a Ionogram showing multiple cusp signature observed at Kazan (epicentral distance 15,148 km), Russia, and b seismogram observed at Obninsk (epicentral distance 14,375 km), Russia.
a Ionogram showing multiple cusp signature observed at Yamagawa (epicentral distance 1124 km), Japan, and b seismogram observed at Tashiro (epicentral distance 1101 km), Japan Fig. 3 Ionospheric disturbance caused by M6.6 aftershock of 2011 Tohoku-Oki earthquake.
The vertical wavelength is less than the bottom-half thickness of the ionosphere, and several cycles of alternating enhancements and depletions of electron density cause distortion of the ionograms characterized as a multiple cusp signature (MCS) (Maruyama et al. 2011, 2016a, b; Maruyama and Shinagawa 2014).
Maruyama et al. (2011) found the first peculiar "cusp" signatures at virtual altitudes of 200 300 km on the ionogram taken during 1458 15 1458 30 JST, but not during 1443 15 1443 30 JST (also see Liu and Sun, 2011).
"Irreg"., "Cusp", and "Wav y" stand for irregular distortion of the trace, steep cusp signature, and consecutive weak cusp signature in the ionogram.
The magnetic inclination effect on the cusp signature increases quickly above (Isim 60^circ).
The arrows indicate a cusp signature for the O-mode trace.
The disturbance in the trace for (I=72^circ) exhibits a well-developed cusp signature, while that for (I=45^circ) merely shows wiggles.
These were the multituberculates, so-called because their cheek teeth featured multiple cusps, or tubercles.
The group refractive index near reflection is approximated as follows (Davies 1969) and was examined to estimate the magnetic inclination effect on the cusp signature.
