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  • 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals  (9)
  • AGU  (7)
  • Blackwell Publishing  (2)
  • American Association for the Advancement of Science
  • Espoo : Geologian tutkimuskeskus
  • Irkutsk : Ross. Akad. Nauk, Sibirskoe Otd., Inst. Zemnoj Kory
  • Krefeld : Geologischer Dienst Nordhein-Westfalen
  • Lower Hutt : Institute of Geological and Nuclear Sciences
  • 2005-2009  (9)
  • 1955-1959
Collection
Keywords
Publisher
Years
  • 2005-2009  (9)
  • 1955-1959
Year
  • 1
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    Geomagnetic jerks in the polar regions (2009)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: The occurrence of geomagnetic jerks over the Arctic and Antarctic regions is here investigated. Maps of geomagnetic secular acceleration over the polar regions are produced from the CM4 and CHAOS models and the occurrence of geomagnetic jerks is associated with jumps in secular acceleration. The obtained results confirm that in Antarctica geomagnetic jerks systematically follow geomagnetic jerks in the Arctic region with a time delay from one to three years. Evidence is found of an abrupt change in secular acceleration in both polar regions around 1985, suggesting that the 1985 local jerk could actually be a worldwide event. Combining our results with the results previously obtained on the occurrence of a geomagnetic jerk at low-mid latitudes around 2003, we support the hypothesis of a global extension of an event occurred at the beginning of the 21st century.
    Description: Published
    Description: L15304
    Description: 3.4. Geomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: geomagnetic jerks ; magnetic global models ; geomagnetic secular variation ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.03. Global and regional models ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    A global analysis of the 1991 geomagnetic jerk (2008)
    Blackwell Publishing
    Details
    Publication Date: 2017-04-04
    Description: A recent examination of the geomagnetic annual mean values for the European magnetic observatories has shown the existence of a sudden change in the secular acceleration in about 1991 (Cafarella & Meloni 1995; Macmillian 1996). Using first differences of the Y (east geomagnetic field component) mean values from 74 observatories, the worldwide character of the 1991 impulse has been determined (De Michelis et al. 1998). Using data from 109 observatories widely distributed all over the world, the structure of the secular variation for the X (north) and Z (vertical) magnetic field intensities around 1990 was investigated, and evidence of this most recent jerk was found. External effects were removed from the annual mean data by comparing the long-term variations of the geomagnetic field components at individual observatories with the long-term variations of two geomagnetic indices, aa and Dst, and of a solar index, the Wolf number R. A careful analysis has been carried out on the amplitude of the external disturbance, on its dependence on latitude, and on the weights of the geomagnetic indices in the evaluation of the resulting external field. The secular variation has been evaluated from the corrected annual means. Around 1990, the secular variation can be fitted at many observatories by two straight lines with a sudden and marked change in slope. In this manner the jerk occurrence time and the intensity of the step in the second time derivative (∆X", ∆Y" and ∆Z") were computed. Maps of ∆X", ∆Y" and ∆Z" provide information on the worldwide intensity distribution of the examined event. Maps of the jerk occurrence-time distributions are also given. The mean jerk occurrence time is 1990.1±0.6. Finally, a spherical harmonic analysis was used to complete the quantitative description of this phenomenon in order to study the trend of the energy density spectrum as a function of the harmonic degree n.
    Description: Published
    Description: 545-556
    Description: 3.4. Geomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: geomagnetic variation ; geomagnetism ; jerk ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Multifractality and Punctuated Equilibrium in the Earth's Magnetic Field Polarity Reversals (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: The Earth's magnetic field has reversed its polarity hundreds of times in the Earth's history. This phenomenon is generally viewed as due to a Poisson nonstationary process. Here, the geomagnetic chron time length sequence for the past 166 Ma, is analyzed using a multifractal approach, based on "singularity analysis". The existence of a multifractal structure is the signature of the occurrence of "punctuated equilibrium", which can be read as an indication of a critical configuration of the geodynamo. The results obtained are compared with those from a prototypical model of a dynamical system, introduced by Seki & Ito [1993], and are discussed in the context of fluid motions within the Earth's outer liquid core.
    Description: Published
    Description: 293-296
    Description: 3.4. Geomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: Magnetic field polarity reversals ; Multifractal approach ; Punctuated equilibrium ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Assessing the timing of greigite formation and the reliability of the Upper Olduvai polarity transition record from the Crostolo River, Italy (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: The Crostolo River section in Italy yielded a detailed record of the Upper Olduvai geomagnetic polarity transition that has been used to support the hypothesis of deep mantle control on the transitional geomagnetic field. The paleomagnetic record is carried by the authigenic iron sulphide, greigite, which was interpreted to have formed shortly after deposition. Our detailed scanning electron microscope investigations indicate the presence of at least 3 generations of pyrite, which usually forms with greigite as a precursor. This suggests that the total magnetization is a complex composite that produced a smoothed record of transitional field behaviour.
    Description: Published
    Description: L05307
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: greigite ; Upper Olduvai polarity transition ; Crostolo river ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Worldwide character of the 1991 geomagnetic jerk (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: A recent examination of the geomagnetic element annual mean values fbr the European magnetic observatories, has shown the existence of a sudden change in the secular acceleration at about 1991. In this work the space time character of the 1991 impulse is investigated and its worldwide character is evidenced; an evaluation of the amplitude spatial distribution is given for the Y component, analysing data relative to 74 magnetic observatories. The external effects were removed from the annual mean data and successively the Y secular variation has been evaluated from the corrected annual means. Moreover the worldwide character of the intensity of the step in the second time derivative is compared with the character of the previous well known jerk events of 1969 and 1978.
    Description: Published
    Description: 377-380
    Description: 3.4. Geomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: Geomagnetic field ; Secular variation ; Geomagnetic jerk ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 6
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    Reply to Comment by M. Dumberry (2008)
    AGU
    In:  Reply to Comment on “Could the Mw = 9.3 Sumatra Earthquake Trigger a Geomagnetic Jerk?”
    Details
    Publication Date: 2017-04-04
    Description: We thank M. Dumberry for providing the opportunity to discuss further the article [Florindo et al., 2005] in which we suggested that the Sumatra earthquake could have triggered a geomagnetic jerk. Dumberry is against our hypothesis for different reasons: (1) The displacement pattern produced by this earthquake is incompatible with the core-mantle boundary (CMB) deformations required for a torsional oscillation; (2) most of the deformations occurred locally, producing an actual mass displacement that has not involved the entire Earth; and (3) no abrupt change in the length of day (LOD) has been observed after this event. Although we agree with some of the considerations proposed by Dumberry, we think that these do not rule out the possibility that a jerk has been triggered by the Sumatra earthquake or that in the future, other earthquakes could induce a change in the flow pattern near the CMB leading to a geomagnetic jerk. On the contrary, we retain that this hypothesis is plausible, although it is more correct to talk about the existence of a possible link between geomagnetic jerks and earthquakes where the earthquake magnitude is not the only discriminating parameter.
    Description: Published
    Description: 343
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: 3.4. Geomagnetismo
    Description: N/A or not JCR
    Description: reserved
    Keywords: Sumatra Earthquake ; Geomagnetic Jerk ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 7
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    Holocene eruptive history of the Stromboli volcano: Constraints from paleomagnetic dating (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: We report on paleomagnetic directions gathered from 33 sites from (mostly Holocene) volcanics from Stromboli, loosely dated at present by few K/Ar and 14C ages. In order to provide dating, the paleomagnetic directions were compared to the Holocene paleosecular variation of the geomagnetic field for the Mediterranean region, derived from direct geomagnetic observations and several archeomagnetic-paleomagnetic data sets. Petrochemical analyses from the paleomagnetic specimens revealed that each Holocene eruptive cycle of Stromboli was characterized by peculiar chemical characteristics. We suggest that before the 20th century AD paroxysms, powerful spatter-forming eruption(s) occurred during the 17th century AD, followed by three centuries of less energetic eruptions, when spattering was limited to the summit cones. A robust data set (4 sites, 52 samples) from the S. Bartolo flow, partially buried below the Stromboli village, constrains its age to 360 BC to 7 AD, in Greek-Roman times. The ca. 6200 years BP age inferred for a scoria exposed below a characteristic pyroclastic succession suggests its correlation with the Secche di Lazzaro pyroclastics, a major phreatomagmatic eruption occurring during the 6th millennium BP, synchronous with the major volcanotectonic collapse of the Sciara del Fuoco. Ages were provided for many lavas from the Neostromboli sequence (including the Labronzo, Nel Cannestrà, and Ginostra flows), indicating that huge effusive activity from lateral fissures fed by an evolving magma chamber occurred in the 6200–8000 years BP time window. The absence of volcanics with ages comprised between the 6th millennium BP and 400 BC implies a puzzling three-millennia "eruption gap" at Stromboli.
    Description: Published
    Description: B09101
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: Stromboli ; palaeomagnetism ; Holocene eruptive history ; secular variation of the geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
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    Could the Mw = 9.3 Sumatra Earthquake Trigger a Geomagnetic Jerk? (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: The magnetic field observed at the Earth’s surface is not a stationary feature. It is characterized by time variations ranging from milliseconds (micropulsations) to millions of years (the time interval between field reversals). Time variations with periods of a year or longer are related to Earth’s outer core sources, whereas for shorter timescales an external origin is invoked (i.e., solar activity). One of the most interesting time variations of the geomagnetic field is represented by the “geomagnetic jerk.” It is idealized as a rapid change in the slope of the secular variation, defined as the first derivative of the geomagnetic field. This means that the secular variation roughly appears as a series of straightline segments separated by geomagnetic jerks.
    Description: Published
    Description: 123
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: 3.4. Geomagnetismo
    Description: N/A or not JCR
    Description: reserved
    Keywords: Sumatra Earthquake ; Geomagnetic Jerk ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
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    Core–mantle boundary deformations and J 2 variations resulting from the 2004 Sumatra earthquake (2007)
    Blackwell Publishing
    Details
    Publication Date: 2017-04-04
    Description: The deformation at the core–mantle boundary produced by the 2004 Sumatra earthquake is investigated by means of a semi-analytic theoretical model of global coseismic and postseismic deformation, predicting a millimetric coseismic perturbation over a large portion of the core–mantle boundary. Spectral features of such deformations are analysed and discussed. The time-dependent postseismic evolution of the elliptical part of the gravity field (J 2) is also computed for different asthenosphere viscosity models. Our results show that, for asthenospheric viscosities smaller than 1018 Pa s, the postseismic J 2 variation in the next years is expected to leave a detectable signal in geodetic observations.
    Description: Published
    Description: 718-724
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: 3.4. Geomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: core–mantle boundary, deformation, rheology, seismic modelling, spectral analysis ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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