倾斜断层不对称分布引起的几何效应——上下盘效应
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摘要
首先介绍了具有加权平均意义的均方根距离Drms.与断层距Drup和发震断层距Dseis相比,均方根距离可以真实地反映观测点与倾斜断层的整体靠近程度.然后利用断层距、发震断层距和均方根距离,通过回归分析分别对1999年集集地震加速度峰值的上下盘效应进行研究.残差分析表明上盘的加速度峰值明显大于相同断层距或发震断层距处下盘的加速度峰值,而相同均方根距离处的上下盘观测点的加速度峰值没有明显差异.这说明上下盘效应是一种由于倾斜断层的不对称分布引起的几何效应,因此进行地震动衰减分析时,如果采用均方根距离作为观测点与断层之间的距离标准,上下盘效应对近断层地震动的影响可以忽略.
Root-mean-square distance Drms with characteristic of weighted-average is introduced in this paper firstly. Comparing with rupture distance Drup and seismogenic distance Dseis, Drms can exactly reflect general proximity of a site to a dipping fault plane. Then, the hanging wall/footwall effects on the peak ground acceleration (PGA) during the 1999 Jiji(Chi-Chi) earthquake are evaluated by regression analysis using Drup, Dseis and Drms, respectively. The logarithmic residuals illustrate that the PGA on hanging wall is much greater than that on footwall at the same Drup or Dseis. In contrast, there is no significant difference between the PGA on hanging wall and that on footwall at the same Drms. The result indicates that the hanging wall/footwall effect is a geometric effect caused by the asymmetry of dipping fault. Therefore, the hanging wall/footwall effect on the near-fault ground motions can be ignored in the future attenuation analysis if root-mean-square distance is used as the site-to-source distance measure.
Root-mean-square distance Drms with characteristic of weighted-average is introduced in this paper firstly. Comparing with rupture distance Drup and seismogenic distance Dseis, Drms can exactly reflect general proximity of a site to a dipping fault plane. Then, the hanging wall/footwall effects on the peak ground acceleration (PGA) during the 1999 Jiji(Chi-Chi) earthquake are evaluated by regression analysis using Drup, Dseis and Drms, respectively. The logarithmic residuals illustrate that the PGA on hanging wall is much greater than that on footwall at the same Drup or Dseis. In contrast, there is no significant difference between the PGA on hanging wall and that on footwall at the same Drms. The result indicates that the hanging wall/footwall effect is a geometric effect caused by the asymmetry of dipping fault. Therefore, the hanging wall/footwall effect on the near-fault ground motions can be ignored in the future attenuation analysis if root-mean-square distance is used as the site-to-source distance measure.
引文
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Oglesby D D,Archuleta RJ,Nielsen S B.2000.The three di mensional dynamics of dipping faults[J].Bull Seism SocAmer,90:616--628.
Shabestari K T,Yamazaki F.2003.Near-fault spatial variation in strong ground motion due to rupture directivity andhanging wall effects fromthe Chi-Chi,Tai wan earthquake[J].Earthquake Engng Struct Dyn,32:2197--2219.
刘启方,袁一凡,金星.2004.断层附近地面地震动空间分布[J].地震学报,26(2):183--192.
陶夏新,王国新.2003.近场强地震动模拟中对破裂的方向性效应和上盘效应的表达[J].地震学报,25(2):191--198.
许力生,俞言祥,陈运泰.2003.中国强地面运动研究进展[J].地震学报,25(5):475--478.
俞言祥,高孟潭.2001.台湾集集地震近场地震动的上盘效应[J].地震学报,23(6):615--621.
张晓志,胡进军,谢礼立,王海云.2006.近断层基岩强地面运动影响场的显式有限元数值模拟[J].地震学报,28(6):638--644.
Abrahamson N A,Silva WJ.1997.Empirical response spectral attenuation relations for shallowcrustal earthquakes[J].SeismRes Lett,68(1):94--109.
Abrahamson N A,Somerville P G.1996.Effects of the hanging wall andfootwall on ground motions recorded duringtheNorthridge earthquake[J].Bull Seism Soc Amer,86(1B):S93--S99.
Brune J N.1996.Precariously balanced rocks and ground-motion maps for southern California[J].Bull SeismSoc Amer,86(1A):43--54.
Chang T Y,Cotton F,Tsai Y B,Angelier J.2004.Quantification of hanging-wall effects on ground motion:Some in-sights fromthe1999Chi-Chi earthquake[J].Bull Seism Soc Amer,94(6):2186--2197.
Iwata T,Sekiguchi H,Irikura K.2000.Rupture process of the1999Chi-Chi,Tai wan,earthquake and its near-sourcestrong ground motions[C]∥Proc.International Workshop on Annual Commemoration of Chi-Chi Earthquake.Tai-pei,Tai wan,Sept.18--20:36--46.
Lee C T,Cheng C T,Liao C W,Tsai Y B.2001.Site classification of Tai wanfree-field strong-motion stations[J].BullSeismSoc Amer,91:1283--1297.
Oglesby D D,Archuleta RJ,Nielsen S B.2000.The three di mensional dynamics of dipping faults[J].Bull Seism SocAmer,90:616--628.
Shabestari K T,Yamazaki F.2003.Near-fault spatial variation in strong ground motion due to rupture directivity andhanging wall effects fromthe Chi-Chi,Tai wan earthquake[J].Earthquake Engng Struct Dyn,32:2197--2219.
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