论震源辐射问题(英文)
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摘要
地震震源辐射过程是现代地震学中一个复杂而关键的课题 ,而震源谱的研究则是认识震源辐射的重要一环。地震波由震源传播至地球表面 ,经历了一系列诸如路径衰减、地壳表层放大和场地效应等物理作用。其中震波衰减效应包括几何扩散、非弹性衰减 (YQ(f) )和近地表高频衰减。地壳放大作用主要发生于表层或浅层波阻抗梯度带。为了更确切地描述和理解震源辐射谱 ,必须从观测到的地面运动记录中把地震源谱分离出来 ,从而消除传播路径和地表场地效应。强震运动记录是研究震源谱的基本资料。采用频率域方法 ,以傅里叶变换为工具 ,可使时间域的卷积问题简化为频率域的乘积运算。研究区域含日本、墨西哥、土尔其、加利福尼亚、加拿大西部(BritishColumbia)和北美东部 (ENA)等典型构造区。结果表明 ,在适当消除路径和场地效应之后 ,震源谱的基本特征只随震级变化 ,而与研究地区无直接关系 ,亦即震源谱基本独立于构造区域、震源距和震源深度。这对于未来强震运动预测和地震灾害评估具有十分重要的理论和实际意义。与此同时 ,高频衰减因子 (Kappa)与构造环境有关 :低Kappa工资值相应于较稳定的板内构造环境下的硬岩场地 (如北美东部 ) ,而相对较高的Kappa值则相应于比较活跃的构造环境下的场地条件 ,如日本、墨西哥、?
Isolating source spectra is an important step toward for better understanding earthquake source radiation where the nucleation processes is a complex but essential area in modern seismology. To study the spectrum of ground motion radiated from the earthquake source, we must first remove the path and site effects from observed ground motions. Attenuation effects include geometric spreading, anelastic attenuation, and near-surface attenuation. There are also crustal amplification effects, which can be significant where there exists a strong velocity contrast or gradient. Comparing the earthquake source radiation from six tectonic regions: California, Mexico, Turkey, Japan, eastern North America (ENA) and British Columbia (B.C., Canada), I find that source spectra are approximately independent of region, distance, and depth when path and site effects are properly removed. Kappa values vary regionally. The lowest kappa value corresponds to the hard rock sites in a stable intraplate environment (ENA) while generally higher kappa values correspond to the site conditions in active tectonic environments such as Japan, Mexico, B.C., California, and Turkey.
Isolating source spectra is an important step toward for better understanding earthquake source radiation where the nucleation processes is a complex but essential area in modern seismology. To study the spectrum of ground motion radiated from the earthquake source, we must first remove the path and site effects from observed ground motions. Attenuation effects include geometric spreading, anelastic attenuation, and near-surface attenuation. There are also crustal amplification effects, which can be significant where there exists a strong velocity contrast or gradient. Comparing the earthquake source radiation from six tectonic regions: California, Mexico, Turkey, Japan, eastern North America (ENA) and British Columbia (B.C., Canada), I find that source spectra are approximately independent of region, distance, and depth when path and site effects are properly removed. Kappa values vary regionally. The lowest kappa value corresponds to the hard rock sites in a stable intraplate environment (ENA) while generally higher kappa values correspond to the site conditions in active tectonic environments such as Japan, Mexico, B.C., California, and Turkey.
引文
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BooreDMandJoynerWB .1997.Siteamplificationsforgenericrocksites.Bull.Seism.Soc.Am.,87:327341.
CastroRR ,MunguiaLandBruneJN .1995.SourcespectraandsiteresponsefromPandSwavesoflocalearthquakesintheOaxaca,Mexico,subductionzone.Bull.Seism.Soc.Am.,85:923936.
ChenSZ .2000.GlobalComparisonsofEarthquakeSourceSpectra.Ph.D .thesis,CarletonUniversity,436pp,Ottawa.ChenSZandAtkinsonGM .2002.Globalcomparisonsofearthquakesourcespectra.Bull.Seis.Soc.Am.,92:885895.
ChinB HandAkiK .1991.Simutaneousstudyofthesource,path,andsiteeffectsonstronggroundmotionduringthe1989LomaPrietaearthquake:Apreliminaryresultonpervasivenonlinearsiteeffects.Bull.Seism.Soc.Am.,81:18591884.
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HatzfeldD ,KarakostasV ,ZiaziaM ,etal.1997.TheKozaniGrevena(Greece)earthquakeof13May1995revisitedfromadetailedseis mologicalstudy.Bull.Seism.Soc.Am.,87:463473.
HumphreyJrJRandAndersonJG .1992.Shear waveattenuationandsiteresponseinGuerrero,MexicoBull.Seism.Soc.Am.,81:16221645.
HumphreyJr.JRandAndersonJG .1994.SeismicsourceparametersfromtheGuerrerosubductionzoneBull.Seism.Soc.Am.,84:17541769.
KutasRI ,KobolevVPandTsvyashchenkoVA .1998.HeatflowandgeothermalmodeloftheBlackSeadepressionTectonophysics,291:91100.
PapageorgiouASandAkiK .1983.Aspecificbarriermodelforthequantitativedescriptionofinhomogeneousfaultingandthepredictionofstronggroundmotion:I.DescriptionofthemodelBull.Seism.Soc.Am.,73:693722.
RaoofM ,HerrmannRBandMalagniniL .1999.Attenuationandexcitationofthree componentgroundmotioninsouthernCaliforniaBull.Seism.Soc.Am.,89:888902.
SatoT ,HelmbergerDV ,SomervillePG ,etal.1998a.Estimationsofregionalandlocalstrongmotionsduringthegreat1923Kanto,Japan,earthquake(Ms8.2),Part1:sourceestimationofacalibrationeventandmodelingofwavepropagationpathsBull.Seism.Soc.Am.,88:183205.
SatoT ,GravesRW ,SomervillePG ,etal.1998b.Estimationsofregionalandlocalstrongmotionsduringthegreat1923Kanto,Japan,earthquake(Ms8.2),Part2:forwardsimulationofseismogramsusingvariable sliprupturemodelsandestimationofnear faultlong peri odgroundmotions.Bull.Seism.Soc.Am.,88:206227.
ValdesCM ,MooneyWD ,SinghSK ,etal.1986.CrustalstructureofOaxaca,Mexico,fromseismicrefractionmeasurementsBull.Seism.Soc.Am.,76:547563.
AtkinsonGMandBooreDM 1995.NewgroundmotionrelationsforeasternNorthAmerica.Bull.Seism.Soc.Am.,85:1730
AtkinsonGMandChenSZ .1997.RegionalSeismogramsfromhistoricalearthquakesinsoutheasternCanada.Seism.Res.Lett.,68:797807.
AtkinsonGMandHanksTC .1995.Ahigh frequencymagnitudescale.Bull.Seism.Soc.Am.,85:825833.
AtkinsonGMandCassidyJF .2000.Integrateduseofseismographandstrongmotiondatatodeterminesoilamplification:ResponsetotheFraserRiverDeltatotheDuvallandGeorgiaStraitearthquakes.Bull.Seism.Soc.Am.,90:10281040.
BooreDMandJoynerWB .1997.Siteamplificationsforgenericrocksites.Bull.Seism.Soc.Am.,87:327341.
CastroRR ,MunguiaLandBruneJN .1995.SourcespectraandsiteresponsefromPandSwavesoflocalearthquakesintheOaxaca,Mexico,subductionzone.Bull.Seism.Soc.Am.,85:923936.
ChenSZ .2000.GlobalComparisonsofEarthquakeSourceSpectra.Ph.D .thesis,CarletonUniversity,436pp,Ottawa.ChenSZandAtkinsonGM .2002.Globalcomparisonsofearthquakesourcespectra.Bull.Seis.Soc.Am.,92:885895.
ChinB HandAkiK .1991.Simutaneousstudyofthesource,path,andsiteeffectsonstronggroundmotionduringthe1989LomaPrietaearthquake:Apreliminaryresultonpervasivenonlinearsiteeffects.Bull.Seism.Soc.Am.,81:18591884.
ChristensenN .1996.Poisson’sratioandcrustalseismologyJ .Geophys.Res.,101:31393156.
ChristensenNandMooneyW .1995.Seismicvelocitystructureandcompositionofthecontinentalcrust:Aglobalview,J .Geophys.Res.,100:97619788.
GallartJ ,VidalNandDanobeitiaJJ 1995.MultichannelseismicimageofthecrustalthinningattheNEIberianmargincombiningnormalandwide anglereflectiondata.Geophys.Res.Lett.,22:489492.
HatzfeldD ,KarakostasV ,ZiaziaM ,etal.1997.TheKozaniGrevena(Greece)earthquakeof13May1995revisitedfromadetailedseis mologicalstudy.Bull.Seism.Soc.Am.,87:463473.
HumphreyJrJRandAndersonJG .1992.Shear waveattenuationandsiteresponseinGuerrero,MexicoBull.Seism.Soc.Am.,81:16221645.
HumphreyJr.JRandAndersonJG .1994.SeismicsourceparametersfromtheGuerrerosubductionzoneBull.Seism.Soc.Am.,84:17541769.
KutasRI ,KobolevVPandTsvyashchenkoVA .1998.HeatflowandgeothermalmodeloftheBlackSeadepressionTectonophysics,291:91100.
PapageorgiouASandAkiK .1983.Aspecificbarriermodelforthequantitativedescriptionofinhomogeneousfaultingandthepredictionofstronggroundmotion:I.DescriptionofthemodelBull.Seism.Soc.Am.,73:693722.
RaoofM ,HerrmannRBandMalagniniL .1999.Attenuationandexcitationofthree componentgroundmotioninsouthernCaliforniaBull.Seism.Soc.Am.,89:888902.
SatoT ,HelmbergerDV ,SomervillePG ,etal.1998a.Estimationsofregionalandlocalstrongmotionsduringthegreat1923Kanto,Japan,earthquake(Ms8.2),Part1:sourceestimationofacalibrationeventandmodelingofwavepropagationpathsBull.Seism.Soc.Am.,88:183205.
SatoT ,GravesRW ,SomervillePG ,etal.1998b.Estimationsofregionalandlocalstrongmotionsduringthegreat1923Kanto,Japan,earthquake(Ms8.2),Part2:forwardsimulationofseismogramsusingvariable sliprupturemodelsandestimationofnear faultlong peri odgroundmotions.Bull.Seism.Soc.Am.,88:206227.
ValdesCM ,MooneyWD ,SinghSK ,etal.1986.CrustalstructureofOaxaca,Mexico,fromseismicrefractionmeasurementsBull.Seism.Soc.Am.,76:547563.
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