震源机制与应力体系关系模拟研究

Simulation on relationship between stress regimes and focal mechanisms of earthquakes

为理解震源机制和所作用的应力张量之间的关系,模拟了东西向挤压、垂直向拉张的挤压应力体系,南北向挤压、东西向拉张的走滑应力体系和垂直向挤压、东西向拉张的拉张应力体系所产生震源机制及其剪应力和正应力的表现.结果表明:挤压应力体系可以产生逆断型、走滑型和逆走滑型的震源机制,并随着应力形因子R的增大,逆断型震源机制数目逐渐减小,而走滑型和逆走滑型震源机制数目逐渐增加;走滑应力体系兼有各种类型的震源机制,随着R值的增大,正断型和正走滑型震源机制数目逐渐减小,而逆断型和逆走滑型震源机制数目逐渐增加;拉张应力体系兼有正断型、走滑型和正走滑型震源机制,随着R值的增加,正断型震源机制数目逐渐增加,而走滑型和正走滑型震源机制数目逐渐减小.挤压应力体系在震源机制节面上的最大剪应力分布在R=0时沿倾角45°分布,随着R值增大至1,逐渐演变为沿着以(0°,90°)和(180°,90°)为中心的圆弧分布;拉张应力体系的最大剪应力分布则随着R值自0增大至1,最大剪应力自以(0°,90°)和(180°,90°)为中心的圆弧分布逐渐演变为沿倾角45°分布;走滑应力体系则随着R值自0增大至1,最大剪应力自以(0°,90°)和(180°,90°)为中心的圆弧分布逐渐演变为以(90°,90°)为中心的圆弧分布.三种应力体系所表现的震源机制P,T轴分布呈现复杂多样性:R越小,震源机制的T轴分布在拉张主应力周围的区域范围越小,而P轴分布在挤压轴周围的区域范围越大,R=0.5时两者分布区域范围均衡,R超过0.5时越接近1,震源机制的P轴分布在挤压主应力周围的区域范围越小,而T轴分布在拉张轴附近的区域范围越大.

In order to understand the relationship between tectonic stress tensors and focal mechanism of earthquakes,the focal mechanisms and shear stress and normal stress projected on their nodal planes of focal mechanisms are simulated.They are under the compressional stress regimes with E-W compression and vertical extension,the strike-slip stress regime with N-S compression and E-W extension,and the extensional stress regime with vertical compression and E-W extension,respectively.The results show that the compressional stress regime can generate focal mechanism types of thrust,strike-slip and thrust-strike-slip.As the stress shape ratio(R)increases,the number of thrust and thrust-strike-slip types of focal mechanism gradually increases,while that of thrust type of focal mechanism decreases.The strike-slip stress regime can generate all types of focal mechanism.As the stress shape ratio(R)increases,the number of thrust and thrust-strike-slip types of focal mechanism gradually increases,while that of normal and normal strike-slip type of focal mechanism decreases.The extensional stress regime can generate the focal mechanism types of normal,strike-slip and normal-strike-slip.As the stress shape ratio(R)increases,the number of normal type focal mechanism gradually increases,but the number of strike-slip and normal strike-slip type of focal mechanism decreases.In compressional stress regime,the nodal planes of the focal mechanisms with the maximum shear stress are the belt with dip angle of 45°when R=0.As the Rincreases,the nodal planes of the focal mechanisms with the maximum shear stress gradually evolves into two arc-shaped zones centered at(0°,90°)and(180°,90°)respectively.In extensional stress regime,as Rbecomes from 0 to 1,the nodal planes of the focal mechanisms with the maximum shear stress gradually evolve from the 2 arcshaped zones centered at(0°,90°)and(180°,90°)respectively,to the belt with the dip angle of45°.In strike-slip stress regime,as the Rfrom 0 to 1,the nodal planes of the focal mechanisms with the maximum shear stress gradually evolves from two arc-shaped zones centered at(0°,90°)and(180°,90°)respectively,into the arc shaped zone centered at(90°,90°).The Pand Taxes of the focal mechanisms generated by the 3 stress regimes show complexity and diversity.The less Ris,the larger the range of Taxis distribution is,and the smaller the range of Paxes distribution is.The ranges of the Pand Taxes distribution are equal when R=0.5.When R>0.5,as Rincreases from 0.5 to 1,the range of the Paxis gradually decreases,and that of the Paxis gradually increases.