芦山MS7.0地震与Northridge MW6.7地震地表变形场对比研究*
杜吉亮1,武艳强1,2,邹镇宇1

(1中国地震局地震预测研究所(中国地震局地震预测重点实验室),北京 100036; 2中国地震局第一监测中心,天津300180)

芦山地震; Northridge地震; 震前变形背景; GPS同震位移

Comparison of Deformation Field Pertaining to Lushan MS7.0 Earthquake and Northridge MW6.7 Earthquake
DU Jiliang1,WU Yanqiang1,2,ZOU Zhenyu1

(1.CEA Key Laboratory of Earthquake Prediction,Institute of Earthquake Science, CEA, Beijing 100036,China)(2.First Crust Deformation Monitoring and Application Center,CEA,Tianjin 300180,China)

Lushan MS7.0 earthquake; Northridge MW6.7 earthquake; pre-seismic deformation background; GPS co-seismic displacement

备注

2013年四川芦山“4·20”MS7.0地震和1994年美国Northridge MW6.7地震的近场同震位移均表现出破裂未达地表的特征,利用1999～2007年GPS资料对比分析了2次地震的震前变形特征与同震位移的关联性。结果 显示,芦山震源区存在较为显著的挤压应变积累(挤压应变率方位角约为284°),沿芦山地震破裂节面剪切变形不明显; 芦山地震的同震位移场表现为逆冲兼少量左旋特征,反映了整个孕震周期的应变积累特性,可能表明震前10余年的观测并不能代表整个孕震周期特征。Northridge地震前,地表变形表现为右旋-挤压特征,同震以逆冲破裂为主,近场表现出类似“圆屋顶形”的东西两侧水平运动和垂直向上运动,GPS观测到的震前变形与同震释放的变形存在一定程度的不一致性。相同震中距测点结果表明:Northridge地震的同震地表位移幅度明显大于芦山地震,前者震前挤压应变积累速度显著大于1999～2007年芦山地震震源区的应变积累背景。

The near field co-seismic displacement distributions pertaining to the 2013 Lushan MS7.0 earthquake and the 1994 Northridge MW6.7 earthquake showed the specific characteristics with fracture not reaching the crustal surface.We compared and analyzed the relationship between the pre-seismic deformation and the co-seismic deformation of these two earthquakes using GPS data from 1999 to 2007.The analysis results of Lushan MS7.0 earthquake showed that there exited the obvious compressive strain accumulation(the azimuth is about 284°)in the focal area,however,the shear deformation along the rupture section was not obvious.The co-seismic deformations showed the characteristics of levorotation and extrusion,which reflected the strain accumulation characteristics in the whole seismogenic period and may indicate that the observation about 10 years before the earthquake cannot represented the characteristics in the whole seismogenic period.Before the Northridge earthquake,the characteristic of dextrorotation and extrusion of surface deformation was in dominant near the focal region.The co-seismic deformation of the earthquake mainly showed thrust rupture,and the horizontal movement in east and west directions and uplift movement were significant in near field which liked “dome” shape.As a result,the characteristic between pre-seismic and co-seismic deformations showed difference to a certain degree.In conclusion,the magnitude of the co-seismic deformation of the Northridge MW6.7 earthquake was greater than that of the Lushan MS7.0 earthquake reflected by the results of the stations with the same epicenter distance,and the pre-seismic extrustion strain accumulation rate of the Northridge earthquake was faster than that of the Lushan earthquake during 1999 and 2007.