利用数字地震台网资料联合反演福建地区Q值、场地响应和震源参数
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摘要
文中利用福建数字地震台网1998年建网以来记录的2.5级以上地震的波形资料,采用Atkinson等提出的方法计算了福建地区地震波非弹性衰减系数、几何扩散系数和台站场地响应。考虑到该方法在计算台站场地响应时得到的结果是相对场地响应,利用Moya等提出的方法对台站场地响应进行重新计算,对震源谱的低频水平和拐角频率进行联合反演,并计算了参与反演的地震的新参数(地震矩、应力降和破裂半径),同时讨论了它们之间的关系。反演结果表明福建地区地壳平均Q值与频率的关系为Q=504.1×f0.332,而场地响应均表现为与频率相关并基本在1附近波动,这与福建数字地震台站基本建立在基岩之上的实际情况相符合。震源参数的计算结果表明,地震矩与震级以及震源谱拐角频率的相关性较好,而地震矩与应力降以及应力降与震源半径之间的依赖关系不很明确,这可能与参与计算的地震数量以及震级范围有关。
Using the waveform data of M≥2.5 earthquakes from Fujian digital seismic station network since 1998, the inelastic attenuation coefficient, geometric diffusion coefficient, site response and seismic source parameters of seismic waves of Fujian area are calculated based on the algorithms proposed by Atkinson et al. Considering that the site response calculated by Atkinson's method is only the relative response, the method proposed by Moya is used to recalculate the site response. The low frequency level and corner frequency of seismic source spectrum are inversed and the new seismic parameters (seismic moment, stress drop, rupture radius) taking part in the inversion are calculated. In the meantime, the relationships between them are discussed. The inversion results indicate that the relationship between average Q value of Fujian area and the frequency is Q=504.1×f 0.332, and the site response is around 1 and correlated to frequency.This result is coincident to the situation that Fujian digital seismic stations are almost built on the bedrock. Calculations of seismic source parameters suggest that there is good correlations between seismic moment and seismic magnitude, while the correlations between seismic moment and stress drop, the stress drop and source radius are not so well, due to, possibly, the lack of the quantity of earthquakes and the limit of seismic magnitude that take part in the inversion.
Using the waveform data of M≥2.5 earthquakes from Fujian digital seismic station network since 1998, the inelastic attenuation coefficient, geometric diffusion coefficient, site response and seismic source parameters of seismic waves of Fujian area are calculated based on the algorithms proposed by Atkinson et al. Considering that the site response calculated by Atkinson's method is only the relative response, the method proposed by Moya is used to recalculate the site response. The low frequency level and corner frequency of seismic source spectrum are inversed and the new seismic parameters (seismic moment, stress drop, rupture radius) taking part in the inversion are calculated. In the meantime, the relationships between them are discussed. The inversion results indicate that the relationship between average Q value of Fujian area and the frequency is Q=504.1×f 0.332, and the site response is around 1 and correlated to frequency.This result is coincident to the situation that Fujian digital seismic stations are almost built on the bedrock. Calculations of seismic source parameters suggest that there is good correlations between seismic moment and seismic magnitude, while the correlations between seismic moment and stress drop, the stress drop and source radius are not so well, due to, possibly, the lack of the quantity of earthquakes and the limit of seismic magnitude that take part in the inversion.
引文
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刘建华,刘福田,王凤霞,等.1999.单台Lg尾波QcLg的测量研究[J].地球物理学报,42(3):371—381.LIUJian hua,LIUFu tian,WANGFeng xia,etal.1999.Ameasuringstudyforsingle traceLgcodaQcLg[J].Chi neseJGeophys,42(3):371—381(inChinese).
AkiK.1969.Analysisoftheseismiccodaoflocalearthquakesasscatteredwaves[J].JGeophysRes,74:615—631.
AtkinsonGM,MereuRF.1992.TheshapeofgroundmotionattenuationcurvesinsoutheasternCanada[J].Bull SeisSocAmer,82:2014—2031.
BindiD,SpallarossaD,AuglieraP,etal.2001.Sourceparametersestimatedfromtheaftershockofthe1997Umbria Marche(Italy)seismicsequence[J].BullSeisSocAmer,91(3):448—455.
BruneJN.1970.Tectonicstressandthespectraofseismicshearwavesfromearthquakes[J].JGeophysRes,75:4997—5009.
ChengCC,Mitchell.1981.CrustalQintheUnitedStatesfrommultimodesurfacewaves[J].BullSeisSocAmer,
71:161—181.
DziewonskiAMandJSteim.1982.Dispersionandattenuationofmantlewavesfromwaveforminversion[J].Geo physJRastroSoc,70:503—527.
HollandJH.1975.AdaptationinNatureandArtificialSystem[M].AnnArbor:universityofMichiganpress.1—132.
HoughSE,LeesJM,MonasteroF.1999.AttenuationandsourcepropertiesattheCosoGeothermalarea,California[J].BullSeisSocAmer,89(6):1606—1619.
JinA,AkiK.1988.SpatialandtemporalcorrelationbetweencodaQandseismicityinChina[J].BullSeisSocA mer,78(2):741—769.
KeiitiAki,PaulGRichards.1980.Quantitativeseismology:TheoryandMethodsVolumeⅡ[M].825.
MitchellBJ.1975.RegionalRayleighwaveattenuationinNorthAmerica[J].JGeophysRes,81:4904—4916.
MoyaCA,AguirreJ,IrikuraK.2000.Inversionofsourceparametersandsiteeffectsfromstronggroundmotionre cordsusinggeneticalgorithms[J].BullSeisSocAmer,90(4):977—992.
RomanowiczB.1995.AglobaltomographicmodelofshearattenuationintheupperMantle[J].JGeophysRes,12:375—394.
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