Geomagnetic Disturbances Accompanying the Great Japanese Earthquake of March 11, 2011

Resumo

This work analyzes the geomagnetic field variations recorded at the Magnetic Observatory of Karazin Kharkiv National University (in the period range of 1–1000 s) that accompanied the Japanese earthquake of March 11, 2011. Due to strong magnetic disturbances before and on the day of the main shock, the magnetic precursor was not identified. The geomagnetic field variations that followed the main shock were detected. If the disturbances are related to the earthquake, their propagation velocities are 2.2 km/s and 240–800 m/s. Such velocities are typical for seismic and acoustic-gravity waves, respectively. Long-period (20, 60, and 100–120 min), almost synchronous variations in the geomagnetic field level with an amplitude of 4–8 nT were found following the earthquake. The delay time of the leading edge of these disturbances increased with increasing distance between the epicenter and the observatory, while their amplitude decreased. The geomagnetic field disturbances were most likely transported by means of slow MHD waves.