Trapped waves of the 27 November 1945 Makran tsunami: observations and numerical modeling

The 27 November 1945 earthquake in the Makran Subduction Zone triggered a destructive tsunami that has left important problems unresolved. According to the available reports, high waves persisted along the Makran coast and at Karachi for several hours after the arrival of the first wave. Long-duration sea-level oscillations were also reported from Port Victoria, Seychelles. On the other hand, only one high wave was reported from Mumbai. Tide-gauge records of the tsunami from Karachi and Mumbai confirm these reports. While the data from Mumbai shows a single high wave, Karachi data shows that high waves persisted for more than 7 h, with maximum wave height occurring 2.8 h after the arrival of the first wave. In this paper, we analyze the cause of these persistent high waves using a numerical model. The simulation reproduces the observed features reasonably well, particularly the persistent high waves at Karachi and the single high wave at Mumbai. It further reveals that the persistent high waves along the Makran coast and at Karachi were the result of trapping of the tsunami-wave energy on the continental shelf off the Makran coast and that these coastally-trapped edge waves were trapped in the along-shore direction within a ∼300-km stretch of the continental shelf. Sensitivity experiments establish that this along-shore trapping of the tsunami energy is due to variations in the shelf width. In addition, the model simulation indicates that the reported long duration of sea-level oscillations at Port Victoria were mainly due to trapping of the tsunami energy over the large shallow region surrounding the Seychelles archipelago.     

Statistical study of spatial variation of response spectrum using free field records of dense strong motion arrays

Spatial variation of acceleration response spectra is examined using strong motion records for a large number of events from dense accelerometer arrays at Chiba in Japan and SMART-1 in Lotung, Taiwan. The effects of earthquake component, structural damping, earthquake magnitude, focal depth, epicentral distance, structural time period, and station separation on the intra-event variation of response spectra are examined first through an empirical analysis and then through a least-square regression fit for parametric study. A very large scatter of the response spectra ratio is observed for both arrays, especially for SMART-1 array. The mean values of the ratio vary from 10 to 20 per cent for Chiba array while they vary from 25 to 50 per cent for SMART-1 array. The coefficients of variation of the ratio range from 5 to 25 per cent for Chiba array and 30 to 50 per cent for SMART-1 array. The correlation among response spectra is found to be inversely proportional to station separation and shows frequency dependence. For larger time periods, the correlation is lower and not higher. The correlation is also lower for UD earthquake component as compared to the two horizontal components. For higher damping ratio, the correlation among spectra is higher. The effect of the earthquake magnitude, focal depth and epicentral distance on the spatial variation is complex. The three parameters having implicit interdependence, considering their combined effect, a positive contribution to the value of ratio of response spectra is observed in the case of larger earthquake events. Furthermore, as mentioned above, the spatial variation for SMART-1 array is much larger than that for Chiba array. This difference can be attributed mainly to the difference in distance between the instruments in the two arrays. However, some of the difference is considered to be due to site specific characteristics. Copyright © 1999 John Wiley & Sons, Ltd.     

Gravitational instability of a Hall plasma in the presence of suspended particles

The gravitational instability of an infinite homogeneous and infinitely conducting selfgravitating gas particle medium in the presence of suspended particles of a Hall plasma is considered. The particular cases of the effects of Hall currents and suspended particles on the waves propagated along and perpendicular to magnetic field have been discussed. Jeans's criterion determines the gravitational instability.     

Rainfall flood hazard at nuclear power plants in India

Flood hazard evaluation is an important input for Nuclear Power Plants external events safety studies. In the present study, flood hazard at various nuclear sites in India due to rainfall has been evaluated. Hazard estimation is a statistical procedure by which rainfall intensity versus occurrence frequency is estimated from historical records of rainfall data and extrapolated with asymptotic extreme value distribution. Rainfall data needed for flood hazard assessment are daily annual maximum rainfall (24?h data). The observed data points have been fitted using Gumbel, power law and exponential distribution, and return period has been estimated. To study the stationarity of rainfall data, a moving window estimate of the parameters has been performed. The rainfall pattern is stationary in both coastal and inland regions over the period of observation. The coastal regions show intense rainfall and higher variability than inland regions. Based on the plant layout, catchment area and drainage capacity, the prototype fast breeder reactor (PFBR) site is unlikely to be flooded.     

Evidence of decay of flux ratio of Fe to Fe-Ni line features with electron temperature in solar flares

We report observational evidence of the decay of the flux ratio of Fe to Fe-Ni line features as a function of plasma electron temperature in solar flares in comparison to that theoretically predicted by Phillips (2004). We present the study of spectral analysis of 14 flares observed by the Solar X-ray Spectrometer (SOXS) — Low Energy Detector (SLD) payload. The SLD payload employs the state-of-the-art solid state detectors, viz., Si PIN and Cadmium-Zinc-Telluride (CZT) devices. The sub-keV energy resolution of Si PIN detector allows us to study the Fe-line and Fe-Ni line features appearing at 6.7 and 8 keV, respectively, in greater detail. In order to best-fit the whole spectrum at one time in the desired energy range between 4 and 25 keV we considered Gaussian-line, the multi-thermal power-law and broken power-law functions. We found that the flux ratio of Fe to Fe-Ni line features decays with flare electron temperature by the asymptotic form of polynomial of inverse third order. The relative flux ratio is ∼30 at temperature 12 MK which drops to half, ∼15 at 20 MK, and at further higher temperatures it decreases smoothly reaching to ∼8 at ∼50 MK. The flux ratio, however, at a given flare plasma temperature, and its decrease with temperature is significantly lower than that predicted theoretically. We propose that the difference may be due to the consideration of higher densities of Fe and Fe-Ni lines in the theoretical model of Phillips (2004). We suggest revising the Fe and Fe-Ni line densities in the corona. The decay of flux ratio explains the variation of equivalent width and peak energy of these line features with temperature.     

Sedimentary variations of geomorphic subenvironments at Al-Lith area,central-west coast of Saudi Arabia,Red Sea

Sediment characteristics are the indicators of the intensity and geological history of the processes active in an area. Their association with different geomorphic features also signifies the present day conditions of deposition. In this study, variations in sediment characteristics associated with different geomorphic features, such as the coastal zone, two islands and a lagoon in the Al-Lith area of central-west coast of Saudi Arabia have been analysed. Whereas, the detrital sediments (sand?+?mud) are common (61–87 %) in most of the subunits of the coastal zone; the nondetrital (carbonate rich) sediments are more common (54–95 %) on the two islands as well as the lagoon; indicating distinct sources of sediments in these regions. The variation of sediment texture between sand and sandy silt in most geomorphic units, also shows that they are exposed to high-energy conditions, whereas occurrence of heavy minerals in small proportions (<7 %) indicates limited inputs from land-based igneous and metamorphic rocks. Sediment mean size vs. standard deviation shows that the sediment characteristics of a geomorphic unit (e.g. beach or sand bar) on the coast and on the island are different owing to different processes responsible for their formation.     

Watershed Delineation in Flat Terrain of Thar Desert Region in North West India – A Semi Automated Approach Using DEM

Thar desert spreads in western part of Rajasthan, northern part of Gujarat, and some parts of Punjab and Haryana. The terrain is dominated by slightly sloping plains, broken by some dunes and low barren hills. The area is characterized by low average annual rainfall which is erratic in distribution and intensity. Drought will remain a major hindrance for agricultural production in Thar desert. Due to water stress condition, many watershed based development activities has been adopted by government and non-government organizations for the growth and sustainable development of this region. The need of this hour is preparation of a national level watershed atlas of 1:50,000 scale because majority of thematic maps are being produced presently on same or 1:10,000 scale. The manual delineation of watershed boundary in flat terrain based on topographic map will be time consuming and less accurate in the absence of prominent contour lines. Automated approach for watershed delineation using Digital Elevation Model (DEM) along a suitable algorithm has the advantage because the output is not only less time consuming but also independent from human decisions. Hence, a case study has been carried out in Churu sub-basin part of Indus basin which is located in Thar desert region. Depression less DEM with different spatial resolutions was used as input in hydrology tool of ArcGIS spatial analyst function for characterization of watersheds. The Churu sub-basin has been divided into various numbers of watersheds with an average size of 600 km². These watershed boundaries have been validated with respect to high resolution satellite imageries (IRS P6 LISS IV), Survey of India toposheets, ancillary data and limited field checks.     

The Indus-Tsangpo suture zone in Ladakh, northwest Himalaya: Further palaeomagnetic data and implications

A total of 81 samples (244 specimens) from Upper Cretaceous Indus Molasse and Middle to Upper Cretaceous Dras Flyschoids of the Indus-Tsangpo suture zone in Ladakh (northwest Himalaya) has been studied by thermal demagnetization methods.Both formations showed a characteristic magnetization component indicative for equatorial to low northern palaeolatitudes of acquisition. Similar palaeolatitudes have been obtained before from secondary magnetization components of Early Tertiary age in the Ladakh Intrusives and in the Tibetan Sedimentary Series of central Nepal. The present characteristic components are interpreted likewise as secondary magnetizations which stabilized between 50 and 60 m.y. ago, during Greater India's collision with Asia's southern margin.The Dras Flyschoids show another magnetic component which, in case of primary origin, indicates acquisition at a low southern palaeolatitude. If correct, this interpretation supports recent suggestions for Late Cretaceous obduction of an island arc on Greater India's northern margin.     

Textural characteristics and morphosedimentary environment of foreshore zone along Ganpatipule,Maharashtra, India

The cross-shore profile and the textural distribution of foreshore sediments of Ganpatipule beach along Maharashtra coast covering two annual cycles are examined. Ganpatipule beach depicts erosion and accretion of the berm, reduction and widening of foreshore widths during the monsoon (June–September) and post-monsoon (October–May), respectively with net sediment accretion during the study period due to the changes in the wave characteristics. A direct correlation is observed between the median sediment grain size and beach-face slopes signifying high wave energy ensuing to a gentle to very gentle slope. The sediments are mainly medium grain size, moderately well sorted, bimodal, very fine skewed to very coarse skewed and very platykurtic to very leptokurtic in nature. The binary plots of the textural parameters (mean, skewness, kurtosis, and standard deviation) depicted a characteristic beach environment of deposition. The study shows that the sediment is concentrated in the environment of rolling and bottom suspension. The study on grain size distribution of sediments could be used to assess the wave energy condition prevailing along the coastal area.     

Variation of Seismic Coda Wave Attenuation in the Garhwal Region, Northwestern Himalaya

Seismic coda wave attenuation ( $ Q_{\text{c}}^{ - 1} $ ) characteristics in the Garhwal region, northwestern Himalaya is studied using 113 short-period, vertical component seismic observations from local events with hypocentral distance less than 250?km and magnitude range between 1.0 to 4.0. They are located mainly in the vicinity of the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT), which are well-defined tectonic discontinuities in the Himalayas. Coda wave attenuation ( $ Q_{\text{c}}^{ - 1} $ ) is estimated using the single isotropic scattering method at central frequencies 1.5, 3, 5, 7, 9, 12, 16, 20, 24 and 28?Hz using several starting lapse times and coda window lengths for the analysis. Results show that the ( $ Q_{\text{c}}^{ - 1} $ ) values are frequency dependent in the considered frequency range, and they fit the frequency power law ( $ Q_{\text{c}}^{ - 1} \left( f \right) = Q_{0}^{ - 1} f^{ - n} $ ). The Q ₀ (Q _c at 1?Hz) estimates vary from about 50 for a 10?s lapse time and 10?s window length, to about 350 for a 60?s lapse time and 60?s window length combination. The exponent of the frequency dependence law, n ranges from 1.2 to 0.7; however, it is greater than 0.8, in general, which correlates well with the values obtained in other seismically and tectonically active and highly heterogeneous regions. The attenuation in the Garhwal region is found to be lower than the Q _c ^?1 values obtained for other seismically active regions of the world; however, it is comparable to other regions of India. The spatial variation of coda attenuation indicates that the level of heterogeneity decreases with increasing depth. The variation of coda attenuation has been estimated for different lapse time and window length combinations to observe the effect with depth and it indicates that the upper lithosphere is more active seismically as compared to the lower lithosphere and the heterogeneity decreases with increasing depth.