抄録
An earthquake source mechanism is described from the standpoint that the dynamic characteristics of friction play a more important role in the dislocation motion than the boundary condition does. By considering an earthquake dislocation as a slip motion in a mechanical system involving friction, which depends upon velocity during slip, a displacement time function G(t)=1-exp(-t/τ)(1+t/τ) which satisfies the necessary continuity criterion is derived. The rise time of the source time function, which must be directly dominated by the physical conditions on the source region, is straightforward estimated from the time constant
τ=(π/8K)(υ/β)W/β
where K is (λ+μ)/(λ+2μ) for dip slip and 1/2 for strike slip, and λ and μLame's constants, υ the propagating velocity of dislocation, β the shear wave velocity and W the fault width. The values derived from the above formula agree quite well with those determined on the basis of the seismic wave data for all the earthquakes investigated.
Seismic wave energy and its efficiency are discussed in relation to the physical controlling factors in the source region. It is noteworthy that the seismic wave energy is related explicitly to the fault width, and that the seismic efficiency depends only upon the ratio of the shear or compressional wave velocity to the propagating velocity of dislocation, the ratio of the fault length to width, and the ratio of the stress drop to the in situ stress before or after dislocation. It is shown that the amount of the total seismic wave energy is very small compared with that of the elastic energy released by an earthquake dislocation. This suggests that an earthquake source may be a great heat source.
