2009年姚安地震序列定位及震源区三维P波速度结构研究
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摘要
利用2009年7月9日姚安MS6.0地震序列的到时数据,应用双差层析成像方法,对地震进行了重定位,并反演了震源区的三维速度结构.经过资料选取,共有873次余震事件参加了反演.重定位结果显示,姚安地震余震序列呈WNW向条带状分布,大部分地震的震源深度集中在3—12km之间.从余震的深度分布随时间的变化推测,姚安MS6.0地震震源区的应力分布经过3次调整,开始的40个小时,应力从下向上调整;随后的20个小时,余震散布在3—23km深度范围内,应力在较大深度范围内调整;从第60个小时之后,12km以下的应力调整结束,主要是浅部应力释放.三维速度结构结果表明,姚安主震发生在低速体与高速体的过渡区域,余震主要分布在高低速过渡带及高速体一侧.结合重定位结果,推测在这一高低速过渡带附近存在隐伏断层,走向大约为N65°W.
The Yaoan,Yunnan,MS6.0 earthquake occurred on July 9,2009.By inverting seismic phase arrival time data and using the double-difference tomography approach(Zhang and Thurber),the aftershocks were relocated and a 3-D P-wave velocity structure around the earthquake source region were obtained.After data selection 873 aftershocks were used for inversion.The relocation result shows that aftershocks distribute in a belt with WNW--ESE trend.Focal depth of most aftershocks is between 3 km and 12 km.By analyzing the change of focal depth with time we infer that the stress in the focal region underwent three time adjustment.The stress was adjusted from bottom to top in the first 40 hours,and then was adjusted in a larger depth range in the following 20 hours.After 60 hours,the stress adjustment stopped below the depth of 12 km and the stress was released mainly in the shallow crust.The obtained 3-D velocity structure indicates that the mainshock occurred in a transition zone between low and high velocity bodies.The aftershocks mainly distribute in the velocity transition zone and by the side of the high velocity body.Combining with the relocation result,we infer that there exists a buried fault with ~N65°W strike in the transition zone between low and high velocity anomalies.
The Yaoan,Yunnan,MS6.0 earthquake occurred on July 9,2009.By inverting seismic phase arrival time data and using the double-difference tomography approach(Zhang and Thurber),the aftershocks were relocated and a 3-D P-wave velocity structure around the earthquake source region were obtained.After data selection 873 aftershocks were used for inversion.The relocation result shows that aftershocks distribute in a belt with WNW--ESE trend.Focal depth of most aftershocks is between 3 km and 12 km.By analyzing the change of focal depth with time we infer that the stress in the focal region underwent three time adjustment.The stress was adjusted from bottom to top in the first 40 hours,and then was adjusted in a larger depth range in the following 20 hours.After 60 hours,the stress adjustment stopped below the depth of 12 km and the stress was released mainly in the shallow crust.The obtained 3-D velocity structure indicates that the mainshock occurred in a transition zone between low and high velocity bodies.The aftershocks mainly distribute in the velocity transition zone and by the side of the high velocity body.Combining with the relocation result,we infer that there exists a buried fault with ~N65°W strike in the transition zone between low and high velocity anomalies.
引文
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Zhang H,Thurber C H.2003.Double-difference tomography:The method andits applicationtothe Haywardfault,Cal-ifornia[J].Bull Seism Soc Amer,93:1875--1889.
Zhang H,Thurber C H.2005.Adaptive mesh seismic tomography based on tetrahedral and Voronoi diagrams:Applica-tion to Parkfield,California[J].J Geophys Res,110:B04303,doi:10.1029/2004JB003186.
Zhao D,Hasegawa A,Horiuchi S.1992.Tomographic imaging of P and S wave velocity structure beneath northeasternJapan[J].J Geophys Res,97:19909--19928.
黄嫒,杨建思,张天中.2006.2003年新疆巴楚伽师地震序列的双差法重新定位研究[J].地球物理学报,49(1):162--169.
雷建设,赵大鹏,苏金蓉,张光伟,李凤.2009.龙门山断裂带地壳精细结构与汶川地震发震机理[J].地球物理学报,52(2):339--345.
刘瑞丰,陈培善,李强.1993.云南及邻近地区三维速度图象[J].地震学报,15(1):61--67.
王新岭,刘杰,张国民,赵翠萍.2005.姚安地震序列与永胜地震序列的高精度定位[J].中国地震,21(3):386--397.
杨智娴,陈运泰,郑月军,于湘伟.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[J].中国科学,33(增刊):129--134.
张建国,刘丽芳,李西,谢英情.2009.姚安、大姚中强震区地震构造初析[J].地震地质,31(3):536--543.
张杰卿,刘杰,周龙泉.2009.2000年姚安地震余震区的速度和衰减结构层析成像分析[J].地震,29(3):126--135.
赵翠萍.2006.1997—2003年新疆伽师震源区特征的地震学方法研究[D].北京:中国地震局地球物理研究所:39--42.
Bannister S,Thurber C,Louie J.2006.Detailed fault structure highlighted by finely relocated aftershocks,Arthur’sPass,New Zealand[J].J Geophys Res,33:L18315,doi:10.1029/2006GL027462.
Dorbath C,Woerd J V,Arefiev S S,Rogozhin E A,Aptekman J Y.2008.Geological and seismological field observationsin the epicentral region of the27September2003MW7.2Gorny Altay earthquake(Russia)[J].Bull Seism Soc A-mer,98(6):2849--2865.
Okada T,Hasegawa A,Suganomata J,Zhao D,Zhang H,Thurber C.2007.Imagingthe source area of the1995south-ern Hyogo(Kobe)earthquake(M7.3)using double-difference tomography[J].Earth Planet Sci Lett,253:143--150.
Okada T,Umino N,Matsuzawa T,Nakajima J,Uchida N,Akayama T,Hirahara S,Sato T,Hori S,Kono T,YabeY,Ariyoshi K,Gamage S,Shimizu J,Suganomata J,Kita S,Yui S,Arao M,Hondo S,Mizukami T,TsushimaH,Yaginum T,Hasegawa A,Asano Y,Zhang H,Thurber C.2005.Aftershock distribution and3Dseismic veloci-ty structure inand around the focal area of the2004mid Niigata prefecture earthquake obtained by applying double-difference tomography todense temporary seismic network data[J].Earth Planets Space,57:435--440.
Okada T,Yaginuma T,Umino N,Matsuzawa T,Hasegawa A,Zhang H,Thurber C.2006.Detailed imaging of thefault planes of the2004Niigata-Chuetsu,central Japan,earthquake sequence by double-difference tomography[J].Earth Planet Sci Lett,244:32--43.
Okada T,Hasegawa A,Suganomata J,Umino N,Zhang H,Thurber C.2007.Imagingthe heterogeneous source area ofthe2003M6.4northern Miyagi earthquake,NEJapan,by double-difference tomography[J].Tectonophysics,430:67--81.
ScarfìL,Langer H,Scaltrito A.2009.Seismicity,seismotectonics and crustal velocity structure of the Messina Strait(Italy)[J].Phys Earth Planet Interi,177:65--78.
Thurber C,Zhang H,Waldhauser F,Hardebeck J,Michael A,Eberhart-Phillips D.2006.Three-dimensional compres-sional wavespeed model,earthquake relocations,andfocal mechanisms for the Parkfield,California Region[J].BullSeismSoc Amer,96(4B):S38--S49.
Waldhauser F,Ellsworth W.2000.A double-diference earthquake location algorithm:Method and application to thenorthern Hayward fault,California[J].Bull Seism Soc Amer,90(6):1353--1368.
Zhang H,Thurber C H.2003.Double-difference tomography:The method andits applicationtothe Haywardfault,Cal-ifornia[J].Bull Seism Soc Amer,93:1875--1889.
Zhang H,Thurber C H.2005.Adaptive mesh seismic tomography based on tetrahedral and Voronoi diagrams:Applica-tion to Parkfield,California[J].J Geophys Res,110:B04303,doi:10.1029/2004JB003186.
Zhao D,Hasegawa A,Horiuchi S.1992.Tomographic imaging of P and S wave velocity structure beneath northeasternJapan[J].J Geophys Res,97:19909--19928.
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