鲜水河—安宁河—则木河断裂带上可能存在的凹凸体:来自背景地震活动性的证据
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摘要
基于1992—2002年小震双差重新定位结果,沿鲜水河—安宁河—则木河断裂带走向的震源剖面作b值及局部复发时间TL值的空间扫描,以确定断裂带上可能存在的凹凸体。结果显示,b值沿断裂带走向具明显的空间非均匀性,与地表几何结构的分段变异是相应的。异常短的TL值及低b值出现在鲜水河断裂带的炉霍—道孚间、安宁河断裂带的石棉—冕宁段以及则木河断裂带的西昌—普格段,表明在间震期这些段落破裂产生的小震平均震级大于其他段落上的小震,是断裂带中相对活跃的段落。由b值与应力成反比的关系,推测这些段落可能为断裂带上凹凸体所在地,成为现今应力积累的闭锁段,是未来主震初始破裂最有可能形成的段落,其中石棉—冕宁段的地震危险性最大。而在鲜水河断裂带南东段的乾宁—康定—石棉一带,尽管历史地震与现今小震都异常活跃,但具有异常高的b值及TL值估计,表明现今应力水平较低,目前可能成为以小震活动为主的蠕滑段,不具大震危险性。
We mapped b value and local recurrence time TL along the 700km long, left-lateral strike slip Xianshuihe-Anninghe-Zemuhe fault zone using the relocated microseismicity between 1992 and 2002 that projected onto the cross section to identify the possible locations of asperities. Strong variations in b value are observed along the strike of the fault zone, which are consistent with the surface faulting segmentation in geometry. The anomalously short local recurrence time TL and low b value estimates appear on the Luhuo-Daofu segment of the Xianshuihe fault zone, the Shimian-Mianning segment of the Anninghe fault zone, and the Xichang-Puge segment of the Zemuhe fault zone, suggesting that these segments may be the relatively active parts that produce relatively larger microearthquakes than average during the inter seismic interval time. With the hypothesis that b value is inversely proportional to the stress, we interpret these three segments as the possible asperities on the fault zone, where the future mainshock will be initiated as the high stress has been accumulated there. The risk from the Shimian-Mianning segment is especially noticeable, which is a well-known historic earthquake gap. The anomalously high b value and long TL estimates on the southeastern segment of the Xianshuihe fault zone along Qianning-Kangding-Shimian suggest that this segment may be creeping under low stress at present, and no near future mainshock is expected, although both the historic earthquakes and microseismicity are active there.
We mapped b value and local recurrence time TL along the 700km long, left-lateral strike slip Xianshuihe-Anninghe-Zemuhe fault zone using the relocated microseismicity between 1992 and 2002 that projected onto the cross section to identify the possible locations of asperities. Strong variations in b value are observed along the strike of the fault zone, which are consistent with the surface faulting segmentation in geometry. The anomalously short local recurrence time TL and low b value estimates appear on the Luhuo-Daofu segment of the Xianshuihe fault zone, the Shimian-Mianning segment of the Anninghe fault zone, and the Xichang-Puge segment of the Zemuhe fault zone, suggesting that these segments may be the relatively active parts that produce relatively larger microearthquakes than average during the inter seismic interval time. With the hypothesis that b value is inversely proportional to the stress, we interpret these three segments as the possible asperities on the fault zone, where the future mainshock will be initiated as the high stress has been accumulated there. The risk from the Shimian-Mianning segment is especially noticeable, which is a well-known historic earthquake gap. The anomalously high b value and long TL estimates on the southeastern segment of the Xianshuihe fault zone along Qianning-Kangding-Shimian suggest that this segment may be creeping under low stress at present, and no near future mainshock is expected, although both the historic earthquakes and microseismicity are active there.
引文
[1]四川省地震局.鲜水河—安宁河—则木河断裂带1∶50000活动断裂填图资料.1995.
[1]Wyss M,Brune J N.The Alaska earthquake of28March1964:Acomplex multiple rupture[J].Bull Sei m Soc Am,1967,57(5):1017-1023.
[2]Lay T,Kanamori H,Ruff L.The asperity model andthe na-ture of large subduction zone earthquakes[J].Earthquake Prediction Res,1982,1:3-72.
[3]Aki K.Asperities,barriers,characteristic earthquakes and strong motion prediction[J].J Geophy Res,1984,89(B7):5867-5872.
[4]Wiemer S,Wyss M.Mapping the frequency-magnitude dis-tributionin asperities:Ani mprovedtechnique to calculate re-currence ti mes[J]-J Geophy Res,1997,102(B7):15115-15128.
[5]Miyamura S,Omote S,Teissryre R,et al.Multiple shocks and earthquake series pattern[J].Bull Int Inst SeismolEarthquake Eng,1964,2:71-92.
[6]Lay T,Kanamori H.The asperity model of earthquake sources and its i mplication for triggering and discri mination[M]∥Earthquake prediction:Aninternational review,Mau-rice Ewing Ser,4,Vol.Washington D C,AGU,1981:579-592.
[7]Christensen D H,Beck S L.The rupture process andtectonic i mplications of the great1964Prince William Sound earth-quake[J].Pure Appl Geophys,1994,142(1):29-53.
[8]Wyss M.Locked and creeping patches along the Hayward fault,California[J].Geophys Res Lett,2001,28(18):3537-3540.
[9]Scholz C H.The frequency-magnitude relation of microfrac-turingin rock and its relation to earthquakes[J].Bull Sei m Soc Am,1968,58(1):399-415.
[10]Urbancic TI,Trifu CI,Long J M,et al.Space-ti me corre-lations ofbvalues with stress release[J].Pure Appl Geo-phys,1992,139(3-4):449-462.
[11]Wyss M,Schorlemmer D,Wiemer S.Mapping asperities by mini ma of local recurrence ti me:San Jacinto-Elsinore fault zones[J].J Geophy Res,2000,105(B4):7829-7844.
[12]ncel A O,Wyss M.The major asperities of the1999Mw=7.4Izmit earthquake defined bythe microseismicity of thetwo decades beforeit[J].Geophys J Int,2000,143(3):501-506.
[13]Zuniga F R,Wyss M.Most andleast-likelylocations of large to great earthquakes along the pacific coast of Mexico esti-mated fromlocal recurrence ti mes based onb-values[J].Bull Sei mSoc Am,2001,91(6):1717-1728.
[14]Wyss M,Matsumura S.Most likely location of large earth-quakes inthe Kanto and Tokai areas,Japan,based onthelo-cal recurrence ti mes[J].Physics of the Earth and Planetary Interiors,2002,131(2):173-184.
[15]Xu X W,Wen X Z,Zheng R Z,et al.Pattern of latest tec-tonic motion and its dynamics for active blocks in Sichuan-Yunnan region,China[J].Sciencein China:Series D,2003,46(Suppl):210-226.
[16]Zhang G M,Ma H S,Wang H,et al.Boundaries between active-tectonic blocks and strong earthquakes in the China mainland[J].Chinese J Geophys,2005,48(3):602-610(in Chinese).
[17]Yi G X,Wen X Z,Fan J,et al.Assessing current faulting behaviours and seismic risk of the Anninghe-Aemuhe fault zone fromseismicity parameters[J].Acta Seismologica Sini-ca,2004,26(30):294-303(in Chinese).
[18]Yi G X,Fan J,Wen X Z.Study on faulting behaviour and fault-segments for potential strong earthquake risk along the central-southern segment of Xianshuihe fault zone based on current seismicity[J].Earthquake,2005,25(1):58-65(in Chinese).
[19]Zhu A L,Xu X W,Zhou Y S,et al.Relocation of smallearthquakes in western Sichuan,China and its i mplications for active tectonics[J].Chinese J Geophys,2005,48(3):629-636(in Chinese).
[20]Wiemer S.Analysis of Seismicity:New Techniques and Case studies[D].Fairbanks,Alaska:University of Alaska,1996.
[21]Wiemer S.Asoftware package to analyze seismicity:ZMAP[J].Seism Res Lett,2001,72(3):373-382.
[22]Wiemer S,Wyss M.Mini mum magnitude of completeness in earthquake catalogs:Examples from Alaska,the western US and Japan[J].Bull Seismol Soc Am,2000,90(4):859-869.
[23]Shi Y,Bolt B.The standard error of the magnitude frequency bvalue[J].Bull SeismSoc Am,1982,72(5):1677-1687.
[24]Ren J W,Li P.Earthquake-caused landforms and paleoseis-mic study on the northern segment of the Zemuhe fault[J].Seismology and Geology,1989,11(1):27-34(in Chinese).
[25]Tang R C,Han WB.Active Faults and Earthquakes in Si-chuan[M].Beijing:Seismological Press,1993:50-159(in Chinese).
[26]Tang R C,Wen D H,Deng T G,et al.Preli minary study on the surface rupture feature and seismogenics of the1973Lu-huoM7.9earthquake[J].Chinese J Geophys,1976,19(1):17-27(in Chinese).
[27]Wen X Z,Du P S,Long D X.Character of rupture segmen-tation of the Xianshuihe-Anninghe-Zemuhe fault zone,west-ern Sichuan[J].Seismology and Geology,2000,22(1):1-8(in Chinese).
[28]Amelung F,King G.Earthquake scaling laws for creeping and non-creepingfaults[J].Geophys Res Lett,1997,24(5):507-510.
[29]Frohlich C,Davis S.Teleseismicbvalues:Or,much ado a-bout1.0[J].J Geophys Res,1993,98(B1):631-644.
[30]Chen P S,Bai T X,Li B K.b-value and earthquake occur-rence period[J].Chinese J Geophys,2003,46(4):510-519(in Chinese).
[31]Rubin A M,Gillard D,Got J L.Streaks of microearthquakes along creeping faults[J].Nature,1999,400:635-641.
[15]徐锡伟,闻学泽,郑荣章,等.川滇地区活动块体最新构造变动样式及其动力来源[J].中国科学:D辑,2003,33(增刊):151-162.
[16]张国民,马宏生,王辉,等.中国大陆活动地块边界带与强震活动[J].地球物理学报,2005,48(3):602-610.
[17]易桂喜,闻学泽,范军,等.由地震活动参数分析安宁河—则木河断裂带的现今活动习性及地震危险性[J].地震学报,2004,26(30):294-303.
[18]易桂喜,范军,闻学泽.由现今地震活动分析鲜水河断裂带中南段活动习性与强震危险地段[J].地震,2005,25(1):58-65.
[19]朱艾斓,徐锡伟,周永胜,等.川西地区小震重新定位及其活动构造意义[J].地球物理学报,2005,48(3):629-636.
[24]任金卫,李坪.则木河断裂北段地震地貌及古地震研究[J].地震地质,1989,11(1):27-34.
[25]唐荣昌,韩渭宾.四川活动断裂与地震[M].北京:地震出版社,1993.
[26]唐荣昌,文德华,邓天岗,等.1973年炉霍7.9级地震的地裂缝特征及地震成因的初步探讨[J].地球物理学报,1976,19(1):17-27.
[27]闻学泽,杜平山,龙德雄.安宁河断裂带小相岭段古地震的新证据及最晚事件的年代[J].地震地质,2000,22(1):1-8.
[30]陈培善,白彤霞,李保昆.b值和地震复发周期[J].地球物理学报,2003,46(4):510-519.
[1]Wyss M,Brune J N.The Alaska earthquake of28March1964:Acomplex multiple rupture[J].Bull Sei m Soc Am,1967,57(5):1017-1023.
[2]Lay T,Kanamori H,Ruff L.The asperity model andthe na-ture of large subduction zone earthquakes[J].Earthquake Prediction Res,1982,1:3-72.
[3]Aki K.Asperities,barriers,characteristic earthquakes and strong motion prediction[J].J Geophy Res,1984,89(B7):5867-5872.
[4]Wiemer S,Wyss M.Mapping the frequency-magnitude dis-tributionin asperities:Ani mprovedtechnique to calculate re-currence ti mes[J]-J Geophy Res,1997,102(B7):15115-15128.
[5]Miyamura S,Omote S,Teissryre R,et al.Multiple shocks and earthquake series pattern[J].Bull Int Inst SeismolEarthquake Eng,1964,2:71-92.
[6]Lay T,Kanamori H.The asperity model of earthquake sources and its i mplication for triggering and discri mination[M]∥Earthquake prediction:Aninternational review,Mau-rice Ewing Ser,4,Vol.Washington D C,AGU,1981:579-592.
[7]Christensen D H,Beck S L.The rupture process andtectonic i mplications of the great1964Prince William Sound earth-quake[J].Pure Appl Geophys,1994,142(1):29-53.
[8]Wyss M.Locked and creeping patches along the Hayward fault,California[J].Geophys Res Lett,2001,28(18):3537-3540.
[9]Scholz C H.The frequency-magnitude relation of microfrac-turingin rock and its relation to earthquakes[J].Bull Sei m Soc Am,1968,58(1):399-415.
[10]Urbancic TI,Trifu CI,Long J M,et al.Space-ti me corre-lations ofbvalues with stress release[J].Pure Appl Geo-phys,1992,139(3-4):449-462.
[11]Wyss M,Schorlemmer D,Wiemer S.Mapping asperities by mini ma of local recurrence ti me:San Jacinto-Elsinore fault zones[J].J Geophy Res,2000,105(B4):7829-7844.
[12]ncel A O,Wyss M.The major asperities of the1999Mw=7.4Izmit earthquake defined bythe microseismicity of thetwo decades beforeit[J].Geophys J Int,2000,143(3):501-506.
[13]Zuniga F R,Wyss M.Most andleast-likelylocations of large to great earthquakes along the pacific coast of Mexico esti-mated fromlocal recurrence ti mes based onb-values[J].Bull Sei mSoc Am,2001,91(6):1717-1728.
[14]Wyss M,Matsumura S.Most likely location of large earth-quakes inthe Kanto and Tokai areas,Japan,based onthelo-cal recurrence ti mes[J].Physics of the Earth and Planetary Interiors,2002,131(2):173-184.
[15]Xu X W,Wen X Z,Zheng R Z,et al.Pattern of latest tec-tonic motion and its dynamics for active blocks in Sichuan-Yunnan region,China[J].Sciencein China:Series D,2003,46(Suppl):210-226.
[16]Zhang G M,Ma H S,Wang H,et al.Boundaries between active-tectonic blocks and strong earthquakes in the China mainland[J].Chinese J Geophys,2005,48(3):602-610(in Chinese).
[17]Yi G X,Wen X Z,Fan J,et al.Assessing current faulting behaviours and seismic risk of the Anninghe-Aemuhe fault zone fromseismicity parameters[J].Acta Seismologica Sini-ca,2004,26(30):294-303(in Chinese).
[18]Yi G X,Fan J,Wen X Z.Study on faulting behaviour and fault-segments for potential strong earthquake risk along the central-southern segment of Xianshuihe fault zone based on current seismicity[J].Earthquake,2005,25(1):58-65(in Chinese).
[19]Zhu A L,Xu X W,Zhou Y S,et al.Relocation of smallearthquakes in western Sichuan,China and its i mplications for active tectonics[J].Chinese J Geophys,2005,48(3):629-636(in Chinese).
[20]Wiemer S.Analysis of Seismicity:New Techniques and Case studies[D].Fairbanks,Alaska:University of Alaska,1996.
[21]Wiemer S.Asoftware package to analyze seismicity:ZMAP[J].Seism Res Lett,2001,72(3):373-382.
[22]Wiemer S,Wyss M.Mini mum magnitude of completeness in earthquake catalogs:Examples from Alaska,the western US and Japan[J].Bull Seismol Soc Am,2000,90(4):859-869.
[23]Shi Y,Bolt B.The standard error of the magnitude frequency bvalue[J].Bull SeismSoc Am,1982,72(5):1677-1687.
[24]Ren J W,Li P.Earthquake-caused landforms and paleoseis-mic study on the northern segment of the Zemuhe fault[J].Seismology and Geology,1989,11(1):27-34(in Chinese).
[25]Tang R C,Han WB.Active Faults and Earthquakes in Si-chuan[M].Beijing:Seismological Press,1993:50-159(in Chinese).
[26]Tang R C,Wen D H,Deng T G,et al.Preli minary study on the surface rupture feature and seismogenics of the1973Lu-huoM7.9earthquake[J].Chinese J Geophys,1976,19(1):17-27(in Chinese).
[27]Wen X Z,Du P S,Long D X.Character of rupture segmen-tation of the Xianshuihe-Anninghe-Zemuhe fault zone,west-ern Sichuan[J].Seismology and Geology,2000,22(1):1-8(in Chinese).
[28]Amelung F,King G.Earthquake scaling laws for creeping and non-creepingfaults[J].Geophys Res Lett,1997,24(5):507-510.
[29]Frohlich C,Davis S.Teleseismicbvalues:Or,much ado a-bout1.0[J].J Geophys Res,1993,98(B1):631-644.
[30]Chen P S,Bai T X,Li B K.b-value and earthquake occur-rence period[J].Chinese J Geophys,2003,46(4):510-519(in Chinese).
[31]Rubin A M,Gillard D,Got J L.Streaks of microearthquakes along creeping faults[J].Nature,1999,400:635-641.
[15]徐锡伟,闻学泽,郑荣章,等.川滇地区活动块体最新构造变动样式及其动力来源[J].中国科学:D辑,2003,33(增刊):151-162.
[16]张国民,马宏生,王辉,等.中国大陆活动地块边界带与强震活动[J].地球物理学报,2005,48(3):602-610.
[17]易桂喜,闻学泽,范军,等.由地震活动参数分析安宁河—则木河断裂带的现今活动习性及地震危险性[J].地震学报,2004,26(30):294-303.
[18]易桂喜,范军,闻学泽.由现今地震活动分析鲜水河断裂带中南段活动习性与强震危险地段[J].地震,2005,25(1):58-65.
[19]朱艾斓,徐锡伟,周永胜,等.川西地区小震重新定位及其活动构造意义[J].地球物理学报,2005,48(3):629-636.
[24]任金卫,李坪.则木河断裂北段地震地貌及古地震研究[J].地震地质,1989,11(1):27-34.
[25]唐荣昌,韩渭宾.四川活动断裂与地震[M].北京:地震出版社,1993.
[26]唐荣昌,文德华,邓天岗,等.1973年炉霍7.9级地震的地裂缝特征及地震成因的初步探讨[J].地球物理学报,1976,19(1):17-27.
[27]闻学泽,杜平山,龙德雄.安宁河断裂带小相岭段古地震的新证据及最晚事件的年代[J].地震地质,2000,22(1):1-8.
[30]陈培善,白彤霞,李保昆.b值和地震复发周期[J].地球物理学报,2003,46(4):510-519.
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