Centre for Earth Science Studies

About: Centre for Earth Science Studies is a government organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Monsoon & Granulite. The organization has 478 authors who have published 572 publications receiving 9395 citations.

Predecessors of the giant 1960 Chile earthquake

Abstract: It is commonly thought that the longer the time since last earthquake, the larger the next earthquake's slip will be. But this logical predictor of earthquake size, unsuccessful for large earthquakes on a strike-slip fault, fails also with the giant 1960 Chile earthquake of magnitude 9.5 (ref. 3). Although the time since the preceding earthquake spanned 123 years (refs 4, 5), the estimated slip in 1960, which occurred on a fault between the Nazca and South American tectonic plates, equalled 250-350 years' worth of the plate motion. Thus the average interval between such giant earthquakes on this fault should span several centuries. Here we present evidence that such long intervals were indeed typical of the last two millennia. We use buried soils and sand layers as records of tectonic subsidence and tsunami inundation at an estuary midway along the 1960 rupture. In these records, the 1960 earthquake ended a recurrence interval that had begun almost four centuries before, with an earthquake documented by Spanish conquistadors in 1575. Two later earthquakes, in 1737 and 1837, produced little if any subsidence or tsunami at the estuary and they therefore probably left the fault partly loaded with accumulated plate motion that the 1960 earthquake then expended.

GIS and AHP Techniques Based Delineation of Groundwater Potential Zones: a case study from Southern Western Ghats, India.

Abstract: Over-exploitation of groundwater and marked changes in climate over the years have imposed immense pressure on the global groundwater resources. As demand of potable water increases across the globe for human consumption, agriculture and industrial uses, the need to evaluate the groundwater potential and productivity of aquifers also increases. In the recent years, geographic information system based studies have gained much prominence in groundwater exploration because it is rapid and will provide first - hand information on the resource for further developments. Therefore, the present study has been undertaken with an objective to delineate the groundwater potential of a small tropical river basin located in the western side of the Western Ghats in India as an example. A combination of geographical information system and analytical hierarchical process techniques (AHP) was used in the present study. A total of 12 thematic layers such as Geology, Geomorphology, Land Use/Land Cover, Lineament density, Drainage density, Rainfall, Soil, Slope, Roughness, Topographic Wetness Index, Topographic Position Index and Curvature were prepared and studied for groundwater potential zone demarcation. Weights assigned to each class in all the thematic maps are based on their characteristics and water potential capacity through AHP method. The accuracy of the output was cross-validated with information on groundwater prospects of the area and the overall accuracy of the method comes to around 85%. The groundwater potential zone map thus obtained was categorized into five classes-very high, high, moderate, low and very low. The study reveals that about 59% of the river basin is covered under moderate groundwater potential zone. The low and high groundwater potential zones are observed in 29% and 11% respectively. Area under very high and very low potential zones are recorded only in very limited areas in the basin.

Arrested charnockite formation in southern India and Sri Lanka

Abstract: Arrested prograde charnockite formation in quartzofeldspathic gneisses is widespread in the high-grade terrains of southern India and Sri Lanka Two major kinds of orthopyroxene-producing reactions are recognized Breakdown of calcic amphibole by reaction with biotite and quartz in tonalitic/granitic “gray gneiss” produced the regional orthopyroxene isograd, manifest in charnockitic mottling and veining of “mixed-facies” exposures, as at Kabbal, Karnataka, and in the Kurunegala District of the Sri Lanka Central Highlands Chemical and modal analyses of carefully chosen immediately-adjacent amphibole gneiss and charnockite pairs show that the orthopyroxene is produced by an open system reaction involving slight losses of CaO, MgO and FeO and gains of SiO2 and Na2O Rb and Y are depleted in the charnockite Another kind of charnockitization is found in paragneisses throughout the southern high-grade area, and involves the reaction of biotite and quartz±garnet to produce orthopyroxene and K-feldspar Although charnockite formation along shears and other deformation zones at such localities as Ponmudi, Kerala is highly reminiscent of Kabbal, close pair analyses are not as suggestive of open-system behavior This type of charnockite formation is found in granulite facies areas where no prograde amphibole-bearing gneisses exist and connotes a higher-grade reaction than that of the orthopyroxene isograd Metamorphic conditions of both Kabbaltype and Ponmudi-type localities were 700°–800° C and 5–6 kbar Lower P(H2O) in the Ponmudi-type metamorphism was probably the definitive factor CO2-rich fluid inclusions in quartz from the Kabbaltype localities support the concept that this type of charnockite formation was driven by influx of CO2 from some deep-seated source The open-system behavior and high oxidation states of the metamorphism are in accord with the CO2-streaming hypothesis CO2-rich inclusions in graphitebearing charnockites of the Ponmudi type, however, commonly have low densities and compositions not predictable by vapor-mineral equilibrium calculations These inclusions may have suffered post-metamorphic H2 leakage or some systematic contamination Neither the close-pair analyses nor the fluid inclusions strongly suggest an influx of CO2 drove charnockite formation of the Ponmudi type The possibility remains that orthopyroxene and CO2-rich fluids were produced by reaction of biotite with graphite without intervention of fluids of external origin Further evidence, such as oxygen isotopes, is necessary to test the CO2-streaming hypothesis for the Ponmudi-type localities

Characteristics of Deformation and Past Seismicity Associated with the 1819 Kutch Earthquake, Northwestern India

Abstract: The 1819 earthquake in Kutch, northwestern India, is one of the most significant events to have occurred in a plate-interior setting. Despite being the second largest among the stable continental region (SCR) earthquakes, this event has not been analyzed within the context of present-day understanding of earthquake seismology. Coseismic changes related to this earthquake include massive ground deformation in a wide low-lying tidal-flat area. Although detailed historic accounts of this earthquake exist, many questions regarding the mode of deformation and the seismic history of the region remain unresolved. We explored the region nearly 180 years after the earthquake, and the information gathered adds to our understanding of this event and provides a fresh perspective on this unique intraplate seismogenic zone. A 90-km-long tract of elevated land with a peak height of 4.3 m is the most visible surface expression of this earthquake. We surveyed and analyzed the morphological features of this scarp and also carried out exploratory trenching in this region. The scarp morphology is suggestive of a growing fold related to a buried north-dipping thrust rather than a discrete fault that could have resulted from a surface rupture. The extensive liquefaction field associated with the earthquake offered an ideal setting to explore the paleoearthquake history. Age data of liquefaction features suggest that a previous event of comparable size must have occurred 800–1000 years ago. Seismic activity appears to be related to the reactivation of an ancient rift in a stress regime that is dominated by nearly north–south compression.

Environmental effects of river sand mining: a case from the river catchments of Vembanad lake, Southwest coast of India

Abstract: Rivers in the southwest coast of India are under immense pressure due to various kinds of human activities among which indiscriminate extraction of construction grade sand is the most disastrous one. The situation is rather alarming in the rivers draining the Vembanad lake catchments as the area hosts one of the fast developing urban-cum-industrial centre, the Kochi city, otherwise called the Queen of Arabian Sea. The Vembanad lake catchments are drained by seven rivers whose length varies between 78 and 244 km and catchment area between 847 and 5,398 km2. On an average, 11.73 million ty−1 of sand and gravel are being extracted from the active channels and 0.414 million ty−1 of sand from the river floodplains. The quantity of instream mining is about 40 times the higher than the sand input estimated in the gauging stations. As a result of indiscriminate sand mining, the riverbed in the storage zone is getting lowered at a rate of 7–15 cm y−1 over the past two decades. This, in turn, imposes severe damages to the physical and biological environments of these river systems. The present paper deals with the environmental effects of indiscriminate sand mining from the small catchment rivers in the southwest coast of India, taking the case of the rivers draining the Vembanad lake catchments as an example.