伝播性破壊確率モデルと最大加速度・rms加速度

抄録

Non-uniform slip on a heterogeneous fault is investigated to describe the detail of earthquake rupture processes. The fault is parameterized by average stress drop and fault size to model the deterministic part of the faulting process. The size of small scale fault heterogeneities and the variance of local stress drop are introduced to describe the stochastic part of the faulting. Nonuniform slip (or non-uniform stress drop) tends to increase the high frequency contents of S-waves, and thus controlls the excitation of strong ground motion. Short-waves from the heterogeneous fault are generated as an energy-additive form by the stochastic fracturing of random fault heterogeneities. This brings us a seismic directivity effect particular to the incoherent short-waves, which is different from the seismic Doppler effect on the long-waves. This short-period seismic directivity predicts the azimuthal variation of short-wave amplitudes as
(1-v cos θ/β)^-1/2
for a unilateral faulting and
{1-(v cos θ/β)2}^-1/2
for a bilateral faulting, where v is an average rupture velocity, θ is the station azimuth from the fault-propagating direction, and β is S-wave velocity. Maximum and root-mean square accelerations are derived theoretically in terms of the variance of local stress drops, number density of fault heterogeneities, and fault size considering the short-period seismic directivity.