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| 西藏安多最新史前大地震的地质证据及其年龄 | |
| 引用本文： | 吴中海,叶培盛,王成敏,吴珍汉,赵华.西藏安多最新史前大地震的地质证据及其年龄[J].第四纪研究,2009,29(3):608-615. |
| 作者姓名： | 吴中海 叶培盛 王成敏 吴珍汉 赵华 |
| 作者单位： | 1. 中国地质科学院地质力学研究所,北京,100081 2. 中国地质科学院水文地质环境地质研究所,石家庄,050061 |
| 基金项目： | 科学技术部国际科技合作项目，国家自然科学基金，中国地质科学院地质力学研究所基本科研业务费资助项目 |
| 摘 要： | 在西藏安多地区进行活动断裂研究过程中，进行地表调查和探槽开挖，证实错那－安多地堑北缘主边界断裂上的最新地表断层陡坎实际是该区史前大地震的地表遗迹。根据地表观察和实地测量结果可知，该区最新古地震断坎的延伸范围可达 26～36km，平均垂直位移量达 1.0～1.4m。相关地层－地貌体的年代学测试结果和古地震破裂参数表明，最新的古地震发生在距今约 10.0～8.1ka期间，估计当时的古地震震级介于 6.9～7.3级之间，当时的极震区烈度可能≥Ⅸ度。此古地震破裂的发现表明，青藏高原中部正断层型大地震之后的沉寂时间可以长达近万年，明显长于藏南裂谷带上的正断层型古地震活动间隔。由于安多地区最新大地震之后的离逝时间已足以积累类似强度的大地震，因此，该区未来的大地震危险性较高。 |
| 关 键 词： | 青藏高原 蓬错－安多地堑系 活动断裂 古地震 青藏铁路 |
THE MOST RECENT SURFACE NORMAL FAULTING AND ITS AGE ALONG THE NORTHERN MARGIN OF TSONAAMDO GRABEN IN CENTRAL TIBET |
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| Wu Zhonghai,Ye Peisheng,Wang Chengmin,Wu Zhenhan,Zhao Hua.THE MOST RECENT SURFACE NORMAL FAULTING AND ITS AGE ALONG THE NORTHERN MARGIN OF TSONAAMDO GRABEN IN CENTRAL TIBET[J].Quaternary Sciences,2009,29(3):608-615. | |
| Authors: | Wu Zhonghai Ye Peisheng Wang Chengmin Wu Zhenhan Zhao Hua |
| Institution: | Institute of Geomechanics|Chinese Academy of Geological Sciences|Beijing 100081;The Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences|Shijiazhuang 050061 |
| Abstract: | Based on surface surveying and excavated trench investigation，we discovered evidences for the most recent palaeoearthquake event at Tsona－Amdo Basin. The NE normal fault scarps along the normal faults at the north margin of the NE Tsona－Amdo Graben was likely generated by a paleoearthquake. The surface measuring results indicate that the maximum and minimum vertical displacements of the fault scarps are 1.4±0.1m and 0.6±0.2m respectively. The small fault scarp intermittent extends southwestward from the north of Amdo Town to around the Zhasha Village along the north margin of the Tsona－Amdo Basin，and is about 26km or 36km long. The trenching profile crossing the surface rupture reveals that there is only a set of colluviums along the small fault scarp，and demonstrates the deduction that the surface normal faulting expressed as small fault scarps on surface was resulted from a severe palaeoearthquake. The optically stimulated luminescence(OSL)dating results of the youngest terrace(T1)deposits offset by the surface rupture indicate that the most recent palaeoearthquake occurred after about 13.8～17.8ka before present，and the OSL age of the soil layer overlying the youngest terrace deposits infers that the most recent palaeoearthquake occurred before about 6.2ka before present. In trench profile，three OSL ages(including one terrace deposits and two fault colluviums)suggest that the recent paleoearthquake occurred during 10.0～8.1ka before present. Based on empirical formula between earthquake magnitude and surface rupture length and displacementse，the estimated magnitude and maximum intensity of the most recent palaeoearthquake occurred at Amdo is probable of MS6.9～7.3 and ≥Ⅸ degree. Regional research shows that similar surface ruptures of palaeoearthquake are also distributed along the normal faults at the eastern margin of the Peng CoDung Co Graben that constitutes the southern segment of the Peng Co－Amdo Graben system. The oldest surface rupture is located at the southeastern edge of the Dung Co Graben，and occurred probably at about 28.2ka before present，but the youngest surface normal faulting runs along the northeastern margin of the Dung Co Graben，occurring at about 1320±60A.D. The new discovers show that the quiescence period between two severe earthquake events resulted from normal faulting may last for ten thousands years or even longer along the Peng Co－Amdo Graben system in Central Tibet. The quiescence period after severe earthquake is obviously longer than that along the SN trending rift in Southern Tibet. It implies that the magnitude of extension deformation in Southern Tibet should be greater than that in Central Tibet. The displacements of T2 formed during 39.9～42.3kaB.P. indicate an average vertical slip rate of 0.14±0.03mm/a for the normal fault at the northern margin of the Amdo Basin. Based on the slip rate，the quiescence period has been long enough to cumulate a similar magnitude severe earthquake along the northern margin fault of the TsonaAmdo Basin. |
| Keywords: | Tibet Peng Co－Amdo Graben system active fault palaeoearthquake normal fault |
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