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Earthquake size, recurrence and rupture mechanics of large surface-rupture earthquakes along the Himalayan Frontal Thrust of India.

机译：印度喜马拉雅山前冲断面的大型表面破裂地震的地震大小，复发和破裂机制。

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摘要

Plate motion models and GPS measurements indicate that the India-Eurasia convergence continues today at a rate of ∼40--50 mm/year. Between ∼10 and 20 mm/year of the total ∼40--50 mm/year is taken up by thrusting along the Himalayan Frontal Thrust (HFT). This ongoing India-Eurasia convergence has produced three major historical earthquakes (1905 Kangra, 1934 Bihar-Nepal, and 1950 Assam Earthquake) during the past century. None of the events are reported to have produced coseismic surface ruptures. Lack of primary surface rupture during these historical earthquakes has led previous workers to interpret the HFT as a blind thrust, or more strictly, as characterized by a fault plane that does not reach the surface. Towards understanding the relationship between strain accumulation and strain release in the context of mechanics of the earthquake and mountain building process and quantifying the seismic hazard associated with the globes largest continental thrust system, I describe the late Quaternary expression and paleoseismic evidence for great surface-rupture earthquakes at six sites along the Himalayan Frontal Thrust (HFT) system of India. Our observations span a distance of ∼250 km along strike of the HFT. Uplifted and truncated fluvial strath terraces resulting from the Holocene displacements on the HFT are preserved along canyons of the Ghaggar, Markanda, Shajahanpur, and Kosi Rivers. Dividing the elevation of the bedrock straths by the maximum radiocarbon ages of the terrace surface abandonments yield an estimate of the vertical uplift rate equal to ∼4--6 mm/year, which when assumed to be the result of slip on a thrust dipping at ∼20°--45° is equivalent to a fault slip rate of ∼6--18 mm/year or shortening rate of ∼4--16 mm/year. Trench exposures reveal the HFT to break surface sediments near the cities and villages of Chandigarh, Kala Amb, Rampur Ganda, Lal Dhang, and Ramnagar. Radiocarbon ages of samples obtained from displaced sediments indicate surface rupture at each sites took place after ∼AD 1200 and before ∼AD 1700. Uncertainties attendant to the radiocarbon dating currently do not allow an unambiguous definition of a capping bound on the age of the displacement at each site or whether or not the displacements at all sites were contemporaneous. Trench exposures and vertical separations measured across scarps at Rampur Ganda, Lal Dhang, and Ramnagar are interpreted to indicate single-event displacements of ∼11--38 m. Dividing the observed single-event vertical displacements by the estimated longer-term uplift rates indicate{09}∼1330--3250 years would be required to accumulate the slip sufficient to produce similar sized displacements. (Abstract shortened by UMI.)
机译：板块运动模型和GPS测量结果表明，印度-欧亚大陆的融合今天以每年40--50毫米的速度持续。沿喜马拉雅山顶推力（HFT）推挤，每年约40--50 mm /年之间约10至20 mm /年。在过去的一个世纪中，这种持续的印度-欧亚大陆融合造成了三场重大的历史地震（1905年的坎格拉，1934年的比哈尔-尼泊尔和1950年的阿萨姆邦地震）。据报道，这些事件均未引起同震表面破裂。在这些历史地震中，由于缺乏主要的地表破裂，以前的工作人员将HFT解释为盲冲，或更严格地讲，其特征是没有到达地表的断层。为了理解在地震和山区建造过程中力学作用下的应变积累与释放之间的关系，并量化与地球最大的大陆逆冲系统有关的地震危险，我描述了晚第四纪的表达和古地震证据，证明了巨大的地表破裂印度喜马拉雅前冲（HFT）系统沿线六个地点发生地震。我们的观测沿高空走时的走向跨越了约250公里的距离。沿加特加尔河，马尔坎达河，沙贾汉普尔河和科西河的峡谷保存了由高新世时期全新世位移引起的隆起和截断的河床阶地。将基岩层的高程除以阶地表遗弃的最大放射性碳年龄可以得出垂直上升率的估计值，该估计值等于每年约4--6 mm，当假定为推力倾角为约20°--45°相当于约6至18毫米/年的断层滑动率或约4--16毫米/年的缩短率。沟渠暴露表明，高频辐射破坏了昌迪加尔，卡拉·安布，拉姆布尔·甘达，拉尔·唐和拉姆纳加尔等城市和村庄附近的地表沉积物。从位移沉积物中获得的样品的放射性碳年龄表明，每个地点的表面破裂发生在大约公元1200年之后和大约公元1700年之前。放射性碳定年所带来的不确定性目前尚不能明确界定在该位置的位移年龄的上限。每个站点，或者所有站点的位移是否同时发生。在Rampur Ganda，Lal Dhang和Ramnagar的陡坡上测得的海沟暴露和垂直间距被解释为表明单事件位移约为11--38 m。将观测到的单事件垂直位移除以估计的长期上升率表明{09}〜1330--3250年，将需要积累足够的滑动以产生相似大小的位移。 （摘要由UMI缩短。）

著录项

  • 作者

    Kumar, Senthil.;

  • 作者单位

    University of Nevada, Reno.;

  • 授予单位 University of Nevada, Reno.;
  • 学科 Geology.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 103 p.
  • 总页数 103
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;
  • 关键词

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