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Thermodynamic Changes in the Process of Megathrust Earthquake of magnitude 9
  • Hiroyuki Kikuchi
Hiroyuki Kikuchi
Seismic Lab

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Sharp decrease of entropy production rate (EPR) is observed in the process of the Great East Japan Earthquake (GEJE) of magnitude 9. The EPR, a thermodynamic property of a fluctuating system, is calculated from the binarized velocity deviation of the background vibration. The background signal of the GEJE process includes a micron / second scale velocity signal that exhibits the dominant frequency of 1 Hz to 10 Hz in the Fourier amplitude spectrum. Paying attention to the negative curvature of the spectrum in the frequency range, we define alpha-tremor as the degree of negative curvature of the spectrum in the frequency range from 2.97 Hz to 9.80 Hz. The positive and non-positive alpha-tremor represent an arbitral weak velocity signal. The alpha-tremor has been shown to be invariant in binarizing the velocity fluctuation signal. Therefore, the binarized velocity and the raw velocity signal are equivalent as long as the background vibration is considered as the alpha-tremor fluctuation. The binarized velocity signal is divided into sets with 10 data, and the vibration state is defined for each set considering the degree of dispersion of the 10 signals. Then the transition rate from one state to the other is calculated, followed by the EPR calculation. The EPR is evaluated for ground vibration data acquired every 0.05 seconds from 2008 to 2014 at the seismic station 188 km away from the epicenter of GEJE which occurred in 2011.