Effect of surface wave inversion non-uniqueness on 1D seismic ground response analysis

Surface wave methods are increasingly being used for geotechnical site characterization. The methodology is based on the dispersive characteristic of Rayleigh waves in vertically heterogeneous medium. Experimental dispersion curve is inverted to obtain one-dimensional shear-wave velocity profile by inverse problem solution. Uncertainty associated with this surface wave inversion has drawn much attention. Inverse problem solution can provide different equivalent shear-wave velocity profiles, which may lead to different seismic site response analysis. In this study, a neighborhood algorithm has been used for inversion of dispersion curve to get a set of equivalent shear-wave velocity profiles. These equivalent velocity profiles are then used for 1D ground response analysis for different input motion record of the same earthquake at different epicentral distances. Results show significant variation in amplification spectrum in terms of maximum amplification as well as peak frequency. The extent of this uncertainty largely depends on the characteristics of the ground motion records at different epicentral distances. A linear variation is observed between mean coefficients of variation of amplification spectrum and epicentral distance of ground motion records. A gradual increase in mean value of peak frequency and peak amplification with the epicentral distance is also observed.     

Evidence for climatic and oceanographic controls on terrigenous sediment supply to the Indian Ocean sector of the Southern Ocean over the past 63,000?years

Multiple proxy studies on sediment core SK 200/22a from the sub-Antarctic sector of the Indian Ocean revealed millennial-scale fluctuations in terrigenous input during the last 63,000?years. The marine isotope stages 1 (MIS 1) and MIS 3 are characterized by generally low concentrations of magnetic minerals, being dominated by fine-grained magnetite and titano-magnetite. Within the chronological constraints, periods of enhanced terrigenous input and calcite productivity over the last 63,000?years are nearly synchronous with the warming events recorded in Antarctic ice cores. An equatorward shift of the westerly wind system in association with a strengthening of the Antarctic Circumpolar Current (ACC) system may have promoted wind-induced shallow-water erosion around oceanic islands, leading to enhanced terrigenous input to the core site. Major ice-rafted debris events at 13?C23, 25?C30, 45?C48 and 55?C58?ka BP are asynchronous with ??¹⁸O and carbonate productivity records. This out-of-phase relation suggests that ice-sheet dynamics and ACC intensity were the primary factors influencing ice rafting and terrigenous input to the Indian sector of the Southern Ocean, with only limited support from sea-surface warming.     

Assessment of Impact on Seafloor Features in INDEX Area

Abstract

Observations on seafloor features from subbottom profiling and seabed photography data show that the undisturbed and natural conditions before the benthic disturbance undergo a substantial change after operation of the disturber. The effects can be seen in the form of deep trenches and grooves, formed by the action of the sleds and the pumping of the sediment along its path, as well as sediment piles on either side of the track. Biological traces such as fecal coils, casts, tubes, burrows, and trails get obliterated in the areas of disturbance and resedimentation. The smooth, uniform nature of the seafloor observed in pre-disturbance phase shows microtopographic changes in and around the disturbed area as a result of sediment excavation and resettlement. Vertical mixing as well as lateral transport of sediment alter the geological, biological, physical, and chemical conditions on the seafloor, which need to be monitored over time to assess the process and the time taken for restoration of environmental conditions.     

Estimation of Sediment Properties during Benthic Impact Experiments

Sediment properties, such as water content and density, have been used to estimate the dry and wet weights, as well as the volume of sediment recovered and discharged, during benthic impact experiments conducted in the Pacific and Indian Oceans. The estimates show that the weights of dry (355-1332 t) and wet sediment (1651-4888 t) recovered during the experiments, are not only a function of the total duration and distance covered during the experiment, but also depend on water content and density of the sediment. Estimation of dry sediment and its volumetric ratio in the discharge, are key parameters for calculating the discharged volume. The estimated volume of wet sediment recovered (1427-4049 m 3 ) as well as discharged (2693-6951 m 3 ) during the experiments, provide important inputs to evaluate the sediment resettlement and migration. Using these estimates, the average depth of excavation on the seafloor, can also been calculated. However, the stages of sediment recovery and discharge are expressed differently in some of the experiments. In order to standardize these, different stages have been identified, and definitions of certain terms have been suggested, for use in the future. The methods of calculating different properties, as well as weight and volume of discharged sediment are described in the paper for use in other applications concerning deep-sea discharges.     

Formulation of Time Series Vegetation Index from Indian Geostationary Satellite and Comparison with Global Product

To study impact of climate change on vegetation time series vegetation index has a vital role to know the behaviour of vegetation dynamics over a time period. INSAT 3A CCD (Charged Couple Device) is the only geostationary sensor to acquire regular coverage of Asia continent at 1 km × 1 km spatial resolution with high temporal frequency (half-an-hour). A formulation of surface reflectances in red, near infrared (NIR), short wave infrared (SWIR) and NDVI from INSAT 3A CCD has been defined and integrated in the operational chain. The atmospheric correction of at-sensor reflectances using SMAC (Simple Model for Atmospheric Correction) model improved the NDVI by 5–40% and also increased its dynamic range. The temporal dynamics of 16-day NDVI composite at 0500 GMT for a growing year (June 2008–March 2009) showed matching profiles with reference to global products (MODIS TERRA) over known land targets. The root mean square deviation (RMSD) between the two was 0.14 with correlation coefficient (r) 0.84 from 200 paired datasets. This inter-sensor cross-correlation would help in NDVI calibration to add continuity in long term NDVI database for climate change studies.     

Effects of site–city interaction and polarization of the incident S-wave on the transfer function and fundamental frequency of structures

Natural Hazards - The variation of 2D fundamental frequency of stand-alone structure on rock $$ ({F}_{{02{\text{D}}}}^{\text{S}} ) $$ and in a basin $$ ({F}_{{02{\text{D}}}}^{\text{BS}} ) $$ with...     

A Numerical Study of Effects of Valley-Weathering and Valley-Shape-Ratio on the Ground Motion Characteristics

A study of combined effects of valley-weathering and valley-shaperatio on the ground motion characteristics and associated differential ground motion (DGM) is documented in this paper. In order to properly quantify the weathering effects, a forth-order-accurate staggered-grid viscoelastic time-domain finite-difference program has been used for the simulation of SH-wave responses. Simulated results revealed that the defocusing caused by valley is frequency-independent in contrast to the ridge-focusing. A decrease of average spectral amplification (ASA) with an increase of shape-ratio of the non-weathered triangular and elliptical valleys was obtained. Overall, the amplification and de-amplification pattern was larger in case of triangular valleys as compared to the elliptical valleys. It can be concluded that the dwelling within or near the topcorners of weathered valleys may suffer more damage as compared to their surroundings. A weathered triangular valley with large shape-ratio may cause unexpected damage very near its top-corners since both the ASA and DGM are largest.