Magnetic Pulsations Triggered by Microseismic Ground Motion

Geomagnetic pulsations with an enhanced amplitude of 0.1–1 nT in a frequency band of 0.1–0.2 Hz were observed by three three-component magnetometers. The geomagnetic pulsations exhibit slight time difference that is unusually observed within a limited area of ∼5 × 5 km² at the northern end of Taiwan. The time difference suggests the geomagnetic pulsations are not dominated by global effects but local ones. We compare the seismic signals recorded by the cosited broadband seismometers for investigating potential mechanisms of these geomagnetic pulsations. Results from analysis of both seismic and geomagnetic data exhibit consistent source azimuths from the Pacific Ocean to the northeast of the observation sites with a wave propagation speed of ∼2.9 km/s estimated based on P-SV-type microseisms. Polarization and particle motion analyses demonstrate that the geomagnetic pulsations move with an elliptical rotation form, showing a close association with the P-SV-type microseisms. The 90° phase difference between the horizontal and vertical components of the geomagnetic signals suggests that the time-lagged geomagnetic pulsations are possibly caused by the motional induction effect after the arrivals of P-SV-type microseisms.