Coda Q Estimates in the Koyna Region, India

—The coda Q, Q _c ?, have been estimated for the Koyna region of India. The coda waves of 76 seismograms from thirteen local earthquakes, recorded digitally in the region during July–August, 1996, have been analyzed for this purpose at nine central frequencies viz., 1.5, 2.0, 3.0, 4.0, 6.0, 8.0, 12.0, 16.0 and 24.0 Hz using a single backscattering model. All events with magnitude less than 3 fall in the epicentral distances less than 60 km and have focal depths which range from 0.86 to 9.43 km. For the 30 sec coda window length the estimated Q _c values vary from 81 to 261 at 1.5 Hz and 2088 to 3234 at 24 Hz, whereas the mean values of Q _c with the standard error vary from 148 ± 13.5 at 1.5 Hz to 2703 ± 38.8 at 24 Hz. Both the estimated Q _c values and their mean values exhibit the clear dependence on frequency in the region and a frequency dependence average attenuation relationship, Q _c = 96f ^1.09, has been obtained for the region, covering an approximate area of 11500 km² with the surfacial extent of about 120 km and depth of 60 km.¶Lapse time dependence of Q _c has also been studied for the region, with the coda waves analyzed at five lapse time windows from 20 to 60 sec duration with the difference of 10 sec. The frequency dependence average Q _c relationships obtained at these window lengths Q _c = 66f ^1.16 (20 sec), Q _c = 96f ^1.09 (30 sec), Q _c =131f ^1.04 (40 sec), Q _c = 148f ^1.04 (50 sec), Q _c = 182f ^1.02 (60 sec) show that the frequency dependence (exponentn) remains mostly stationary at all the lapse time window lengths, while the change in Q ₀ value is significant. Lapse time dependence of Q _c in the region is also interpreted as the function of depth.     

Possible transient emission from Cygnus X-3 at TeV energies during October 1985 radio flare

The Gulmarg gamma-ray telescope (threshold energy 6 TeV) was tracking Cygnus X-3 on four days in October 1985, around the time the source produced one of its most outstanding radio flares. Examined here is the behaviour of the event rates recorded during this period with a time-resolution of 216 s. Two episodes of higher event rates, each several minutes in duration and having a Poissonian significance of 4, were recorded on 10 and 12 October, suggesting possible activity at TeV energies during the radio flare period of Cygnus X-3.     

Evaluation of relief aspects morphometric parameters derived from different sources of DEMs and its effects over time of concentration of runoff (T<Subscript>C</Subscript>)

An attempt has been made to study the relief aspects from three different sources of Digital Elevation Models (DEMs) viz., Survey of India (SOI) topographic map (1:25,000), Shuttle Radar Topography Mission (SRTM-90 m and SRTM-30 m) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER-30 m). These aspects are evaluated to examine differences among them and their influence on time of concentration (T_C) of runoff at Moolbari Experimental Watershed (MEW), Sub Himalayan region (Shimla, District of Himachal Pradesh) India. For detailed study of relief aspects, morphometry parameters, SOI topographic map (as base map) were used. The results show that the relief aspects morphometric parameters derived from the SRTM_30m and ASTER_30m lie between SOI topographic map, and SRTM_90m. We estimated T_C of 21 micro watersheds from different sources DEMs by using Kirpich, Johnstone, Témez, and Barnsby equation only. Témez and Barnsby equation demonstrate high potential for the identification of T_C from SOI Topographic map, SRTM_90m, ASTER and SRTM_30m DEMs. T_{C_Topo} has a positive relationship with T_C__SRTM90m, T_C__ASTER and T_C__SRTM30m for both Témez, and Barnsby equation with R²=0.804_{Topo & SRTM90m}, 0.810_{Topo & ASTER} & 0.839_{Topo & SRTM30m} and 0.712_{Topo & SRTM90m}, 0.747 _{Topo & ASTER} & 0.785 _{Topo & SRTM30m}. Further statistical test of Témez, and Barnsby equation based T_C, only Témez equation based T_C qualify/satisfy the statistical test. by considering all freeware DEMs a Semi-empirical model (SEM) has been developed, where T_C predicted in term of T_C__Topo is a function of T_{C_SRTM90m}, T_{C_ASTER} and T_{C_SRTM30m}. This SEM has R²=0.883 and adjusted R= 0.874, Multiple R=0.907 and with Standard Error =2.131 at 95% confidence level. Comparison of the T_C derived from the multiple regressions among three DEMs with T_C__Topo shows an RMSE of 3.803, R-RMSE of 0.169, NRMSE of 0.342, R² of 0.89, and RMSE% of 3.296 for Témez equation.     

Indian monsoon variability during the last 46 kyr: isotopic records of planktic foraminifera from southwestern Bay of Bengal

The Indian monsoon carries large amounts of freshwater to the northern Indian Ocean and modulates the upper ocean structure in terms of upwelling and productivity. Freshwater-induced stratification in the upper ocean of the Bay of Bengal is linked to the changes in the Indian monsoon. In this study, we test the usefulness of δ¹⁸O and δ¹³C variability records for Globigerina bulloides and Orbulina universa to infer Indian monsoon variability from a sediment core retrieved from the southwestern Bay of Bengal encompassing the last 46 kyr record. Results show that the northeast monsoon was dominant during the Last Glacial Maximum. Remarkable signatures are observed in the δ¹⁸O and δ¹³C records during the Marine Isotope Stage (MIS) 3 to MIS-1. Our study suggests that Indian monsoon variability is controlled by a complex of factors such as solar insolation, North Atlantic climatic shifts, and coupled ocean–atmospheric variability during the last 46 kyr.     

Satellite detection of thermal precursors of Yamnotri,Ravar and Dalbandin earthquakes

Prior to the occurrence of an earthquake, the region undergoes intensive physiochemical changes. Such changes trigger degassing charge generation leading to positive change in the thermal regime and consequently creation of an earthquake preparation zone. These changes in thermal regime can be detected by the thermal sensors onboard various polar orbiting satellites. Recent researches have demonstrated that thermal infrared sensors onboard satellites (e.g., NOAA-AVHRR and Terra/Aqua-MODIS) can detect temporal transient thermal infrared anomalies prior to an earthquake. The paper presents satellite-based thermal observations associated with Yamnotri (July 22, 2007, India), Ravar (October 14, 2004, Iran) and Dalbandin (January 19, 2011, Pakistan) earthquakes. In the case of Yamnotri earthquake, the region attained around 5–8°C higher than the normal temperature on July 21, 2007 in the area, just 1 day before the earthquake. Whereas, in the case of Ravar earthquake, the region has shown 5–7°C higher temperature on October 06, 2004 about 6 days before the occurrence of the main earthquake event. Dalbandin earthquake showed a maxima on January 17, 2011, just 2 days before the main shock with the raised temperature of around 8–10°C. Another common observation in all these earthquakes is the disappearance of short-term transient thermal anomaly just before the main shock.     

Geo-hydrological database modeling for integrated multiple hazards and risk assessment in Lesser Himalaya: a GIS-based case study

The main objective of the study was to assess the integrated multiple hydrological hazards and their environmental and socio-economic risks in Himalaya through geographical information system (GIS) and database management system (DBMS). The Dabka Watershed constitutes a part of the Kosi Basin in the Kumaun Lesser Himalaya has been selected for the case illustration. The Dabka DBMS is constituted of three GIS modules, that is, geo-informatics, hydro-informatics and hazard-informatics. Through the integration and superimposing of these modules prepared Hydrological Hazard Index to identify the level of vulnerability for existing hydrological hazards and their socio-economic and environmental risks. The results suggested that geo-environmentally most stressed barren land areas have high rate of runoff, flood magnitude, erosion sediment load and denudation during rainy season particularly in the month of August (i.e., respectively, 84.56 l/s/km², 871.80 l/s/km², 78.60 t/km² and 1.21 mm/year), which accelerates high hazards and their socio-economic and environmental risks, whereas geo-environmentally least stressed dense forest areas experience low rate of stream runoff, flood magnitude, erosion sediment load and denudation in the same season and month (i.e., respectively, 20.67 l/s/km², 58.12 l/s/km², 19.50 t/km² and 0.20 mm/year) comparatively have low hazards and their socio-economic and environmental risks. The other frazzled geo-environment that also found highly vulnerable for natural hazards and their risks is agricultural land due to high stream runoff, flood magnitude, erosion sediment load and denudation rates (i.e., respectively, 53.15 l/s/km², 217.95 l/s/km², 90.00 t/km² and .92 mm/year). This makes it necessary to take up an integrated and comprehensive sustainable land use policy for the entire Himalaya region based on the scientific interpretation of the crucial linkages between land use and hydrological hazards, that is, floods, erosion, landslides during rainy season and drought due to dry-up of natural springs and streams during summer season. The study would help the village, district and state development authority to formulate decision support system for alternate planning and management for the Himalaya region.     

Do alternative spatial healthcare access measures tell the same story?

To effectively target area and population with relatively poorer healthcare access requires information on how access to healthcare varies spatially. Considering hospitals as important components of the healthcare system, this case study of Central Missouri presents a comparison of the relatively underserved areas and population based on the results from three alternative indicators of spatial hospital access calculated at three different levels of geography. Results indicate that the alternative spatial healthcare access indicators show considerably different pictures of the relative ranking of census units, and identification of the relatively underserved areas and population. The relative ranking of census units and the identification of relatively underserved area and population are all critical indicators for policy makers when public resources are limited and distributive choices must be made.     

Investigation on failure mechanism of nailed soil slopes under surcharge loading: testing and analysis

This paper presents the laboratory test results of nailed soil slopes to study the behaviour of reinforced slopes under surcharge load. Tests were conducted on nailed soil slopes of three different slope angles (β = 30°, 45°and 60°) and nail inclinations (i = 0°, 15° and 30°). Each slope is reinforced with a number of hollow aluminium nails placed in three rows. The failure response, load-settlement, nail forces at the centre of nails and the distribution of nail forces along the length are examined during the tests. The numerical simulation of the model tests is performed by a 3-D finite element program. The numerical results are found in agreement to the corresponding experimental results. It is observed that the nails inclined at 0° to the horizontal give the maximum improvement in the load carrying capacity of the slopes followed closely by the 15° nail inclination. The maximum nail forces are observed in the topmost row of nails and decreases with the depth. The distribution of the nail forces along the nail are also found to be varying with respect to the failure surface of the slopes.