巨大地震が励起したランダムな位相をもつ短周期実体波

抄録

A spectral analysis has been developed to obtain an approximate spectrum of short-period waves with nearly random phases. The analysis method has been applied to more than 900 short-period seismograms of recent great earthquakes in the world. Short-period seismic moment M₁, which represents an estimate of earthquake source spectrum at a period of about 1 to 2 seconds, has been evaluated for 79 earthquakes covering the range of seismic moment M₀ from 7.5×10²⁹ to 7.5×10²⁴ dyne·cm. It has been shown that seismic moment M₀ is approximately in proportion to the square of short-period seismic moment M₁ in the above dynamic range. A relation between short-period seismic moment and bodywave magnitude m_b* redetermined from maximum trace amplitudes of P-wave trains has been obtained;
logM₁=1.24m_b*+17.9.
The former relation would give constraint to understand the rupture mechanism of irregular faults and the latter would give a quantitative measure to evaluate the overall excitation of short-period seismic waves due to large earthquakes.