Geomagnetic field intensity variation over the past 400 years

2023 Fiscal Year Final Research Report

• Project/Area Number: 19K04020
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Doshisha University
• Principal Investigator: Fukuma Koji 同志社大学, 理工学部, 准教授 (80315291)
• Co-Investigator(Kenkyū-buntansha): 伊藤 久敏 一般財団法人電力中央研究所, 原子力リスク研究センター, 上席研究員 (50371406)
• Project Period (FY): 2019-04-01 – 2024-03-31
• Keywords: 古地球磁場強度 / テリエ法 / 地磁気永年変化 / 球面調和モデル

Outline of Final Research Achievements

To determine variations in the intensity of the Earth's magnetic field over the past 400 years, lava samples collected from the island of Reunion in the southern Indian Ocean were measured using the Thellier method. Samples taken from the upper or lower clinkers of the lavas are suitable for determining geomagnetic field intensities, and past geomagnetic field intensities were determined at 10 of the 12 sites according to strict criteria using temperature intervals determined from prior thermal demagnetization. The geomagnetic field intensities at Reunion Island are consistent with the ARCH spherical harmonic model, and the geomagnetic fields of Europe, the southern Indian Ocean, and East Asia can be reconstructed with a single reliable model.

Free Research Field

古地磁気学

Academic Significance and Societal Importance of the Research Achievements

地球磁場強度は19世紀半ばに機器観測が始まって以来100年で約5%の割合で単調に減少しており，単純に外挿すれば約 2000 年後には地球磁場強度はゼロになる．地球磁場強度の減少はいつから始まったのか，単調な減少なのか，それとも周期的な変動の減少局面を観測しているだけなのかという問いに答えるには機器観測が始まる前の地球磁場強度を知る必要がある．今回の研究により，溶岩の上部もしくは下部クリンカから採取してテリエ法で測定すれば，機器観測に比肩できる精度で地球磁場強度を求められることがわかった．