scholarly journals Archaeomagnetism of four pottery kilns in central Portugal: Implications for secular variation and dating

2018 ◽  
Vol 4 (1) ◽  
Author(s):  
Michael Edwin Evans ◽  
Antonio Correia
Keyword(s):  
High Precision ◽  
Secular Variation ◽  
Reference Curve ◽  
Geomagnetic Secular Variation ◽  
Geographic Coverage ◽  
Archaeomagnetic Dating ◽  
Central Portugal

We report archaeomagnetic results from four pottery kilns in Portugal which are thought to belong to the period of Roman rule (3rd Century BCE-4th Century CE). Very few details have been published to date, so this broad assignment is based on the general archaeological context at each site. Our motivation was to see if a more precise chronology could be established by means of archaeomagnetic dating. Concomitant goals were to compare these results from Portugal to their counterparts in Spain and to expand geographic coverage of the regional geomagnetic secular variation reference curve. Experimentally, all the samples behaved in a very coherent manner during progressive alternating-field demagnetization and yielded high-precision mean archaeomagnetic directions (a95<3°) for each site. The results suggest that two of the kilns, Castelo de Vide and Peniche, were most likely in use during the late 1st/early 2nd centuries CE, whereas the two kilns at Seixal are somewhat younger, dating to the late 2nd to early 4th centuries CE.

Archaeomagnetic Dating in the American Southwest

1980 ◽  
Vol 45 (3) ◽  
pp. 507-517 ◽  
Author(s):  
Jeffrey L. Eighmy ◽  
Robert S. Sternberg ◽  
Robert F. Butler
Keyword(s):  
Pilot Study ◽  
Secular Variation ◽  
Master Curve ◽  
American Southwest ◽  
Geomagnetic Secular Variation ◽  
Rate Dependent ◽  
Precision Limit ◽  
Archaeomagnetic Dating ◽  
Dependent Processes ◽  
Error Of Measurement

Although archaeomagnetic dating seems straightforward in principle, there are practical limitations which are not generally understood. Unlike rate-dependent processes such as isotopic dating, archaeomagnetic dating requires the construction of a master record of geomagnetic secular variation. Error is inherent in such a master curve due to statistical uncertainties regarding both the magnetic directions and ages of the samples used to create the curve. The master curve itself is thus best represented as a ribbon rather than a line. Features being dated have their own error of measurement of magnetic direction, and deriving a date involves an interpretation based on the relation between the oval of confidence for the unknown and the ribbon representing the master curve. Thus a practical precision limit for archaeomagnetic dating is about ± 20 years under optimal circumstances, but the limit will generally be higher. Our pilot study revealed no major discrepancies between our work and the curves of DuBois (1975).

scholarly journals Four decades of European geomagnetic secular variation and acceleration

2010 ◽  
Vol 52 (5) ◽  
Author(s):  
Giuliana Verbanac ◽  
Monika Korte ◽  
Mioara Mioara Mandea
Keyword(s):  
Secular Variation ◽  
Geomagnetic Secular Variation

Correction for Geomagnetic Secular Variation Effects: A New Method (Case Study of the Altai Geodynamic Network)

2021 ◽  
Vol 62 (2) ◽  
pp. 255-262
Author(s):  
D.A. Kuleshov ◽  
P.G. Dyadkov ◽  
V.V. Plotkin
Keyword(s):  
Secular Variation ◽  
Surface Deformation ◽  
Liquid Core ◽  
New Method ◽  
Space Distribution ◽  
Main Magnetic Field ◽  
Positive Anomaly ◽  
Geomagnetic Secular Variation ◽  
Using Data ◽  
Curie Surface

Abstract ––The study focuses on detection of geomagnetic secular variation and the respective correction of tectonomagnetic data. A new technique is proposed for picking the secular variation component in the Earth’s main magnetic field recorded by precise measurements at 100 to 500 km sites on the surface. Long-period field variations presumably arise from fluid motions in the liquid core, at depths of 3000 km, whereas the sizes of observation networks are within 500 km. The sources of secular variation, irrespective of their configuration, are much deeper than those of tectonomagnetic anomalies located above the Curie surface depths of ~10 to 20 km. Therefore, the surfaces that represent the space distribution of secular variation must be smoother than the respective surfaces for tectonomagnetic anomalies. The problem is thus to separate the regional and local signals from the two types of sources located at different depths. The new method is tested using data of yearly geomagnetic measurements at more than 30 repeat stations of a ~120 km long geodynamic network in Gorny Altai spanning the period from 2004 through 2018. The secular variation pattern is reconstructed by quadratic interpolation. The precise data corrected for secular variation of the main field reveal previously hidden tectonomagnetic anomalies up to 12 nT. The 3 nT positive anomaly falls within the zone of surface deformation caused by the Mw = 7.3 Chuya earthquake of 27 September 2003.

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