伽师震源区中等强度地震矩张量反演及其应力场特征
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摘要
使用区域数字地震台站记录的宽频带长周期波形资料,在时间域反演了1997～2004年伽师震源区52次中等强度地震的矩张量.反演结果揭示,在小尺度的伽师震源区内,震源机制解的P轴、T轴和N轴呈现出明显的分区特征.本文进一步把伽师震源区分为东区和西区,分别反演了东区与西区的应力场.应力场反演结果表明,东区的应力场主压应力轴走向为321°,基本水平.最大主张应力走向68°,倾角40°.截至2004年7月,伽师震源区西部的应力场一直较为稳定,最大主压应力方向为12°,最大主张应力方向282°,二者都基本水平,中等主应力轴基本直立.自西向东,伽师震源区最大主压应力轴逆时针旋转了49°,并且西区张应力的水平作用较为显著,东区压应力的水平作用显著.应力场的这种非均匀变化特征与GPS观测得到的地壳运动速率的空间分布以及塔里木盆地边界附近的地形地貌特征有很好的一致性.震源区深部结构的陡变以及位于震源区东部边界规模较大的NW走向的普昌断裂和色力布亚隐伏断裂可能对产生这种横向非均匀的局部应力场起了重要的作用.
Moment tensors of 52 moderate earthquakes occurred in Jiashi source region,Xinjiang,from 1997 to 2004 were determined in time domain by using the long period waveforms recorded by regional broadband stations.The results demonstrate significant variations of the orientation and plunge of P,T and N axis from west to east.Therefore,we further divided the whole region into two parts,which are called the western part and the eastern part,and performed the stress tensor inversion respectively.The results show that in the eastern part,the maximum principal axis σ1 is almost horizontal and trends 321°,the minimum principal axis σ3 trends 68° with a plunge of 40°,and σ2trends 213° with a plunge about 40°.Till 2004,the stress within the western part remained stable,with the σ1and σ3 nearly horizontal and trending to 12° and 282° respectively,the middle axis σ2 almost vertical.Thus the maximum principal stress σ1 significantly rotates counterclockwise from N10°E in the west part to N39°W in the east part across the whole studied region.Compared with the stress field in the eastern part,the western part is under a stronger horizontal tension effect.This bilateral perturbation of stress field is consistent with the pattern of crustal deformation rate from GPS observation,as well as the topography map at the structure boundary between Tarim basin and Tienshan.We infer that both the sharp deformation in the deep crust and the large-scale NW-trending Puchang and Selibuya fault structures may play a crucial role in forming the local stress perturbation.
Moment tensors of 52 moderate earthquakes occurred in Jiashi source region,Xinjiang,from 1997 to 2004 were determined in time domain by using the long period waveforms recorded by regional broadband stations.The results demonstrate significant variations of the orientation and plunge of P,T and N axis from west to east.Therefore,we further divided the whole region into two parts,which are called the western part and the eastern part,and performed the stress tensor inversion respectively.The results show that in the eastern part,the maximum principal axis σ1 is almost horizontal and trends 321°,the minimum principal axis σ3 trends 68° with a plunge of 40°,and σ2trends 213° with a plunge about 40°.Till 2004,the stress within the western part remained stable,with the σ1and σ3 nearly horizontal and trending to 12° and 282° respectively,the middle axis σ2 almost vertical.Thus the maximum principal stress σ1 significantly rotates counterclockwise from N10°E in the west part to N39°W in the east part across the whole studied region.Compared with the stress field in the eastern part,the western part is under a stronger horizontal tension effect.This bilateral perturbation of stress field is consistent with the pattern of crustal deformation rate from GPS observation,as well as the topography map at the structure boundary between Tarim basin and Tienshan.We infer that both the sharp deformation in the deep crust and the large-scale NW-trending Puchang and Selibuya fault structures may play a crucial role in forming the local stress perturbation.
引文
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[2]Dreger D S,Savage B.Aftershocks of the1952Kern County,California,Earthquake Sequence.Bull.Seism.Soc.Am.,1998,89:1094～1108
[3]Kim S G,Kraeva N.Source parameter determination of local earthquakes in Lorea using moment tensor inversion of single station data.Bull.Seismol.Soc.Am.,1999,89(4):1077～1082
[4]Tan Y,Zhu L,Hel mberger D V,Saikia C K.Locating and modeling regional earthquakes with two stations.J.Geophys.Res.,2006,111,B01306,doi:10.1029/2005JB003775
[5]Fan G,Wallace T.The determination of source parameters for small earthquakes from a single,very broadband seismic station.Geophys.Res.Lett.,1991,18(8):1385～1388
[6]Dreger D S,Hel mberger D V.Determination of source parameters at regional distances withthree-components sparse network data.J.Geophys.Res.,1993,98:8107～8125
[7]Romanowicz B,Dreger B D,Pasyanos M,et al.Monitoring of strain release in central and northern California using broadband data.Geophys.Res.Let.,1993,20:1643～1646
[8]Randall G E,Ammom C J,Owens T J.Mooment tensor estimation using regional seismograms froma Tibetan Plateauprotable network deployment.J Geophys Res.,1995,22(13):1665～1668
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[12]Saikia K S.Modified frequency-wavenumber algorithm for regional seismograms using Filon′s quadrature:modeling of Lg waves in eastern North America.Geophys.Journ.Int.,1994,118:142～158
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[16]Kuge K,Kawakatsu H.Significant of non-double couple component of deep and intermediate-depth earthquakes:implications from moment tensor inversions of long-period seismic waves.Phys.Earth and Planetary Interior.,1993,75:243～226
[17]Gephart J W,Forsyth D W.An improved method for determining the regional stress tensor using earthquake focal mechanismdata:application to the San Fernando earthquake sequence.J.Geophys.Res.,1984,89:9305～9320
[18]Gephart J W.Stress and the direction of slip on fault planes.Tectonics,1990,9(4):845～858
[19]Ghose S,Hamberger M W.Source parameters of moderate-sized earthquakes in Tienshan,central Asia form regional moment tensor inversion.Geophys.Res.Let.,1998,26:3181～3184
[20]许忠淮,汪素云,黄雨蕊等.由大量地震测量资料推断的我国大陆构造应力场.地球物理学报,1989,32(5):536～647Xu Z H,Wang S Y,Huang Y R,et al.Tectonic stress field in continental China inferred from many earthquake data.Chinese J.Geophys.(in Chinese),1989,32(5):536～647
[21]刁桂苓,王海涛,高国英等.伽师强震系列应力场的转向过程.地球物理学报,2005,48(5):1062～1068Diao G L,Wang H T,Gao G Y,et al.A deflection process for the stress field of the Jiashi strong earthquake sequence.Chinese J.Geophys.(in Chinese),2005,48(5):1062～1068
[22]崔效峰,谢富仁,赵建涛.伽师及周围地区现代构造应力场构造特征研究.地震学报,2005,28(4):347～356Cui X F,Xie F R,Zhao J T.Characteristics of recent tectonic stress field in Jiashi,Xinjiang and adjacent regions.Acta Seismologica Sinica(in Chinese),2005,28(4):347～356
[23]赖院根,刘启元,陈九辉等.新疆伽师强震群区的横波分裂与应力场特征.地球物理学报,2002,45(1):83～93Lai Y G,Liu Q Y,Chen J H,et al.Features of the S-wave splittg and stress field in the Xinjiang Jiashi strong earthquake region.Chinese J.Geophys.(in Chinese),2002,45(1):83～93
[24]Zhao D,Xu Y,Wiens D,et al.Depth extent of the Lau back-arc spreading center and its relation to subduction processes.Science,1997,278:254～257
[25]Kao H,Jacques A.Stress tensor inversion for the Chi-Chi earthquake sequence anditsimplications on regional collision.Bull.Seism.Soc.Am.,2001,91(5):1028～1040
[26]Prejean S,Ellsworth WL,Zoback M,et al.Fault structure and kinematics of the Long Valley Caldera region,California,revealed by high-accuracy earthquake hypocenters and focal mechanismstress inversions.J.Geophys.Res.,2002,107:1397,doi:10.1029/2001JB001168
[27]Horton S P,Kim W Y,Mithers M.The6June2003bardwell,kentucky,earthquake sequence:evidence for a locally perturbed stress field in the Mississippi embayment.Bull.Seism.Soc.Am.,2005,95:431～445
[28]Kato A,Sakai S,Hirata N,et al.Imaging the seismic structure and stress fieldinthe source region of the2004mid-Niigata prefecture earthquake:structural zones of weakness and seismogenic stress concentration by ductile flow.J.Geophys.Res.,2006,111(B8):B08308,10.1029/2005JB004016
[29]沈军,陈建波,王翠等.2003年2月24日新疆巴楚-伽师Ms6.8级地震发震构造.地震地质,2006,28(2):205～212Shen J,Chen J B,Wang C,et al.The seismogenic tectonics of theMs6.8Bachu-Jiashi,Xinjiang Earthquake in Feb.24,2003.Seismology and Geology(in Chinese),2006,28(2):205～212
[30]张培震,王琪,马宗晋.中国大陆现今构造运动的GPS速度场与活动地块.地学前缘,2002,9(2):430～441Zhang P Z,Wang Q,Ma Z J.GPS velocity field and active crustal blocks of contemporary tectonic deformation in continental China.Earth Science Frontiers(in Chinese),2002,9(2):430～441
[31]王琪,丁国瑜,乔学军等.天山现今地壳快速缩短与南北地块的相对运动.科学通报,2000,45(14):1543～1547Wang Q,Ding G Y,Qiao X J,et al.,The contemporary crustal shortening of Tienshan and its movement relative to the South-North block.Chinese Science Bulletin,2000,45(14):1543～1547
[2]Dreger D S,Savage B.Aftershocks of the1952Kern County,California,Earthquake Sequence.Bull.Seism.Soc.Am.,1998,89:1094～1108
[3]Kim S G,Kraeva N.Source parameter determination of local earthquakes in Lorea using moment tensor inversion of single station data.Bull.Seismol.Soc.Am.,1999,89(4):1077～1082
[4]Tan Y,Zhu L,Hel mberger D V,Saikia C K.Locating and modeling regional earthquakes with two stations.J.Geophys.Res.,2006,111,B01306,doi:10.1029/2005JB003775
[5]Fan G,Wallace T.The determination of source parameters for small earthquakes from a single,very broadband seismic station.Geophys.Res.Lett.,1991,18(8):1385～1388
[6]Dreger D S,Hel mberger D V.Determination of source parameters at regional distances withthree-components sparse network data.J.Geophys.Res.,1993,98:8107～8125
[7]Romanowicz B,Dreger B D,Pasyanos M,et al.Monitoring of strain release in central and northern California using broadband data.Geophys.Res.Let.,1993,20:1643～1646
[8]Randall G E,Ammom C J,Owens T J.Mooment tensor estimation using regional seismograms froma Tibetan Plateauprotable network deployment.J Geophys Res.,1995,22(13):1665～1668
[9]Wang C Y,Herrmann R B.A numerical study of P,SV,SH-wave generation in a plane layered medium.Bull.Seism.Soc.Am.,1980,70:1015～1036
[10]Herrmann R B,Wang C Y.A comparison of synthetic seismograms.Bull.Seism.Soc.Am.,1985,75:41～56
[11]Haskell N A.Total energy and energy spectral density of elastic wave radiation from propagating faults.Bull.Seismol.Soc.Am.,1964,54:1811～1841
[12]Saikia K S.Modified frequency-wavenumber algorithm for regional seismograms using Filon′s quadrature:modeling of Lg waves in eastern North America.Geophys.Journ.Int.,1994,118:142～158
[13]刘启元,陈九辉,李顺成等.新疆伽师强震群区三维地壳上地幔S波速度结构及其地震成因的探讨.地球物理学报,2000,43(3):356～365Liu Q Y,Chen J H,Li S C,et al.Passive seismic experiment in Xinjiang Jiashi strong earthquake region and discussion on its seismic genesis.Chinese J.Geophys.(in Chinese),2000,43(3):356～365
[14]张先康,赵金仁,张成科等.帕米尔东北侧地壳结构研究.地球物理学报,2002,45(5):665～671Zhang X K,Zhao J R,Zhang C K,et al.Crustal structure at the North-east side of the Pamirs.Chinese J.Geophys.(in Chinese),2002,45(5):665～671
[15]赵翠萍.1997～2003年新疆伽师震源区特征的地震学方法研究[博士论文].北京:中国地震局地球物理研究所,2006Zhao C P,Seismological studies on the characteristics of Jiashi Source Region from1997to2003[Ph.D.thesis](in Chinese).Beijing:Institute of Earthquake Sciences,China Earthquake Administration,2006
[16]Kuge K,Kawakatsu H.Significant of non-double couple component of deep and intermediate-depth earthquakes:implications from moment tensor inversions of long-period seismic waves.Phys.Earth and Planetary Interior.,1993,75:243～226
[17]Gephart J W,Forsyth D W.An improved method for determining the regional stress tensor using earthquake focal mechanismdata:application to the San Fernando earthquake sequence.J.Geophys.Res.,1984,89:9305～9320
[18]Gephart J W.Stress and the direction of slip on fault planes.Tectonics,1990,9(4):845～858
[19]Ghose S,Hamberger M W.Source parameters of moderate-sized earthquakes in Tienshan,central Asia form regional moment tensor inversion.Geophys.Res.Let.,1998,26:3181～3184
[20]许忠淮,汪素云,黄雨蕊等.由大量地震测量资料推断的我国大陆构造应力场.地球物理学报,1989,32(5):536～647Xu Z H,Wang S Y,Huang Y R,et al.Tectonic stress field in continental China inferred from many earthquake data.Chinese J.Geophys.(in Chinese),1989,32(5):536～647
[21]刁桂苓,王海涛,高国英等.伽师强震系列应力场的转向过程.地球物理学报,2005,48(5):1062～1068Diao G L,Wang H T,Gao G Y,et al.A deflection process for the stress field of the Jiashi strong earthquake sequence.Chinese J.Geophys.(in Chinese),2005,48(5):1062～1068
[22]崔效峰,谢富仁,赵建涛.伽师及周围地区现代构造应力场构造特征研究.地震学报,2005,28(4):347～356Cui X F,Xie F R,Zhao J T.Characteristics of recent tectonic stress field in Jiashi,Xinjiang and adjacent regions.Acta Seismologica Sinica(in Chinese),2005,28(4):347～356
[23]赖院根,刘启元,陈九辉等.新疆伽师强震群区的横波分裂与应力场特征.地球物理学报,2002,45(1):83～93Lai Y G,Liu Q Y,Chen J H,et al.Features of the S-wave splittg and stress field in the Xinjiang Jiashi strong earthquake region.Chinese J.Geophys.(in Chinese),2002,45(1):83～93
[24]Zhao D,Xu Y,Wiens D,et al.Depth extent of the Lau back-arc spreading center and its relation to subduction processes.Science,1997,278:254～257
[25]Kao H,Jacques A.Stress tensor inversion for the Chi-Chi earthquake sequence anditsimplications on regional collision.Bull.Seism.Soc.Am.,2001,91(5):1028～1040
[26]Prejean S,Ellsworth WL,Zoback M,et al.Fault structure and kinematics of the Long Valley Caldera region,California,revealed by high-accuracy earthquake hypocenters and focal mechanismstress inversions.J.Geophys.Res.,2002,107:1397,doi:10.1029/2001JB001168
[27]Horton S P,Kim W Y,Mithers M.The6June2003bardwell,kentucky,earthquake sequence:evidence for a locally perturbed stress field in the Mississippi embayment.Bull.Seism.Soc.Am.,2005,95:431～445
[28]Kato A,Sakai S,Hirata N,et al.Imaging the seismic structure and stress fieldinthe source region of the2004mid-Niigata prefecture earthquake:structural zones of weakness and seismogenic stress concentration by ductile flow.J.Geophys.Res.,2006,111(B8):B08308,10.1029/2005JB004016
[29]沈军,陈建波,王翠等.2003年2月24日新疆巴楚-伽师Ms6.8级地震发震构造.地震地质,2006,28(2):205～212Shen J,Chen J B,Wang C,et al.The seismogenic tectonics of theMs6.8Bachu-Jiashi,Xinjiang Earthquake in Feb.24,2003.Seismology and Geology(in Chinese),2006,28(2):205～212
[30]张培震,王琪,马宗晋.中国大陆现今构造运动的GPS速度场与活动地块.地学前缘,2002,9(2):430～441Zhang P Z,Wang Q,Ma Z J.GPS velocity field and active crustal blocks of contemporary tectonic deformation in continental China.Earth Science Frontiers(in Chinese),2002,9(2):430～441
[31]王琪,丁国瑜,乔学军等.天山现今地壳快速缩短与南北地块的相对运动.科学通报,2000,45(14):1543～1547Wang Q,Ding G Y,Qiao X J,et al.,The contemporary crustal shortening of Tienshan and its movement relative to the South-North block.Chinese Science Bulletin,2000,45(14):1543～1547
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