and/or somatic anomalies. We reviewed the imaging and clinical information of patients who underwent brain magnetic resonance imaging in our hospital, between 2005 and 2012. Callosal anomalies were isolated in 13 patients, accompanied by other CNS anomalies in 10 patients, associated with only non-CNS somatic anomalies in four patients, and with both CNS and non-CNS abnormalities in four patients. Out of 31 patients, four developed normally, without impairments in motor or cognitive functions. Five of nine patients with cerebral palsy were accompanied by other CNS and/or somatic anomalies, and showed worse Gross Motor Function Classification System scores, compared with the other four patients with isolated callosal anomaly. In addition, patients with other CNS anomalies also had a higher seizure risk. PMID:24639939

Kim, Young Uhk; Park, Eun Sook; Jung, Soojin; Suh, Miri; Choi, Hyo Seon

2014-01-01

355

Labrador Sea: the extent of continental and oceanic crust and the timing of the onset of seafloor spreading  

Microsoft Academic Search

Regional reflection seismic profiles across the Labrador Sea originally acquired in 1977 have been reprocessed and reinterpreted. Zones of different structural style have been identified. The seismic interpretations have been used to constrain magnetic modelling and oceanic crust has been confirmed from magnetic anomaly 27N and seaward. However, all attempts to model the area landward of magnetic anomaly 27N as

James A. Chalmers; Kirsten Holt Laursen

1995-01-01

356

Complex lymphatic anomalies.  

PubMed

Complex lymphatic anomalies include several diagnoses with overlapping patterns of clinical symptoms, anatomic location, imaging features, hematologic alterations, and complications. Lymphatic malformations likely arise through anomalous embryogenesis of the lymphatic system. Analysis of clinical, imaging, histologic, and hematologic features is often needed to reach a diagnosis. Aspiration of fluid collections can readily define fluid as chylous or not. The presence of chyle indicates dysfunction at the mesenteric or retroperitoneal level or above the cisterna chyli due to reflux. The imaging patterns of generalized lymphatic anomaly (GLA) and Gorham-Stout disease have been segregated with distinctive bone lesions and peri-osseous features. More aggressive histology (spindled lymphatic endothelial cells), clinical progression, hemorrhage, or moderate hematologic changes should raise suspicion for kaposiform lymphangiomatosis. Biopsy may be needed for diagnosis, though avoidance of rib biopsy is advised to prevent iatrogenic chronic pleural effusion. Lymphangiography can visualize the anatomy and function of the lymphatic system and may identify dysfunction of the thoracic duct in central conducting lymphatic anomalies. Local control and symptom relief are targeted by resection, laser therapy, and sclerotherapy. Emerging data suggest a role for medical therapies for complications of complex lymphatic anomalies. Outcomes include recurrent effusion, infection, pain, fracture, mortality, and rarely, malignancy. Complex lymphatic anomalies present significant diagnostic and therapeutic challenges. Results from a phase 2 study of sirolimus in these and other conditions are expected in 2014. Improved characterization of natural history, predictors of poor outcomes, responses to therapy, and further clinical trials are needed for complex lymphatic anomalies. PMID:25241096

Trenor, Cameron C; Chaudry, Gulraiz

2014-08-01

357

Crustal structure and magnetic lineation along two geo-traverses from western continental margin of India to Eastern Somali Basin, NW Indian Ocean  

NASA Astrophysics Data System (ADS)

Shipborne gravity and magnetic data along two parallel geo-traverses spanning from western continental margin of India to off Seychelles are used to delineate crustal structure and magnetic pattern of major structural features - western continental margin of India, Laxmi Basin, Laxmi Ridge, Arabian Basin, slow spreading Carlsberg Ridge and Eastern Somali Basin. The seismically constrained gravity models along the geo-traverses suggest considerable variation in crustal thickness - about 38 km on continental shelf of western India to about 4 km of the Eastern Somali Basin. The Eastern Somali Basin is characterized by thin oceanic crustal thickness (~3 to 4 km) as compared to its conjugate Arabian Basin where thickness varies from 5 to 6 km. The magnetic anomalies along the geo-traverse reveal three distinct zones: (i) a zone of relative high frequency short wavelength younger anomalies over the axial parts of the Carlsberg Ridge, (ii) a zone of well developed Early Tertiary magnetic anomalies in both the Arabian and Eastern Somali basins, and (iii) relative magnetic quiet zone, between the above two zones, representing a hiatus in spreading. Based on the results, we present a comparative analysis of crustal configuration and magnetic pattern of major structural features of the study area and discuss its tectonic evolution.

Chaubey, A. K.; Anshu, A.; Sreejith, K.; Pandey, A.

2012-12-01

358

Magnetic order and lattice anomalies in the J{sub 1}-J{sub 2} model system VOMoO{sub 4}  

SciTech Connect

High-resolution x-ray and neutron powder-diffraction measurements were performed on polycrystalline VOMoO{sub 4}. Below {approx_equal}40 K the system orders in a simple Neel antiferromagnetic state (propagation vector k-vector=0), indicating a dominant role of the nearest-neighbor interactions. The order is three dimensional but the reduced saturated magnetic moment m of 0.41 (1) {mu}{sub B}/V{sup 4+} at 2 K indicates strongly two-dimensional character and enhanced quantum fluctuations. On cooling, there is no evidence of a reduction of the crystal symmetry. However, neutron diffraction indicates an anomalous evolution of the lattice parameters, which can be related to the onset of magnetic correlations.

Bombardi, A. [Diamond Light Source Ltd., Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom); Chapon, L.C. [ISIS, CCLRC Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom); Margiolaki, I.; Mazzoli, C. [European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex 9 (France); Gonthier, S.; Duc, F. [Centre d'Elaboration des Materiaux et d'Etudes Structurales, CNRS, 31055 Toulouse Cedex (France); Radaelli, P.G. [ISIS, CCLRC Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom); Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

2005-06-01

359

Strictly anomaly mediated supersymmetry breaking  

NASA Astrophysics Data System (ADS)

We consider an extension of the minimal supersymmetric Standard Model with anomaly mediation as the only source of supersymmetry breaking, and the tachyonic slepton problem solved by a gauged U(1) symmetry. The extra gauge symmetry is broken at high energies in a manner preserving supersymmetry, while also introducing both the seesaw mechanism for neutrino masses, and the Higgs ?-term. We call the model strictly anomaly mediated supersymmetry breaking. We present typical spectra for the model and compare them with those from so-called minimal anomaly mediated supersymmetry breaking. We find a Standard Model-like Higgs of mass 125 GeV with a gravitino mass of 140 TeV and tan??=16. However, the muon anomalous magnetic moment is 3? away from the experimental value. The model naturally produces a period of hybrid inflation, which can exit to a false vacuum characterized by large Higgs vacuum expectation values, reaching the true ground state after a period of thermal inflation. The scalar spectral index is reduced to approximately 0.975, and the correct abundance of neutralino dark matter can be produced by decays of thermally produced gravitinos, provided the gravitino mass (and hence the Higgs mass) is high. Naturally light cosmic strings are produced, satisfying bounds from the cosmic microwave background. The complementary pulsar timing and cosmic ray bounds require that strings decay primarily via loops into gravitational waves. Unless the loops are extremely small, the next generation pulsar timing array will rule out or detect the string-derived gravitational radiation background in this model.

Hindmarsh, Mark; Jones, D. R. Timothy

2013-04-01

360

Spread spectrum image steganography.  

PubMed

In this paper, we present a new method of digital steganography, entitled spread spectrum image steganography (SSIS). Steganography, which means "covered writing" in Greek, is the science of communicating in a hidden manner. Following a discussion of steganographic communication theory and review of existing techniques, the new method, SSIS, is introduced. This system hides and recovers a message of substantial length within digital imagery while maintaining the original image size and dynamic range. The hidden message can be recovered using appropriate keys without any knowledge of the original image. Image restoration, error-control coding, and techniques similar to spread spectrum are described, and the performance of the system is illustrated. A message embedded by this method can be in the form of text, imagery, or any other digital signal. Applications for such a data-hiding scheme include in-band captioning, covert communication, image tamperproofing, authentication, embedded control, and revision tracking. PMID:18267522

Marvel, L M; Boncelet, C R; Retter, C T

1999-01-01

361

Sea Floor Spreading  

NSDL National Science Digital Library

Sea floor spreading is demonstrated using a model consisting of two classroom desks and an 8-foot strip of paper. Changes in polarity are indicated using a felt marker. The investigation supports material presented in chapter 3, "What Heats the Earth's Interior?" in the textbook Energy flow, part of the Global System Science (GSS), an interdisciplinary course for high school students that emphasizes how scientists from a wide variety of fields work together to understand significant problems of global impact.

362

Orbital studies of lunar magnetism  

NASA Technical Reports Server (NTRS)

Limitations of present lunar magnetic maps are considered. Optimal processing of satellite derived magnetic anomaly data is also considered. Studies of coastal and core geomagnetism are discussed. Lunar remanent and induced lunar magnetization are included.

Mcleod, M. G.; Coleman, P. J., Jr.

1982-01-01

363

Survey and Interpretation Geophysical of Magnetic Isochrones 4n.2 a 2A.3 (7.9 3.6 Ma) in the Central Part of the Rivera Plate  

NASA Astrophysics Data System (ADS)

This study shows the results of six campaigns marine geophysics BABRIP06 in 2006, MAMRIV07 in 2007, MAMRIV08 in 2008, GUAYRIV10 in 2010, BATIBAJA11 in 2011 and MAMRIV12 in 2012, in the abyssal plain in the East Pacific Rise (EPR), on board the UNAM vessel, B/O El Puma. The oceanographic campaigns single beam bathymetric data collected and marine magnetic data. The results allow analyze and study the magnetic texture in the central north of the Rivera plate associated with geological structures and behavior of the seafloor to the isochronous 5A. The systematic survey of the magnetic data provided high resolution on the guidelines of the magnetic anomalies associated with cortical spreading between 7.9 and 3.6 Ma, generated by the northern segment of the East Pacific Rise (EPR), between the Rivera and Tamayo Oceanic Transformants. Multibeam bathymetry data and the acoustic reflectivity of the six campaigns are correlated with the geometry of the magnetic anomalies and seismic reflection profiles to understand the processes that formed the highlight recreational ocean in this area. The main results in this study is the identification of continuous magnetic isochrones 4n.2 to 2A.3, magnetic anomalies associated with seamounts, the geometry of the isochrones associated with a propagator and magnetic anomaly identification of isochronous 3n.3 had not been demonstrated by other oceanographic surveys. Possibly oceanic spreading rate was slower during these epochs and the identification of a cross anomaly was due to a fracture zone that generated the propagator.

Perez, D. A.; Mortera-Gutierrez, C. A.; Bandy, W. L.; Valle, S.

2013-05-01

364

PREDICTING ROOT SPREAD FROM TRUNK DIAMETER AND BRANCH SPREAD  

Microsoft Academic Search

Trunk diameter and branch crown spread were linearly correlated with root spread in honey locust (Gleditsia triancamhos var. inermis), green ash (Fraxinus pennsylvanica), poplar (Populus X generosa), red maple (Acer rubrum) and southern magnolia (Magnolia grandiflora) but not in live oak (Quercus virginiana). Maximum root spread (excluding live oak) ranged from 1.68 times the dripline forash to 3.77 for magnolia.

Edward F. Gilman

1989-01-01

365

Euro-African MAGSAT anomaly-tectonic observations  

NASA Technical Reports Server (NTRS)

Preliminary satellite (MAGSAT) scalar magnetic anomaly data are compiled and differentially reduced to radial polarization by equivalent point source inversion for comparison with tectonic data of Africa, Europe and adjacent marine areas. A number of associations are evident to constrain analyses of the tectonic features and history of the region. The Precambrian shields of Africa and Europe exhibit varied magnetic signatures. All shields are not magnetic highs and, in fact, the Baltic shield is a marked minimum. The reduced-to-the-pole magnetic map shows a marked tendency for northeasterly striking anomalies in the eastern Atlantic and adjacent Africa, which is coincident to the track of several hot spots for the past 100 million years. However, there is little consistency in the sign of the magnetic anomalies and the track of the hot spots. Comparison of the radially polarized anomalies of Africa and Europe with other reduced-to-the-pole magnetic satellite anomaly maps of the Western Hemisphere support the reconstruction of the continents prior to the origin of the present-day Atlantic Ocean in the Mesozoic Era.

Hinze, W. J.; Olivier, R.; Vonfrese, R. R. B.

1985-01-01

366

Euro-african MAGSAT Anomaly-tectonic Observations  

NASA Technical Reports Server (NTRS)

Preliminary satellite (MAGSAT) scalar magnetic anomaly data are compiled and differentially reduced to radial polarization by equivalent point source inversion for comparison with tectonic data of Africa, Europe and adjacent marine areas. A number of associations are evident to constrain analyses of the tectonic features and history of the region. The Precambrian shields of Africa and Europe exhibit varied magnetic signatures. All shields are not magnetic highs and, in fact, the Baltic shield is a marked minimum. The reduced-to-the-pole magnetic map shows a marked tendency for northeasterly striking anomalies in the eastern Atlantic and adjacent Africa, which is coincident to the track of several hot spots for the past 100 million years. However, there is little consistency in the sign of the magnetic anomalies and the track of the hot spots. Comparison of the radially polarized anomalies of Africa and Europe with other reduced-to-the-pole magnetic satellite anomaly maps of the Western Hemisphere support the reconstruction of the continents prior to the origin of the present-day Atlantic Ocean in the Mesozoic Era.

Hinze, W. J.; Vonfrese, R. R. B. (principal investigators); Olivier, R.

1984-01-01

367

Mars Crustal Remanent Magnetism: An Extinct Dynamo Leaves a Record of Field Reversals in the Heavily Cratered Highlands  

NASA Technical Reports Server (NTRS)

The Mars Global Surveyor spacecraft, in a highly elliptical polar orbit about Mars, obtained vector magnetic field measurements just above the surface of Mars (altitudes > 100 kilometers). Crustal magnetization, largely confined to the most ancient, heavily cratered Mars highlands, is frequently organized in east-west trending linear features, the largest of which extends over 2000 km. A representative set of survey passes are modeled using uniformly magnetized thin plates and a generalized inverse methodology. Crustal remanent magnetization exceeds that deduced for the largest terrestrial magnetic anomalies by more than an order of magnitude. Groups of quasi-parallel linear features of alternating magnetic polarity are found. They are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on Earth but with a much larger spatial scale.

Connerney, John E.; Acuna, Mario H.; Ness, Norman F.; Wasilewski, Peter J.

1999-01-01

368

Astrometric solar system anomalies  

SciTech Connect

There are at least four unexplained anomalies connected with astrometric data. perhaps the most disturbing is the fact that when a spacecraft on a flyby trajectory approaches the Earth within 2000 km or less, it often experiences a change in total orbital energy per unit mass. next, a secular change in the astronomical unit AU is definitely a concern. It is increasing by about 15 cm yr{sup -1}. The other two anomalies are perhaps less disturbing because of known sources of nongravitational acceleration. The first is an apparent slowing of the two Pioneer spacecraft as they exit the solar system in opposite directions. Some astronomers and physicists are convinced this effect is of concern, but many others are convinced it is produced by a nearly identical thermal emission from both spacecraft, in a direction away from the Sun, thereby producing acceleration toward the Sun. The fourth anomaly is a measured increase in the eccentricity of the Moon's orbit. Here again, an increase is expected from tidal friction in both the Earth and Moon. However, there is a reported unexplained increase that is significant at the three-sigma level. It is produent to suspect that all four anomalies have mundane explanations, or that one or more anomalies are a result of systematic error. Yet they might eventually be explained by new physics. For example, a slightly modified theory of gravitation is not ruled out, perhaps analogous to Einstein's 1916 explanation for the excess precession of Mercury's perihelion.

Nieto, Michael Martin [Los Alamos National Laboratory; Anderson, John D [PROPULSION LABORATORY

2009-01-01

369

A Waveguide Interpretation of `Temprerature-Latitude Spread F' on Equatorial Ionograms  

Microsoft Academic Search

A waveguide model is presented for propagation of radio waves along elongated irregu- larities aligned parallel to the earth's magnetic field in the equatorial ionosphere. This theory is applied to analyze the frequency spread ionograms often observed during the equatorial night, particular attention being devoted to the detailed striations of the spread; similar spread-F stria- tions on arctic ionograms are

M. L. V. Pitteway; Robert Cohen

1961-01-01

370

MAGSAT anomaly field data of the crustal properties of Australia  

NASA Technical Reports Server (NTRS)

Progress is reported in producing maps of Australia showing; crustal magnetic anomalies at constant elevation; bulk surface magnetization; and the geomagnetic field intensity, inclination and declination for the Australian region from global models of the geomagnetic field derived from MAGSAT data. The development of a data base management system is also considered.

1983-01-01

371

Dealing with Ebstein's anomaly.  

PubMed

Ebstein's anomaly is a complex congenital disorder of the tricuspid valve. Presentation in neonatal life and (early) childhood is common. Disease severity and clinical features vary widely and require a patient-tailored treatment. In this review, we describe the natural history of children and adolescents with Ebstein's anomaly, including symptoms and signs presenting at diagnosis. Current classification strategies of Ebstein's anomaly are discussed. We report on diagnostic methods for establishing the severity of disease that might enhance decision on the timing of surgical intervention. Furthermore, we describe different surgical options for severely ill neonates and multiple surgical interventions after infancy. Only with ample knowledge and understanding of the above, this complex and diverse group of patients can be correctly treated in order to improve not only duration, but also quality of life. PMID:24169373

Geerdink, Lianne M; Kapusta, Livia

2014-04-01

372

Hybrid spread spectrum radio system  

DOEpatents

Systems and methods are described for hybrid spread spectrum radio systems. A method, includes receiving a hybrid spread spectrum signal including: fast frequency hopping demodulating and direct sequence demodulating a direct sequence spread spectrum signal, wherein multiple frequency hops occur within a single data-bit time and each bit is represented by chip transmissions at multiple frequencies.

Smith, Stephen F. (London, TN) [London, TN; Dress, William B. (Camas, WA) [Camas, WA

2010-02-09

373

The Galapagos Spreading Center  

NSDL National Science Digital Library

In this lesson, with a focus on mid-ocean ridges, students will discover how new ocean floor is formed. They will study the processes involved in creating new seafloor at a mid-ocean ridge, investigate the Galapagos Spreading Center system, and understand the different types of plate motion associated with ridge segments and transform faults. This hands-on activity uses online data resources and includes: focus questions, learning objectives, teaching time, audio/visual materials needed, background information, learning procedures, evaluations, extensions, as well as resources and student handouts.

374

Analysis and interpretation of MAGSAT anomalies over north Africa  

NASA Technical Reports Server (NTRS)

Crustal anomaly detection with MAGSAT data is frustrated by inherent resolving power of the data and by contamination from external and core fields. Quality of the data might be tested by modeling specific tectonic features which produce anomalies that fall within proposed resolution and crustal amplitude capabilities of MAGSAT fields. To test this hypothesis, north African hotspots associated with Ahaggar, Tibesti and Darfur were modeled as magnetic induction anomalies. MAGSAT data were reduced by subtracting external and core fields to isolate scalar and vertical component crustal signals. Of the three volcanic areas, only the Ahaggar region had an associated anomaly of magnitude above error limits of the data. Hotspot hypothesis was tested for Ahaggar by seeing if predicted magnetic signal matched MAGSAT anomaly. Predicted model magnetic signal arising from surface topography of the uplift and the Curie isothermal surface was calculated at MAGSAT altitudes by Fourier transform technique modified to allow for variable magnetization. Curie isotherm surface was calculated using a method for temperature distribution in a moving plate above a fixed hotspot. Magnetic signal was calculated for a fixed plate as well as a number of plate velocities and directions.

Phillips, R. J.

1985-01-01

375

Chiral anomaly and diffusive magnetotransport in weyl metals.  

PubMed

We present a microscopic theory of diffusive magnetotransport in Weyl metals and clarify its relation to the chiral anomaly. We derive coupled diffusion equations for the total and axial charge densities and show that the chiral anomaly manifests as a magnetic-field-induced coupling between them. We demonstrate that a universal experimentally observable consequence of this coupling in magnetotransport in Weyl metals is a quadratic negative magnetoresistance, which will dominate all other contributions to magnetoresistance under certain conditions. PMID:25541802

Burkov, A A

2014-12-12

376

Chiral Anomaly and Diffusive Magnetotransport in Weyl Metals  

NASA Astrophysics Data System (ADS)

We present a microscopic theory of diffusive magnetotransport in Weyl metals and clarify its relation to the chiral anomaly. We derive coupled diffusion equations for the total and axial charge densities and show that the chiral anomaly manifests as a magnetic-field-induced coupling between them. We demonstrate that a universal experimentally observable consequence of this coupling in magnetotransport in Weyl metals is a quadratic negative magnetoresistance, which will dominate all other contributions to magnetoresistance under certain conditions.

Burkov, A. A.

2014-12-01

377

Three-dimensional geologic structures from inversion of gravity anomalies  

E-print Network

map showing study area and major structures in the region (Nicholas and Rozendal, 1975; Flawn et al, 1961). The interpretation of the anomaly involved the use of the inversion technique, geologic information, well logs, and seismic and magnetic...THREE-DIMENSIONAL GEOLOGIC STRUCTURES FROM INVERSION OF GRAVITY ANOMALIES A Thesis by CHARLES ALVIN HINSON Submitted to the Graduate College of Texas A8M University in partial fulfillment of the requirement for the degree of MASTER...

Hinson, Charles Alvin

1976-01-01

378

Rifts in Spreading Wax Layers  

E-print Network

We report experimental results on the rift formation between two freezing wax plates. The plates were pulled apart with constant velocity, while floating on the melt, in a way akin to the tectonic plates of the earth's crust. At slow spreading rates, a rift, initially perpendicular to the spreading direction, was found to be stable, while above a critical spreading rate a "spiky" rift with fracture zones almost parallel to the spreading direction developed. At yet higher spreading rates a second transition from the spiky rift to a zig-zag pattern occurred. In this regime the rift can be characterized by a single angle which was found to be dependent on the spreading rate. We show that the oblique spreading angles agree with a simple geometrical model. The coarsening of the zig-zag pattern over time and the three-dimensional structure of the solidified crust are also discussed.

Rolf Ragnarsson; J. Lewis Ford; Christian D. Santangelo; Eberhard Bodenschatz

1995-10-19

379

Venus - Ishtar gravity anomaly  

NASA Technical Reports Server (NTRS)

The gravity anomaly associated with Ishtar Terra on Venus is characterized, comparing line-of-sight acceleration profiles derived by differentiating Pioneer Venus Orbiter Doppler residual profiles with an Airy-compensated topographic model. The results are presented in graphs and maps, confirming the preliminary findings of Phillips et al. (1979). The isostatic compensation depth is found to be 150 + or - 30 km.

Sjogren, W. L.; Bills, B. G.; Mottinger, N. A.

1984-01-01

380

Fetal cardiac anomalies  

Microsoft Academic Search

Fetal cardiac anomalies are increasingly identified during regular obstetric scanning. About 21000 pregnancies will have an abnormality of the four chamber view and a further 11000 will have an abnormality of the great arteries. These cases can then be referred to the specialist in fetal cardiology for further evaluation and counselling. There is a higher rate of chromosomal and other

Lindsey D. Allan

1996-01-01

381

Genetics Home Reference: Peters anomaly  

MedlinePLUS

... the individuals affected with Peters anomaly have low vision early in life and about a quarter are legally blind. Due to a lack of visual stimulation, some individuals develop "lazy eye" (amblyopia). Peters anomaly ...

382

Dielectric anomalies in CoCr2O4  

NASA Astrophysics Data System (ADS)

We investigate the magnetic,dielectric, and thermodynamic properties of CoCr2O4 polycrystalline samples. AC susceptibility and specific heat measurements show the existence of two distinct magnetic transitions in this material. Neutron scattering experiments confirm a ferrimagnetic ordering transition at Tc=95 K and a transition to a spiral magnetic phase below TN 25 K. We observe a significant dielectric anomaly coincident with the onset to long-range spiral magnetic order, and a separate feature with significant thermal hysteresis above T=50 K. We associate this higher temperature dielectric anomaly with short-range spiral magnetic order, and discuss these results in the context of utilizing magnetodielectric couplings to capacitively probe short range magnetic structures.

Lawes, G.; Melot, B.; Page, K.; Ederer, C.; Hayward, M. A.; Proffen, Th.; Seshadri, R.

2006-03-01

383

Impact of relative phase shift on inward turbulent spreading  

NASA Astrophysics Data System (ADS)

The relative cross-phase between density, temperature, and potential perturbations plays a major role in turbulent spreading and transport. Nonlinear Landau-Fluid simulations show that the electron wave-particle resonances provide a relatively strong parallel damping effect on the electron temperature perturbation and can induce a relative cross-phase shift of smaller than ?/2 angle between E × B velocity and the electron temperature perturbation for large electron temperature gradient, which yields a large spreading for electron. The relative phase for ions is about ?/2 and has no turbulent spreading effect on it. The inward turbulent spreading stops at the position where the radial turbulent correlation length is shorter than the magnetic surface spacing. The temperature pedestal height determines the energy loss due to the turbulent spreading.

Ma, C. H.; Xu, X. Q.; Xi, P. W.; Xia, T. Y.

2015-01-01

384

The Interpretation and Synthesis of Certain Spread-F Configurations Appearing on Equatorial Ionograms  

Microsoft Academic Search

On ionograms obtained near the magnetic equator the rectangular configuration called 'equatorial spread F' arises from scattering in the vertical plane (passing through the iono- sonde) normal to thin, magnetic field-aligned irregularities located at or beneath the base of the F layer (Cohen and Bowles, 1961). It is shown in the present paper that some strikingly different spread-F configurations on

Wynne Calvert; Robert Cohen

1961-01-01

385

Occurrence Patterns of Topside Spread F on Alouette Ionograms  

Microsoft Academic Search

The extent and frequency of occurrence of spread F, as shown on 8400 ionograms taken by the Alouette satellite, have been investigated. These ionograms were taken during the solstice periods of December 1962 and June 1963. The spread F observed was found to be consistent with three proposed qualitative radio-propagation models. These models involve- aspect-sensitive scattering from thin magnetic-field-aligned irregularities,

James D. Hice; Bernadine Frank

1966-01-01

386

Geochemical and geophysical anomalies in the western part of the Sheep Creek Range, Lander County, Nevada  

USGS Publications Warehouse

Extensive geochemical anomalies are present along the west side of the Sheep Creek Range in Lander County, Nev. Anomalous concentrations of zinc, arsenic, mercury, silver, copper, lead, and to some extent gold, molybdenum, and antimony occur in iron-rich material along fracture planes and in quartz veins in Paleozoic formations. A magnetic anomaly occurs over a pediment at the southern part of the range, close to one of the geochemical anomalies. Gravity and electrical resistivity measurements suggest that the magnetic anomaly is caused by an intrusive igneous mass rather than by a block of downfaulted basalt. A limited amount of shallow drilling would clarify the geochemical and geophysical data.

Gott, Garland Bayard; Zablocki, Charles J.

1968-01-01

387

Magnetic vector data from the western Caribbean reveal possible origin  

NASA Astrophysics Data System (ADS)

During a cruise with RV Meteor in the spring of 2010, magnetic measurements were carried out in the central and western Caribbean with up to six magnetic sensors deployed at the same time. These were i) a towed gradiometer consisting of two Overhauser sensors, ii) two towed vector magnetometers, and iii) two shipboard oriented vector magnetometers. While the gradiometer data provide total field magnetic anomalies free from external variations, the vector data can be analyzed with different methods in the space and wavenumber domains. In the case of the towed vector data, attitude control is challenging whereas shipboard data require a very thorough compensation for the ship's magnetic field. The data were analyzed with the goal to gain insight into the origin of the basement rocks especially of the western Caribbean. Position and strike direction of magnetic anomalies in the Columbia basin possibly hold the key to distinguish between an origin of the crust in the Pacific ocean and an alternative in situ formation between the Americas. On six long profiles in the Columbia basin and adjacent regions we find consistently strike directions of the magnetic anomalies around N100°E which seems to be incompatible with a Pacific origin of the crust. Three Project Magnet aeromagnetic vector profiles crossing the research area at different angles were analyzed with the same method and yield very similar results. In our interpretation, the crust underlying the Columbia basin formed during the Cretaceous at a roughly E-W trending spreading center between the Americas. Since the crust likely formed during the Cretaceous Superchron (C 34), the strike direction we find in our data probably does not represent typical seafloor spreading anomalies. Instead we believe it is related to changes in the intensity of the Earth's magnetic field which are known to have left correlated traces in oceanic crust formed during this period. The analysis methods we used are sensitive to intensity changes just as well as to polarity changes. We can demonstrate that the data quality is high and that the strike direction signal is clear and well correlated between the different profiles and that it is also consistent between towed, shipboard, and aeromagnetic sensors.

Barckhausen, U.; Engels, U.