巴姆地震变形场和应力场:Ⅱ.用FEPG有限元方法求解
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摘要
本文利用 FEPG 有限元程序对2003年12月的巴姆地震变形场和应力场进行了模拟计算。2003年12月26日,巴姆地区发生6.6级地震。Nakamura、Suzuki 等人利用余震资料和地震破坏程度的分布图分析了余震震中的统计分布形式,得到了此次地震的发震断层是巴姆断层以西大约5km 的 Arg-e-Bam 隐伏断层的结论。凌勇等人从差分干涉雷达(D-InSAR)出发,得到了此次地震的同震干涉条纹和雷达视线方向的位移场,并从雷达干涉的相干图上确定了发震断层的痕迹。他们还利用 Okada 程序模拟计算了此次地震的位移场,模拟计算的结果与 D-InSAR 测量的位移场比较符合。Okada 程序从断层的位错为出发点进行计算,从运动学角度对此次地震变形场和应力场进行研究;本文从动力学的角度出发,研究远场区域边界的应力状态以及断层的物性参数的变化对巴姆地震形变场的影响,将各种计算结果进行对比的同时也和前人的结果相比较。本文计算中采用了凌勇等人的断层参数,即 Arg-e-Bam 隐伏断层为近南北走向,向东倾斜,近直立的倾角,右旋走滑,其(Strike,dip,slip)为(175°,80°,173°)。断层未延伸到地表,自地面以下1km 处往下延伸16km 的宽度,断层长度为20km。对断层的杨氏模量、泊松比、断层附近区域的边界受力大小、两个主应力的比例以及主应力的方向的改变对计算结果的影响做了讨论。最后通过上述几组计算结果建立了一个与前人结果较为符合的巴姆地震参数模型。通过计算,一方面揭示了应力状态和物性参数的影响,另一方面也说明 Arg-e-Bam 隐伏断层是此次地震的发震断层这一结论是可信的。
The deformation and stress field of Bam earthquake Mw6.6 was computationally simulated in this study using FEPG finite element program.Barn earthquake Mw6.6 occurred in the southeastern part of Iran at 1:56 UTC(5:26 in local time)on December 26,2003.Nakamura and Suzuki analyzed the statistical distribution of aftershock epicenters and pointed it out that the fault on which the earthquake occurred should be a blind steeply-dipping,right lateral strike-slip fault(Arg-e-Bam fault)about 5 km to the west of Bam fault.Ling et al.has obtained the co-seismic interferometry fringes and deformation field along the radar direction using D-InSAR data.The trace of the earthquake fault was clearly displayed on the D-InSAR image.They also calculated the northern,eastern,and vertical displacement components simulated from Arg-e-Bam rupture using Okada's program.The result agrees with the one from the D-InSAR measurement very well.However,Okada program does not implicit the stress state of the rupture.In this paper,we used the finite element program to carry out a dynamic simulation of the earthquake process.We studied the effects of far field stress state and the material parameters on the co-seismic deformation field.The results using different models and parameters were compared to each other and also to the previous results.The influences of Young's modulus,Poisson ratio,boundary stress,including the value of stress, ratio between major stress and minor stress、the direction of major/minor stress were studied.From the calculation result,the parameter combination and far field stress field were obtained,which matches the InSar measurement as well as the Okada calculation very well.Our result verified the conclusion that Arg-e-Bam Fault is the rupture fault of Bam earthquake on December 26,2003.
The deformation and stress field of Bam earthquake Mw6.6 was computationally simulated in this study using FEPG finite element program.Barn earthquake Mw6.6 occurred in the southeastern part of Iran at 1:56 UTC(5:26 in local time)on December 26,2003.Nakamura and Suzuki analyzed the statistical distribution of aftershock epicenters and pointed it out that the fault on which the earthquake occurred should be a blind steeply-dipping,right lateral strike-slip fault(Arg-e-Bam fault)about 5 km to the west of Bam fault.Ling et al.has obtained the co-seismic interferometry fringes and deformation field along the radar direction using D-InSAR data.The trace of the earthquake fault was clearly displayed on the D-InSAR image.They also calculated the northern,eastern,and vertical displacement components simulated from Arg-e-Bam rupture using Okada's program.The result agrees with the one from the D-InSAR measurement very well.However,Okada program does not implicit the stress state of the rupture.In this paper,we used the finite element program to carry out a dynamic simulation of the earthquake process.We studied the effects of far field stress state and the material parameters on the co-seismic deformation field.The results using different models and parameters were compared to each other and also to the previous results.The influences of Young's modulus,Poisson ratio,boundary stress,including the value of stress, ratio between major stress and minor stress、the direction of major/minor stress were studied.From the calculation result,the parameter combination and far field stress field were obtained,which matches the InSar measurement as well as the Okada calculation very well.Our result verified the conclusion that Arg-e-Bam Fault is the rupture fault of Bam earthquake on December 26,2003.
引文
Dziewonski A M and Anderson D L.1981． Preliminary Reference Earth Model.Plays.Earth Planet.Int.,25:297-356
Ling Y,Zeng QM,Luo Y aud Zhao YH.2006． Deformation and stress field of Bam earthquake:I.InSar and Okada calculation.Acta Petrologica Sinica,22(9) :2367-2374(in Chinese with English abstract)
Nakamura T,Suzuki S,Sadeghi H,Aghda SMF,Matsushima T,Ito Y,Hosseini SK,Gandomi AJ & Maleki M.2005． Source fault structure of the 2003 Bam earthquake,southeastern Iran,inferred from the aftershock distribution and its relation to the heavily damaged area:Existence of the Arg-e-Bam fault proposed.Geophys.Res.Lett.,32:L09308,doi:10． 1029/2005GL022631
Okada Y.1985． Surface derormation due to shear and tensile faults in a half-space.Bull.Seism.Soc.Am.,75:1135-1154
Talebian M et al.2004． The 2003 Bam(Iran)earthquake:rupture of a blind strike-slip fault,Geophys.Res.Lett.,31,doi:10． 1029/2004GL020058
Yagi Y.2004． Preliminary Results of Rupture Process for 2003 December 26 Southeastern IRAN.Earthquake,IISEE
凌勇.2005． 基于 D-InSAR 的巴姆 Mw6． 6地震变形场研究.北京:北京大学[硕士学位论文]
凌勇,曾祺明,罗扬,赵永红.2006． 巴姆地震变形场和应力场:Ⅰ.用差分干涉雷达和 Okada 方法求解.岩石学报,22(9) :2367-2374
梁国平.2003． 基于 FEPG 的有限元方法.北京:北京飞箭软件有限公司
梁国平.1988． 有限元程序自动生成系统“FEPG”软件包.北京:中国科学院数学研究所
Ling Y,Zeng QM,Luo Y aud Zhao YH.2006． Deformation and stress field of Bam earthquake:I.InSar and Okada calculation.Acta Petrologica Sinica,22(9) :2367-2374(in Chinese with English abstract)
Nakamura T,Suzuki S,Sadeghi H,Aghda SMF,Matsushima T,Ito Y,Hosseini SK,Gandomi AJ & Maleki M.2005． Source fault structure of the 2003 Bam earthquake,southeastern Iran,inferred from the aftershock distribution and its relation to the heavily damaged area:Existence of the Arg-e-Bam fault proposed.Geophys.Res.Lett.,32:L09308,doi:10． 1029/2005GL022631
Okada Y.1985． Surface derormation due to shear and tensile faults in a half-space.Bull.Seism.Soc.Am.,75:1135-1154
Talebian M et al.2004． The 2003 Bam(Iran)earthquake:rupture of a blind strike-slip fault,Geophys.Res.Lett.,31,doi:10． 1029/2004GL020058
Yagi Y.2004． Preliminary Results of Rupture Process for 2003 December 26 Southeastern IRAN.Earthquake,IISEE
凌勇.2005． 基于 D-InSAR 的巴姆 Mw6． 6地震变形场研究.北京:北京大学[硕士学位论文]
凌勇,曾祺明,罗扬,赵永红.2006． 巴姆地震变形场和应力场:Ⅰ.用差分干涉雷达和 Okada 方法求解.岩石学报,22(9) :2367-2374
梁国平.2003． 基于 FEPG 的有限元方法.北京:北京飞箭软件有限公司
梁国平.1988． 有限元程序自动生成系统“FEPG”软件包.北京:中国科学院数学研究所
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