nT Amplitude Research Articles

Monchique alkaline magmatic intrusion (SW Iberia): Geophysical modeling and relationship with active seismicity and hydrothermalism

Monchique is a prominent 902 m topographic high in SW Iberia, which stands out in the general flat landscape of southern Portugal. It lies to the north of the Africa-Eurasia plate boundary, which locally accommodates a slow oblique convergence (∼5 mm/yr). Monchique comprises alkaline magmatic rocks of Late Cretaceous age, intruded in a post-rift context. It hosts the most active seismic cluster in mainland Portugal and important hydrothermal activity.This work investigates the relationship between the alkaline intrusion, local seismicity and hydrothermalism.We present magnetic and gravity modeling based on new drone-borne magnetic data and ground gravity data. New magnetic mapping of Monchique shows a ∼ 15 km long dipolar anomaly with 7–8 km wavelength and 2000 nT amplitude. 3D magnetic inversion models the main Monchique intrusion as a high-susceptibility body, 15 km long and 6 km wide, located below the Monchique mountain and extending 5–7 km depth. 2D forward modeling and geological interpretation further support the existence of ENE-WSW oriented dike-like gabbroic bodies that may extend deeper, around which syenite units have later emplaced.We relocate the seismicity using NonLinLoc and a 3D regional tomographic model, and find that earthquakes align along four main lineations that radiate outwards from the intrusion. We also find that most earthquakes cluster between 8 and 18 km depth, below the magmatic intrusion. The b-value at the core of the seismic cluster is higher than at the surrounding region, possibly related to the local hydrothermalism. We present five new focal mechanisms that are compatible with the regional stress field, supporting a regional tectonic control.The emplacement of the Monchique alkaline intrusion left fractures in the lithosphere that currently act as preferred pathways for fluids. In the context of the present-day stress field, the enhanced fracturing and fluid circulation facilitate the localization of small-magnitude earthquakes.

Characterizing the source of a prominent magnetic anomaly in the southwestern part of the Cuddapah basin

The total magnetic intensity anomaly (TMI) map of the Proterozoic intracratonic Cuddapah basin shows the presence of a prominent high–low–high anomaly of about 600 nT amplitude at its southern end. The source of this anomaly is inferred to be a mafic intrusive body due to a thermal plume that might have initiated the basin evolution. Though some quantitative studies have been carried out over this anomaly, the magnetic body remains ambiguous as only a part of this anomaly was modelled along the E–W direction. In present study, we model this anomaly by a 2.5D algorithm and analytical signal of the vertical integral (ASVI) of the TMI approach. A near circular outline of the causative body has been delineated by the analysis of ASVI, which also revealed three characteristic zones of the near surface irregularities. The 2.5D modelling along a SW–NE profile across the anomaly yielded the main body of about 10 km wide top at 3.5 km depth and 40 km wide at 25 km depth. The Curie temperature depth in this region is 30–40 km and this allows the source to be magnetic at this depth. It is inferred from both ASVI and modelling that the main body is bifurcated into two in its south-western part between Parnapalle and Muddanuru while it attains a lopolithic shape over the remaining part. Existing regional aeromagnetic data elucidates shape of the mafic intrusive both laterally and vertically.

Geophysical signature of the Tunnunik impact structure, Northwest Territories, Canada

AbstractIn 2011, the discovery of shatter cones confirmed the 28 km diameter Tunnunik complex impact structure, Northwest Territories, Canada. This study presents the first results of ground‐based electromagnetic, gravimetric, and magnetic surveys over this impact structure. Its central area is characterized by a ~10 km wide negative gravity anomaly of about 3 mGal amplitude, roughly corresponding to the area of shatter cones, and associated with a positive magnetic field anomaly of ~120 nT amplitude and 3 km wavelength. The latter correlates well with the location of the deepest uplifted strata, an impact‐tilted Proterozoic dolomite layer of the Shaler Supergroup exposed near the center of the structure and intruded by dolerite dykes. Locally, electromagnetic field data unveil a conductive superficial formation which corresponds to an 80–100 m thick sand layer covering the impact structure. Based on the measurements of magnetic properties of rock samples, we model the source of the magnetic anomaly as the magnetic sediments of the Shaler Supergroup combined with a core of uplifted crystalline basement with enhanced magnetization. More classically, the low gravity signature is attributed to a reduction in density measured on the brecciated target rocks and to the isolated sand formations. However, the present‐day fractured zone does not extend deeper than ~1 km in our model, indicating a possible 1.5 km of erosion since the time of impact, about 430 Ma ago.

Magnetic Field Observations on Cassini's Proximal Periapsis Passes: Planetary Period Oscillations and Mean Residual Fields

AbstractWe analyze periapsis pass magnetic field data from the final 23 orbits of the Cassini spacecraft at Saturn, uniquely encompassing auroral, subauroral, ring region, and intra‐ring field lines, to determine the planetary period oscillations (PPOs) and mean residual fields in these regions. Dual modulation by northern and southern PPO systems is found almost continuously, demonstrating for the first time the presence of PPOs on and inside ring region field lines. The azimuthal component displays the largest ~10–15nT PPO amplitudes on auroral field lines, falling across the subauroral region to ~3–5 nT on main ring field lines in the northern hemisphere, less in the southern hemisphere, while increasing to ~5–8 nT on D ring and intra‐D ring field lines. Auroral and subauroral amplitudes mapped along field lines are in good agreement with previous analyses in regions of overlap. Colatitudinal and radial field oscillations generally have a half and a quarter the amplitude of the azimuthal component, respectively. Inner region oscillation phases are typically several tens of degrees “earlier” than those of outer subauroral and auroral regions. Mean residual poloidal fields (internal and ring current fields subtracted) show quasi‐sinusoidal latitude variations of ~2.5nT amplitude, with radial and colatitudinal fields approximately in quadrature. Mean azimuthal fields peaking at ~15 nT are approximately symmetrical about the equator on and inside D ring field lines as previously reported, but are unexpectedly superposed on ~3–5nT “lagging” fields which extend continuously through the ring region onto subauroral field lines north and south.

Very weak oscillating magnetic field disrupts the magnetic compass of songbird migrants.

Previously, it has been shown that long-distance migrants, garden warblers (Sylvia borin), were disoriented in the presence of narrow-band oscillating magnetic field (1.403 MHz OMF, 190 nT) during autumn migration. This agrees with the data of previous experiments with European robins (Erithacus rubecula). In this study, we report the results of experiments with garden warblers tested under a 1.403 MHz OMF with various amplitudes (∼0.4, 1, ∼2.4, 7 and 20 nT). We found that the ability of garden warblers to orient in round arenas using the magnetic compass could be disrupted by a very weak oscillating field, such as an approximate 2.4, 7 and 20 nT OMF, but not by an OMF with an approximate 0.4 nT amplitude. The results of the present study indicate that the sensitivity threshold of the magnetic compass to the OMF lies around 2-3 nT, while in experiments with European robins the birds were disoriented in a 15 nT OMF but could choose the appropriate migratory direction when a 5 nT OMF was added to the stationary magnetic field. The radical-pair model, one of the mainstream theories of avian magnetoreception, cannot explain the sensitivity to such a low-intensity OMF, and therefore, it needs further refinement.

Mapping geoelectric fields during magnetic storms: Synthetic analysis of empirical United States impedances

AbstractEmpirical impedance tensors obtained from EarthScope magnetotelluric data at sites distributed across the midwestern United States are used to examine the feasibility of mapping magnetic storm induction of geoelectric fields. With these tensors, in order to isolate the effects of Earth conductivity structure, we perform a synthetic analysis—calculating geoelectric field variations induced by a geomagnetic field that is geographically uniform but varying sinusoidally with a chosen set of oscillation frequencies that are characteristic of magnetic storm variations. For north‐south oriented geomagnetic oscillations at a period of T0=100 s, induced geoelectric field vectors show substantial geographically distributed differences in amplitude (approximately a factor of 100), direction (up to 130∘), and phase (over a quarter wavelength). These differences are the result of three‐dimensional Earth conductivity structure, and they highlight a shortcoming of one‐dimensional conductivity models (and other synthetic models not derived from direct geophysical measurement) that are used in the evaluation of storm time geoelectric hazards for the electric power grid industry. A hypothetical extremely intense magnetic storm having 500 nT amplitude at T0=100 s would induce geoelectric fields with an average amplitude across the midwestern United States of about 2.71 V/km, but with a representative site‐to‐site range of 0.15 V/km to 16.77 V/km. Significant improvement in the evaluation of such hazards will require detailed knowledge of the Earth's interior three‐dimensional conductivity structure.

Geoscientific investigation of a remanent anomaly - Teetulpa, South Australia

We investigate a small (100 metre width) 150 nT amplitude magnetic anomaly delineated in a high-resolution aeromagnetic survey in the Teetulpa Goldfield of the southern Flinders Ranges. We believe that the anomaly is due to a kimberlite pipe, part of a field already known in the general region. As is quite common with kimberlites, the magnetization is clearly dominated by remanence. Modelling the anomaly reveals that the source is very shallow, and would have outcropped at some stage. Follow-up ground geophysical, geochemical and biogeochemical investigations are planned to establish a methodology for integrated studies as follow-up to high resolution aeromagnetic surveys.

Magnetic mapping and soil magnetometry of hydrocarbon prospective areas in western Ukraine

Magnetic measurements in a number of hydrocarbon structures suggest the existence of local magnetic anomalies with certain nT amplitude reflecting the structure contours of the oil and gas deposits, which could therefore be used as a criterion for identifying hydrocarbon traps. Hydrocarbon migration and the microseepage effect changing the composition of magnetic minerals and reaching as high as the near-surface areas and soils cause local magnetic anomalies and changes in the magnetic properties of soils. Magnetic studies on the Orchovychi oil and gas field, Carpathian Foredeep, Western Ukraine, revealed specific features of the local magnetic field and the magnetic properties of soil. A local magnetic anomaly with amplitude of 6-8 nT and a width of about 4 km was detected in the structure of the magnetic field within the Outer zone of the Carpathian Foredeep. The anomaly relates to hydrocarbon deposit areas with complex morphology. Magnetic susceptibility (MS) of soils in the Orhovychi oil and gas field showed a close correlation with landscape changes. Soils were found to show magnetic susceptibility anomalies in close proximity to productive hydrocarbon areas.

Historically largest geomagnetic sudden commencement (SC) since 1868

Being stimulated by the previously reported large amplitude (202 nT at Kakioka) geomagnetic sudden commencement (SC) on 24 March 1991, we searched larger amplitude SCs in the past. We tried to collect old magnetograms and used the list of SC observed at Kakioka (27.5° gm.lat.) for the period 1924 to 2013 and Colaba (10.5°)-Alibag (10.3°) for 1868 to 1967. We found that the largest amplitude SC occurred on 24 March (the same day as 1991 SC), 1940. The H-component amplitude is larger than 273 nT at Kakioka and 310 nT at Alibag. We could also obtain the copy of the magnetogram of Cape Town (−33.3°) which shows 164 nT amplitude. The statistical analysis shows that the occurrence rate of SCs is less than 5% for amplitude larger than 50 nT and less than 1% for amplitude larger than 100 nT at both Kakioka and Alibag. Large amplitude SCs tend to occur during the declining phase of the solar activity. Finally, we discussed the possible increase of the dynamic pressure associated with the interplanetary shock causing the largest SC.

Magnetic disturbance generation during the historic magnetic storm in September 1859

The model calculation of a magnetic disturbance, which was registered at Colaba observatory (India) during the historic giant magnetic storm on September 1–2, 1859, is illustrated. The calculation demonstrates that the observed, unusually fast, 2-h main phase of this storm, when the negative amplitude of the geomagnetic field vector H component was −1600 nT, and an extremely fast (1.5-h) initial field recovery phase from the maximum to the −110 nT amplitude can be generated. The following models of the magnetospheric current systems were used in the calculations: the ring current (DR), the magnetospheric magnetopause current (DCF), the magnetotail current system (DT), and the high-latitude current system (DP). The unusual time variation in the registered geomagnetic disturbance is related to the probable fast and considerable equatorward shift of the high-latitude currents during the main phase of the analyzed giant storm and to the same fast backward motion of these currents during the initial field recovery phase. The unusually large amplitude of the registered geomagnetic disturbance could have been caused by the total contribution of the indicated magnetospheric current systems during the time when the storm was generated as a result of the interaction between the magnetosphere and the solar plasma ejected during the gigantic solar flare before the storm.

Magnetic Investigations of Buried Palaeohearths Inside a Palaeolithic Cave (Lazaret, Nice, France)

ABSTRACTWe present a magnetic study of palaeohearths within Lazaret cave (Nice, France) that demonstrates how to recognize fired structures in similar geological contexts. Using magnetic field and susceptibility mapping, excavated and potentially still‐buried palaeohearths of the cave are investigated. Our study reveals some difficulties in conducting a magnetic field survey to detect combustion features in a cave due to noise and ambiguities in anomaly assignment. To overcome these difficulties, discrete measurements and a specific post‐processing methodology were applied to remove the magnetic noise generated by surrounding artificial sources. In addition, experimental and numerical modelling constrained by laboratory examinations of the magnetic mineralogy were performed to better identify the magnetic imprint of such fireplaces. We confirm that a short‐term fireplace produces a thin ash‐bearing layer characterized by a high magnetic susceptibility and a high frequency dependence due to a large proportion of grains of pseudo‐single‐domain (PSD) size. Such a burnt soil layer is the main source of the ca. 50 nT amplitude magnetic field anomaly at a sensor height of 15 cm observed over the excavated palaeohearth, as well as over an experimental hearth. Copyright © 2013 John Wiley & Sons, Ltd.

Physiological Magnetic Stimulation for Arousal of Elderly Car Driver Evaluated With Electro-Encephalogram and Spine Magnetic Field

Reliable evaluation for the arousal effect of magnetized olivine-crushed-stone-crammed vinyl pipe set on an elderly car driver's spine has been carried out measuring a four-points electroencephalogram using driving simulators considering a defined arousal index β/(δ+θ) . A sintered-magnetized-spherical-particles-crammed pipe is developed for realization of periodically pulse distributed surface magnetic field train matching with the magneto-protonics principle. Transition of the magnetic field time series generated from the spine with application of the physiological magnetic stimulation have also been measured using the amorphous wire and CMOS IC based pico-Tesla resolution magneto-impedance sensor, in which existence of alternative areas of cooperativeness and anti-cooperativeness for transition of the arousal index each other along the spine length direction is suggested. A special point on the central spine generating a large bio magnetic field of around 10 nT amplitude as well as corresponding pit of the stomach position was found.

Control of the energetic proton flux in the inner radiation belt by artificial means

Earth's inner radiation belt located inside L = 2 is dominated by a relatively stable flux of trapped protons with energy from a few to over 100 MeV. Radiation effects in spacecraft electronics caused by the inner radiation belt protons are the major cause of performance anomalies and lifetime of Low Earth Orbit satellites. For electronic components with large feature size, of the order of a micron, anomalies occur mainly when crossing the South Atlantic Anomaly. However, current and future commercial electronic systems are incorporating components with submicron size features. Such systems cannot function in the presence of the trapped 30–100 MeV protons, as hardening against such high‐energy protons is essentially impractical. The paper discusses the basic physics of the interaction of high‐energy protons with low‐frequency Shear Alfven Wave (SAW) under conditions prevailing in the radiation belts. Such waves are observed mainly in the outer belt, and it is believed that they are excited by an Alfven Ion Cyclotron instability driven by anisotropic equatorially trapped energetic protons. The paper derives the bounce and drift‐averaged diffusion coefficients and uses them to determine the proton lifetime as a function of the spectrum and amplitude of the volume‐averaged SAW resonant with the trapped energetic protons. The theory is applied to the outer and inner radiation belts. It is found that the resonant interaction of observed SAW with nT amplitude in the outer belt results in low flux of trapped protons by restricting their lifetime to periods shorter than days. A similar analysis for the inner radiation belt indicates that broadband SAW in the 1–10 Hz frequency range and average amplitude of 25 pT would reduce the trapped energetic proton flux by more than an order of magnitude within 2 to 3 years. In the absence of naturally occurring SAW waves, such reduction can be achieved by injecting such waves from ground‐based transmitters. The analysis indicates that such reduction requires injection of less than 10 kW of SAW power. Increasing the power will result in the further decrease of the trapped flux. The paper concludes with a brief discussion of techniques that can inject such waves using ground‐based transmitters.

Regular daily variations in satellite magnetic total intensity data

Abstract. Regular magnetic daily quiet time (Sq) variations in total intensity of about 30 nT amplitude are determined in Universal Time (UT) from satellite magnetic field measurements. The CHAMP satellite traverses all hours of local time in 132 days and the Sq variations in total intensity are therefore calculated as an average over the 132 days for each hour of UT. Results are compared with the Sq daily variations in total intensity for the region above the ionosphere calculated from Malin's (1973) spherical harmonic analysis of the Sq Fourier coefficients for hourly mean value magnetic data from a global distribution of ground-based magnetic observatories. From the reasonable agreement between the two calculations, we conclude that low-Earth orbit satellites that traverse all hours of local time can determine Sq variations in total intensity above the ionosphere.

In-flight calibration of the NEAR magnetometer

The science objectives for the Near Earth Asteroid Rendezvous (NEAR) Magnetometer Experiment (MAG) are to measure a possible magnetic field of 433 Eros to 5 nT accuracy and secondarily to detect asteroid-solar wind interaction signatures. Because the MAG sensor is body mounted, achieving this accuracy required detailed analysis of spacecraft magnetic fields during cruise. Sources of magnetic contamination identified prior to launch and during cruise are: propulsion latch valves, fixed 190 nT residual held, solar arrays and power harness, variable 15 to 60 nT field, power distribution terminal board, /spl sim/30 nT field with 5 nT variations, power shunting circuitry, 1-5 nT variations, the MAG sensor survival heater, 6 nT steps and attitude control momentum wheels, and 1 nT amplitude at 0.5 to 10 Hz from each of four wheels. Analysis of cruise data was used to create accurate /spl plusmn/1 nT models for the fixed and variable fields with signals below 0.5 Hz to provide correction of the raw data. The spacecraft field corrections and MAG calibration were validated with data from the Earth swing-by of January 1997. Comparison of solar wind magnetic held measurements from the WIND spacecraft and NEAR from January 22-24, 1997, before and after the Earth swing-by maneuver, confirm that the resulting NEAR magnetic field measurements are accurate to 1-2 nT.

Upper crust of the Pilbara Craton, Australia; 3D geometry of a granite/greenstone terrain

The Pilbara Craton in Northwest Australia is a 600×550 km region of early-mid Archaean granite/greenstone terrain, dominated by granite domes, and in part covered by younger rocks. Gravity and magnetic anomalies are used to map the granite/greenstone surface under cover, and infer the depth extent of the granite/greenstone structures. A published seismic refraction interpretation gives a two layer crust for the Pilbara Craton, with the layers separated by a velocity gradient at about 14 km. Some magnetic anomalies have a 1000–3600 nT amplitude, a width at one-half amplitude of 9 km, and a strike length of >100 km. Their causative bodies have a top at 1–2 km, an average apparent susceptibility of 0.1–0.2 (SI), and importantly a base about 14 km. The magnetic material is thought to be a small proportion of banded iron formation within the greenstone belts. Gravity anomalies are interpreted to indicate that granite margins are generally steep, and many granites have a base at a similar level to one another. The shape of the gravity anomalies over the granite/greenstone boundaries, and the amplitude of the anomalies (up to 650 μm s −2) together with the inferred granite/greenstone density contrast, are consistent with both the granites and greenstones extending to a depth of 14 km. The domes are therefore vertical cylinders extending to mid-crustal depths. The great depth of the greenstone belts is consistent with the domal structure being due to convective crustal overturn. The Pilbara Craton may be unusual, because greenstone belts elsewhere in the world have smaller amplitude gravity anomalies (commonly 200–400 μm s −2), a shallower inferred base to the greenstone belt (generally <8 km), and the base of the greenstone belt is thought to be truncated.

Record of a previously unidentified short geomagnetic event from an upper Miocene sedimentary sequence, and preferred path of the transitional VGPs

Numerous short features in the ocean magnetic anomaly patterns (25–100 nT amplitude, 8–25 km wavelength: tiny wiggles) have been identified in several independent magnetic profiles, and have been modelled either as short polarity intervals (‘cryptochrons’) or as palaeointensity fluctuations (Cande & Kent 1992). In the last few years, several authors (e.g. Tauxe et al. 1994; Lowrie & Lanci 1994; Hartl, Tauxe & Constable 1993) have identified, on high-resolution magnetostratigraphic sections, short polarity intervals, correlated with cryptochrons deriving from the ocean floor. The record of a previously undetected short normal-polarity event, lasting about 11 kyr, from an upper Tortonian-lower Messinian sedimentary sequence (e.g. Compagnoni et al. 1992) in central Italy (42.0°N, 13.0°E), is reported here. The north virtual geomagnetic polar (VGP) path of the R-N transition appears to be strongly confined to a meridian band passing over the Americas about 90° away from the site longitude, as reported in recent years for a large number of reversals. This short feature is lacking in the corresponding ocean-floor magnetic anomaly patterns, probably because of the difficulties of resolving polarity intervals as short as this one in ocean magnetic profiles.

Analysis of multi-channel seismic refection and magnetic data along 13� N latitude across the bay of bengal

Analysis of the multi-channel seismic reflection, magnetic and bathymetric data collected along a transect, 1110 km long parallel to 13° N latitude across the Bay of Bengal was made. The transect is from the continental shelf off Madras to the continental slope off Andaman Island in water depths of 525 m to 3350 m and across the Western Basin (bounded by foot of the continental slope of Madras and 85° E Ridge), the 85° E Ridge, the Central Basin (between the 85° E Ridge and the Ninetyeast Ridge), the Ninetyeast Ridge and the Sunda Arc. The study revealed eight seismic sequences, H1 to H8 of parallel continuous to discontinuous reflectors. Considering especially depth to the horizons, nature of reflection and on comparison with the published seismic reflection results of Currayet al. (1982), the early Eocene (P) and Miocene (M) unconformities and the base of the Quaternary sediments (Q) are identified on the seismic section. Marked changes in velocities also occur at their boundaries. In the Western Basin the acoustic basement deepening landward is inferred as a crystalline basement overlain by about 6.7 km of sediment. In the Central Basin possibly thicker sediments than in the Western Basin are estimated. The sediments in the Sunda Arc area are relatively thick and appears to have no distinct horizons. But the entire sedimentary section appears to be consisting of folded and possibly faulted layers. The comparatively broader wavelength magnetic anomalies of the Central Basin also indicate deeper depth of their origin. Very prominent double humped feature of the 85° E Ridge and broad basement swell of the Ninetyeast Ridge are buried under about 2.8 km thick sediments except over the prominent basement high near 92° E longitude. The positive structural relief of the buried 85° E Ridge in the area is reflected in magnetic signature of about 450 nT amplitude. Flexural bulge of the 85° E Ridge and subsidence of the Ninetyeast Ridge about 24 cm my−1 rate since early Eocene period have been inferred from the seismic sequence analysis.

A new method for determining magnetization direction from gravity and magnetic anomalies: application to the deep structure of the Worcester Graben

The aeromagnetic field over the Worcester Graben, a major N-S-oriented, fault-bounded sedimentary basin, shows a large positive anomaly of 100 nT amplitude near the town of Tetbury. A new method for the determination of the magnetization direction of the causative body was employed that searches for the maximum correlation between the observed gravity anomaly and the pseudo-gravity anomaly computed for a range of orientations of the magnetization vector. The method suggests a vertical magnetization for the causative body of the Tetbury anomaly. A three-dimensional magnetic model of the body has the form of a cone, elongated N-S, whose base is at 6.0 km and upper surface at 3.1 km as indicated by power spectrum analysis of the anomaly. A two-dimensional model derived from the gravity field and constrained by the surface geology, borehole data and existing density measurements cannot simulate the observed anomaly over the centre of the graben. However, when the magnetic body is included in the gravity model, the fit is much improved. The western side of the body is probably imaged on a seismic reflection profile to the north. The body magnetic model of the body has the form of a cone, elongated N-S, whose base is at 6.0 km and upper surface at 3.1 km as indicated by power spectrum analysis of the anomaly. A two-dimensional

Ultrahigh resolution marine magnetic anomaly profiles: A record of continuous paleointensity variations?

A distinctive pattern of small‐scale marine magnetic anomalies (25–100 nT amplitude, 8–25 km wavelength: tiny wiggles) is superimposed on the more generally recognized seafloor spreading pattern between anomalies 24 and 27 in the Indian Ocean. By normalizing and stacking multiple profiles, it is demonstrated that this pattern of tiny wiggles is a high‐resolution recording of paleodipole field behavior between chrons C24 and C27. The pattern of tiny wiggles between anomalies 26 and 27 is compared to an ultrafast spreading (82 mm/yr half rate) profile from the southeast Pacific where a similar signal is observed, confirming the paleodipole field origin of the anomalies. Two basic models are considered in which the tiny wiggles are attributed either to short polarity intervals or to paleointensity fluctuations. We conclude that tiny wiggles are most likely caused by paleointensity fluctuations of the dipole field and are a ubiquitous background signal to most fast spreading magnetic profiles. The implications of this study are that (1) tiny wiggles may provide information on the temporal evolution of the geomagnetic dynamo; (2) the small‐scale anomalies observed in the Jurassic quiet zones may be due to paleointensity fluctuations; (3) tiny wiggles are potential time markers in large regions of uniform crustal polarity such as the Cretaceous quiet zones; and (4) much of the variance in anomaly profiles normally attributed to crustal emplacement processes, particularly at fast and ultrafast spreading rates, is actually due to intensity variations in the paleomagnetic field.