The Variation of Ancient Geomagnetic Field Intensity for the Territory of Hungary

1986 Journal of geomagnetism and geoelectricity  
The investigation of the ancient geomagnetic field intensity for the last 2,000 years was carried out, utilizing the Thellier method. Thermomagnetic analysis showed that the natural remanence of the samples is thermoremanent in nature. The archaeomagnetic results showed that there are secular variations in the intensity change, with periods of about 200-400 years superimposed upon the long-term decrease of intensity. The aim of this work was to investigate the ancient geomagnetic field
more » ... in Hungary during the past 2,000 years. Collection of the samples was made from four places in Hungary: Estergom and Visegrad near Budapest, Diosgyor near Mishkolz, and Gorsium (today's Tac). It consisted of 40 objects of different ages: there were bricks from ancient buildings and burned clay fragments. The Thellier method (THELLIER and THELLIER, 1959) was used to estimate the ancient geomagnetic field intensity. The samples of this collection were quite suitable for this method. The results of thermomagnetic analysis showed that the ancient remanent magnetization is of thermal origin, as illustrated in Fig. 1 . The results of the left side of this picture refer to one specimen; and the results at the right side refer to the other specimen. We used the Thellier step-by-step double-heating method (THELLIER and THELLIER, 1959) . This method allows estimation of the correct value of NRM which took place before the change caused by external influences, namely, VRM. It is shown by open circles in Fig. la ; the values of NRM are shown by dark circles, and those of TRM by crosses. NRM against TRM in Fig. 1b gives the value of ancient total intensity. In the case of the first sample, there is: 1) a good correspondence between the ancient NRM and the modern one and a similar change of both NRM and TRM (Fig. 1a) ; 2) straight-line dependence of the ratio NRM-TRM (Fig. 1b) ; 3) a stable direction of NRM during the experiment, within approximately two our collection were not oriented, we calculated ancient D and 1 in order to estimate the stability of NRM during the experiment); and, finally, 4) a very stable mineralogical (and consequently magnetic) state of the samples. This latter point was confirmed by close results of initial partial NRM and those obtained after two control heatings to the same temperature, as is shown by the squares in Fig. 1a . The majority of the samples of this collection give adequate results 1369
doi:10.5636/jgg.38.1369 fatcat:awrfqstecbcdpmu4wt6vgyn2qm