Does Glacial-Interglacial Transition Affect Sediment Accumulation in Monsoon-Dominated Regions?

The spatio-temporal changes in sedimentation rate along the continental margin of the monsoon-dominated eastern Arabian Sea during the last 24 kyr have been estimated from a compilation of 58 radiocarbon dated cores, in order to understand the effect of glacial-interglacial variation on sedimentation. The sedimentation rate has been computed for four-time slices, viz. the last glacial maximum, glacial-interglacial transition, early Holocene and late Holocene. We report that the average sedimentation rate in the slope to the abyssal region of the entire eastern Arabian Sea, although higher during the Holocene as compared with that during the last glacial maximum and glacial-interglacial transition, does not significantly vary during all four-time intervals. The sedimentation rate during any particular time interval, however, varies from core to core, thus indicating zonal changes. We report four zones of relatively high sedimentation rate, viz. the northeastern Arabian Sea, the region off the Gulf of Khambhat, the region off Goa and Mangalore, and off the southern tip of India. We suggest that a complex interaction of land-ocean-atmospheric processes controlled sedimentation rate in the eastern Arabian Sea during the last 24 kyr in such a way that the average sedimentation rate does not vary significantly, even during highly contrasting climatic conditions.     

A Study of Source Parameters, Site Amplification Functions and Average Effective Shear Wave Quality Factor Qseff from Analysis of Accelerograms of the 1999 Chamoli Earthquake, Himalaya

The accelerograms of the 1999 Chamoli earthquake and nine of its aftershocks, which occurred in Uttaranchal Himalaya, have been analyzed to investigate their source parameters, the site amplification functions and the average effective shear-wave quality factor Q_seff in the region. The fault plane solution of the main shock is obtained using the spectral amplitudes of SH waves (approximated by transverse components of accelerograms) of the high-energy packets observed in the accelerograms of the main shock. It is found to be comparable with the reported solutions in other studies. Similarly the other source parameters (viz., seismic moment = (5.03±1.7) × 10²⁵ dyne-cm, stress drop = 65 bars, source duration = 5.2 s and moment magnitude = 6.4) estimated for the main shock are consistent with the values obtained in other studies. The stress drops estimated for the aftershocks vary from 23 bars to 153 bars and the seismic moment from 1.4 × 10²³ dyne-cm to 2.9 × 10²³ dyne-cm. The average estimated values of the effective shear-wave quality factor Q_seff vary from 655±359 in the Uttaranchal sector of Himalaya and 1475±130 in the Delhi region. In general, the Q_seff value increases with an increase in the epicentral distance reflecting the penetration of the waves into deeper layers of the crust as the epicentral distance of the observation point increases. These values of Q_seff indicate that in general the curst is at low temperatures that will promote brittle behavior and conditions for episodic failure as compared to creep, under the accumulated strains from plate collision at the Himalaya plate boundary. The site amplification characteristics at sites have been identified from the frequency bands of significant amplification observed in the spectral ratios of the horizontal to the vertical component records. The decay of peak ground acceleration (PGA) values with distance has been investigated using the empirical regression curves vis-à-vis the site amplification factors.     

Regional Groundwater Assessment of Krishna River Basin Using Integrated GIS Approach

The groundwater occurrence and movement within the flow systems are governed by many natural factors like topography, geology, geomorphology, lineament structures, soil, drainage network and land use land cover (LULC). Due to complex natural geological/hydro-geological regime a systematic planning is needed for groundwater exploitation. It is even more important to characterize the aquifer system and delineate groundwater potential zones in different geological terrain. The study employed integration of weighted index overlay analysis (WIOA) and geographical information system (GIS) techniques to assess the groundwater potential zones in Krishna river basin, India and the validation of the result with existing groundwater levels. Different thematic layers such as geology, geomorphology, soil, slope, LULC, drainage density, lineament density and annual rainfall distribution were integrated with WIOA using spatial analyst tools in Arc-GIS 10.1. These thematic layers were prepared using Geological survey of India maps, European Digital Archive of Soil Maps, Bhuvan (Indian-Geo platform of ISRO, NRSC) and 30 m global land cover data. Drainage, watershed delineation and slope were prepared from the Shuttle Radar Topography Mission digital elevation model of 30 m resolution data. WIOA is being carried out for deriving the normalized score for the suitability classification. Weight factor is assigned for every thematic layer and their individual feature classes considering their significant importance in groundwater occurrence. The final map of the study area is categorized into five classes very good, good, moderate, poor and very poor groundwater potential zones. The result describes the groundwater potential zones at regional scale which are in good agreement with observed ground water condition at field level. Thus, the results derived can be very much useful in planning and management of groundwater resources in a regional scale.     

Eroding islands of Gulf of Mannar,Southeast India: a consequence of long-term impact of coral mining and climate change

Natural Hazards - Lightning is one of the most widespread and deadly hazards in Bangladesh. Bangladesh has among the highest death rates of any country. The main objective of this study is to...     

Coherent structures and spectral shapes of kinetic Alfvén wave turbulence in solar wind at 1 AU

This paper presents the generation of kinetic Alfv én wave(KAW) coherent structures of magnetic filaments applicable to solar wind at 1 AU, when the background plasma density is modified by parallel ponderomotive force and Joule heating. The inhomogeneity in the magnetic field, which was included as a perturbation in the transverse direction of the magnetic field, takes energy from the main pump KAWs and generates the filamentary structures. When the intensity is high enough, the filaments are broken down and the energy initially confined to low wavenumbers is redistributed to higher wavenumbers, leading to cascades of energy at small scales less than the ion acoustic gyroradius or comparable to electron gyroradius.The magnetic field spectral profile is generated from the numerical simulation results, and its dependence on different directions of the wavevector and initial conditions of the simulation representing the transverse magnetic field inhomogeneity is studied. The relevance of these results with other spacecraft observations and measurements is also pointed out.     

Apposite of atmospheric electric parameters with the energy coupling function (ε) during geomagnetic storms at high latitude

In this paper we are concerned with the variation of the atmospheric electric field and the air–earth current due to the excessive power generated by the solar wind-magnetosphere dynamo during geomagnetic storms, recorded at Maitri in Antarctica during 2004. A major part of the power generated by the solar wind-magnetosphere dynamo is used in the formation of the ring current and the rest is utilized for Joule heating and auroral particle precipitation. The method adopted by Frank-Kamenetsky et al. [Frank-Kamenetsky A.V., Troshichev O.A., Burns G.B., Papitashvili V.O., 2001. Variations of atmospheric electric field in the near-pole region related to the interplanetary magnetic field. J. Geophys. Res. 106, A1, 179–190.] was utilized to delineate the variations due to the signatures of tropical thunderstorm activity from the geoelectric data; while statistical methods used in our earlier studies were used to delimit variation due to the constant buffeting of the solar wind. We find that the solar wind-magnetosphere energy coupling function (ε) to be well correlated with the atmospheric electric parameters during the onset of geomagnetic disturbances. However the correlation breaks down during minor storms and sub-storm events.     

Evaluation of elemental enrichments in surface sediments off southwestern Taiwan

Surface slices of 20 sediment cores, off southwestern Taiwan, and bed sediment of River Kaoping were measured for major and trace elements (Al, As, Ca, Cd, Cl, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, Ti, V, and Zn) to evaluate the geochemical processes responsible for their distribution, including elemental contamination. Major element/Al ratio and mean grain size indicate quartz-dominated, coarse grained sediments that likely derived from sedimentary rocks of Taiwan and upper crust of Yangtze Craton. Bi-plot of SiO₂ versus Fe₂O₃^T suggests the possible iron enrichment in sediments of slag dumping sites. Highest concentrations of Cr, Mn, P, S, and Zn found in sediments of dumping sites support this. Correlation analysis shows dual associations, detrital and organic carbon, for Cr, P, S, and V with the latter association typical for sediments in dumping sites. Normalization of trace elements to Al indicates high enrichment factors (>2) for As, Cd, Pb, and Zn, revealing contamination. Factor analysis extracted four geochemical associations with the principal factor accounted for 25.1% of the total variance and identifies the combined effects of dumped iron and steel slag-induced C–S–Fe relationship owing to authigenic precipitation of Fe–Mn oxyhydroxides and/or metal sulfides, and organic matter complexation of Fe, Mn, Ca, Cr, P, and V. Factors 2, 3, and 4 reveal detrital association (Ti, Al, Ni, Pb, Cu, and V), effect of sea salt (Cl, Mg, Na, and K) and anthropogenic component (As and Zn)-carbonate link, respectively, in the investigated sediments.     

Attenuation of P,S, and coda waves in Koyna region,India

The attenuation properties of the crust in the Koyna region of the Indian shield have been investigated using 164 seismograms from 37 local earthquakes that occurred in the region. The extended coda normalization method has been used to estimate the quality factors for P waves and S waves , and the single back-scattering model has been used to determine the quality factor for coda waves (Q _c). The earthquakes used in the present study have the focal depth in the range of 1–9 km, and the epicentral distance vary from 11 to 55 km. The values of and Q _c show a dependence on frequency in the Koyna region. The average frequency dependent relationships (Q = Q ₀ f ⁿ) estimated for the region are , and . The ratio is found to be greater than one for the frequency range considered here (1.5–18 Hz). This ratio, along with the frequency dependence of quality factors, indicates that scattering is an important factor contributing to the attenuation of body waves in the region. A comparison of Q _c and in the present study shows that for frequencies below 4 Hz and for the frequencies greater than 4 Hz. This may be due to the multiple scattering effect of the medium. The outcome of this study is expected to be useful for the estimation of source parameters and near-source simulation of earthquake ground motion, which in turn are required in the seismic hazard assessment of a region.     

Modelling of Strong Ground Motions from 1991 Uttarkashi,India, Earthquake Using a Hybrid Technique

We present a simple and efficient hybrid technique for simulating earthquake strong ground motion. This procedure is the combination of the techniques of envelope function (Midorikawa et al. Tectonophysics 218:287–295, 1993) and composite source model (Zeng et al. Geophys Res Lett 21:725–728, 1994). The first step of the technique is based on the construction of the envelope function of the large earthquake by superposition of envelope functions for smaller earthquakes. The smaller earthquakes (sub-events) of varying sizes are distributed randomly, instead of uniform distribution of same size sub-events, on the fault plane. The accelerogram of large event is then obtained by combining the envelope function with a band-limited white noise. The low-cut frequency of the band-limited white noise is chosen to correspond to the corner frequency for the target earthquake magnitude and the high-cut to the Boore’s f _max or a desired frequency for the simulation. Below the low-cut frequency, the fall-off slope is 2 in accordance with the ω² earthquake source model. The technique requires the parameters such as fault area, orientation of the fault, hypocenter, size of the sub-events, stress drop, rupture velocity, duration, source–site distance and attenuation parameter. The fidelity of the technique has been demonstrated by successful modeling of the 1991 Uttarkashi, Himalaya earthquake (Ms 7). The acceptable locations of the sub-events on the fault plane have been determined using a genetic algorithm. The main characteristics of the simulated accelerograms, comprised of the duration of strong ground shaking, peak ground acceleration and Fourier and response spectra, are, in general, in good agreement with those observed at most of the sites. At some of the sites the simulated accelerograms differ from observed ones by a factor of 2–3. The local site geology and topography may cause such a difference, as these effects have not been considered in the present technique. The advantage of the technique lies in the fact that detailed parameters such as velocity-Q structures and empirical Green’s functions are not required or the records of the actual time history from the past earthquakes are not available. This method may find its application in preparing a wide range of scenarios based on simulation. This provides information that is complementary to the information available in probabilistic hazard maps.