汶川地震强地面运动模拟
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摘要
基于确定性震源模型的方法主要用于计算低频(<1Hz)地震波,难以计算高频地震波;高频(>1Hz)地震动常用经验格林函数法或随机方法,对低频地震动模拟不够准确.本文在确定性震源模型方法基础上,尝试采用分解给定的震源模型的方法来模拟宽频带(0.1—10Hz)强地面运动,即采用分级离散断层面和分解断层面破裂单元上升时间的方法,增加震源时间函数中的高频信号,从而避免了对地震记录丰富程度和准确性的依赖.文中模拟计算了汶川MS8.0地震在8个地震观测台的地震动,将模拟结果和观测记录进行了加速度时程曲线和傅里叶振幅谱的对比分析.对比结果显示,模拟估计的地震动峰值加速度和持续时间与观测记录的数据基本在±50%的精度范围内相同,傅里叶振幅谱显示模拟结果有得到10Hz左右的高频成分.四川盆地中的台站模拟结果高频衰减比观测记录要快,原因是模拟过程没有考虑场地效应.对强地震动模拟还是要综合考虑震源、传播路径和场地的影响.研究结果表明,此改变震源输入的确定性方法可应用于模拟近断层宽频强地面运动.
Theoretical seismology method based on deterministic source function is mainly used in the low frequency wave simulation,since it is hard to simulate high frequency component precisely.High frequency wave can be simulated with stochastic approach or using empirical green's function,but these technique does not work for low frequency.Based on the deterministic simulation method,we try to simulate the broadband frequency(0.1—10 Hz) strong ground-motion by subdividing the slip distribution across the fault plane.This method is to discretize the fault in second order and decompose the rise time variation to increase the high frequency components in the source function,so as to avoid the dependence on the accuracy and richness of seismic records.We simulated ground motions of Wenchuan earthquake at 8 selected stations located near the fault.The results show an overall agreement on the peak acceleration and duration within ±50% tolerance between the simulated and observed accelerations.The simulated Fourier spectra have the components as high as 10 Hz.The simulated Fourier spectrum at the stations in Sichuan basin attenuate faster than the observed because the method did not consider site effect.The strong ground motion simulation should take all the source,propagation path and site effect into consideration.Result of this study indicates that this deterministic method of changing input source function can be applied to simulation of near-fault strong ground motion in broad frequency band.
Theoretical seismology method based on deterministic source function is mainly used in the low frequency wave simulation,since it is hard to simulate high frequency component precisely.High frequency wave can be simulated with stochastic approach or using empirical green's function,but these technique does not work for low frequency.Based on the deterministic simulation method,we try to simulate the broadband frequency(0.1—10 Hz) strong ground-motion by subdividing the slip distribution across the fault plane.This method is to discretize the fault in second order and decompose the rise time variation to increase the high frequency components in the source function,so as to avoid the dependence on the accuracy and richness of seismic records.We simulated ground motions of Wenchuan earthquake at 8 selected stations located near the fault.The results show an overall agreement on the peak acceleration and duration within ±50% tolerance between the simulated and observed accelerations.The simulated Fourier spectra have the components as high as 10 Hz.The simulated Fourier spectrum at the stations in Sichuan basin attenuate faster than the observed because the method did not consider site effect.The strong ground motion simulation should take all the source,propagation path and site effect into consideration.Result of this study indicates that this deterministic method of changing input source function can be applied to simulation of near-fault strong ground motion in broad frequency band.
引文
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王海云,谢礼立.2008.近断层地震动模拟现状[J].地球科学进展,23(10):1043-1049.
谢礼立,陶夏新,王国新.2001.强地震动估计和地震危险性评定[J].东北地震研究,17(1):1-8.
章文波,于湘伟.2010.1999年台湾集集大地震强地面运动的模拟[J].地震工程与工程振动,(3):1-11.
张勇,冯万鹏,许力生,周成虎,陈运泰.2008.2008年汶川大地震的时空破裂过程[J].中国科学:D辑,38(10):1186-1194.
赵志新,赵昭,徐纪人,久保田隆二.2006.用数值模拟格林函数方法合成近源地面运动地震图[J].科学通报,51(18):2181-2188.
Aki K,Richards P G.1980.Quantitative Seismology:Theory and Methods[M].San Francisco:New York W H Free-man&CoLtd:800-848.
Bjerrum L W,Sorensen M B,Atakan K.2010.Strong ground-motion simulation of the12May2008MW7.9Wenchuanearthquake,using various slip models[J].Bull Seism Soc Amer,100(5B):2396-2424.
Boore D M.1983.Stochastic simulation of high-frequency ground motions based on seismological models of the radiatedspectra[J].Bull Seism Soc Amer,73(6A):1865-1884.
Boore D M.2003.Simulation of ground motion using the stochastic method[J].Pure Appl Geophs,160(3):635-676.
Chen X F.1999.Seismogram Synthesis in multi-layered half-space PartⅠ:Theoretical formulations[J].Earthquake Re-search in China,(02):53-78.
Hartzell S.1978.Earthquake after shocks as Green’s functions[J].Geophs Res Lett,5(1):1-4.
Irikura K.1983.Semi-empirical estimation of strong ground motions during large earthquakes[J].Bull Disas Prev ResInst,Kyoto Univ,33(Part2),No298:63-104.
Irikura K.1986.Prediction of strong acceleration motion using empirical Green’s function[C]∥Proc7th Japan EarthqEng Symp:151-156.
Motazedian D,Atkinson G M.2005.Stochastic finite-fault modeling based on a dynamic corner frequency[J].Bull SeismSoc Amer,95(3):995-1010.
Nakamura T,Seiji T,Yoshiyuki K,Yoshiko Y.2009.Rupture process of the2008Wenchuan,China earthquake in-ferred from teleseismic waveform inversion and forward modeling of broadband seismic waves[J].Tectonophysics,491(1-4):72-84.
Olson A H,Apsel R J.1982.Finite faults and inverse theory with applications to the1979Imperial Valley earthquake[J].Bull Seism Soc Amer,72(6A):1969-2001.
Pitarka A,Somerville P,Fukushima Y,Uetake T,Irikura K.2000.Simulation of near-fault strong-ground motion usinghybrid Green’s functions[J].Bull Seism Soc Amer,90(3):566-586.
Zhang W,Shen Y,Chen X.2008.Numerical simulation of strong ground motion for the MS8.0Wenchuan earthquake of12May2008[J].Science in China:Series D,51(12):1673-1682.
王海云,谢礼立.2008.近断层地震动模拟现状[J].地球科学进展,23(10):1043-1049.
谢礼立,陶夏新,王国新.2001.强地震动估计和地震危险性评定[J].东北地震研究,17(1):1-8.
章文波,于湘伟.2010.1999年台湾集集大地震强地面运动的模拟[J].地震工程与工程振动,(3):1-11.
张勇,冯万鹏,许力生,周成虎,陈运泰.2008.2008年汶川大地震的时空破裂过程[J].中国科学:D辑,38(10):1186-1194.
赵志新,赵昭,徐纪人,久保田隆二.2006.用数值模拟格林函数方法合成近源地面运动地震图[J].科学通报,51(18):2181-2188.
Aki K,Richards P G.1980.Quantitative Seismology:Theory and Methods[M].San Francisco:New York W H Free-man&CoLtd:800-848.
Bjerrum L W,Sorensen M B,Atakan K.2010.Strong ground-motion simulation of the12May2008MW7.9Wenchuanearthquake,using various slip models[J].Bull Seism Soc Amer,100(5B):2396-2424.
Boore D M.1983.Stochastic simulation of high-frequency ground motions based on seismological models of the radiatedspectra[J].Bull Seism Soc Amer,73(6A):1865-1884.
Boore D M.2003.Simulation of ground motion using the stochastic method[J].Pure Appl Geophs,160(3):635-676.
Chen X F.1999.Seismogram Synthesis in multi-layered half-space PartⅠ:Theoretical formulations[J].Earthquake Re-search in China,(02):53-78.
Hartzell S.1978.Earthquake after shocks as Green’s functions[J].Geophs Res Lett,5(1):1-4.
Irikura K.1983.Semi-empirical estimation of strong ground motions during large earthquakes[J].Bull Disas Prev ResInst,Kyoto Univ,33(Part2),No298:63-104.
Irikura K.1986.Prediction of strong acceleration motion using empirical Green’s function[C]∥Proc7th Japan EarthqEng Symp:151-156.
Motazedian D,Atkinson G M.2005.Stochastic finite-fault modeling based on a dynamic corner frequency[J].Bull SeismSoc Amer,95(3):995-1010.
Nakamura T,Seiji T,Yoshiyuki K,Yoshiko Y.2009.Rupture process of the2008Wenchuan,China earthquake in-ferred from teleseismic waveform inversion and forward modeling of broadband seismic waves[J].Tectonophysics,491(1-4):72-84.
Olson A H,Apsel R J.1982.Finite faults and inverse theory with applications to the1979Imperial Valley earthquake[J].Bull Seism Soc Amer,72(6A):1969-2001.
Pitarka A,Somerville P,Fukushima Y,Uetake T,Irikura K.2000.Simulation of near-fault strong-ground motion usinghybrid Green’s functions[J].Bull Seism Soc Amer,90(3):566-586.
Zhang W,Shen Y,Chen X.2008.Numerical simulation of strong ground motion for the MS8.0Wenchuan earthquake of12May2008[J].Science in China:Series D,51(12):1673-1682.
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