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  • 1
    Publication Date: 2017-04-04
    Description: One of the main challenges of paleomagnetic research is to obtain high-resolution geomagnetic field intensity reconstructions. For the last millennia, these reconstructions are mostly based on archeomagnetic data. However, the quality of the intensity data available in the databases is very variable, and the high scatter observed in the records clearly suggests that some of them might not be reliable. In this work we investigate how the geomagnetic field intensity reconstructions and, hence, our present knowledge of the geomagnetic field in the past, are affected by the quality of the data selected for modeling the Earth’s magnetic field. For this purpose we rank the European archeointensity data in four quality categories following widely accepted paleomagnetic criteria based on the methodology used during the laboratory treatment of the samples and on the number of specimens retained to calculate the mean intensities. Four geomagnetic field regional models have been implemented by applying the revised spherical cap harmonic analysis to these four groups of input data. Geomagnetic field models strongly depend on the used data set. The model built using all the available data (without any preselection) appears to be the less accurate, indicating some internal inconsistencies of the data set. In addition, some features of this model are clearly dominated by the less reliable archeointensity data, suggesting that such features might not reflect real variations of the past geomagnetic field. On the contrary, the regional model built on selected high-quality intensity data shows a very consistent intensity pattern at the European scale, confirming that the main intensity changes observed in Europe in the recent history of the geomagnetic field occurred at the continental scale.
    Description: Published
    Description: 2515–2530
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: open
    Keywords: Geomagnetism ; Paleomagnetism ; Archeomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
    Publication Date: 2017-04-04
    Description: First archaeointensity determinations have been obtained from Ethiopia. Seven bricks (34 specimens) from the Däbsan archaeological remains were subjected to archaeointensity determination by means of classical Thellier–Thellier experiment including tests for magnetic anisotropy and magnetic cooling rate dependency. The age of the Däbsan Palace is well controlled by historical information: between 1603, when land grants were conceded to the Jesuits and the Catholicism was established as the official religion in Ethiopia, and the age of the Palace foundation in 1626–27. Successful archaeointensity determinations were obtained in 27 specimens from five individual bricks revealing an average field value of 33.5 ± 1.1 lT, which is 11–26% lower than expected values from global geomagnetic models based on historical and archaeomagnetic data. Global models for 1615 AD predict a low in central-southern Africa related to past location of the present Southern Atlantic Anomaly (SAA). Our results suggest that the field intensity in central Africa may have been slightly lower than global model predictions. This would indicate that the low could be probably more extended towards central-eastern Africa (or more intense) than previously considered. Further data from this region are especially welcome to delineate the evolution of the SAA.
    Description: Published
    Description: 24 - 35
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Paleomagnetic secular variation ; Archeomagnetism ; Paleointensity ; Central Africa ; Geomagnetic models ; South Atlantic Anomaly ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Publication Date: 2019-03-14
    Description: Since the pioneering studies in archeomagnetism in the second half of the 20th century, the number of archeomagnetic studies has increased exponentially. The huge density of archeomagnetic data collected during these years allows us to describe the past spatial and temporal evolution of the Earth’s magnetic field during the last millennia. Most of the data are located in the Northern Hemisphere, but currently, thanks to the strong effort of the paleomagnetic community, new collections of data are coming from the Southern Hemisphere, homogenizing the present database. Although the data distribution presents some epochs and locations where the data are still very scarce, they describe, to a greater or lesser degree of accuracy, the past behavior of the geomagnetic field. At regional scales, the use of archeomagnetic data permits the construction of paleosecular variation curves for the geomagnetic field elements: declination, inclination, and intensity. These curves describe the evolution of the elements at different times for the last millennia. During the last five years novel techniques, such as Bayesian statistics, bootstrap algorithms, or the Markov chain Monte Carlo method, have been applied to extract the most useful information from archeomagnetic data to build accurate and reliable curves. The accuracy of these curves can be exploited as a tool for archeomagnetic dating, assigning possible ages to archeological artifacts or volcanic lava flows with unknown age. At global scales, archeomagnetic data are jointly treated with other paleomagnetic data to generate continuous geomagnetic field models, reconstructing the past evolution of the geomagnetic field not only at the Earth’s surface, but also at the core-mantle boundary, shedding light on the past evolution of complex geodynamo processes.
    Description: Published
    Description: 99-158
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: restricted
    Keywords: Archeomagnetism ; Paleomagnetism ; 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 ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.08. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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