Trend and spatial distribution of rainfall & rainy days over Andaman & Nicobar Islands

The present study examines the characteristics and climatological features of daily rainfall data over Andaman & Nicobar Islands. Analysis of rainfall data reveals a large monthly deviation over the northern latitudes as compare to southern latitudes of Andaman & Nicobar Islands. Also, it is found that rainfall increases from north to south latitudes in all the seasons except monsoon, where a reverse pattern exists. In trend analysis, a statistically significant decreasing trend (confidence level >95?%) is observed for yearly rainfall and rainy days over the region. Analysis of daily rainfall intensity for each year shows increasing trend for frequency of rather heavy rain (35.6?C64.4?mm) and significant decreasing trend for frequencies of light rain (2.5?C7.5?mm), and very heavy rain (>124.5?mm) over the region. Many times, very heavy rain events are associated with cyclonic disturbances affecting Andaman & Nicobar Islands region. The analysis of cyclonic disturbances over the region reveals a stronger and more significant decreasing trend. So, one of the causes for decreasing trend in very heavy rain over Andaman & Nicobar Islands may be due to significant decreasing frequency of cyclonic disturbances affecting this region.     

Temporal divergence in cropping pattern and its implications on geospatial drought assessment

Time series data on cropping pattern at disaggregated level were analysed and its implications on geospatial drought assessment were demonstrated. An index of Cropping Pattern Dissimilarity (CP-DI) between a pair of years, developed in this study, proved that the cropping pattern of a year has a higher degree of similarity with that of recent past years only and tends to be dissimilar with longer time difference. The temporal divergence in cropping pattern has direct implications on geospatial approach of drought assessment, in which, time series NDVI data are compared for drought interpretation. It was found that, seasonal NDVI profiles of drought year and normal year did not show any anomaly when the cropping patterns were dissimilar and two normal years having dissimilar cropping pattern showed different NDVI profiles. Therefore, it is suggested that such temporal comparisons of NDVI are better restricted to recent past years to achieve more objective interpretation.     

Crustal thickness and Poisson’s ratio variations across the northwest Himalaya and eastern Ladakh

Crustal thickness and Poisson’s ratios are estimated across the northwest (NW) Himalaya and eastern Ladakh applying H-k stacking method on receiver functions of teleseismic earthquakes recorded at 16 broadband seismological stations. The results show significant lateral variation of crustal thickness from the Lesser and Higher Himalaya (～50 km thick) to Ladakh (～80 km thick) through the Indus Tsangpo Suture Zone (ITSZ). The Indian Moho is continuously traceable across the ITSZ which is consistent with the underthrusting of the Indian plate beyond the surface collision boundary. The estimated Poisson’s ratios in the Lesser and Higher Himalaya are low (0.249–0.253), suggesting felsic composition of the crust. The Poisson’s ratio is intermediate in the Tethyan Himalaya (0.269–0.273) and high beneath Ladakh (0.280–0.303), indicating the effect of aqueous fluid/partial melt present in the crust.     

Earthquake precursory research in western Himalaya based on the multi-parametric geophysical observatory data

The opening of cracks and influx of fluids in the dilatancy zone of impending earthquake is expected to induce short-term changes in physical/chemical/hydrological properties during earthquake build-up cycle, which should be reflected in time-varying geophysical fields. With this rationale, eleven geophysical parameters are being recorded in continuous mode at the Multi-Parametric Geophysical Observatory (MPGO), in Ghuttu, Garhwal Himalaya, for earthquake precursory research. The critical analysis of various geophysical time series indicates anomalous behavior at few occasions; however, the data is also influenced by many external forces. These external influences are the major deterrent for the isolation of precursory signals. The recent work is focused on the data adoptive techniques to estimate and eliminate effects of solar-terrestrial and hydrological/environmental factors for delimiting the data to identify short-term precursors. Although any significant earthquake is not reported close to the observatory, some weak precursory signals and coseismic changes have been identified in few parameters related to the occurrence of moderate and strong earthquakes.     

Historical temporal variation in precipitation over Western Himalayan Region: 1857-2006

This study has examined the temporal variation in monthly, seasonal annual precipitation over the Western Himalayan Region(WHR) and the influence of global teleconnections, like the North Atlantic Oscillation(NAO) and Southern Oscillation(SO) Indices on seasonal annual precipitation. The Mann–Kendall non-parametric test is applied for trend detection and the Pettitt–Mann–Whitney test is used to detect possible shift. Maximum entropy spectral analysis is applied to find the periodicity in annual seasonal precipitation. The study shows a non-significant decreasing trend in annual precipitation over WHR for the period 1857-2006. However, in seasonal precipitation, a significant decreasing trend is observed in monsoon and a significant increasing trend in post-monsoon season during the same period. The significant decrease in monsoon precipitation may be due to weakening of its teleconnection with NAO as well as SO Indices mainly during last three decades. It is observed that the probable change of year in annual monsoon precipitation over WHR is 1979. The study also shows significant periodicities of 2.3-2.9 years and of 3.9-4.7 years in annual seasonal precipitation over WHR.     

Palynology in hydrocarbon exploration: High impact palynological studies in Western Offshore and Krishna-Godavari Basin

This paper presents an updated account of palynostratigraphic, source rock evaluation and palaeoenvironment data on Western Offshore and Krishna Godavari (K-G) Basins. Forty three dinoflagellate biohorizons have been identified in the Tertiary subsurface of Mumbai Offshore, facilitating a high resolution correlation of Oil bearing horizons. In K-G Basin integrated palynostratigraphic data and the composite general lithologies for the Mesozoic and Cenozoic have been presented in a tabular form; Eighty two dinoflagellate biohorizons have been identified. A very fine dinoflagellate based stratigraphic resolution has been achieved at most levels making it useful in geological modelling for hydrocarbon exploration in both Western Offshore and K-G Basin.     

A toppled structure with sliding in the Siwalik Hills, midwestern Nepal

Not only the high mountainous regions but also the southern hilly regions of Nepal frequently suffer from landslides and debris flows. An interesting toppled structure with sliding was distinguished on an excavated slope facing the major highway in one such region, the Siwalik Hills. These hills are mostly composed of alternating beds of sandstones and mudstones of the Siwalik Group. A distinct contrast in the direction of dip of the strata was recognized on the excavated slope; the strata in the upper portion of the slope dipped southward, whereas those of the foot slope dipped northward. This indicated that toppling of strata had occurred. The northward direction of toppling and the angle and axis of rotation of the block were determined by examining the distribution of the attitudes of the strata.

Steeply dipping strata influenced by southward thrusting along the major tectonic line, contrasting rigidity between sandstone and mudstone, and rapid dissection by a river were the major causes of the toppling. The bottom surface of the toppled part dipped gently not only northward but also partially westward, showing that the toppled block slid westward after toppling. Evidence for tension cracking and scarplets on the top slope indicated that the block was still actively sliding.

Because steeply dipping sandstone and mudstone strata are widely distributed in the Siwalik Hills, similar structures are inferred to exist in many places. Therefore, the investigation of such slope structures is important, and their instability must be evaluated before road construction and excavation projects are carried out in Nepal.     

Estimation of Q p and Q s of Kinnaur Himalaya

The attenuation characteristics of the Kinnaur area of the North West Himalayas were studied using local earthquakes that occurred during 2008–2009. Most of the analyzed events are from the vicinity of the Panjal Thrust (PT) and South Tibetan Detachment Thrust, which are well-defined tectonic discontinuities in the Himalayas. The frequency-dependent attenuation of P and S waves was estimated using the extended coda normalization method. Data from 64 local earthquakes recorded at 10 broadband stations were used. The coda normalization of the spectral amplitudes of P and S waves was done at central frequencies of 1.5, 3, 6, 9, and 12 Hz. Q _p increases from about 58 at 1.5 Hz to 706 at 12 Hz, and Q _s increases from 105 at 1.5 Hz to 1,207 at 12 Hz. The results show that the quality factors for both P and S waves (Q _p and Q _s) increase as a function of frequency according to the relation Q?=?Q _o f ⁿ , where Q _o is the corresponding Q value at 1 Hz frequency and “n” is the frequency relation parameter. We obtained Q _p?=?(47?±?2)f ^(1.04±0.04) and Q _s?=?(86?±?4)f ^(0.96±0.03) by fitting power law dependency model for the estimated values of the entire study region. The Q ₀ and n values show that the region is seismically very active and the crust is highly heterogeneous. There was no systematic variation of values of Q _p and Q _s at different frequencies from one tectonic unit to another. As a consequence, average values of these parameters were obtained for each frequency for the entire region, and these were used for interpretation and for comparison with worldwide data. Q _p values lie within the range of values observed for some tectonically active regions of the world, whereas Q _s values were the lowest among the values compared for different parts of the world. Q _s/Q _p values were >1 for the entire range of frequencies studied. All these factors indicate that the crust is highly heterogeneous in the study region. The high Q _s/Q _p values also indicate that the region is partially saturated with fluids.