Lapse time and frequency-dependent attenuation characteristics of coda waves in the Northwestern Himalayas

We analyzed the local earthquakes waveform recorded on a broadband seismic network in the northwestern Himalayan Region to compute lapse time and frequency dependence of coda Q (Q _c). The observed Q _c values increase with increasing lapse time at all frequency bands. The increase in Q _c values with lapse time is attributed to an increase in Q _c with depth. This implies that attenuation decreases with increasing depth. The approximate radius of medium contributing to coda generation varies from 55 to 130 km. By comparing the Q _c values with those from other regions of the world, we find that they are similar to those obtained from tectonically active regions. The estimated Q _c values show a frequency-dependent relationship, Q _c = Q ₀ f ⁿ , where Q ₀ is Q _c at 1 Hz and n represents degree of frequency dependence. They represent the level of heterogeneity and tectonic activity in an area. Our results show that northwest Himalayas are highly heterogeneous and tectonically very active. Q ₀ increases from 113 ± 7 to 243 ± 10 and n decreases from 1.01 ± 0.05 to 0.85 ± 0.03 when lapse time increases from 30 to 70 s. As larger time window sees the effect of deeper part of the Earth, it is concluded that Q ₀ increases and n decreases with increasing depth; i.e., heterogeneity decreases with depth in the study area.     

Climate change and sediment flux from the Roof of the World

Potential rises in global temperature are likely to have major impacts on high altitude environments, including glacier recession and permafrost degradation. In turn, these could have far‐reaching impacts on riverine sediment flux. Such impacts are emerging in the Himalayas and Tibet Plateau region, one of the world's largest and most environmentally‐sensitive cold regions. Closer monitoring is urgently required to track changing trends of sediment load from the interactions of glacial recession treat, rainfall changes and human interventions, and to study the implications of such changes for the large Asian river systems of the region. Copyright © 2010 John Wiley & Sons, Ltd.     

近30年珠穆朗玛峰国家自然保护区冰川变化的遥感监测

利用1976、1988和2006年的3期陆地卫星遥感数据,采用面向对象的解译方法并结合专家知识分类规则自动提取珠穆朗玛峰国家自然保护区(以下简称珠峰保护区)3个时期的冰川信息,并利用遥感、地理信息系统和图谱的方法对冰川时空分布特征和变化及其原因与不确定性进行了分析。结果如下:(1)2006年珠峰保护区内冰川面积为2710.17±0.011km²,为研究区总面积的7.41%,主要分布在研究区南部海拔4700～6800m的高山区;(2)1976-2006年,珠峰保护区冰川持续退缩明显,总面积减少501.91±0.035km²,冰湖扩张迅速(净增加36.88±0.035km²);研究区南坡子流域冰川退缩率(16.79%)高于北坡子流域(14.40%);珠峰保护区冰川以退缩为主,退缩冰川主要分布于海拔4700～6400m,退缩区上限海拔为6600～6700m;(3)1976年以来,气温显著上升和降水减少是冰川退缩的关键因素。     

2001-2015年喜马拉雅南麓地区植被变化遥感监测

本文应用喜马拉雅南麓地区MODIS NDVI 植被遥感数据和格点数据,采用趋势线分析、多元回归等方法分析了该研究区2001-2015 年植被 NDVI_max 时空变化特征,同时利用Person 相关分析探讨了植被 NDVI_max 时空变化特征与气候因子的响应关系。结果表明：（1）2001-2015 年,喜马拉雅南麓地区年内平均 NDVI_max 1~3 月份呈下降趋势,4~6 月份开始缓慢生长,6~9 月份进入植被生长高峰期,10 月份开始逐渐降低;植被 NDVI_max 平均值为0.59,植被覆盖度较高;空间上植被覆盖度总体呈东南高西北低,由东南向西北递减;平均 NDVI_max 随海拔变化表现出明显规律性,80%的植被主要分布在较低海拔区（<4 050 m）。（2）15 a 间,喜马拉雅南麓地区植被 NDVI_max 变化具有阶段性特征,年均 NDVI_max 呈三个变化阶段：2001-2006 年和2010-2015 年分别以0.003 9·a^-1、0.005 3·a^-1 的速率增长,而2006-2010 年以-0.007 0·a^-1 的速率减少。植被生长季 NDVI_max 呈4 个阶段：2001-2004 和2007-2010 年分别以-0.001 8·a^-1、-0.010 6·a^-1 的速率逐年减少,但2005、2006 两年（0.014 8·a^-1）快速增长至最大值,2010-2015 年（0.006 3 a^-1）波动增长。空间上大部分地区表现出不显著退化,但少部分地区表现出不显著改善（0.05< p<0.01）,而西段低海拔区表现出极显著改善。（3）喜马拉雅南麓地区植被的变化主要由温度和降水量共同影响,此外,高海拔区气温上升引起的冰川融水对植被生长起到一定的作用,中部低海拔区可能还受到人类活动的影响。     

Glaciochemical records from Naimona’Nyi ice core in the Himalayas

A 6-m ice core was recovered in 2004 from the Naimona’Nyi Glacier, the middle Himalayas. Empirical orthogonal function (EOF) analysis on the major ion reveals that EOF1 represents the variations of majority of ions which may be originated from crustal aerosols. Comparing the calcium concentrations from the Naimona’Nyi with these from Dasuopu, East Rongbuk and Guliya ice cores, it is observed that calcium, a good indicator of the input of crustal aerosol in snow, concentrates mostly in the Guliya ice core located on the northern Tibetan Plateau, and gradually decreases from west to east in the Himalayas.     

喜马拉雅山珠穆朗玛峰北坡绒布冰川消融速率特征分析

根据1959年和2009年在喜马拉雅山珠穆朗玛峰北坡绒布冰川获得的冰川消融数据, 分析了该冰川消融速率变化特征.结果表明: 1) 在珠峰绒布冰川表碛覆盖区, 表碛厚度随海拔升高而降低. 2) 不同厚度表碛下的冰川消融速率差别较大; 当表碛厚度>8.5 cm时, 消融速率随表碛厚度的增加而减小; 促进冰川消融的表碛厚度阈值大于5 cm. 3) 从冰川消融速率的空间分布看, 绒布冰川大部分区域的消融速率<20 mm·d^-1, 最大消融速率出现在海拔5 400~5 450 m处. 4) 绒布冰川消融速率受表碛厚度和气温综合影响, 低海拔处表碛太厚, 高海拔处气温较低, 冰川消融在上述两海拔处均受抑制, 冰川消融速率较小; 在中海拔处, 表碛相对较薄, 气温相对较高, 冰川消融速率最大; 冰川日均消融速率与日均正积温正相关. 5) 喜马拉雅山南坡冰川消融速率大于北坡冰川消融速率.     

世界史视角下青藏高原对我国的地缘安全 屏障作用

青藏高原不仅是自然地理上的地球第三极、世界屋脊,也是地缘政治上的一道安全屏障。目前关于青藏高原的历史地缘政治研究鲜少,与其战略价值不相称。本研究重点论述历史时期围绕青藏高原周边及其内部的政治地理事实,从中原王朝和高原地方政权两个不同视角,多尺度对比分析地理环境与地缘安全的关系,得出“青藏高原是我国的地缘安全屏障”这一结论。具体而言,它在历史上对来自中亚和南亚的威胁起到屏蔽或阻隔的作用。大高原的存在和不可逾越性——喜马拉雅山脉若是“城墙”,则青藏高原就是“城郭”——使得它对外部威胁起到阻挡入侵、对内起到新月形保护的作用,即地缘政治屏蔽效应。东亚大陆具有“背高原而面大海”的地理形便。这种形势直至近代新技术革命导致海洋势力的入侵而发生变化。不过,在可预见的时间里,青藏高原的地貌和地理环境不会发生根本改变。总之,青藏高原不仅是我国的生态安全屏障,也是我国的地缘政治安全屏障。中华文明长达两千年的相对安全发展,很大程度上得益于青藏高原的屏障功能。     

A primitive cladid crinoid from the Jiacun Group,Tibet (Darriwilian,Middle Ordovician)

A collection of numerous crinoid pluricolumnals from the uppermost Darriwilian (Middle Ordovician) of Tibet were derived from one biological species of crinoid. The specimens were collected from well‐lithified, bioclastic shelf limestones of the upper part of the Lower Chiatsun Group, Pygodus serra Biozone; coeval rocks of similar lithology outcrop at the summit of Everest. A new crinoid morphospecies, Segmentocolumnus (col.) hanshessi, is tentatively considered a ‘stem‐group cladid’, perhaps a dendrocrinid. The proxistele is broad and pentagonal in section with a broad, pentagonal axial canal; the mesistele of similar gross morphology is more slender with a regularly heteromorphic column and a similarly wide axial canal; the dististele is a terminal dendritic radice with a pentastellate axial canal. In the mesistele, the meric sutures correspond to the centres of the sides of the column, but in the dististele they occur in the angles. This range of morphologies would have led to their inclusion in at least two morphogenera if they had not been closely associated; as they belong to a single biological species, they have been ‘lumped’ together herein. This is a rare contribution to our knowledge of the early crinoids from a region outside Europe and North America. Copyright © 2012 John Wiley & Sons, Ltd.     

西藏喜马拉雅瑞替阶和赫塘阶菊石组合及其生物年代学对比

基于西藏聂拉木拉弄拉地区的格米格剖面新近逐层采集的菊石及缝合线研究,已识别出晚三叠世瑞替阶Choristoceras marshi组合,过渡带Neophyllites-Choristoceras组合,下赫塘阶Psiloceras calliphyllum组合和中赫塘阶Discamphiceras pleuronotum组合。作为东特提斯唯一的三叠系-侏罗系界线地层剖面,格米格菊石组合序列提供了特提斯范围内三叠/侏罗系界线菊石组合(或菊石带)以及地层对比的基础:Choristoceras marshi组合可以和欧洲,南美的秘鲁和智利的MARSHI菊石带,北美的内瓦达,不列颠哥伦比亚(加拿大)等地CRICKMAYI菊石带比较。Neophyllites-Choristoceras组合可和北美的内瓦达侏罗系底部TILMANNI菊石带Neophyllites和Choristoceras共生动物群比较。Psiloceras calliphyllum组合能够和北阿尔卑斯地区CALLIPHYLLUM菊石带比较, 证明北阿尔卑斯地区三叠系和侏罗系之间存在地层缺失。