西藏当雄地区活动断裂遥感解译研究及活动性分析
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摘要
西藏当雄地区位于青藏高原腹地,发育有羊八井—当雄—谷露裂陷盆地,是亚东—羊八井—谷露—那曲裂谷系的重要组成部分,总体呈NE向展布。该区中部为纵贯全区的念青唐古拉山脉,西北部和东南部以山岳地貌为主。区内规模较大的念青唐古拉山南东麓断裂带是西藏东部与西部在地质构造和地貌上的一条重要分界,为一重要转换构造带,该区经历过强烈的构造运动,岩浆活动特别强烈,地震活动十分频繁。
本文在收集、整理西藏当雄及邻区的遥感、地质地貌及地震等资料的基础上,采用高分辨率遥感影像解译的方法对典型的活动构造地貌,如断层崖、断层陡坎、水系转弯、山脊错断等进行了提取。利用PS-InSAR处理结果探讨了研究区地壳形变特征,PS和SBAS处理结果显示盆地边缘抬升速率大约为1.7mm/a。最大抬升达到3.34mm/year的速率；盆地中间的平坦地形部分整体相对平稳,平均形变速率在±0.5mm/year左右。这种变形趋势可能是由于青藏高原中部地壳近东西向的伸展变形造成的。利用DEM数据提取了研究区水系并计算了水系密度,研究区内部水系密集发育,呈格子状展布,主要支流与小支流排列相互平行,并常有近乎直角之转折,水系之发育明显受到构造的强烈控制。水系密度图清晰地反映了当雄地区新构造隆起和沉降的特征。水系密度的梯度带则代表了构造隆起和凹陷的交接部位,往往是活动断裂分布的地带。念青唐古拉山地区水系密度较低,由南向北总体成NNE-NE-NNE向的带状分布,反映了该地区仍有相对较强的构造上升与沉降活动。最后结合研究区地震资料以及2008年当雄地震InSAR处理结果,探讨了当雄地区地震活动的特征,该区地震的活动具有明显的周期性。Ms6.0—6.9级的地震大体上以18年左右的周期重复出现,在1960—1980年之间出现一段地震平静期,只发生一次4.0级的小型地震,这可能是由于1952年发生在谷露地堑西侧的的7.5级强震释放了该区大部分的累积应变能,导致1952年之后该区地震活动相对平静。1980年以后该区大体上以4.0—5.0左右的中小地震为主,规模最大的为2008年当雄6.6级地震,持续的小震释放了能量,强震机率降低。
Dangxiong area totally NE trending in Tibet is located in the middle of the Tibet plateau and develops the Yangbajing-Dangxiong-Gulu faulted basin which is an important part of the Yadong-Gulu-Naqu rift system. Nyenchen Tonglha Mountains runs through the middle of this area and the northwest and southeast part is mountains landform. Nyenchen tanglha southeast foothill fault zone is one of the biggest faults in this area. It is not only an important conversion tectonic belt but also a board line in tectonic and landform between the east and west Tibet. Magma and seismic activity is very intensive and frequent because of the strong tectonic movement.
Based on the remote sensing,geology and seismic data, we use high resolution remote sensing image extracting the typical active structure landforms such as fault scarps, fault escarpments, river turning and offset ridges. The crust deformation features are discussed according to the PS-InSAR results. The results show that the uplifting rate on the edge of the basin is about 1.7mm/a and the maximum rate is nearly 3.34mm/year. This deformation trend is probably caused by the nearly E-W crust stretching deformation in the middle of the Tibet plateau. DEM data is used to extract river system and calculate water density. Rivers develop intensive within the study area and showing distribution of grid. Main tributaries and small tributaries arrange parallel to each other and often show right angle bends. The development was clear ly controlled by strong structure. Water density map reflects uplift and subsidence features of new structure. Water density gradient zone represents the transfer of structural parts of uplift and subsidence. It is usually the distribution zones of active faults. The density is low in Nyainqentanglha Mountain area and spread overall NNE-NE-NNE direction from south to north. It shows that there is still relatively strong uplift and subsidence in the region.
Finally, we analyse the seismic data and the 2008 Dangxiong earthquake InSAR processing results and discuss the seismic activity features. The results show that the seismic activity in this region is periodic. Ms6.0-6.9 earthquakes generally appear in the period of 18 years. There is a seismically quiet period between 1960 and 1980 and only occurs a small 4.0 earthquake. This is probably due to the Ms 7.5-magnitude earthquake occurred in the west of Gulu graben.This earthquake releases the cumulative strain energy and results in a seismically quiet period after 1952. Since 1980, the earthquake magnitude in this area is about 4.0-5.0. The largest earthquake is 2008 Dangxiong Ms 6.6. The continuous small earthquakes release most strain energy and it suggests that the possibility of strong earthquakes reduces.
本文在收集、整理西藏当雄及邻区的遥感、地质地貌及地震等资料的基础上,采用高分辨率遥感影像解译的方法对典型的活动构造地貌,如断层崖、断层陡坎、水系转弯、山脊错断等进行了提取。利用PS-InSAR处理结果探讨了研究区地壳形变特征,PS和SBAS处理结果显示盆地边缘抬升速率大约为1.7mm/a。最大抬升达到3.34mm/year的速率；盆地中间的平坦地形部分整体相对平稳,平均形变速率在±0.5mm/year左右。这种变形趋势可能是由于青藏高原中部地壳近东西向的伸展变形造成的。利用DEM数据提取了研究区水系并计算了水系密度,研究区内部水系密集发育,呈格子状展布,主要支流与小支流排列相互平行,并常有近乎直角之转折,水系之发育明显受到构造的强烈控制。水系密度图清晰地反映了当雄地区新构造隆起和沉降的特征。水系密度的梯度带则代表了构造隆起和凹陷的交接部位,往往是活动断裂分布的地带。念青唐古拉山地区水系密度较低,由南向北总体成NNE-NE-NNE向的带状分布,反映了该地区仍有相对较强的构造上升与沉降活动。最后结合研究区地震资料以及2008年当雄地震InSAR处理结果,探讨了当雄地区地震活动的特征,该区地震的活动具有明显的周期性。Ms6.0—6.9级的地震大体上以18年左右的周期重复出现,在1960—1980年之间出现一段地震平静期,只发生一次4.0级的小型地震,这可能是由于1952年发生在谷露地堑西侧的的7.5级强震释放了该区大部分的累积应变能,导致1952年之后该区地震活动相对平静。1980年以后该区大体上以4.0—5.0左右的中小地震为主,规模最大的为2008年当雄6.6级地震,持续的小震释放了能量,强震机率降低。
Dangxiong area totally NE trending in Tibet is located in the middle of the Tibet plateau and develops the Yangbajing-Dangxiong-Gulu faulted basin which is an important part of the Yadong-Gulu-Naqu rift system. Nyenchen Tonglha Mountains runs through the middle of this area and the northwest and southeast part is mountains landform. Nyenchen tanglha southeast foothill fault zone is one of the biggest faults in this area. It is not only an important conversion tectonic belt but also a board line in tectonic and landform between the east and west Tibet. Magma and seismic activity is very intensive and frequent because of the strong tectonic movement.
Based on the remote sensing,geology and seismic data, we use high resolution remote sensing image extracting the typical active structure landforms such as fault scarps, fault escarpments, river turning and offset ridges. The crust deformation features are discussed according to the PS-InSAR results. The results show that the uplifting rate on the edge of the basin is about 1.7mm/a and the maximum rate is nearly 3.34mm/year. This deformation trend is probably caused by the nearly E-W crust stretching deformation in the middle of the Tibet plateau. DEM data is used to extract river system and calculate water density. Rivers develop intensive within the study area and showing distribution of grid. Main tributaries and small tributaries arrange parallel to each other and often show right angle bends. The development was clear ly controlled by strong structure. Water density map reflects uplift and subsidence features of new structure. Water density gradient zone represents the transfer of structural parts of uplift and subsidence. It is usually the distribution zones of active faults. The density is low in Nyainqentanglha Mountain area and spread overall NNE-NE-NNE direction from south to north. It shows that there is still relatively strong uplift and subsidence in the region.
Finally, we analyse the seismic data and the 2008 Dangxiong earthquake InSAR processing results and discuss the seismic activity features. The results show that the seismic activity in this region is periodic. Ms6.0-6.9 earthquakes generally appear in the period of 18 years. There is a seismically quiet period between 1960 and 1980 and only occurs a small 4.0 earthquake. This is probably due to the Ms 7.5-magnitude earthquake occurred in the west of Gulu graben.This earthquake releases the cumulative strain energy and results in a seismically quiet period after 1952. Since 1980, the earthquake magnitude in this area is about 4.0-5.0. The largest earthquake is 2008 Dangxiong Ms 6.6. The continuous small earthquakes release most strain energy and it suggests that the possibility of strong earthquakes reduces.
引文
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2.谢广林.中国活动断裂遥感信息分析[M].北京：地震出版社,2000.1-18.
3.张景发,王四龙.活动断裂带中遥感数字图像处理技术—以鲜水河活动断裂带为例[J].地震地质,1996,18(3)：1-16.
4.王金辉,王纪存,刘福魁.遥感在活动断裂研究中的应用[J].西部探矿工程,2007,19(3)：117-119.
5.张景发.TM遥感在活动断裂带中的应用研究[R].地震科学联合基金会资助课题最终成果报告,1994.
6.窦爱霞,王晓青,王栋梁等.基于多源数据的活动断裂遥感图像处理技术[J].地震,2010(3)：123-128.
7.李百寿,秦其明,贺电等.基于多空间分辨率遥感影像的喀拉玉尔滚构造带研究[J].地质科技情报,2007,26(5)：100-104.
8.洪顺英,申旭辉,赖木收等.阿尔泰山东缘主要活动断裂影像特征分析[J].地震地质,2006,28(1)：119-128.
9.陈正位,谢平,申旭辉等.藏南宁金抗沙西麓断裂晚第四纪活动特征[J].地球物理学进展,2006,21(1)：118-126.
10付碧宏,时丕龙,王萍等.2008年汶川地震断层北川段的几何学与运动学特征及地震地质灾害效应[J].地球物理学报,2009,52(2)：485-495.
11.吴珍汉,胡道功,刘崎胜等.西藏当雄地区构造地貌及形成演化过程[J].地球学报,2002,23(5)：425-427.
12.吴章明,曹忠权.西藏中部发震构造[J].中国地震,1994,10(1)：20-24.
13. Armijo, Tapponnier P and Han T. Late Cenezoic right-lateral strike-slip faulting in southern Tibet[J]. Geophys. Res.,1989,94:287-238.
14. Armijo, Tapponnier, Mercier L and Tonglin H. Quaternary extension in southern Tibet[J]:Field Observation and Tectonic Implication,1986, GR91(B14),803-872.
15. Molnar P, England P. Late cenozoic uplift of mountain ranges and global climate change[J]. Nature,1990,346(6279):29-34.
16. Harrison T M, Copeland P, KiddWSF, et al. Activation of the Nyainqentanghla shear zone:implications for upl ift of the southern Tibetan Plateau [J].Tectonics, 1995,14(3):658-676.
17. Bulisniuk P M, Bradley R H, Johannes G, et al. Normal faulting in central Tibet since at least 13.5 Myr ago[J]. Nature,2001,412(6847):628-632.
18. Cogan M J, Nelson K D, Kid W S F, et al. shallow structure of the Yadong-Gulu rift, southern Tibet, from refraction analysis of Project INDEPTH common midpoint data[J]. Tectonics,1998,17(1):46-61.
19.贺日政,高锐.西藏高原南北向裂谷研究意义[J].地球物理学进展,2003,18(1)：35-43.
20.吴章明,曹忠权,申屠炳明等.西藏中部活动断层[M].北京：地震出版社.1992,5-17.
21.何凯涛,甘甫平,王永江.高空间分辨率卫星遥感地质微构造及蚀变信息识别[J].国土资源遥感,2009,1：97-99.
22.周谨敞,邵顺妹.活动断裂的遥感影像研究[J].环境遥感,1995,(3)：182-187.
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