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Considerable debate revolves around the relative importance of rock type, tectonics, and climate in creating the architecture of the critical zone. We demonstrate the importance of climate and in particular the rate of water recharge to the subsurface, using numerical models that incorporate hydrologic flowpaths, chemical weathering, and geomorphic rules for soil production and transport. We track alterations in both solid phase (plagioclase to clay) and water chemistry along hydrologic flowpaths that include lateral flow beneath the water table. To isolate the role of recharge, we simulate dry and wet cases and prescribe identical landscape evolution rules. The weathering patterns that develop differ dramatically beneath the resulting parabolic interfluves. In the dry case, incomplete weathering is shallow and surface parallel, whereas in the wet case, intense weathering occurs to depths approximating the base of the bounding channels, well below the water table. Exploration of intermediate cases reveals that the weathering state of the subsurface is strongly governed by the ratio of the rate of advance of the weathering front itself controlled by the water input rate, and the rate of erosion of the landscape. The system transitions between these end‐member behaviours rather abruptly at a weathering front speed ‐ erosion rate ratio of approximately 1. Although there are undoubtedly direct roles for tectonics and rock type in critical zone architecture, and yet more likely feedbacks between these and climate, we show here that differences in hillslope‐scale weathering patterns can be strongly controlled by climate. 相似文献
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D. Shanker H. N. Singh H. Paudyal A. Kumar A. Panthi V. P. Singh 《Pure and Applied Geophysics》2010,167(6-7):655-666
A long-range correlation between earthquakes is indicated by some phenomena precursory to strong earthquakes. Most of the major earthquakes show prior seismic activity that in hindsight seems anomalous. The features include changes in regional activity rate and changes in the pattern of small earthquakes, including alignments on unmapped linear features near the (future) main shock. It has long been suggested that large earthquakes are preceded by observable variations in regional seismicity. Studies on seismic precursors preceding large to great earthquakes with M ≥ 7.5 were carried out in the northeast India region bounded by the area 20°–32°N and 88°–100°E using the earthquake database from 1853 to 1988. It is observed that all earthquakes of M ≥ 7.5, including the two great earthquakes of 1897 and 1950, were preceded by abnormally low anomalous seismicity phases some 11–27 years prior to their occurrence. On the other hand, precursory time periods ranged from 440 to 1,768 days for main shocks with M 5.6–6.5 for the period from 1963 to 1988. Furthermore, the 6 August, 1988 main shock of M 7.5 in the Arakan Yoma fold belt was preceded by well-defined patterns of anomalous seismicity that occurred during 1963–1964, about 25.2 years prior to its occurrence. The pattern of anomalous seismicity in the form of earthquake swarms preceding major earthquakes in the northeast India region can be regarded as one of the potential seismic precursors. Database constraints have been the main barrier to searching for this precursor preceding smaller earthquakes, which otherwise might have provided additional information on its existence. The entire exercise indicates that anomalous seismicity preceding major shocks is a common seismic pattern for the northeast India region, and can be employed for long-range earthquake prediction when better quality seismological data sets covering a wide range of magnitudes are available. Anomalous seismic activity is distinguished by a much higher annual frequency of earthquake occurrence than in the preceding normal and the following gap episodes. 相似文献
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L. Ghezzi R. Petrini C. Montomoli R. Carosi K. Paudyal R. Cidu 《Environmental Earth Sciences》2017,76(19):651
The major ion and trace element chemistry of water samples, including springs, rivers and irrigation ditches, collected during a survey on August 2016 in the Upper Mustang region of the Mustang District of Dhawalagiri Zone (Nepal) has been investigated. The Upper Mustang region, a cold desert, represents a hot-spot for climate change: indeed, violent hailstorms and rainstorms have been recently observed, consequently exposing land to erosion. Results of this study indicate that waters in the region belong to the Ca–HCO3, Ca–Mg–Cl–SO4 and Na–K–Cl-types, reflecting different hydrochemical regimes. Uranium is widespread in waters, with concentrations up to 19 µg/L recorded in a potable water supply. Locally, anoxic conditions affect uranium mobility due to the low solubility of U(IV) minerals. Highly toxic thallium was detected in a thermal spring at an elevated concentration (45 µg/L Tl). The association of thallium with high concentrations of iron suggests that these elements are derived from pyrite oxidation. Detectable levels of thallium were also measured in the water of an irrigation ditch. Lithium concentrations ranged from 7 µg/L to 12 mg/L in the thermal water and showed a strong association with chloride ions. Arsenic concentrations up to 4.7 µg/L were measured in tributaries of the Kali Gandaki river. The data provide evidence that solutes in water have originated from an array of input sources, including carbonate dissolution, the dissolution of soluble salts, silicate weathering and localized sulfide oxidation. In particular, chemical weathering of granitic rocks is likely the primary source for metals and metalloids in waters. Since the erosion rate is a factor affecting lithological weathering, high-intensity rainfalls due to climate change are expected to influence the release and fate of potentially harmful elements in the in the Upper Mustang Valley. 相似文献
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Junming Guo Lekhendra Tripathee Shichang Kang Qianggong Zhang Jie Huang Chhatra Mani Sharma Pengfei Chen Rukumesh Paudyal Dipesh Rupakheti 《地学前缘(英文版)》2022,(1):85-95
Lumbini is a world heritage site located in the southern plains region of Nepal, and is regarded as a potential site for evaluating transboundary air pollution due to its proximity to the border with India. In this study, 82 aerosol samples were collected between April 2013 and July 2014 to investigate the levels of particulate-bound mercury(PBM) and the corresponding seasonality, sources, and influencing factors.The PBM concentration in total suspended particulate(TSP) matter ranged from 6.8 pg m-3 to351.7 pg m-3(mean of 99.7 ± 92.6 pg m-3), which exceeded the ranges reported for remote and rural sites worldwide. The Hg content(PBM/TSP) ranged from 68.2 ng g-1 to 1744.8 ng g-1(mean of 446.9 ±312.7 ng g-1), indicating anthropogenic enrichment. The PBM levels were higher in the dry season(i.e.,winter and the pre-monsoon period) than in the wet season(i.e., the monsoon period). In addition, the δ202 Hg signature indicated that waste/coal burning and traffic were the major sources of Hg in Lumbini during the pre-monsoon period. Meanwhile, precipitation occurring during photochemical processes in the atmosphere may have been responsible for the observed Δ199 Hg values in the aerosol samples obtained during the monsoon period. The PBM concentration was influenced mostly by the resuspension of polluted dust during dry periods and crop residue burning during the post-monsoon period. The estimated PBM deposition flux at Lumbini was 15.7 lg m-2 yr-1. This study provides a reference dataset of atmospheric PBM over a year, which can be useful for understanding the geochemical cycling of Hg in this region of limited data. 相似文献
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A study of local amplification effect of soil layers on ground motion in the Kathmandu Valley using microtremor analysis 总被引：3，自引：1，他引：2
Past researchers have anticipated the occurrence of a great earthquake in the central Himalayas in the near future.This may cause serious damage in the Kathmandu Valley,which sits on an ancient lake be... 相似文献
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On April 25, 2015, Nepal was struck by the MW7.8 Gorkha earthquake followed by an intense aftershock sequence. It was one of the most destructive earthquakes in the Himalayan arc, causing more than 8900 fatalities. In this study, we analyzed the dataset (429 events, magnitude of completeness (Mc) ≥ 4.2 local magnitude) of the first 45 days after the Gorkha earthquake to estimate the seismicity parameters b-value, D-value, and p-value. We used the maximum likelihood method to estimate the b-value and Omori-Utsu parameters, whereas the correlation integral method was applied to estimate the fractal dimension (D-value). The analysis was carried out using running and sliding window techniques. The lowest b-value (0.57 ± 0.04) and the highest D-value (1.65 ± 0.02) were computed at the time of the Gorkha earthquake, after which the b-value significantly increased to a maximum of 1.57. It again dropped to 0.93 at the time of the major aftershock on May 12, 2015. The D-value showed an initial quick drop and then decreased in a wavy pattern until the end of the study period, indicating the clustering and scattering of earthquakes in a fault region. The b-value contour map identified the eastern part of the study area as a high stress region (b = ～0.8), implying that the stress shifted to that region. The D-value contour map reveals that the seismogenic structure shifted from linear to planar in the region. The rate of aftershock decay (p = 0.86 ± 0.04) for a short period reflects that the level of stress decreased rapidly. This study helps to understand the level of stress and seismicity pattern of a region, which could be useful for aftershock studies. 相似文献
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Abstract. A fully interactive microcomputer package consisting of two BASIC programs, OPTP and PTEST, is presented for determining the optimal well discharge. Program PTEST computes the coefficients and exponent of the nonlinear drawdown equation using three-step data from a step-drawdown pumping test. Program OPTP computes the optimal discharge using a single-variable constrained nonlinear programming algorithm. The package, originally written for an IBM-PC, can be adapted to any microcomputer with minor modifications. 相似文献