[S-EM13] Geomagnetism, paleomagnetism and rock magnetism

[SEM13-P04] How many lava flows are needed to obtain averaged paleointensity?

*Yutaka Yoshimura¹, Toshitsugu Yamazaki² (1.Faculty of Social and Cultural Studies, Kyushu University, 2.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords:Paleointensity, Monte Carlo method, Averaged paleointensity, Cretaceous Normal Superchron, PISO-1500

To understand the relationship between paleointensity and reversal frequency over tens of millions of years, we need to determine the number of data or lava flows to calculate the averaged absolute paleointensity. In this study, we applied Monte Carlo methods to the PISO-1500, the absolutely-calibrated stacked relative paleointensity standard curve for the past 1.5 million years, to determine the number of paleointensity data needed for averaging. In the simulation, we assume that the PISO-1500 curve reflects the actual geomagnetic intensity variations. We randomly extract paleointensity data one by one from the Brunhes period of the PISO-1500 curve. We increased the number of randomly selected data from 1 to 60 as repeating the process. We then average them and calculate the probability that the average value is within ±10% of the average value of the overall Brunhes period after repeating the process 1 million times. The probability of accurately estimating the averaged absolute paleointensity was presented as a function of the number of paleointensity data. The certainty of the averaged absolute paleointensity can be discussed by weighting the average value with the probability corresponding to the number of lava flows or cooling units. When we compiled the averaged absolute paleointensity from previous studies with weighting by probability, we found that the average value with a high probability is relatively close to the representative value previously reported from the entire last 200 million years. However, the averaged absolute paleointensity obtained from volcanic rocks about 90 million years ago, the period when the geomagnetic field was not reversed (the Cretaceous Normal Superchron), may have been larger than the average value for the past 200 million years.