Clinoform nucleation and growth in coarse-grained deltas, Loreto basin, Baja California Sur, Mexico: a response to episodic accelerations in fault displacement   总被引：1，自引：0，他引：1  

Estelle Mortimer  Sanjeev Gupta†  Patience Cowie 《Basin Research》2005,17(3):337-359

We investigate the controls on the architecture of coarse‐grained delta progradational units (PUs) in the Pliocene Loreto basin (Baja California Sur, Mexico), a half‐graben located on the western margin of the Gulf of California. Dorsey et al. (1997b) argued that delta progradation and transgression cycles in the basin were driven by episodic fault‐controlled subsidence along the basin‐bounding Loreto fault. Here we test this hypothesis by a detailed analysis of the sedimentary architecture of 11 exceptionally well‐exposed, vertically arranged fluvio‐deltaic PUs, each of which shows lateral facies transition from proximal alluvial facies palaeo‐seaward into distal pro‐delta facies. Of these 11 PUs, seven exhibit a lateral transition from a shoal water to Gilbert‐delta facies associations as they are traced palaeo‐seaward. This transition is characterised by down‐transport development of foresets, which grow in height up to 35 m. Foreset units thicken in a basinward direction, with initially an oblique topset–foreset geometry that becomes increasingly sigmoidal. Each delta is capped by a shell bed that records drowning of the delta top. This systematic transition in delta architecture records increasing water depth through time during individual episodes of progradation. A mechanism that explains this transition is an accelerating rate of fault‐controlled subsidence during each PU. During episodes of low slip rate, shoal‐water deltas prograde across the submerged topography of the underlying delta unit. As displacement rate accelerates, increasing bathymetry at the delta front leads to steepening of foresets and initiation of Gilbert deltas. Subsequent delta drowning results from sediment starvation at the shoreline at high slip rates because of sediment trapping upstream. The observed delta architecture suggests that the long‐term (>100 kyr) history of slip on the Loreto fault was characterised by repetitive episodes of accelerating displacement accumulation. Such episodic fault behaviour is most likely to be because of variations in temporal and spatial strain partitioning between the Loreto fault and other faults in the Gulf of California. A physical explanation for the acceleration phenomenon involves evolving frictional properties on the episodically active Loreto fault.  相似文献   

Avalanche hazard mitigation in east Karakoram mountains     

Singh  Amreek  Juyal  Vikas  Kumar  Bhupinder  Gusain  H. S.  Shekhar  M. S.  Singh  Paramvir  Kumar  Sanjeev  Negi  H. S. 《Natural Hazards》2021,105(1):643-665

Natural Hazards - Karakoram mountains range in north-western part of Himalayas is about 500 km in length and hosts some of the world’s highest peaks and longest glaciers. It is...  相似文献   

Seismic response of simple structures using spring-assisted sliding slabs with coulomb damping     

M. P. Singh  S. R. Malushte 《地震工程与结构动力学》1990,19(2):189-203

Coulomb damping can be utilized effectively to reduce the dynamic response of structures subjected to seismic ground motions. To activate this damping, some parts of a vibrating structure are allowed to slide at rough interfaces. The dynamic response of structures provided with sliding interfaces at the base, between a floor slab and frame and in the cross bracings of a frame has been examined recently. In this paper, a simple slab sliding system provided with a spring to introduce a recovery mechanism and to reduce the sliding displacement requirement for low frequency structures has been examined. The equations of motion for this system are developed. An approach is presented to solve these coupled equations for earthquake induced ground motions. Structures with varying frequency and friction characterisics are considered and the numerical results are presented in response spectrum form. It is observed that, in low frequency structures, provision of a rather weak spring can reduce the sliding displacement requirements without significantly increasing the forces in the supporting frame and the acceleration input to supported secondary systems.  相似文献   

A study of seismic response characteristics of structures with friction damping     

S. R. Malushte  M. P. Singh 《地震工程与结构动力学》1989,18(6):767-783

The effectiveness of introducing Coulomb damping in structures to reduce seismic response is evaluated. Response characteristics of simple one-degree-of-freedom structures with sliding interfaces between the top slab and supporting frame and between the base and foundation are studied and compared. It is shown that, analytically, the top slab sliding system is a special case of the base sliding system. The slab sliding system is seen to offer certain advantages over the base sliding system inasmuch as it provides a more effective reduction in the lateral forces in the supporting frame as well as a better isolation of supported secondary systems, as depicted by a significantly reduced level of floor spectrum response. The analytical ease of predicting the response of the slab sliding system is also demonstrated. The required unobstructed sliding displacements seem to be reasonable except, may be, for flexible systems. The similarities and differences between the hysteretic and slab sliding systems are also highlighted by comparison of their response results.  相似文献   

Assessment of Man-made and Natural Hazards in the Surroundings of Hydropower Projects under Construction in the Beas Valley of Northwestern Himalaya     

Sanjeev Sharma Jagdish C. Kuniyal J. C. Sharma 《山地科学学报》2007,4(3):221-236

Mountain ecosystem,on the earth,has plenty of natural resources. In Himachal Pradesh all the rivers are snowfed and therefore rich in water resources. These resources have been supporting enough for the generation of electricity through introducing hydropower projects since the last decade. However,every developmental activity has its own negative impacts on the surrounding environment. Due to the fragile nature of topography and delicacy of ecology of the Himalaya,it results in lot of disturbances because of high degree of human interferences like construction of major hydropower projects. The increased extent of geological hazards,such as landslides,rock fall and soil erosion,have mainly due to alike developmental interventions in the natural ecosystem. So understanding and analysing such impacts of the hydropower projects have mainly been on the environment in various forms but natural hazards have been frequent ones. The present study,therefore,focuses mainly on the Parbati Stage Ⅱ (800 MW) and the Parbati Stage Ⅲ (520 MW) hydropower projects; both of which fall within the Kullu district of Himachal Pradesh. Based on the perception survey of the local communities,the existing land use pattern,status of total acquired land of the residents by hydropower projects,frequent natural hazards and resultant loss to the local communities due to upcoming construction of hydropower projects surrounding to the Parbati Stage Ⅱ and Ⅲ have been analysed in the paper. Also,the preventive measures to mitigate these adverse impacts have been suggested to strengthen these projects in eco-friendly manner in the mountain context.  相似文献   

Training Images from Process-Imitating Methods   总被引：2，自引：2，他引：0  

Alessandro Comunian  Sanjeev K. Jha  Beatrice M. S. Giambastiani  Gregoire Mariethoz  Bryce F. J. Kelly 《Mathematical Geosciences》2014,46(2):241-260

The lack of a suitable training image is one of the main limitations of the application of multiple-point statistics (MPS) for the characterization of heterogeneity in real case studies. Process-imitating facies modeling techniques can potentially provide training images. However, the parameterization of these process-imitating techniques is not straightforward. Moreover, reproducing the resulting heterogeneous patterns with standard MPS can be challenging. Here the statistical properties of the paleoclimatic data set are used to select the best parameter sets for the process-imitating methods. The data set is composed of 278 lithological logs drilled in the lower Namoi catchment, New South Wales, Australia. A good understanding of the hydrogeological connectivity of this aquifer is needed to tackle groundwater management issues. The spatial variability of the facies within the lithological logs and calculated models is measured using fractal dimension, transition probability, and vertical facies proportion. To accommodate the vertical proportions trend of the data set, four different training images are simulated. The grain size is simulated alongside the lithological codes and used as an auxiliary variable in the direct sampling implementation of MPS. In this way, one can obtain conditional MPS simulations that preserve the quality and the realism of the training images simulated with the process-imitating method. The main outcome of this study is the possibility of obtaining MPS simulations that respect the statistical properties observed in the real data set and honor the observed conditioning data, while preserving the complex heterogeneity generated by the process-imitating method. In addition, it is demonstrated that an equilibrium of good fit among all the statistical properties of the data set should be considered when selecting a suitable set of parameters for the process-imitating simulations.  相似文献   

Aerosol optical depths at Mohal-Kullu in the northwestern Indian Himalayan high altitude station during ICARB     

Jagdish C. Kuniyal  Alpana Thakur  Harinder K. Thakur  Sanjeev Sharma  P. Pant  Pan S. Rawat  K. Krishna Moorthy 《Journal of Earth System Science》2009,118(1):41-48

First time observations of spectral aerosol optical depths (AODs) at Mohal (31.9°N, 77.11°E; altitude 1154 m amsl) in the Kullu valley, located in the northwestern Indian Himalayan region, have been carried out during Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), as a part of the Indian Space Research Organisation-Geosphere Biosphere Program (ISRO-GBP). AODs at six wavelengths are obtained using Microtops-II Sunphotometer and Ozonometer. The monthly mean values of AOD at 500 nm are found to be 0.27 ± 0.04 and 0.24 ± 0.02 during March and April, 2006 respectively. However, their monthly mean values are 0.33 ± 0.04 at 380 nm and 0.20 ± 0.03 nm at 870 nm during March 2006 and 0.31 ± 0.3 at 380 nm and 0.17 ± 0.2 at 870 nm during April 2006, showing a gradual decrease in AOD with wavelength. The Ångstrom wavelength exponent ‘α’ had a mean value of 0.72 ± 0.05, implying reduced dominance of fine particles. Further, the afternoon AOD values are higher as compared to forenoon values by ～ 33.0% during March and by ～ 9.0% during April 2006 and are attributed to the pollutant lifted up from the valley by the evolving boundary layer. Besides the long-range transportation of aerosol particles by airmass from the Great Sahara and the Thar Desert regions to the observing site, the high values of AODs have also been influenced by biomass burning and frequent incidents of forest fire at local levels.  相似文献   

Magnetoelastic shear wave propagation in pre-stressed anisotropic media under gravity     

Nirmala Kumari  Amares Chattopadhyay  Abhishek K. Singh  Sanjeev A. Sahu 《Acta Geophysica》2017,65(1):189-205

The present study investigates the propagation of shear wave (horizontally polarized) in two initially stressed heterogeneous anisotropic (magnetoelastic transversely isotropic) layers in the crust overlying a transversely isotropic gravitating semi-infinite medium. Heterogeneities in both the anisotropic layers are caused due to exponential variation (case-I) and linear variation (case-II) in the elastic constants with respect to the space variable pointing positively downwards. The dispersion relations have been established in closed form using Whittaker’s asymptotic expansion and were found to be in the well-agreement to the classical Love wave equations. The substantial effects of magnetoelastic coupling parameters, heterogeneity parameters, horizontal compressive initial stresses, Biot’s gravity parameter, and wave number on the phase velocity of shear waves have been computed and depicted by means of a graph. As a special case, dispersion equations have been deduced when the two layers and half-space are isotropic and homogeneous. The comparative study for both cases of heterogeneity of the layers has been performed and also depicted by means of graphical illustrations.  相似文献   

Instrumentation Development for In Situ 40Ar/39Ar Planetary Geochronology          下载免费PDF全文

Leah E. Morgan  Madicken Munk  Brett Davidheiser‐Kroll  Nicholas H. Warner  Sanjeev Gupta  Rachel Slaybaugh  Patrick Harkness  Darren F. Mark 《Geostandards and Geoanalytical Research》2017,41(3):381-396

The chronology of the Solar System, particularly the timing of formation of extra‐terrestrial bodies and their features, is an outstanding problem in planetary science. Although various chronological methods for in situ geochronology have been proposed (e.g., Rb‐Sr, K‐Ar), and even applied (K‐Ar), the reliability, accuracy, and applicability of the ⁴⁰Ar/³⁹Ar method makes it by far the most desirable chronometer for dating extra‐terrestrial bodies. The method however relies on the neutron irradiation of samples, and thus a neutron source. Herein, we discuss the challenges and feasibility of deploying a passive neutron source to planetary surfaces for the in situ application of the ⁴⁰Ar/³⁹Ar chronometer. Requirements in generating and shielding neutrons, as well as analysing samples are described, along with an exploration of limitations such as mass, power and cost. Two potential solutions for the in situ extra‐terrestrial deployment of the ⁴⁰Ar/³⁹Ar method are presented. Although this represents a challenging task, developing the technology to apply the ⁴⁰Ar/³⁹Ar method on planetary surfaces would represent a major advance towards constraining the timescale of solar system formation and evolution.  相似文献   

Microbial Decolorization of Reactive Dye Solutions          下载免费PDF全文

Neha Parmar  Sanjeev R. Shukla 《洁净——土壤、空气、水》2015,43(10):1426-1432

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