Radiated energy from the Noto Hanto, Japan, earthquake of March 25, 2007, and its aftershock

Abstract

The Noto Hanto earthquake of March 25, 2007, is a shallow reverse-faulting event with Mw = 6.7. We analyze transverse component accelerograms of the main shock and an aftershock (Mw = 3.6) recorded at 10 strong motion observation stations. The hypocenter of the aftershock is located very close to that of the main shock and the epicentral distances of the stations are between 15 and 65 km. We calculate spectral ratio between records of the main shock and the aftershock in order to obtain source spectral ratio by empirically removing the effects of wave propagation path and surface layers at the stations. Thus obtained source spectral ratio is inconsistent with that expected for the self-similar omega-square source model assuming constant stress drop. Fitting omegasquare source spectral ratio with variable corner frequency to the observed spectral ratio, the radiated energy and the corner frequency for the main shock and the aftershock are estimated. The radiated energy is 6.8 × 1014 J for the main shock and 6.7 × 109 J for the aftershock. The energy-to-moment ratios for the main shock and the aftershock are 5.0 × 10-5 and 2.1 × 10-5. This scale-dependence of the energy-to-moment ratio is similar to that obtained previously for shallow strike-slip earthquakes and reverse-faulting earthquakes in Japan. The relationship between the seismic moment, M0, and the corner frequency, f0, is M0 α f0-3.3±0.2. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB.