Rayleigh wave signature in ionograms induced by strong earthquakes

Abstract

[1] After the magnitude 9.0 earthquake off the Pacific coast of Tohoku (near the east coast of Honshu, Japan), which occurred on 11 March 2011, an unusual multiple-cusp signature (MCS) was observed in ionograms at three ionosonde stations across Japan. To investigate the general characteristics of MCSs, we examined ionograms obtained during the period 1957 to 2011 from five ionosonde stations in Japan after earthquakes with a seismic magnitude of 8.0 or greater. A total of 43 such earthquakes occurred after 1957, as recorded in the database of the United States Geological Survey. MCSs were observed in 8 of 43 earthquakes, allowing us to investigate the specific conditions of MCS appearance. The appearance of MCSs at different epicentral distances exhibits traveling characteristics at a velocity of $4.0 km/s, which is in the range of Rayleigh waves. There is a $7 min offset in delay time after the earthquake at each epicentral distance in the travel-time diagram. This offset is consistent with the propagation time of acoustic waves from the ground to the ionosphere launched by Rayleigh waves. MCSs in ionograms provide a snapshot of vertical disturbances induced by a wave because the sweep time for the whole ionospheric echo traces is much shorter than the propagation time of acoustic waves. The vertical scale of the disturbances is 10$30 km, which corresponds to an acoustic wave period of 20$50 s at ionospheric heights.Citation: Maruyama, T., T. Tsugawa, H. Kato, M. Ishii, and M. Nishioka (2012), Rayleigh wave signature in ionograms induced by strong earthquakes,

Interpretation of deformed ionograms induced by vertical ground motion of seismic Rayleigh waves and infrasound in the thermosphere

“…Such highly deformed ionograms with slant satellite traces as examined in this paper are a rare occurrence. However, when previously examined coseismic ionogram disturbances after 1957 (Maruyama et al, 2012;Maruyama and Shinagawa, 2014) were revisited, a similar effect was identified in two ionograms obtained at ionosonde sites in Japan. Two ionograms were shown in Figs.…”

“…These velocities yield an inclination of 8 • for the infrasound wavefronts. Vertical density gradients in the F1 region of the unperturbed ionosphere are critical for the formation of cusps in the ionogram trace (Maruyama et al, 2012). For realistic simulations of a perturbed ionogram, the background ionospheric profile was numerically produced and parameters in the following equations were determined to fit the synthesized ionogram with the observed ionogram without perturbation shown in Fig.…”

“…After the 2011 M 9.0 Tohoku-oki earthquake in Japan, weak sinusoidal fluctuations to sharp cusptype deformations were observed in ionograms . These differences in the significance of ionogram disturbances were dependent on the amplitudes of the Rayleigh waves that were responsible for them (Maruyama et al, 2012;Maruyama and Shinagawa, 2014).…”

Interaction of Solid Earth, Atmosphere, and Ionosphere

“…An OTH SuperDARN in Hokkaido, Japan, also detected the ionospheric disturbances caused by this earthquake (Nishitani et al, 2011). Conventional sensors such as ionosonde were also used to study the ionospheric disturbances (Liu and Sun, 2011;Maruyama et al, 2011Maruyama et al, , 2012.…”

Ionospheric F2-layer Perturbations Observed After the M8.8 Chile Earthquake on February 27, 2010, at Long Distance from the Epicenter

“…Rayleigh wave signatures in the ionosphere following earthquakes have been measured by Doppler sounding (e.g., Yuen et al 1969;Tanaka et al 1984;Artru et al 2004;Chum et al 2016) using TEC measurements (e.g., Ducic et al 2003;Astafyeva et al 2009;Rolland et al 2011) and the inspection of ionograms (Maruyama et al 2012(Maruyama et al , 2016a(Maruyama et al , 2016b.…”