云南地区水位、水温对尼泊尔Ms8.1地震的响应特征研究

通过统计2015年4月25日尼泊尔MS8.1地震和5月12日MS7.5余震发生时云南地区水位、水温的空间分布、异常形态、变化幅度、起始和结束时间等远场响应特征,分析认为:同震响应主要集中在川滇菱形块体东南部、滇缅弧形块体东部和小滇西一带,即云南地区中西部;同井观测的水位、水温同震响应异常形态多样,单井同测项的同震响应异常形态具有一致性,与地震震级、震中距、方位无关;观测井的记震能力与观测仪器的分辨率、井孔含水层条件等有关,同震响应的异常幅度(ΔH、ΔT)与震级(M)、震中距(D)之间有一定的数量关系;近来云南区域地震活动整体呈现"平静—活动—平静"特征,小震活动有丛集特点,未来一段时间需注意滇西—滇西北和滇西南地区中强地震的危险性。     

GPS观测结果反映的尼泊尔M_w7.8地震孕震特征

针对2015年4月25日尼泊尔Mw7.8地震的孕震特征,本文首先对覆盖尼泊尔及周边地区的5套GPS水平速度场结果进行了融合,得到了近似统一参考框架下的速度场结果;在此基础上通过对此次地震震源区及周边地区的速度场、应变率场、基线时间序列分析,识别了震前变形特征.GPS应变率场结果显示,喜马拉雅主边界断裂存在大范围挤压应变积累,震源区处于近南北向应变积累高值过渡区.跨喜马拉雅构造带的GPS基线时间序列结果表现为持续缩短现象,表明印度板块与欧亚板块之间的持续挤压变形特征,2012年以来的缩短增强现象反映了印度板块对青藏块体的推挤增强作用明显.距离震中较近的西藏南部GPS同震位移结果以南向运动为主且指向震中,反映了青藏高原存在逆冲应变释放现象.综合此次尼泊尔地震前变形和同震应变释放特征,认为此次地震的孕震区域和同震应变释放区域均较大,将会对青藏高原的地壳变形与强震孕育产生深远影响.     

利用非线性台阵叠加方法快速追踪2015年4月25日尼泊尔MW7.9地震破裂能量中心运动轨迹

本文应用一种非线性台阵叠加方法,通过对地震记录瞬时相位信号的延迟叠加来估计信号间的一致性程度,用于在震后快速追踪大地震破裂能量中心相对于震中运动轨迹.基于此方法,文中利用欧洲地震台网不同频率段的数据对2015年4月25日尼泊尔M_W7.9地震的破裂轨迹进行了追踪,并对成像结果的不确定程度进行了估计,且通过理论地震图计算,验证了该结果的可靠性.研究结果表明,该事件为东南向发展的单侧破裂,破裂尺度至少达到120 km.整个破裂过程主要分为三个阶段,第一阶段破裂在震中附近释放小部分能量;第二阶段破裂向东南方向发展,表现出明显的沿断层倾向辐射频率变化的现象,相对更高频的能量辐射在更深处发生;第三阶段破裂继续向东南方向发展,不同频段得到的能量中心运动轨迹趋于一致,这可能提示了滑移范围的逐渐变窄.同时,推断在主喜马拉雅逆冲断裂的更深部（断层深度大于等于20 km处）也存在破裂的可能.     

基于InSAR分析2015年尼泊尔MW7.8地震形变场特征及断层滑动分布反演

2015年4月25日尼泊尔发生了M_W7.8地震, 本文基于震前、 震后两景Sentinel-1A雷达影像, 采用D-InSAR两轨差分干涉法提取了此次地震的同震形变场。 结果显示, 同震形变场位于喜马拉雅造山带—主边界逆冲断裂(MBT)和主前锋逆冲断裂(MFT)附近, 形变场整体表现为自西北向往东南方向延伸近150 km的纺锤形包络状, 以大面积隆起抬升形变为主, 视线向最大隆升形变达1.18 m, 抬升区北侧存在一小沉陷区, 以InSAR观测值定位同震最大形变中心。 基于均匀介质弹性半空间模型(Okada模型)与InSAR观测数据反演了断层滑动分布。 反演结果表明该地震属于典型逆冲型地震, 发震断层为主喜马拉雅逆冲断裂(MHT), 同震破裂从主喜马拉雅逆冲断裂(MHT)向上沿着主前锋逆冲断裂(MFT)传递。 基于InSAR同震形变场局部形变细节, 结合震区地质背景、 断裂分布及断层运动特征, 获得了同震破裂拟出露地表迹线。     

Perturbation study of climate change impacts in a snow‐fed river basin

A physically based distributed hydrological model developed at the University of Yamanashi based on block‐wise use of TOPMODEL and the Muskingum–Cunge method (YHyM/BTOPMC), integrated with a simple degree‐day–based snow accumulation/melt sub‐model, was applied to evaluate hydrological responses under changing climatic conditions in the snow‐fed Kali Gandaki River Basin (KGRB) in Western Nepal. Rainy season precipitation (June to September) in the basin takes up about 80% of the annual precipitation, and dry season runoff is largely contributed by snowmelt. Climate change is likely to increase the probability of extreme events and problems related to water availability. Therefore, the study aimed to simulate runoff pattern under changing climatic conditions, which will be helpful in the management of water resources in the basin. Public domain global data were widely used in this study. The model was calibrated and validated with an acceptable degree of accuracy. The results predicted that the annual average discharge will increase by 2.4%, 3.7%, and 5.7% when temperature increases by 1, 2, and 3 °C compared with the reference scenario. Similarly, maximum, minimum, and seasonal discharges in the monsoon and pre‐monsoon seasons will also increase with rising temperature. Snowmelt runoff is found sensitive to temperature changes in the KGRB. Increasing temperature will cause a faster snowmelt, but precipitation will increase the snowpack and also shed a positive effect on the total annual and monsoonal discharge. For the combined scenarios of increasing temperature and precipitation, the annual average discharge will increase. In contrast, discharge during the increasing temperature and decreasing precipitation will tend to decrease. Copyright © 2012 John Wiley & Sons, Ltd.     

青藏高原及周缘深部结构的重力异常解释与尼泊尔Ms8.1地震

利用离散小波变换获得青藏高原布格重力异常不同尺度的总水平梯度(HGM)和横向、纵向、对角分量平方和的平方根(HVDM)图像。结果表明:1)4、5阶小波细节之和的HGM高值区域存在于尼泊尔喜马拉雅地区、喜马拉雅东构造结和阿尔金断裂带中段,即青藏高原周缘较为活跃的构造带;2)尼泊尔喜马拉雅地区和阿尔金断裂带西段存在5阶小波逼近高值HGM,较高值HGM带呈现环青藏高原形态,反映了青藏高原与周缘构造块体地壳深度变化和岩石圈地幔顶部物质性质的差异性变化特征;3)HVDM高值带分布于喜马拉雅地区、喜马拉雅东构造结地区、阿尔金断裂带和龙门山断裂带,体现了青藏高原周缘构造带形态特征;4)2015尼泊尔Ms8.1地震发生在地壳深部的HGM高-低-高分布形态的低值区和HVDM高值带的边界,是印度板块和欧亚板块持续汇聚及周缘大型走滑断裂带的调节作用、累积能量释放的结果。     

Dominant simple-shear deformation during peak metamorphism for the lower portion of the Greater Himalayan Sequence in West Nepal: New implications for hybrid channel flow-type mechanisms in the Dolpo region

I conducted new vorticity and deformation temperatures studies to test competing models of the exhumation of the mid-crustal rocks exposed in the Dolpo region (West Nepal). My results indicate that the Main Central Thrust is located ∼5 km structurally below the previous mapped locations. Deformation temperature increasing up structural section from ∼450 °C to ∼650 °C and overlap with peak metamorphic temperature indicating that penetrative shearing was responsible for the exhumation of the GHS occurred at “close” to peak metamorphic conditions. I interpreted the telescoping and the inversion of the paleo-isotherms at the base of the GHS as produced mainly by a sub-simple shearing (Wm = 0.88–1) pervasively distributed through the lower portion of the GHS. My results are consistent with hybrid channel flow-type models where the boundary between lower and upper portions of the GHS, broadly corresponding to the tectonometamorphic discontinuity recently documented in west Nepal, represents the limit between buried material, affected by dominant simple shearing, and exhumed material affected by a general flow dominates by pure shearing. This interpretation is consistent with the recent models suggesting the simultaneous operation of channel flow- and critical wedge-type processes at different structural depth.     

Conceptualising the Migration–Food Security Nexus: Lessons from Nepal and Vanuatu

In the past decade, international development practitioners have increasingly argued that migration improves the food security of households at origin, by providing the capital necessary for agricultural intensification or food purchase. These debates have occurred largely in isolation from a discussion of the values that underpin food production and consumption in the communities that migrants call home. We question the assumption that a shift from an agricultural-based economy to an economy based on remittances increases the ability of communities to secure access to food in the face of rapid economic and cultural change. In this paper, we present two independently conducted studies from Nepal and Vanuatu that investigate the impact of out-migration on local perceptions of agricultural and residential land and the meaning given to food security. Our data reveal that the value changes associated with large-scale out-migration have the potential to make the agricultural sector at origin more vulnerable, unproductive, unsustainable or unattractive, leaving a longer-term impact on food security. We offer some reflections on the implications of these findings for the structure of the migration–food security nexus.     

Microfacies analysis and paleoenvironmental significance of palustrine carbonates in the Thakkhola-Mustang Graben (Nepal Himalaya)

The Thakkhola-Mustang Graben represents the extensional tectonic phase of the Tibetan Plateau uplift and whole Himalayan orogeny. It is situated at the northern side of the Dhaulagiri and Annapurna Ranges and south of the Yarlang Tsangpo Suture Zone. Stratigraphically, the oldest sedimentary units are the Tetang and Thakkhola Formations (Miocene), while the Sammargaon, Marpha and Kaligandaki Formations lying disconformably above these formations represent Plio-Pleistocene units. In this study, different lacustrine carbonates and calcretes were investigated within different lithological units and depositional environments to interpret the palaeoenvironmental and palaeoclimatological evolution of the area.Geological mapping, construction of columnar sections and carbonate sampling were carried out in the field, and stable oxygen and carbon isotope analyses and thin section analyses were done in the laboratory. Lacustrine facies contained abundant pelletal, charophytic algae, oncolitic algal micritic palustrine limestones with ostracods, and micritic mudstones with root traces. Stable carbon and oxygen isotope analysis from the carbonates show a range of δ¹³C values from −0.6‰ to 11.1‰ (V-PDB) and δ¹⁸O values from −13.5‰ to −25‰ (V-PDB).Discontinuous growth of oncolites and spherical pellets (25–40 μm in diameter) in micritic limestone, algal mats and charophyte algae indicate the presence of both shallow and deep water carbonates. Ostracods in dark micritic carbonates indicate quiet and calm water conditions. Microfabrics of the carbonates suggest that they were deposited in a flat and shallow lacustrine environment. The δ¹⁸O values of the investigated limestones of the Thakkhola-Mustang Graben suggest that it attained the current elevation level prior to the east-west extension of the Himalaya.     

Participatory 3-dimension mapping: A tool for encouraging multi-caste collaboration to climate change adaptation and disaster risk reduction

This article reflects upon the use of participatory 3-dimensional mapping (P3DM) for facilitating the collaboration of different castes in disaster risk reduction (DRR) and climate change adaptation (CCA). Unequal power relationships amongst upper and lower castes has indeed been identified has a major driver of people's vulnerability to natural hazards, including the negative effects of climate change, in Nepal and elsewhere in South Asia. However, this does not prevent the members of all these castes, including the lowest untouchables, to display significant capacities in facing these natural hazards and changes in climate patterns. It is therefore similarly important to harness those capacities and address the unequal power relationships underpinning vulnerability. Achieving these goals requires fostering dialogue amongst upper and lower castes as well as with other stakeholders of DRR and CCA, e.g. scientists, NGOs, government agencies, which often tend to work with a single caste because it is easier. P3DM provides a platform for such a dialogue as it makes the knowledge of every caste tangible and credible to others. This proves essential in both assessing and planning for reducing the risk of disasters and adapting to climate change. This article particularly documents activities conducted in a small village of the Terai plain of Nepal frequently affected by flooding.