Rotation-induced magnetic field in a coil magnetometer generated by seismic waves

Synchronous seismic and geomagnetic fields are often observed. The magnetic field induced by seismic waves may be one of the main noises for magnetotelluric observation. Previous studies comparing the magnetic field induced by an earthquake to the estimated based on motion induction electromagnetic theory or magnetic azimuth deviation showed large differences in amplitude despite of high degree of synchronization and similarity in waveforms. According to the Faraday's principle, if a coil magnetometer takes a rotational movement in a magnetic field, the magnetic flux in the coil will be changed, generating the so-called rotation-induced magnetic field. Here we seek connection between seismic rotational motion and the rotation-induced magnetic field. The equations based on in-plane and 3-D rotational movement of a coil magnetometer caused by seismic waves passing through are derived, which permit us to predict the rotation-induced magnetic field from seismic records. As a demonstration, by using synchronous seismic and geomagnetic records observed in the Hainan Island, China, during the 2011 off the Pacific coast of Tohoku Earthquake, we successfully predicted the rotation-induced magnetic field in the periods of 5-40 s that agrees with the observed magnetic field in major characteristics including amplitude, phase, frequency, starting time and duration.