华北地区地壳结构特征与强震孕育关系的探讨

将地壳介质视为马克斯威尔体,运用差分和三维有限元方法,探讨分层地壳结构中分别存在低速体( 软包体) 、高速体( 硬包体) 和同时存在高速体和低速体时地壳应力的集中及应力集中随时间变化的演化特征,计算结果表明:(1) 高速体、低速体的存在引起的平均应力和最大剪应力在高速体内和低速体外集中的结果同理论计算一致;(2) 高速体单独存在时,应力扰动值随时间的变化导致平均应力集中程度在高速体内减弱,最大剪应力集中程度则在高速体内进一步增加,这一特征与地壳的蠕变过程一致,并有利于在高速体内孕育和发生强震;(3) 低速体单独存在时,随着时间的推移,最大剪切应力扰动值在低速体上方逐渐增加,该特征对在低速体上方孕育中等强度地震( 有时也可能是强震) 是很有利的;(4) 高速体和低速体同时存在时,平均应力的集中随时间的推移在高速体也是呈减弱的趋势,而最大剪应力的集中则在高速体内较高速体单独存在时更加显著增加。该项研究的意义在于在非均匀性引起的应力集中的基础上研究应力集中随时间变化,探讨强震孕育过程的机理。

APPROACH TO RELATION BETWEEN CHARACTERISTIC OF CRUST STRUCTURE IN NORTH CHINA AND STRONG EARTHQUAKE PREPARATION

Considering crust medium as a Maxwell body, the low velocity body(soft inclusion), high velocity body(hard inclusion) in layer crust structure, and existing the two classes of body, the evolution characteristics of crust stress cocentration and its variation are approached using difference and three dimension finite element methods. The calculation result indicated that (1) the result of average stress and maximum shear stress concentrations inside high velocity body and outside low velocity body consists with theory calculation; (2) when only high velocity body exists, the time variation of stress disturbance value causes the weakening of average stress concentration inside high velocity body, and the concentration of maximum shear stress further increases inside high body, which consists with crust creep process and helps to prepare and occur earthquake inside a high body; (3) when only low velocity body exists, the disturbance value of maximum shear stress gradually increases over the low velocity body, which help to prepare a moderate earthquake (sometimes a strong earthquake); (4) when both high and low velocity bodies exist, the concentration of average stress weakens inside the high velocity body, and the concentration of maximum shear stress increases in the high body more than one alone.