Probabilities for the occurrences of medium to large earthquakes in northeast India and adjoining region

The return periods and occurrence probabilities related to medium and large earthquakes (M _w 4.0–7.0) in four seismic zones in northeast India and adjoining region (20°–32°N and 87°–100°E) have been estimated with the help of well-known extreme value theory using three methods given by Gumbel (1958), Knopoff and Kagan (1977) and Bury (1999). In the present analysis, the return periods, the most probable maximum magnitude in a specified time period and probabilities of occurrences of earthquakes of magnitude M ≥ 4.0 have been computed using a homogeneous and complete earthquake catalogue prepared for the period between 1897 and 2007. The analysis indicates that the most probable largest annual earthquakes are close to 4.6, 5.1, 5.2, 5.5 and 5.8 in the four seismic zones, namely, the Shillong Plateau Zone, the Eastern Syntaxis Zone, the Himalayan Thrusts Zone, the Arakan-Yoma subduction zone and the whole region, respectively. The most probable largest earthquakes that may occur within different time periods have been also estimated and reported. The study reveals that the estimated mean return periods for the earthquake of magnitude M _w 6.5 are about 6–7 years, 9–10 years, 59–78 years, 72–115 years and 88–127 years in the whole region, the Arakan-Yoma subduction zone, the Himalayan Thrusts Zone, the Shillong Plateau Zone and the Eastern Syntaxis Zone, respectively. The study indicates that Arakan-Yoma subduction zone has the lowest mean return periods and high occurrence probability for the same earthquake magnitude in comparison to the other zones. The differences in the hazard parameters from zone to zone reveal the high crustal heterogeneity and seismotectonics complexity in northeast India and adjoining regions.     

Palaeomagnetic results from the Cretaceous Bagh Group in the Narmada Basin, central India: evidence of pervasive Deccan remagnetization and its implications for Deccan volcanism

A palaeomagnetic study of 115 samples (328 specimens) from 22 sites of the Mid- to Upper Cretaceous Bagh Group underlying the Deccan Traps in the Man valley (22°  20'N, 75°  5'E) of the Narmada Basin is reported. A characteristic magnetization of dominantly reverse polarity has been isolated from the entire rock succession, whose depositional age is constrained within the Cretaceous Normal Superchron. Only a few samples in the uppermost strata have yielded either normal or mixed polarity directions. The overall mean of reverse magnetization is D _m=144°, I _m=47° ( α ₉₅=2.8°, k =152, N =18 sites) with the corresponding S-pole position 28.7°S, 111.2°E ( A ₉₅=3.1°) and a palaeolatitude of 28°S±3°. The characteristic remanence is carried dominantly by magnetite. Similar magnetizations of reverse polarity are also exhibited by Deccan basalt samples and a mafic dyke in the study area. This pole position falls near the Late Cretaceous segment of the Indian APWP and is concordant with poles reported from the Deccan basalt flows and dated DSDP cores (75–65  Ma) of the Indian Ocean. It is therefore concluded that the Bagh Group in the eastern part of the Narmada Basin has been pervasively remagnetized by the igneous activity of Deccan basalt effusion. This overprinted palaeomagnetic signature in the Bagh Group indicates a counter-clockwise rotation by 13°±3° and a latitudinal drift northwards by 3°±3° of the Indian subcontinent during Deccan volcanism.     

The dependence of facula-photosphere contrast in molecular lines on dissociation energy

Assuming local thermodynamic equilibrium and the same relative abundances to prevail both in photosphere and faculae, the concentration-optical depth curves for molecules CH, NH, OH, C₂, CN and CO have been obtained for the four combinations of two photospheric and two facular models and the relative excesses of these molecules in the photosphere over those in faculae have been calculated. The change of photospheric model significantly affects the relationship, for a given facular model, between and D ₀, the dissociation energy of the molecule concerned. Besides, the average depth of formation in the facular models and photospheric models shows a relationship with D ₀.     

Finding appropriate interpolation techniques for topographic surface generation for mudslide risk zonation

Mudslides and debris flows are now more common problems in tropical regions than landslides. This article addresses the issue of modelling mudslide-susceptible locations using an information value approach. Landsat 7 (ETM+) was employed to create a land-use map with limited field checks. Other parameters considered were lineament, road, soil, stream network and lithology. Topographic parameters such as slope and aspect play a dominant role in slope stability studies. Maps for slope and aspects were developed from a digital elevation model using statistical surface interpolation techniques. This article offers insight into the importance of the selection of suitable surface interpolation techniques. The three surface interpolation techniques evaluated in the study were: inverse distance weighted, Kriging and Spline. These were found to have varied accuracies of interpolation surfaces for all parameters, including elevation, slope and aspect. Surfaces offering the best accuracy were adopted for the information value approach for mudslide susceptibility zonation.     

Factor analysis in geochemical exploration

Soil samples collected in the vicinity of a small sulfide mineralization were analyzed for Cu, Zn, Cd, Pb, Ag, Mn, Ni, Co, Cr, and Mo. Factor analysis was used to study the interrelationships among these variables. Selective removal of some samples prior to factor analysis proved to be an important tool in exposing “hidden” relationships between samples, variables, and factors. It has been demonstrated that factor analysis is a suitable technique for data reduction in geochemical exploration since factor scores can be used, instead of raw variables, for interpretation of field observations and location of anomalies.     

Dynamics of an Erupting Arched Magnetic Flux Rope in a Laboratory Plasma Experiment

A laboratory plasma experiment has been built to study the eruption of arched magnetic flux ropes (AMFRs) in the presence of a large magnetized plasma. This experiment simulates the eruption of solar AMFRs in two essential steps: i) it produces an AMFR (n=6.0×10¹² cm^?3, $T_{\rm e} = 14~\mathrm{eV}$ , B≈1 kilo-gauss, L=0.51 m) with a persistent appearance that lasts several Alfvén transit times using a lanthanum hexaboride (LaB₆) plasma source, and ii) it generates controlled plasma flows from the footpoints of the AMFR using laser beams. An additional LaB₆ plasma source generates a large magnetized plasma in the background. The laser-generated flows trigger the eruption by injecting dense plasma and magnetic flux into the AMFR. The experiment is highly reproducible and runs continuously with a 0.5 Hz repetition rate; hence, several thousand identical loop eruptions are routinely generated and their spatio-temporal evolution is recorded in three-dimensions using computer-controlled movable probes. Measurements demonstrate striking similarities between the erupting laboratory and solar arched magnetic flux ropes.     

Hydro-morphometrical analyses of sub-himalyan region in relation to small hydro-electric power

The choice of site for small hydropower potentials in the inaccessible tracts of Himalayan region is a difficult task by the conventional methods. Present work suggests a site for developing a multipurpose small reservoir under GIS framework, in the Sub Himalayan region, India. Scarcity of geographical, climate and statistical data was the main problem for development of seasonal precipitation and runoff modeling for assessing water potentials and identification of possible small-scale hydropower sites. Small hydropower potential is mainly regulated by head and its durability available at site depending upon capacity of the watershed, underlying the reservoir, to produce the runoff. The study reveals that the Bari-Ka- Khad watershed (BKW) can be considered as a suitable site of interest for small-scale hydropower installation. It is having maximum drainage density (7.45 km/km²) and maximum available relief ratio (0.12), which demonstrates better capacity to produce runoff. According to drainage texture of BKW (R_t?=?2.35), it come under coarse texture and higher values of Rho coefficient (ρ?=?3.65), suggesting higher hydrologic storage during rainfall and attenuation of effects of erosion during elevated discharge.     

Temporal variations in carbon stock of Pinus roxburghii Sargent forests of Himachal Pradesh,India

The present study was conducted in Solan Forest Division of Himachal Pradesh covering an area of about 57,158 ha. The aim was to estimate and assess the temporal change in carbon stock of the Chil Working Circle, in two forest ranges of the Division, Solan and Dharampur, over the period of 1956-2011. The inventory data of the working plans of Solan Forest Division from 1956-1957, 1984-1985 and 2002- 2003 were used in the present study while field data for biomass estimation was collected for the year 2011. The results showed a declining trend in carbon stock over 1956-1984 period, however, an increasing trend over 1984-2002 was observed, which showed a further increase for the period 2002-2011. These fluctuating trends in the forest carbon stock can be related to increasing anthropogenic pressure on forests and the subsequent introduction of a ban on green felling envisaging efficient forest management, both of which affect the forest carbon pool significantly.