帕米尔-兴都库什地区中源地震的空间分布和震源机制解特征
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摘要
利用国际地震中心(ISC)提供的1964至2003年的高精度地震资料,给出了帕米尔-兴都库什地区中源地震带更完整、更明确的几何形态.兴都库什中源地震带(H带)和帕米尔中源地震带(P带)的倾向和最大深度沿走向有变化,可以进一步划分为HW段(H带西段)、HE段(H带东段)、PSW段(P带西南段)、PM段(P带中段)和PNE段(P带东北段).H带在170~190 km深度附近存在地震空区,其下方地震带的倾角明显大于上方,接近垂直.同时,空区下方的地震带沿东西方向成连续的倒"V"字形,两个分支的交角接近垂直.西段分支属于HW段,较浅,没有双层结构;东段分支属于HE段,较深,有双层结构.中源地震的震源机制解规律明显.兴都库什地区主要以近垂直的T轴和近水平的垂直于地震带走向的P轴为特征.帕米尔地区的震源机制解由西南到东北逐渐由P轴近水平并沿地震带走向,转变为B轴近水平并沿走向,直至T轴近水平并沿走向.同时,P轴方向由西向东逐渐转为恒定地与地震带的走向相垂直.最后,我们讨论了这一地区地震活动可能的动力学成因.
In this paper,high quality seismic data in 1964～2003 from the ISC(International Seismological Centre) catalog is used to present a relatively more complete and definite geometric structure of the intermediate seismic zone in the Pamir-Hindu Kush region.Dip directions and the largest depth of the Hindu Kush intermediate seismic zone(H zone) and the Pamir intermediate seismic zone(P zone) change along the strike,so they can be further divided into five segments: HW(west segment of the H zone),HE(east segment of the H zone),PSW(southwest segment of the P zone),PM(middle segment of the P zone),and PNE(northeast segment of the P zone).There is a seismic gap in the H zone at about 170～190 km depth,beneath which the seismic zone dips nearly vertically.Meanwhile,seismic zone beneath the gap forms an inverted V shape zone,the two branches of which are nearly perpendicular with each other.The west branch within the HW segment does not have double seismic layers.The east branch within the HE segment is deeper and has double seismic layers.Focal mechanism solutions of the intermediate earthquakes have regular patterns.In the Hindu Kush region,most T axes are nearly vertical while most P axes are nearly horizontal and perpendicular to the strike of the seismic zone.In the Pamir region,from southwest to northeast,the horizontal axis along the strike changes from P to B and then T;P axes gradually change to be perpendicular to the strike.At last,we discuss the possible geodynamic explanation for the seismicity in this region.
In this paper,high quality seismic data in 1964～2003 from the ISC(International Seismological Centre) catalog is used to present a relatively more complete and definite geometric structure of the intermediate seismic zone in the Pamir-Hindu Kush region.Dip directions and the largest depth of the Hindu Kush intermediate seismic zone(H zone) and the Pamir intermediate seismic zone(P zone) change along the strike,so they can be further divided into five segments: HW(west segment of the H zone),HE(east segment of the H zone),PSW(southwest segment of the P zone),PM(middle segment of the P zone),and PNE(northeast segment of the P zone).There is a seismic gap in the H zone at about 170～190 km depth,beneath which the seismic zone dips nearly vertically.Meanwhile,seismic zone beneath the gap forms an inverted V shape zone,the two branches of which are nearly perpendicular with each other.The west branch within the HW segment does not have double seismic layers.The east branch within the HE segment is deeper and has double seismic layers.Focal mechanism solutions of the intermediate earthquakes have regular patterns.In the Hindu Kush region,most T axes are nearly vertical while most P axes are nearly horizontal and perpendicular to the strike of the seismic zone.In the Pamir region,from southwest to northeast,the horizontal axis along the strike changes from P to B and then T;P axes gradually change to be perpendicular to the strike.At last,we discuss the possible geodynamic explanation for the seismicity in this region.
引文
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[4]Billington S,Isacks B L,Barazangi M.Spatial distribution and focalmechanisms of mantle earthquakes in the Hindu Kush-Pamir region:acontorted Benioff zone.Geology,1977,5:699~704
[5]Roecker S W,Soboleva O V,Nersesov I L,et al.Seismicity and faultplane solutions of intermediate depth earthquakes in the Pamir-HinduKush region.J.Geophys.Res.,1980,85:1358~1364
[6]Chatelain J L,Roecker S W,Hatzfeld D,et al.Microearthquakeseismicity and fault plane solutions in the Hindu Kush region and theirtectonic implications.J.Geophys.Res.,1980,85(B3):1365~
[7]宁杰远,臧绍先.帕米尔-兴都库什地区地震空间分布特征及应力场特征.地球物理学报,1990,33(6):657~669Ning J Y,Zang S X.The distribution of earthquakes and stress statein Pamir-Hindukush regions.Chinese J.Geophys.(in Chinese),1990,33(6):657~669
[8]Fan G W,Ni J F,Wallace T C.Active tectonics of the Pamirs andKarakorum.J.Geophys.Res.,1994,99(B4):7131~7160
[9]Pegler G,Das S.An enhanced image of the Pamir-Hindu Kushseismic zone from relocated earthquake hypocenters.Geophys.J.Int.,1998,134:573~595
[10]Vinnik L P,Lukk A A,Nersesov I L.Nature of the intermediateseismic zone in the mantle of the Pamir-Hindu Kush.Tectonophysics,1977,28:T9~T14
[11]Pavlis T,Das S.The Pamir-Hindu Kush seismic zone as a strainmarker for flow in the upper mantle.Tectonics,2000,19:103~115
[12]Beloussov V V,Belyaevsky N A,Borisov A A,et al.Structure of thelithosphere along the deep seismic sounding profile:Tien Shan-Pamirs-Karakorum-Himalyas.Tectonophysics,1980,70:193~221
[13]Verma R K,Sekhar C C.Seismotectonics and focal mechanisms ofearthquakes from Pamir-Hindukush regions.Tectonophysics,1985,112:297~324
[14]Wessel P,Smith W H F.New,improved version of the GenericMapping Tools released.EOS Trans.AGU,1998,79:579
[15]GTOPO30:http://edc.usgs.gov/products/elevation/gtopo30/gtopo30.html
[16]Zhu L P,Helmberger D V,Saikia C K,et al.Regional waveformcalibration in the Pamir-Hindu Kush region.J.Geophys.Res.,1997,102(B10):22799~22813
[17]Mellors R J,Pavlis G L,Hamburger M W,et al.Evidence for a high-velocity slab associated with the Hindu Kush seismic zone.J.Geophys.Res.,1995,100(B3):4067~4078
[18]雷建设,周蕙兰,赵大鹏.帕米尔及邻区地壳上地幔P波三维速度结构的研究.地球物理学报,2002,45(6):802~812Lei J S,Zhou H L,Zhao D P.3-D velocity structure of P-wave in thecrust and upper-mantle beneath Pamir and adjacent region.ChineseJ.Geophys.(in Chinese),2002,45(6):802~812
[19]Koulakov I,Sobolev S V.A tomographic image of Indian lithospherebreak-off beneath the Pamir-Hindukush region.Geophys.J.Int.,2006,164(2):425~440
[2]Richter C F.Elementary Seismology.W.H.Freeman&Co.,SanFrancisco,CA,1958
[3]Nowroozi A A.Seismo-tectonics of the Persian plateau,easternTurkey,Caucasus,and Hindu-Kush regions.Bull.Seism.Soc.Am.,1971,61:317~341
[4]Billington S,Isacks B L,Barazangi M.Spatial distribution and focalmechanisms of mantle earthquakes in the Hindu Kush-Pamir region:acontorted Benioff zone.Geology,1977,5:699~704
[5]Roecker S W,Soboleva O V,Nersesov I L,et al.Seismicity and faultplane solutions of intermediate depth earthquakes in the Pamir-HinduKush region.J.Geophys.Res.,1980,85:1358~1364
[6]Chatelain J L,Roecker S W,Hatzfeld D,et al.Microearthquakeseismicity and fault plane solutions in the Hindu Kush region and theirtectonic implications.J.Geophys.Res.,1980,85(B3):1365~
[7]宁杰远,臧绍先.帕米尔-兴都库什地区地震空间分布特征及应力场特征.地球物理学报,1990,33(6):657~669Ning J Y,Zang S X.The distribution of earthquakes and stress statein Pamir-Hindukush regions.Chinese J.Geophys.(in Chinese),1990,33(6):657~669
[8]Fan G W,Ni J F,Wallace T C.Active tectonics of the Pamirs andKarakorum.J.Geophys.Res.,1994,99(B4):7131~7160
[9]Pegler G,Das S.An enhanced image of the Pamir-Hindu Kushseismic zone from relocated earthquake hypocenters.Geophys.J.Int.,1998,134:573~595
[10]Vinnik L P,Lukk A A,Nersesov I L.Nature of the intermediateseismic zone in the mantle of the Pamir-Hindu Kush.Tectonophysics,1977,28:T9~T14
[11]Pavlis T,Das S.The Pamir-Hindu Kush seismic zone as a strainmarker for flow in the upper mantle.Tectonics,2000,19:103~115
[12]Beloussov V V,Belyaevsky N A,Borisov A A,et al.Structure of thelithosphere along the deep seismic sounding profile:Tien Shan-Pamirs-Karakorum-Himalyas.Tectonophysics,1980,70:193~221
[13]Verma R K,Sekhar C C.Seismotectonics and focal mechanisms ofearthquakes from Pamir-Hindukush regions.Tectonophysics,1985,112:297~324
[14]Wessel P,Smith W H F.New,improved version of the GenericMapping Tools released.EOS Trans.AGU,1998,79:579
[15]GTOPO30:http://edc.usgs.gov/products/elevation/gtopo30/gtopo30.html
[16]Zhu L P,Helmberger D V,Saikia C K,et al.Regional waveformcalibration in the Pamir-Hindu Kush region.J.Geophys.Res.,1997,102(B10):22799~22813
[17]Mellors R J,Pavlis G L,Hamburger M W,et al.Evidence for a high-velocity slab associated with the Hindu Kush seismic zone.J.Geophys.Res.,1995,100(B3):4067~4078
[18]雷建设,周蕙兰,赵大鹏.帕米尔及邻区地壳上地幔P波三维速度结构的研究.地球物理学报,2002,45(6):802~812Lei J S,Zhou H L,Zhao D P.3-D velocity structure of P-wave in thecrust and upper-mantle beneath Pamir and adjacent region.ChineseJ.Geophys.(in Chinese),2002,45(6):802~812
[19]Koulakov I,Sobolev S V.A tomographic image of Indian lithospherebreak-off beneath the Pamir-Hindukush region.Geophys.J.Int.,2006,164(2):425~440
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