震源机制与烈度分布的关系（二）

除了通常熟知的震源深度和介质吸收系数对烈度分布有较大影响外,震源的破裂方式（单侧或双侧）,破裂速度的大小和方向,断层长度,断层面倾角和错动方式都对烈度分布有较大影响。尤其是破裂速度的大小和方向对烈度分布的影响更大。破裂速度大,而且方向向上,可使震中烈度增高一度多,极震区面积扩大1-2倍;反之,可使震中裂度降低一度、极震区面积减小许多。 根据震源参数对烈度分布影响的分析,可由历史地震的等震线反推其震源参数。 文中试行反推了三个历史地震的震源参数。

RELATION BETWEEN THE SEISMIC SOURCE MECHANISM AND THE INTENSITY DISTRIBUTION （CONTINUED）

Besides the relatively obvious influence on the distribution of seismic intensity of the depth of focus and of the attenuation factor of the crustal medium, the mode of rupture at the focus （unilateral or bilateral）, the velocity and direction of rupture, length of the dislocating fault surface, its dip angle and the form of dislocation are also relalated to seismic intensity distribution. Particularly, the rupture velocity and rupture direction would have more effect. When the rupture has a greater velocity and upward in direction, the epicentral intensity of an earthquake may be raised by one degree or more and the most destructive area increased by 1-2 times. If the converse is the case, the epicentral intensity can be reduced by one degree or so while the most destructive area may be greatly diminished in size.Based on the analysis of the relation between the distribution of seismic intensity and the seismic source parameters, we can determine the source parameters from the isoseismals of historical earthquakes. For trial, the data of three historical earthquakes occurred in China have been used to get their source parameters.