汶川地震余震序列中2个疑似深于30km余震的波形研究
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摘要
寻找并确认更深的余震,对认识汶川主震的深部构造环境、应力状态具有一定的意义。已有研究表明,绝大多数汶川地震余震深度在20km以内,但近期的研究提出了2个余震可能深于30km的证据,为了确认这2个疑似深震的震源深度,本文通过计算理论地震图测试了震源深度及震中距对P波偏振的影响,并与实际观测的P波偏振信息进行对比分析。此外,还使用近震深度震相sPL波拟合的方法来测定震源深度,确认了这2个地震的深度在10～15km范围。
Accurate depths of aftershocks are a help to understand deep tectonic structure and stress field beneath the Longmenshan fault.Depths of most aftershocks of the MS8.0 Wenchuan earthquake were reported in upper crust(<25km).Recently,some observations were regarded as evidences to two deep aftershocks(>30km).We analyzed broadband seismogram of these events based on P wave polarity and sPL waveform,but they both support the depths less than 20km.To confirm the error source,we investigated residuals of other events with high location precision and considered dominant errors arising from inaccuracy locations of some temporal seismic stations.
Accurate depths of aftershocks are a help to understand deep tectonic structure and stress field beneath the Longmenshan fault.Depths of most aftershocks of the MS8.0 Wenchuan earthquake were reported in upper crust(<25km).Recently,some observations were regarded as evidences to two deep aftershocks(>30km).We analyzed broadband seismogram of these events based on P wave polarity and sPL waveform,but they both support the depths less than 20km.To confirm the error source,we investigated residuals of other events with high location precision and considered dominant errors arising from inaccuracy locations of some temporal seismic stations.
引文
黄媛、吴建平、张天中等,2008,汶川8.0级大地震及其余震序列重定位研究,中国科学(D辑),38,1242～1249。
刘春、吴忠良、蒋长胜,2009,汶川地震序列中较大深度余震的一种可能的直接观测证据,中国地震,25(2),113～122。
罗艳、倪四道、曾祥方等,2010,汶川地震余震区东北端一个余震序列的地震学研究,中国科学:地球科学,40,677～687。
吕坚、苏金蓉、靳玉科,2008,汶川8.0级地震序列重新定位及其发震构造初探,地震地质,30(4),917～925。
马宗晋、张家声、刘国栋,1990,大陆多震层研究现状和讨论,地震地质,12(3),262～264。
万柯松,倪四道,赵里,2010,龙门山周边地区地震波速度结构的有限频率反演,国际地震动态,(6),16～16。
杨智娴、陈运泰、郑月军等,2003,双差地震定位法在我国中西部地区地震精确定位中的应用,中国科学(D辑),33,129～134。
张国民、汪素云、李丽等,2002,中国大陆地震震源深度及其构造含义,科学通报,47,663～668。
张瑞青、吴庆举、李永华等,2008,汶川中强余震震源深度的确定及其意义,中国科学(D辑),38,1234～1241。
赵珠、陈农,1995,龙门山断裂带四川北段震源位置的精确修定,四川地震,4(4),19～30。
赵珠、范军、郑斯华等,1997,龙门山断裂带地壳速度结构和震源位置的精确修定,地震学报,19(6),615～622。
郑勇、马宏生、吕坚等,2009,汶川地震强余震(MS≥5.6)的震源机制解及其与发震构造的关系,中国科学(D辑),39,413～426。
朱艾斓、徐锡伟、刁桂苓等,2008,汶川MS8.0地震部分余震重新定位及地震构造初步分析,地震地质,30(3),759～767。
Bock G,Grunthal G,Wylegalla K,1996,The1985/86Western Bohemia earthquakes:modeling source parameters with syntheticseismograms,Tectonophysics,261,139～146.
Douglas A,1967,Joint epicenter determination,Nature,215,45～48.
Engdahl E R,Hilst R,Buland R,1998,Global teleseismic earthquake relocation with improved travel times and procedures fordepth determination,Bull Seism Soc Am,88,722～743.
Gupta H K,Sarma S V S,Harinarayana T et al,1996,Fluids below the hypocentral region of Latur earthquake,India:Geophysicalindicators,Geophy Res Lett,23,1569～1572.
Kastrup U,Deichmann N,2007,A Fr¨ohlich and D.Giardini(2007).Evidence for an active fault below the northwestern Alpineforeland of Switzerland,Geophys J Int,169,1273～1288.
Kim W Y,Dineva S,Ma S et al,2006,The4August2004,Lake Ontario,Earthquake,Seism Res Lett,77,65～73.
Langston C,1987,Depth of faulting during the1968Meckering,Australia,earthquake sequence determined from waveformanalysis of local seismograms,J Geophys Res,92,11561～11574.
Ma S,Atkinso M G,2006,Focal depths for small to moderate earthquakes(mN≥2.8)in Western Quebec,Southern Ontario,and Northern New York,Bull Seism Soc Am,96,609～623.
Mori J,1991,Estimates of velocity structure and source depth using multiple P waves from aftershocks of the1987Elmore Ranchand Superstition Hills,California,earthquakes,Bull Seism Soc Am,81,508～523.
Murphy J B,Barker B W,2006,Improved Focal-Depth determination through automated identification of the seismic depth phasespP and sP,Bull Seism Soc Am,96,1213～1229.
Romney C,1957,Seismic waves form the Dixie Valley Fairvjew Peak earthquakes,Bull Seism Soc Am,47,301～319.
Royden L H,Burchfie B C,Hilst R D,2008,The geological evolution of the Tibetan Plateau,Science,321,1054～1508.
Saikia C,Woods B,Thio H,2001,Calibration of the regional crustal waveguide and the retrieval of source parameters usingwaveform modeling,Pure Appl Geophys,158,1301～1338.
Scholz C H,2002,The mechanics of earthquakes and faulting.Cambridge University Press.Paperback(Hardback),471,GBP32.95,ISBN0521655404.
Spence W,1980,Relative epicenter determination using P-wave arrival-time differences,Bull Seism Soc Am,70,171～183.
Waldhanser F,Ellsworth W L,2000,A double-difference earthquake location algorithm:method and application to the NorthernHayward Fault California,Bull Seism Soc Am,90,1353～1368..
刘春、吴忠良、蒋长胜,2009,汶川地震序列中较大深度余震的一种可能的直接观测证据,中国地震,25(2),113～122。
罗艳、倪四道、曾祥方等,2010,汶川地震余震区东北端一个余震序列的地震学研究,中国科学:地球科学,40,677～687。
吕坚、苏金蓉、靳玉科,2008,汶川8.0级地震序列重新定位及其发震构造初探,地震地质,30(4),917～925。
马宗晋、张家声、刘国栋,1990,大陆多震层研究现状和讨论,地震地质,12(3),262～264。
万柯松,倪四道,赵里,2010,龙门山周边地区地震波速度结构的有限频率反演,国际地震动态,(6),16～16。
杨智娴、陈运泰、郑月军等,2003,双差地震定位法在我国中西部地区地震精确定位中的应用,中国科学(D辑),33,129～134。
张国民、汪素云、李丽等,2002,中国大陆地震震源深度及其构造含义,科学通报,47,663～668。
张瑞青、吴庆举、李永华等,2008,汶川中强余震震源深度的确定及其意义,中国科学(D辑),38,1234～1241。
赵珠、陈农,1995,龙门山断裂带四川北段震源位置的精确修定,四川地震,4(4),19～30。
赵珠、范军、郑斯华等,1997,龙门山断裂带地壳速度结构和震源位置的精确修定,地震学报,19(6),615～622。
郑勇、马宏生、吕坚等,2009,汶川地震强余震(MS≥5.6)的震源机制解及其与发震构造的关系,中国科学(D辑),39,413～426。
朱艾斓、徐锡伟、刁桂苓等,2008,汶川MS8.0地震部分余震重新定位及地震构造初步分析,地震地质,30(3),759～767。
Bock G,Grunthal G,Wylegalla K,1996,The1985/86Western Bohemia earthquakes:modeling source parameters with syntheticseismograms,Tectonophysics,261,139～146.
Douglas A,1967,Joint epicenter determination,Nature,215,45～48.
Engdahl E R,Hilst R,Buland R,1998,Global teleseismic earthquake relocation with improved travel times and procedures fordepth determination,Bull Seism Soc Am,88,722～743.
Gupta H K,Sarma S V S,Harinarayana T et al,1996,Fluids below the hypocentral region of Latur earthquake,India:Geophysicalindicators,Geophy Res Lett,23,1569～1572.
Kastrup U,Deichmann N,2007,A Fr¨ohlich and D.Giardini(2007).Evidence for an active fault below the northwestern Alpineforeland of Switzerland,Geophys J Int,169,1273～1288.
Kim W Y,Dineva S,Ma S et al,2006,The4August2004,Lake Ontario,Earthquake,Seism Res Lett,77,65～73.
Langston C,1987,Depth of faulting during the1968Meckering,Australia,earthquake sequence determined from waveformanalysis of local seismograms,J Geophys Res,92,11561～11574.
Ma S,Atkinso M G,2006,Focal depths for small to moderate earthquakes(mN≥2.8)in Western Quebec,Southern Ontario,and Northern New York,Bull Seism Soc Am,96,609～623.
Mori J,1991,Estimates of velocity structure and source depth using multiple P waves from aftershocks of the1987Elmore Ranchand Superstition Hills,California,earthquakes,Bull Seism Soc Am,81,508～523.
Murphy J B,Barker B W,2006,Improved Focal-Depth determination through automated identification of the seismic depth phasespP and sP,Bull Seism Soc Am,96,1213～1229.
Romney C,1957,Seismic waves form the Dixie Valley Fairvjew Peak earthquakes,Bull Seism Soc Am,47,301～319.
Royden L H,Burchfie B C,Hilst R D,2008,The geological evolution of the Tibetan Plateau,Science,321,1054～1508.
Saikia C,Woods B,Thio H,2001,Calibration of the regional crustal waveguide and the retrieval of source parameters usingwaveform modeling,Pure Appl Geophys,158,1301～1338.
Scholz C H,2002,The mechanics of earthquakes and faulting.Cambridge University Press.Paperback(Hardback),471,GBP32.95,ISBN0521655404.
Spence W,1980,Relative epicenter determination using P-wave arrival-time differences,Bull Seism Soc Am,70,171～183.
Waldhanser F,Ellsworth W L,2000,A double-difference earthquake location algorithm:method and application to the NorthernHayward Fault California,Bull Seism Soc Am,90,1353～1368..
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