南北地震带地震震源机制解和现今应力特征
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摘要
基于CAP方法,使用地震波形资料,计算得到了2009年1月～2017年8月期间南北地震带及周边区域466个3.5级以上地震震源机制解。在补充收集1976年1月～2017年8月GCMT公布的259个4.5级以上地震震源机制解的基础上,分析了南北地震带地震震源机制解和应力特征。震源机制空间分布显示,不同断裂带、块体间表现出不同的震源机制空间分布特征,该特征与南北地震带不同段落活动构造性质基本吻合。作为青藏高原东边界的南北地震带,由于动力环境复杂,其内部P轴方向具有明显的差异性。这种差异主要表现为:南北地震带北段P轴呈NE向分布;龙门山断裂带及周边除NE段P轴取向为NW—NNW向外,其他地段P轴近EW向;川滇菱形块体内部P轴呈NNW向,而其西边界以西呈NNE向,东边界以东呈NW向,应力方向转换带的与川滇菱形块体边界基本一致。整体而言,南北地震带及近邻P轴方向由北到南发生了顺时针转动。
Using the CAP method,the focal mechanisms of 466 M≥3.5events that occurred in the North-South Seismic Belt from January 2009 to October 2017 have been obtained.Combining the results of 259 focal mechanisms(M≥4.5)from January 1976 to August 2017 from the GCMT,we investigated the characteristics of focal mechanisms and stress in the North-South Seismic Belt of China.The spatial distributions of focal mechanisms differ among different faults and blocks.It is consistent with active tectonics along the North-South Seismic Belt,mostly in eastern margin of the Tibetan Plateau.Under the complex dynamic environment in eastern margin of the Tibetan Plateau,the P axes directions vary much inside the North-South Seismic Belt.The P axes in the northern section of the North-South Seismic Belt are NE direction.In and surround the Longmenshan fault zone the P axes are nearly EW direction except the NE segment which are NW direction.Inside the Sichuan-Yunnan rhombic block the P axes are NNW direction,while in the west of the west boundary are NNE direction,in the east of the east boundary are NW direction.The stress direction transition bands correspond well with the Sichuan-Yunnan rhombic block boundary.Overall,the P axes in the North-South Seismic Belt and its neighbor area have a clockwise rotational pattern from north to south.
Using the CAP method,the focal mechanisms of 466 M≥3.5events that occurred in the North-South Seismic Belt from January 2009 to October 2017 have been obtained.Combining the results of 259 focal mechanisms(M≥4.5)from January 1976 to August 2017 from the GCMT,we investigated the characteristics of focal mechanisms and stress in the North-South Seismic Belt of China.The spatial distributions of focal mechanisms differ among different faults and blocks.It is consistent with active tectonics along the North-South Seismic Belt,mostly in eastern margin of the Tibetan Plateau.Under the complex dynamic environment in eastern margin of the Tibetan Plateau,the P axes directions vary much inside the North-South Seismic Belt.The P axes in the northern section of the North-South Seismic Belt are NE direction.In and surround the Longmenshan fault zone the P axes are nearly EW direction except the NE segment which are NW direction.Inside the Sichuan-Yunnan rhombic block the P axes are NNW direction,while in the west of the west boundary are NNE direction,in the east of the east boundary are NW direction.The stress direction transition bands correspond well with the Sichuan-Yunnan rhombic block boundary.Overall,the P axes in the North-South Seismic Belt and its neighbor area have a clockwise rotational pattern from north to south.
引文
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[23] Klemperer S L.Crustal flow in Tibet:geophysical evidence for the physical state of Tibetan lithosphere,and inferred patterns of active flow[J].Geological Society London Special Publications,2006,268(1):29-70.
[24]许志琴,李海兵,杨经绥.造山的高原—青藏高原巨型造山拼贴体和造山类型[J].地学前缘,2006,13(4):1-17.
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[26]王晓山,吕坚,谢祖军,等.南北地震带震源机制解与构造应力场特征[J].地球物理学报,2015,58(11):4 149-4 162.
[27]王阎昭,王恩宁,沈正康,等.基于GPS资料约束反演川滇地区主要断裂现今活动速率[J].中国科学:地球科学,2008,38(5):582-597.
[2] Patton H.Reference point equalization method for determining the source and path effects of surface waves[J].J Geophys Res,1980,85(B2):821-848.
[3] Patton H,Zandt G.Seismic moment tensors of western U.S.earthquakes and implications for the tectonic stress field[J].J Geophys Res,1991,96(B11):18 245-18 259.
[4] Thio H K,Kanamori H.Moment tensor inversions for local earthquakes using furface waves recorded at TERRAscope[J].Bull Seism Soc Amer,1995,85(4):1 021-1 038.
[5] Wallace T C,Helmberger D V.Determining source parameters of moderate-size earthquakes from regional waveforms[J].Physics of The Earthquake and Planetary Interiors,1982,30(2-3):185-196.
[6] Dreger D S,Helmberger D V.Determination of source parameters at regional distances with threecomponent sparse network data[J].J Geophys Res,1993,98(B5):8 107-8 125.
[7] Fan G,Beck S L,Wallace T C.The seismic source parameters of the 1991Costa Rica aftershock sequence:Evidence for a transcurrent plate boundary[J].J Geophys Res,1994,98(B9):15 759-15 778.
[8] Zhao L S,Helmberger D V.Source estimation from broadband regional seismograms[J].Bull Seism Soc Amer,1994,84(1):91-104.
[9] Zhu L P,Helmberger D V.Advancement in source estimation techniques using broadband regional seismograms[J].Bull Seism Soc Amer,1996,86(5):1 634-1 641.
[10]郑勇,马宏生,吕坚,等.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[J].中国科学:地球科学,2009,39(4):413-426.
[11]罗艳,倪四道,曾详方,等.汶川地震余震区东北端一个余震序列的地震学研究[J].中国科学:地球科学,2010,40(6):677-687.
[12]罗艳,赵里,曾祥方,等.芦山地震序列震源机制及其构造应力场空间变化[J].中国科学:地球科学,2015,45(4):538-550.
[13]韩立波,蒋长胜,包丰.2010年河南太康MS4.6地震序列震源参数的精确确定[J].地球物理学报,2012,55(9):2 973-2 981.
[14]曾祥方,韩立波,倪四道,等.2012年6月24日宁蒗—盐源MS5.7地震震源参数研究[J].地震,2013,33(4):196-205.
[15]吕坚,郑秀芬,肖健,等.2012年9月7日云南彝良MS5.7、MS5.6地震震源破裂特征与发震构造研究[J].地球物理学报,2013,56(8):2 645-2 654.
[16]郑建常,李冬梅,王鹏,等.2013年莱州M4.6地震序列震源机制与发震构造初探[J].地震地质,2015,37(2):384-399.
[17]罗钧,赵翠萍,周连庆.2013年8月香格里拉德钦—德荣MS5.9地震序列震源机制与应力场特征[J].地球物理学报,2015,58(2):424-435.
[18]易桂喜,龙锋,赵敏,等.2014年10月1日越西M5.0地震震源机制与发震构造分析[J].地震地质,2016,38(4):1 124-1 136.
[19]郑秀芬,欧阳彪,张东宁,等.“国家数字测震台网数据备份中心”技术系统建设及其对汶川大地震研究的数据支撑[J].地球物理学报,2009,52(5):1 412-1 417.
[20] Zhu L P,Rivera L A.A note on the dynamic and static displacements from a point source in multilayered media[J].Geophys Res Lett,2002,23(5):435-438.
[21] Laske G,Masters G,Ma Z,Pasyanos M.Update on CRUST1.0-A 1-degree global model of Earth’s crust[J].Geophys Res Abs,2013,15:2658.
[22] Zoback M L.First-and second-order patterns of stress in the lithosphere:The world stress map project[J].J Geophys Res,1992,97(B8):11 703-11 728.
[23] Klemperer S L.Crustal flow in Tibet:geophysical evidence for the physical state of Tibetan lithosphere,and inferred patterns of active flow[J].Geological Society London Special Publications,2006,268(1):29-70.
[24]许志琴,李海兵,杨经绥.造山的高原—青藏高原巨型造山拼贴体和造山类型[J].地学前缘,2006,13(4):1-17.
[25] Meyer B,Tapponnier P,Bourjot L,et al.Crustal thickening in Gansu-Qinghai,lithospheric mantle subduction,and oblique,strike-slip controlled growth of the Tibet plateau[J].Geophysical Journal of International,1998,135:1-47.
[26]王晓山,吕坚,谢祖军,等.南北地震带震源机制解与构造应力场特征[J].地球物理学报,2015,58(11):4 149-4 162.
[27]王阎昭,王恩宁,沈正康,等.基于GPS资料约束反演川滇地区主要断裂现今活动速率[J].中国科学:地球科学,2008,38(5):582-597.