Site classification of Pondicherry using shear-wave velocity and horizontal-to-vertical spectral ratio

Site classification studies play a vital role in earthquake hazard assessment since in situ ground conditions substantially affect the characteristics of incoming seismic waves during earthquakes. Flat areas along the coast and rivers generally consist of thick layers of soft clay and sand. Such deposits amplify certain frequencies of ground motion, thereby attributing to an increase in the damage due to an earthquake. Hence, site classification studies have been carried out using shear-wave velocity, ground response, and corresponding amplification at 83 locations in Pondicherry, a coastal city in India. The present study is aimed at estimating the shear-wave velocity through multichannel analysis of surface waves and to compute the average shear-wave velocity (V _S ³⁰ ), stiffness, and N values using empirical relations. Further, site-response studies (horizontal-to-vertical spectral ratio) were conducted to estimate the ground-response frequencies and corresponding amplifications through Nakamura technique. From the results, the study area was classified into three types, i.e., C-class: with V _S ³⁰ in the range of 360–760 m/s, D-class: with V _S ³⁰ in the range of 180–360 m/s, and E-class: with V _S ³⁰  < 180 m/s following the National Earthquake Hazard Reduction Programme norms (BSSC in NEHRP recommended provisions for seismic regulations for new buildings and other structures (FEMA 450), part 1: provisions. Building Seismic Safety Council for the Federal Emergency Management Agency, Washington, 2003). Finally, a site classification map for Pondicherry region has been prepared, which can be used in urban planning and strengthening of existing structures against future earthquakes.     

On the role of the Planetary Boundary Layer in the numerical simulation of a severe cyclonic storm Nargis using a mesoscale model

The very severe cyclonic storm Nargis of 2008 was a strong tropical cyclone that caused the deadliest natural disaster in the history of Myanmar. The time tested NCAR/PSU MM5 model has been used to simulate the Nargis cyclone, which is designed to have two domains covering the Bay of Bengal with horizontal resolutions of 90 and 30?km. The physics options chosen are Kain?CFritsch 2 for convection, Blackadar (BLA), Burk?CThompson, medium range forecast (MRF), Eta Mellor?CYamada (Eta MY) and Gayno?CSeaman (GS) for Planetary Boundary Layer (PBL) and Simple Ice for explicit cloud physics processes. The experiment was conducted with the model integration starting from April 27, 2008, to May 3, 2008. The performance of the five PBL schemes is evaluated in terms of radius height cross-section of the three component winds, surface heat fluxes of sensible heat and latent heat, equivalent potential temperature (?? _e ), precipitation, track and variation of Central Surface Pressure and wind speed with time. The numerical results show a large impact of the PBL schemes on the intensity and movement of the system. The intensity of the storm is examined in terms of pressure drop, strength of the surface wind and rainfall associated with the storm. The results are compared to the India Meteorological Department observations. These experiments indicate that the intensity of the storm is well simulated with the Eta MY and BLA with finer resolution. The simulated track with MRF compared well with the Joint Typhoon Warning Center observation at landfall position both with the 90 and 30?km resolutions.     

Numerical simulation of cyclonic storms FANOOS, NARGIS with assimilation of conventional and satellite observations using 3-DVAR

In this work, the impact of assimilation of conventional and satellite data is studied on the prediction of two cyclonic storms in the Bay of Bengal using the three-dimensional variational data assimilation (3D-VAR) technique. The FANOOS cyclone (December 6?C10, 2005) and the very severe cyclone NARGIS (April 28?CMay 2, 2008) were simulated with a double-nested weather research and forecasting (WRF-ARW) model at a horizontal resolution of 9?km. Three numerical experiments were performed using the WRF model. The back ground error covariance matrix for 3DVAR over the Indian region was generated by running the model for a 30-day period in November 2007. In the control run (CTL), the National Centers for Environmental Prediction (NCEP) global forecast system analysis at 0.5° resolution was used for the initial and boundary conditions. In the second experiment called the VARCON, the conventional surface and upper air observations were used for assimilation. In the third experiment (VARQSCAT), the ocean surface wind vectors from quick scatterometer (QSCAT) were used for assimilation. The CTL and VARCON experiments have produced higher intensity in terms of sea level pressure, winds and vorticity fields but with higher track errors. Assimilation of conventional observations has meager positive impact on the intensity and has led to negative impact on simulated storm tracks. The QSCAT vector winds have given positive impact on the simulations of intensity and track positions of the two storms, the impact is found to be relatively higher for the moderate intense cyclone FANOOS as compared to very severe cyclone NARGIS.     

Delineation of Fractures through Acoustic Televiewer Log

Boreholes are the only sources for direct measurements of geological and geophysical characteristics of the shallow subsurface of the earth. Borehole imaging tool “Acoustic Televiewer (ATV)” is an advanced probe, which records 3D image of the bore hole wall and is used to obtain oriented images of bore hole and provides substantial information regarding lithology, structural information, detection of fractures and casing of the borehole. The images are highly sensitive to the presence of fractures, the delineation of which becomes accurate and reliable based on these acoustic images. Features identified on log-derived images can be correlated with core samples or can be used as substitute in the poor core recovery zones. In the present study, ATV log from a deep borehole drilled at Khadi Kolavan in Koyna-Warna region of Ratnagiri district, Maharashtra located west of the Western Ghat escarpment in the Deccan Volcanic province, India, is used for interpretation of structural characteristics of the formation. The same was correlated with other conventional logging methods such as resistivity and full waveform sonic (FWS) as well as core logging and rock quality designations (RQD) which generated new understanding of the basement and basalt cover in this region.     

Tropospheric biennial oscillation and south Asian summer monsoon rainfall in a coupled model

In this study Tropospheric Biennial Oscillation (TBO) and south Asian summer monsoon rainfall are examined in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFSv2) hindcast. High correlation between the observations and model TBO index suggests that the model is able to capture most of the TBO years. Spatial patterns of rainfall anomalies associated with positive TBO over the south Asian region are better represented in the model as in the observations. However, the model predicted rainfall anomaly patterns associated with negative TBO years are improper and magnitudes are underestimated compared to the observations. It is noted that positive (negative) TBO is associated with La Niña (El Niño) like Sea surface temperature (SST) anomalies in the model. This leads to the fact that model TBO is El Niño-Southern Oscillation (ENSO) driven, while in the observations Indian Ocean Dipole (IOD) also plays a role in the negative TBO phase. Detailed analysis suggests that the negative TBO rainfall anomaly pattern in the model is highly influenced by improper teleconnections allied to IOD. Unlike in the observations, rainfall anomalies over the south Asian region are anti-correlated with IOD index in CFSv2. Further, summer monsoon rainfall over south Asian region is highly correlated with IOD western pole than eastern pole in CFSv2 in contrast to the observations. Altogether, the present study highlights the importance of improving Indian Ocean SST teleconnections to south Asian summer rainfall in the model by enhancing the predictability of TBO. This in turn would improve monsoon rainfall prediction skill of the model.     

Analysis of multi-channel seismic reflection and magnetic data along 13° N latitude across the Bay of Bengal

Analysis of the multi-channel seismic reflection, magnetic and bathymetric data collected along a transect, 1110 km long parallel to 13° N latitude across the Bay of Bengal was made. The transect is from the continental shelf off Madras to the continental slope off Andaman Island in water depths of 525 m to 3350 m and across the Western Basin (bounded by foot of the continental slope of Madras and 85° E Ridge), the 85° E Ridge, the Central Basin (between the 85° E Ridge and the Ninetyeast Ridge), the Ninetyeast Ridge and the Sunda Arc. The study revealed eight seismic sequences, H1 to H8 of parallel continuous to discontinuous reflectors. Considering especially depth to the horizons, nature of reflection and on comparison with the published seismic reflection results of Currayet al. (1982), the early Eocene (P) and Miocene (M) unconformities and the base of the Quaternary sediments (Q) are identified on the seismic section. Marked changes in velocities also occur at their boundaries.In the Western Basin the acoustic basement deepening landward is inferred as a crystalline basement overlain by about 6.7 km of sediment. In the Central Basin possibly thicker sediments than in the Western Basin are estimated. The sediments in the Sunda Arc area are relatively thick and appears to have no distinct horizons. But the entire sedimentary section appears to be consisting of folded and possibly faulted layers.The comparatively broader wavelength magnetic anomalies of the Central Basin also indicate deeper depth of their origin. Very prominent double humped feature of the 85° E Ridge and broad basement swell of the Ninetyeast Ridge are buried under about 2.8 km thick sediments except over the prominent basement high near 92° E longitude. The positive structural relief of the buried 85° E Ridge in the area is reflected in magnetic signature of about 450 nT amplitude. Flexural bulge of the 85° E Ridge and subsidence of the Ninetyeast Ridge about 24 cm my^–1 rate since early Eocene period have been inferred from the seismic sequence analysis.     

A simple surface energy balance to derive evapotranspiration from remote sensing and conventional meteorological observations

Monthly mean measurements of surface temperature, albedo and normalized difference vegetation index (NDVI) of NOAA AVHRR are processed for Maharashtra. These data are used in combination with monthly average surface meteorological observations in a surface energy balance model to estimate monthly mean actual evapotranspiration (AET) from different climatic zones of Maharasthra,. India. AET is estimated between April and December months for two contrasting monsoons in 1992 and 1995. Estimates reasonably agree with pan evaporation data during growing season and with AET estimated from water balance procedure. AET is low in semi-arid dry land areas of central Maharashtra and significantly high in the humid-perhumid western ghat region and subhumid eastern Maharashtra region. The modeled evapotranspiration show the influence of seasonal vegetation in different climatic zones from the region. The method can be used to obtain large-scale evapotranspiration with minimum ground observations.     

Studies on biodiversity using semivariogram approach from IRS-IC LISS-III data

Present study attempts to utilise the spatial information from IRS-IC LISS-III satellite data, through, tie use of Semivartogram apprqatfu for analyzing the overstorey. diversity In forest stands, Semivariance has been calculated for all the pixels in I5x15 pixel window for each of the forest stand using digital numbers from near infrared channel Variation in semivariance has been correlated to stand density and species composition. Analysis of averaged semivariance for overall diversity of forest stands suggested, decreasing semi variance in the order, mixed dry (feciduous forests, mixed scrub forests followed by dry deciduous forest Semivariance has been found to be highly Correlated to tree density (R² = 0.96) suggesting semivariograms as one of the measures for studies on tree density, canapy cover and diversity patterns.