东昆仑活动断裂带大地震之间的黏弹性应力触发研究

VISCOELASTIC TRIGGERING AMONG LARGE EARTHQUAKES ALONG THE EAST KUNLUN FAULT SYSTEM

对青藏高原北部东昆仑破裂带大地震之间的应力转移和断层相互作用进行研究 .考虑 1937年以来沿此破裂带发生的 5个M≥ 7的地震 :1937年M7.5花石峡地震 ,196 3年MS7.1都兰地震 ,1973年MS7.3玛尼地震 ,1997年MW7.5玛尼地震和 2 0 0 1年MW7.8可可西里地震 ,模拟了黏弹性成层介质中地震断层错动产生的应力演化过程 ,并计算了在后续地震破裂面上产生的库仑破裂应力变化 .结果表明 ,前面 4个地震均造成 2 0 0 1年可可西里地震断层面上库仑破裂应力的增加 ,并且中地壳和下地壳的黏弹性松弛效应使得库仑破裂应力场随着时间的推移而逐渐加强 .在计算过程中定量估计了可可西里地震发生时前面 4个地震同震形变和黏弹性松弛导致可可西里地震破裂面上库仑破裂应力变化之间的比值 ,发现前 3个地震由黏弹性松弛造成的变化远远大于同震形变所造成的变化 .可可西里地震之后应力场的模拟表明东昆仑断层中段的东大滩 -西大滩断层段 (位于可可西里地震破裂以东及都兰地震以西 )的库仑破裂应力显著增加 ,变化值达 0 .0 5～ 0 .1MPa ,预示这一地区地震危险性的增加 .

We study the stress transfer and triggering of large earthquakes along the East Kunlun fault system, northern Tibet. Five M≥7 earthquakes occurred along the fault zone during the past 70 years are considered: the M7.5 Huashi Canyon earthquake, the 1963 M S 7.1 Dulan earthquake, the 1973 M S7.3 Manyi earthquake, the 1997 M S7.5 Manyi earthquake, and the 2001 M W7.8 Kokoxili earthquake. We simulate the stress evolution process produced by seismic dislocations in layered viscoelastic media, and calculate the Coulomb failure stress change on the fault plane of each subsequent earthquake. The result shows that the Coulomb failure stress on the fault plane of the Kokoxili earthquake was increased by the previous 4 earthquakes, and theviscoelastic relaxation gradually enhanced the Coulomb failure stress field as time elapsed. By evaluating the Coulomb failure stress changes produced by the coseismic rupture and viscoelastic relaxation of the 4 preceding large earthquakes, we find that the Coulomb failure stress changes produced by the viscoelastic relaxation are much more significant than that produced by the coseismic deformation in 3 of the 4 earthquakes. The stress field simulation indicates that after the Kokoxili earthquake the Coulomb failure stress in the Xidatan-Dongdatan segment (between the Kokoxili and Dulan segments) of the East Kunlun fault is increased as much as 0.05～0.10 MPa, implying increased probability of seismic hazard in this region.