Multi‐instrument observation on co‐seismic ionospheric effects after great Tohoku earthquake

Abstract

[1] In this paper, evidence of quake-excited infrasonic waves is provided first by a multi-instrument observation of Japan's Tohoku earthquake. The observations of co-seismic infrasonic waves are as follows: 1, effects of surface oscillations are observed by local infrasonic detector, and it seems these effects are due to surface oscillation-excited infrasonic waves instead of direct influence of seismic vibration on the detector; 2, these local excited infrasonic waves propagate upwards and correspond to ionospheric disturbances observed by Doppler shift measurements and GPS/TEC; 3, interactions between electron density variation and currents in the ionosphere caused by infrasonic waves manifest as disturbances in the geomagnetic field observed via surface magnetogram; 4, within 4 hours after this strong earthquake, disturbances in the ionosphere related to arrivals of Rayleigh waves were observed by Doppler shift sounding three times over. Two of the arrivals were from epicenter along the minor arc of the great circle (with the second arrival due to a Rayleigh wave propagating completely around the planet) and the other one from the opposite direction. All of these seismo-ionospheric effects observed by HF Doppler shift appear after local arrivals of surface Rayleigh waves, with a time delay of 8-10 min. This is the time required for infrasonic wave to propagate upwards to the ionosphere.

Ionospheric disturbances (infrasound waves) over the Czech Republic excited by the 2011 Tohoku earthquake

“…It is necessary to note that the infrasound background noise level increases with decreasing frequency by more than 20 dB per decade [see Laštovička et al , 2010, Figure 6], thus, the background noise for ∼50 s period waves (0.02 Hz) is more than 40 dB higher than for waves at frequencies of several Hz. The infrasound waves originated from the 11 March 2011 Tohoku earthquake that propagated relatively large distances (∼2500 km) from the epicenter, were observed in China [ Hao et al , 2012].…”

“…Thus, it is probable that the first ionospheric perturbations were caused by shock‐acoustic waves that carried the majority of available electrons, possibly propagating at supersonic speed at low altitudes [ Astafyeva et al , 2011]. The ionospheric disturbances and atmospheric infrasound waves were also observed at larger distances (∼2500 km), over China [ Hao et al , 2012].…”

Latitude and Longitude Dependence of Ionospheric TEC and Magnetic Perturbations From Infrasonic‐Acoustic Waves Generated by Strong Seismic Events

“…Recent interest has focused on piezomagnetic effects associated with stress buildup and release in a fault before and during large EQs (e.g., Utada et al, 2011, and references therein). Although the M 9.1 11 March 2011 Tohoku EQ (Hao et al, 2012(Hao et al, , 2013Utada et al, 2011) apparently generated magnetic field fluctuations, there was additional evidence for coseismic magnetic perturbations. Although the M 9.1 11 March 2011 Tohoku EQ (Hao et al, 2012(Hao et al, , 2013Utada et al, 2011) apparently generated magnetic field fluctuations, there was additional evidence for coseismic magnetic perturbations.…”

Ionospheric response to infrasonic‐acoustic waves generated by natural hazard events

“…Ground-based magnetometer measurements from Sumatran [Hasbi et al, 2009;Iyemori et al, 2005] and Tohoku earthquake events [Hao et al, 2012] appear to show convincing evidence for sizable dynamo currents associated with acoustic perturbations from these earthquakes. In particular, magnetometer infrasound-frequency fluctuations are roughly delayed from the earthquake occurrence time by the acoustic wave travel time to the E region ionosphere, just as in our simulations.…”