A natural electric current that flows underground. The soil, sand, and rocks that make up the earth's crust have a certain degree of electrical conductivity. Therefore, time-dependent changes in the magnetic field, such as geomagnetic storms and daily geomagnetic variations, cause these telluric currents in the earth through electromagnetic induction. As the current is very weak, it is measured as a potential difference between two points several hundred meters to several kilometers apart. This potential difference is often about 10 to 1000 mV/km (millivolts per kilometer). Since the current flows due to magnetic field fluctuations, the north-south component of the telluric current is closely related to the east-west component of the magnetic field, and vice versa. By analyzing the relationship between these components, it is possible to determine how the electrical conductivity of the earth changes with depth. This method is called magnetotellurics. [Kano Naga] Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend |
地中を流れている自然電流。地殻を構成している土、砂、岩石などはある程度の電気伝導度をもつ。そのため磁気嵐(あらし)や地磁気日変化などの磁場の時間変化が、電磁誘導によって地中に引き起こすのがこの地電流である。電流としては非常に微弱なので、数百メートルから数キロメートル離れた2地点間の電位差として測定する。この電位差は10~1000mV/km(キロメートル当りミリボルト)程度の大きさをもつことが多い。磁場変動が原因で電流が流れるので、地電流の南北成分は磁場の東西成分と、また地電流の東西成分は磁場の南北成分と密接に関係している。これらの成分間の関係を解析することにより、地下の電気伝導度が深さの方向にどのように変化しているかが求められる。この方法をマグネトテルリクスmagnetotellurics法という。 [河野 長] 出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例 |
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