Abstract
This study reports on geomagnetic pulsations excited by traveling Rayleigh waves. The geomagnetic total intensity fields recorded using 12 magnetometers are utilized to examine seismo-magnetic pulsations induced by the 2011 M 9.0 Tohoku-oki earthquake. Geomagnetic data and seismograms from 4 co-located seismometers are examined and cross-compared to determine whether magnetic variations result changes in space weather or traveling Rayleigh waves. A 150-250 s band-pass filter was adopted to determine the arrival times and amplitudes of the seismo-magnetic pulsations. Seismo-magnetic pulsations with pronounced periods of about 200 s and amplitudes of 0.2-1.2 nT appear at distances ranging from 190-4600 km from the epicenter. Pulse speed of 3.8 km s^(-1) estimated from the epicentral distances and arrival times indicates that the seismo-magnetic pulsations were induced by Rayleigh waves produced by the Tohoku-oki earthquake. The seismo-magnetic pulsations constantly lag seismic wave pulses by about 6.3 minutes, confirming that ionospheric conductivity affects magnetic fields.
Highlights
At 05:46:23 UT, 11 March 2011, a destructive M 9.0 earthquake (142.86°E, 38.10°N) occurred off the east coast of the Tohoku-oki region of Honshu, Japan
Geomagnetic total intensity field measurements with 1 Hz resolution at 12 stations: 1 in Taiwan, 4 in Japan, 3 in China, 3 in Australia, and 1 in French Polynesia, were utilized to survey magnetic pulsations possibly triggered by the Tohoku-oki earthquake seismic waves
The consistent lead times observed at various locations and distinct epicentral distances allow us to have a better understanding of the possible magnetic pulsation causal mechanisms
Summary
At 05:46:23 UT (universal time), 11 March 2011, a destructive M 9.0 earthquake (142.86°E, 38.10°N) occurred off the east coast of the Tohoku-oki region of Honshu, Japan. Magnetic pulsations directly induced from seismic waves can be observed in a wide frequency band from VLF to ULF using either 3-component magnetometers or magnetotelluric equipment within an epicentral distance of ~500 km. These pulsations are usually very tiny (~10-1 nT) and close in amplitude to the background noise (Johnston et al 1981; Guglielmi et al 2004). Geomagnetic total intensity field measurements with 1 Hz resolution at 12 stations: 1 in Taiwan (a reference station in Taiwan’s network), 4 in Japan, 3 in China, 3 in Australia, and 1 in French Polynesia (see Fig. 1), were utilized to survey magnetic pulsations possibly triggered by the Tohoku-oki earthquake seismic waves. The consistent lead times observed at various locations and distinct epicentral distances allow us to have a better understanding of the possible magnetic pulsation causal mechanisms
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