结合余震反投影成像2001年昆仑山M_w7.8地震破裂过程
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摘要
反投影方法在地震破裂过程研究中有着重大应用,但其在时差校正方面仍存在一些值得改进的地方。传统反投影时差校正是利用主震震中处观测值与理论到时值来计算校正项,并应用于整个震源区。而当地震破裂尺度较大时,震区各点在地球模型结构上的差异较大,仅仅用主震震中来进行校正会产生较大误差。因此,本文在传统反投影时差校正基础上加入余震信息,来改善传统反投影方法对破裂尺度较大地震时差校正中存在的这一缺陷,并将其应用到2001年昆仑山地震的破裂过程成像中。结果表明,利用单一震中进行时差校正成像结果在距震中较小范围内效果较好,在距其较远的范围内成像结果较差,而利用余震共同进行时差校正后,成像结果得到了明显的改善。由此可见,结合余震信息来进行时差校正的方法可有效改善反投影成像的结果,尤其是对破裂尺度较大的地震破裂过程的成像结果有较大的改善作用。
The back-projection method has a great application in the study of seismic rupture process,but there are still some merits to be improved in the area of time difference correction.The traditional back-projection move out correction is applied to the whole fo-cal area based on the observed values at the epicenter of the main shock and the theoretical values to calculate the correction term.However,when the scale of earthquake rupture is large,there is a great difference in the structure of the earth model between different points in the earthquake area,and the correction of the epicenter of the main shock will cause great errors.Therefore,in this paper,aftershock information is added on the basis of the traditional back-projection time difference correction to improve the defect of the traditional back-projection method in the correction of the large seismic time difference in the rupture scale,and it is applied to the imaging of the rupture process of the Kunlun mountain earthquake in 2001.The results show that time difference correction imaging with a single epicenter is better in a small range from the epicenter,and the imaging results are poor in a far range from the epicenter,but the imaging results are improved obviously after the use of aftershocks in the joint time difference correction.It can be seen that the method of time difference correction based on aftershock information can effectively improve the results of backprojection imaging,especially for the seismic rupture process with larger rupture scale.
The back-projection method has a great application in the study of seismic rupture process,but there are still some merits to be improved in the area of time difference correction.The traditional back-projection move out correction is applied to the whole fo-cal area based on the observed values at the epicenter of the main shock and the theoretical values to calculate the correction term.However,when the scale of earthquake rupture is large,there is a great difference in the structure of the earth model between different points in the earthquake area,and the correction of the epicenter of the main shock will cause great errors.Therefore,in this paper,aftershock information is added on the basis of the traditional back-projection time difference correction to improve the defect of the traditional back-projection method in the correction of the large seismic time difference in the rupture scale,and it is applied to the imaging of the rupture process of the Kunlun mountain earthquake in 2001.The results show that time difference correction imaging with a single epicenter is better in a small range from the epicenter,and the imaging results are poor in a far range from the epicenter,but the imaging results are improved obviously after the use of aftershocks in the joint time difference correction.It can be seen that the method of time difference correction based on aftershock information can effectively improve the results of backprojection imaging,especially for the seismic rupture process with larger rupture scale.
引文
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[11]Wang D,Takeuchi N,Kawakatsu H,et al.Estimating high frequency energy radiation of large earthquakes by image deconvolution back-projection[J].Earth&Planetary Science Letters,2016,449:155-163.
[2]Ishii M,Shearer P M,Houston H,et al.Teleseismic P wave imaging of the 26December 2004Sumatra‐Andaman and 28 March 2005Sumatra earthquake ruptures using the Hi‐net array[J].Journal of Geophysical Research Solid Earth,2007,112(B11):-.
[3]Xu Y,Koper K D,Sufri O,et al.Rupture imaging of the Mw 7.9 12 May 2008 Wenchuan earthquake from back projection of teleseismic P waves[J].Geochemistry Geophysics Geosystems,2009,10(4):-.
[4]Yao H,Shearer P M,Gerstoft P.Subevent location and rupture imaging using iterative backprojection for the 2011Tohoku Mw 9.0earthquake[J].Geophysical Journal International,2012,190(2):1 152-1 168.
[5]王文明,温联星.反投影与极化分析联合方法确定大地震的破裂过程[C]//中国地球物理2013——第十分会场论文集,2013.
[6]张旭,许力生.基于等矩反投影方法的地震破裂过程研究[J].国际地震动态,2015(9):27-27.
[7]Rawlinson N,Kennett B L N.Rapid estimation of relative and absolute delay times across a network by adaptive stacking[J].Geophysical Journal of the Royal Astronomical Society,2004,157(1):332-340.
[8]Muirhead K J.Eliminating False Alarms when detecting Seismic Events Automatically[J].Nature,1968,217(5128):533-534.
[9]Kanasewich E R.Nth-Root Stack Nonlinear Multichannel Filter[J].Geophysics,2012,38(2):327-338.
[10]Wang D,Mori J,Koketsu K.Fast rupture propagation for large strike-slip earthquakes[J].Earth&Planetary Science Letters,2016,440:115-126.
[11]Wang D,Takeuchi N,Kawakatsu H,et al.Estimating high frequency energy radiation of large earthquakes by image deconvolution back-projection[J].Earth&Planetary Science Letters,2016,449:155-163.