玉树M_S7.1级地震部分余震重新定位及发震构造分析
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摘要
综合利用玉树震区应急流动台站观测数据和青海地震台网固定台站观测数据,依据最新的人工地震宽角反射/折射剖面的速度模型,采用Hypo2000地震定位法,对2010年4月18日至4月29日期间玉树震区发生的部分余震进行了重新定位.重新定位后,震源位置的水平和垂直方向平均误差分别为1.35km和4.68km,走时残差为0.49s.震源深度分布范围为1.48～19.85km,平均震源深度为10.28km.定位研究结果表明:玉树地震余震沿北西-南东向的甘孜—玉树断裂带的北支,即玉树—隆宝断裂分布,长约97km.余震分布特征在主震(微观震中)两侧存在差异,可能反映了两侧构造特征存在差异.截止到4月29日,主震东南仍是应力的主要释放区域,余震强度大且活动密集的区域位于主震东南距主震约5km、横向范围约20km.主震破裂区的大部分应力在主震过程中得以释放,主震时应力未释放的区域成为主要的余震分布区.余震的连续发生可能已造成主震破裂区相互连通,且破裂范围向西北方向扩展.玉树主震及余震的发震构造为甘孜—玉树断裂的北支,即玉树—隆宝断裂段,断层性质为北东倾向的高角度左旋走滑断层.发震断层的倾角和宽度在帮洞两侧有所不同,帮洞以东发震断层宽度约为12km,倾角约为83°;而帮洞以西发震断层宽度约为6.5km,断层倾角约减缓为63°.
Using the data recorded by both movable and fixed digital seismic monitoring networks in Qinghai province as well as the latest crustal velocity model determined with seismic wide angle reflection/refraction profile,a part of the Yushu earthquake aftershocks occurred from April 18 to 29,2010,were relocated accurately by means of Hypoinverse-2000 location algorithm.After relocation,the vertical and horizontal average errors are 1.35 km and 4.68 km,respectively and the root-mean-square residual error of the travel time is 0.49s.The focal depth range is 1.48～19.85 km,and the average focal depth is 10.28 km.The results show that the Yushu earthquake aftershocks are mostly distributed along the northern segment of NW-SE trending Garzê-Yushu fault zone,i.e.Yushu-Longbao fault with a length about 97 km.On the two sides of the principal earthquake(micro epicenter),the aftershock distribution presents different characteristics,which may suggest the different structural features.The densest aftershock area with higher strength,which is about 5 km from the main shock and its range is about 20 km,lay on the southeast of the main shock.Until April 29,the southeast of the main shock is still the major area of stress release.During the occurrence of main shock,much of the stress of the main shock rupture zone is released and the regions where the stress is not released became the major areas with aftershocks taking place.Continuous occurrence of aftershocks may have led to the main shock rupture zone connected to each other,and the rupture extended toward the northwest.The seismogenic fault of Yushu main shock and aftershocks is the northern branch of Garzê-Yushu fault zone,i.e.Yushu-Longbao fault,which dips to northeast with high-angle left-lateral strike-slip.The seismogenic fault dip angle and the fault width are different on the two sides of Bangdong.On the east of Bangdong,the dip angle and the fault width are about 83 degree and 12 km respectively while on its west,the fault width is about 6.5 km and the dip angle descends to 60 degree.
Using the data recorded by both movable and fixed digital seismic monitoring networks in Qinghai province as well as the latest crustal velocity model determined with seismic wide angle reflection/refraction profile,a part of the Yushu earthquake aftershocks occurred from April 18 to 29,2010,were relocated accurately by means of Hypoinverse-2000 location algorithm.After relocation,the vertical and horizontal average errors are 1.35 km and 4.68 km,respectively and the root-mean-square residual error of the travel time is 0.49s.The focal depth range is 1.48～19.85 km,and the average focal depth is 10.28 km.The results show that the Yushu earthquake aftershocks are mostly distributed along the northern segment of NW-SE trending Garzê-Yushu fault zone,i.e.Yushu-Longbao fault with a length about 97 km.On the two sides of the principal earthquake(micro epicenter),the aftershock distribution presents different characteristics,which may suggest the different structural features.The densest aftershock area with higher strength,which is about 5 km from the main shock and its range is about 20 km,lay on the southeast of the main shock.Until April 29,the southeast of the main shock is still the major area of stress release.During the occurrence of main shock,much of the stress of the main shock rupture zone is released and the regions where the stress is not released became the major areas with aftershocks taking place.Continuous occurrence of aftershocks may have led to the main shock rupture zone connected to each other,and the rupture extended toward the northwest.The seismogenic fault of Yushu main shock and aftershocks is the northern branch of Garzê-Yushu fault zone,i.e.Yushu-Longbao fault,which dips to northeast with high-angle left-lateral strike-slip.The seismogenic fault dip angle and the fault width are different on the two sides of Bangdong.On the east of Bangdong,the dip angle and the fault width are about 83 degree and 12 km respectively while on its west,the fault width is about 6.5 km and the dip angle descends to 60 degree.
引文
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[18]任俊杰,谢富仁,刘冬英等.2010年玉树地震的构造环境、历史地震活动及其复发周期估计.震灾防御技术,2010,5(2):228-233.Ren J J,Xie F R,Liu D Y,et al.Study of tectonics,seismicity and recurrence interval of Yushu 2010earthquake,Qinghai Province.Technology for Earthquake DisasterPrevention(in Chinese),2010,5(2):228-233.
[19]汪一鹏.青藏高原活动构造基本特征.∥中国地震局科技发展司《活动断裂研究》编委会编.活动断裂研究理论与应用6.北京:地震出版社,1998:135-144.Wang Y P.Principal features of the active tectonics inTibetan Planteau.∥China Earthquake Administration,Technology Development Division,Research on Active FaultEditorial Committee.Active Faults Research Theory andApplication-6.Beijing:Seismological Press,1998:135-144.
[20]Klein F W.User′s Guide to HYPOINVERSE-2000,aFORTRAN Program to Solve for Earthquake Location andMagnitudes,version1.1.U.S.Geol.Surv.Open File Rep.,02-171,2007.
[21]王有学,钱辉.青海东部地壳速度结构特征研究.地学前缘,2000,7(4):568-579.Wang Y X,Qian H.Study of crustal velocity structure ineast Qinghai.Earth Science Frontiers(in Chinese),2000,7(4):568-579.
[2]周荣军,马声浩,蔡长星.甘孜—玉树断裂带的晚第四纪活动特征.中国地震,1996,12(4):251-260.Zhou R J,Ma S H,Cai C X.Late Quaternary active featuresof the Ganzi-Yushu fault zone.Earthquake Research in China(in Chinese),1996,12(4):250-260.
[3]闻学泽,徐锡伟,郑荣章等.甘孜—玉树断裂的平均滑动速率与近代大地震破裂.中国科学D辑:地球科学,2003,33(S1):199-208.Wen X Z,Xu X W,Zheng R Z,et al.Average slip-rate ofthe Garze-Yushu fault and ruptures of the recent largeearthquakes.Science in China Series D:Earth Sciences(inChinese),2003,33(S1):199-208.
[4]闻学泽,黄胜睦,江在雄.甘孜—玉树断裂带的新构造特征与地震危险性估计.地震地质,1985,7(3):23-32.Wen X Z,Huang S M,Jiang Z X.Neotectonic features ofthe Ganzi-Yushu fault zone and assessment of its earthquakerisk.Seismology and Geology(in Chinese),1985,7(3):23-32.
[5]李闽峰,刑成起,蔡长星等.玉树断裂活动性研究.地震地质,1995,17(3):218-224.Li M F,Xing C Q,Cai C X,et al.Research on activity ofYushu fault.Seismology and Geology(in Chinese),17(3):218-224.
[6]倪四道,王伟涛,李丽.2010年4月14日玉树地震:一个有前震的破坏性地震.中国科学D辑:地球科学,2010,40(5):535-537.Ni S D,Wang W T,Li L.The April 14th,2010 Yushuearthquake,a devastating earthquake with foreshocks.Science in China Series D:Earth Sciences(in Chinese),2010,40(5):535-537.
[7]李金臣,潘华,张志忠.青海玉树7.1级地震构造背景.国际地震动态,2010,(5):1-5.Li J C,Pan H,Zhang Z Z.The seismotectonic setting ofYushu Ms7.1 earthquake in Qinghai province.RecentDevelopments in World Seismology(in Chinese),2010,(5):1-5.
[8]张勇,许力生,陈运泰.2010年青海玉树地震震源过程.中国科学D辑:地球科学,2010,40(7):819-821.Zhang Y,Xu L S,Chen Y T.Source process of the 2010Yushu,Qinghai,Ms7.1earthquake.Science in China SeriesD:Earth Sciences(in Chinese),2010,40(7):819-821.
[9]张勇,许力生,陈运泰.2010年4月14日青海玉树地震破裂过程快速反演.地震学报,2010,32(3):361-365.Zhang Y,Xu L S,Chen Y T.Fast inversion of ruptureprocess for 14April 2010Yushu,Qinghai,earthquake.ActaSeismologica Sinica(in Chinese),32(3):361-365.
[10]陈正位,杨攀新,李智敏等.玉树7.1级地震断裂特征与地震地表破裂带.第四纪研究,2010,30(3):628-631.Cheng Z W,Yang P X,Li Z M,et al.Characteristics ofMs7.1 Yushu earthquake fault and the surface rupture.Quaternary Sciences,2010,30(3):628-631.
[11]USGS.USGS Centroid Moment Solution.http://earthquakeusgs.gov/earthquake/eqinthenews/2010/vacp/neicvacpcmt.php,2010.4.14[2011-01-05].
[12]刘超,许力生,陈运泰.2010年4月14日青海玉树地震快速矩张量解.地震学报,32(3):366-368.Liu C,Xu L S,Chen Y T.Quick moment tensor solution for14April 2010Yushu,Qinghai,earthquake.Acta SeismologicaSinica(in Chinese),2010,32(3):366-368.
[13]许力生,邸海滨,冯万鹏等.2010年青海玉树Ms7.1级地震近断层地面运动估计.地球物理学报,2010,53(6):1366-1373.Xu L S,Di H B,Feng W P,et a1.Estimation of the fault-near ground motion of the 2010 Yushu,Qinghai,Ms7.1earthquake.Chinese J.Geophys.(in Chinese),2010,53(6):1366-1373.
[14]常利军,丁志峰,王椿镛.2010年玉树7.1级地震震源区横波分裂的变化特征.地球物理学报,2010,53(11):2613-2619.Chang L J,Ding Z F,Wang C Y.Variations of shear wavesplitting in the 2010 Yushu Ms7.1 earthquake region.Chinese J.Geophys.(in Chinese),2010,53(11):2613-2619.
[15]陈立春,王虎,冉康勇等.玉树Ms7.1级地震地表破裂与历史大地震.科学通报,2010,55(13):1200-1205.Chen L C,Wang H,Ran K Y,et al.Surface rupture ofYushu,Qinghai,Ms7.1earthquake and big earthquakes inhistory.Chinese Science Bulletin(in Chinese),2010,55(13):1200-1205.
[16]刘云华,单新建,屈春燕等.青海玉树Ms7.1级地震地表形变场特征研究.中国科学(D辑):地球科学,2010,40(10):1310-1320.Liu Y H,Shan X J,Qu C Y,et al.Earthquake deformationfield characteristics associated with the 2010 Yushu Ms7.1earthquake.Science in China Series D:Earth Sciences(inChinese),2010,40(10):1310-1320.
[17]张永双,马寅生,胡道功等.玉树地震地表破裂调查与灾后重建避让选址研究.地质学报,2010,84(5):593-605.Zhang Y S,Ma Y S,Hu D G,et a;.Investigation andresearch on the surface rupture of the Yushu earthquake andreconstruction site selection.Acta Geolo Gica Sinica(inChinese),2010,84(5):593-605.
[18]任俊杰,谢富仁,刘冬英等.2010年玉树地震的构造环境、历史地震活动及其复发周期估计.震灾防御技术,2010,5(2):228-233.Ren J J,Xie F R,Liu D Y,et al.Study of tectonics,seismicity and recurrence interval of Yushu 2010earthquake,Qinghai Province.Technology for Earthquake DisasterPrevention(in Chinese),2010,5(2):228-233.
[19]汪一鹏.青藏高原活动构造基本特征.∥中国地震局科技发展司《活动断裂研究》编委会编.活动断裂研究理论与应用6.北京:地震出版社,1998:135-144.Wang Y P.Principal features of the active tectonics inTibetan Planteau.∥China Earthquake Administration,Technology Development Division,Research on Active FaultEditorial Committee.Active Faults Research Theory andApplication-6.Beijing:Seismological Press,1998:135-144.
[20]Klein F W.User′s Guide to HYPOINVERSE-2000,aFORTRAN Program to Solve for Earthquake Location andMagnitudes,version1.1.U.S.Geol.Surv.Open File Rep.,02-171,2007.
[21]王有学,钱辉.青海东部地壳速度结构特征研究.地学前缘,2000,7(4):568-579.Wang Y X,Qian H.Study of crustal velocity structure ineast Qinghai.Earth Science Frontiers(in Chinese),2000,7(4):568-579.
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