Genesis of a new slab tear fault in the Indo-Australian plate,offshore northern Sumatra,Indian ocean

Following the December 2004 and March 2005 major shallow foci inter-plate earthquakes in the north Sumatra region, a slab-tear fault located within the subducting Indian plate ruptured across the West Sunda Trench (WST) within the marginal intra-plate region. Trend, length and movement pattern of this New Tear Fault (NTF) segment is almost identical to another such slab-tear fault mapped previously by Hamilton (1979), located around 160 km south of NTF. Seismic activity along the NTF remained quasi-stable till the end of the year 2011, when an earthquake of magnitude 7.2 occurred on 10.01.2012 just at the tip of NTF, only around ～100 km within the intra-plate domain west of WST. The NTF rupture propagated further towards SSW with the generation of two more large earthquakes on 11.04.2012. The foreshock (10.01.12; M7.2) — mainshock (11.04.12; M 8.6) — aftershock (11.04.12; M 8.2) sequence along with numerous smaller magnitude aftershocks unmistakably define the extension of NTF, a slab-tear fault that results tectonic segmentation of the convergent plate margin. Within the intra-plate domain most earthquakes display consistent left-lateral strike slip mechanism along NNE trending fault plane.     

Forest cover change prediction using hybrid methodology of geoinformatics and Markov chain model: A case study on sub-Himalayan town Gangtok,India

In the Himalayan states of India, with increasing population and activities, large areas of forested land are being converted into other land-use features. There is a definite cause and effect relationship between changing practice for development and changes in land use. So, an estimation of land use dynamics and a futuristic trend pattern is essential. A combination of geospatial and statistical techniques were applied to assess the present and future land use/land cover scenario of Gangtok, the subHimalayan capital of Sikkim. Multi-temporal satellite imageries of the Landsat series were used to map the changes in land use of Gangtok from 1990 to 2010. Only three major land use classes (built-up area and bare land, step cultivated area, and forest) were considered as the most dynamic land use practices of Gangtok. The conventional supervised classification, and spectral indices-based thresholding using NDVI (Normalized Difference Vegetation Index) and SAVI (Soil Adjusted Vegetation Index) were applied along with the accuracy assessments. Markov modelling was applied for prediction of land use/land cover change and was validated. SAVI provides the most accurate estimate, i.e., the difference between predicted and actual data is minimal. Finally, a combination of Markov modelling and SAVI was used to predict the probable land-use scenario in Gangtok in 2020 AD, which indicted that more forest areas will be converted for step cultivation by the year 2020.     

Fractal study of seismicity in order to characterize the various tectonic blocks of North-east Himalaya,India

Three major projects initiated by the European Commission within its 7th Framework Programme that have studied the weather phenomena and their projections to the future in relation to their impacts and implications to the European transport systems have recently been concluded. All of the transport modes were covered, as well as all of the critical phenomena present within the European area. The three projects (that ran from 2009 and 2012) are as follows: (1) EWENT (Extreme Weather impacts on European Networks of Transport—www.ewent.vtt.fi); (2) ECCONET (Effects of climate change on the inland waterway networks—www.ecconet.eu); (3) WEATHER (Weather Extremes: Assessment of Impacts on Transport and Hazards for European Regions—www.weather-project.eu). In this Foreward to the Special Issue on “Vulnerability of Transportation to Extreme Weather and Climate Change,” the key results of the above three projects are addressed concisely, offering the reader a broader view of their findings; since some of these are enveloped in the research papers hosted in this volume, they will not be covered in detail. However, the rich output of these projects in the form of “Project Deliverables” and “Reports” is also an important source of information on the findings and results from these three projects which are publicly available on the projects’ Web sites. The purpose of this Foreward is to bring to the attention of the interested reader these sources and overview briefly some of the projects’ outcomes. Also, a short comparative discussion on selected findings is made, outlining agreements and disagreements between the projects.     

A study of mylonites from parts of the Salem-Attur shear zone (Tamil Nadu) and its tectonic implications

The E-W running Salem-Attur shear zone demarcates the tectonic boundary between Archaean Dharwar Craton in the north and Proterozoic Southern granulite terrane in the south. This study reveals that the shear zone is a low angle thrust. The thrust zone is around 10 m thick and it merges with the main shear zone along the strike. The thrust is developed on charnockite near Odyarpatti, which is retrograded into schists. Further, it is marked by gently dipping mylonitic foliation and subhorizontal lineation. The S-C fabric, mantled porphyroclasts and intragranular faults indicate northeasterly slip along the thrust. Recumbent shear folds SF₁ are developed within the thrust zone. The thrust has been folded by late stage F₂ fold which has brought variation in the orientation of the mylonitic foliation from subhorizontal to vertical attitude; the mylonitic lineations have been rotated to subvertical orientation also. Additionally, the F₂ crenulations and shear cleavages and intersection lineations are superimposed on the mylonitic fabric. Thrusting along the Salem-Attur shear zone is probably the cause for upliftment of the charnockites to the upper crust. Post-upliftment stage has witnessed brittle deformation in the form of development of shear fractures in NNE-SSW and E-W directions. Pseudotachylites are emplaced along these fractures.     

Modelling the pore fluid diffusion process in aftershock initiation for 2004 Sumatra earthquake: implications for marine geohazard estimation in the Andaman region

The role of fluid injection on the occurrence and migration path for the aftershocks of 2004 Sumatra earthquake (Mw 9.3) and January 2005 Andaman earthquake swarm within the aftershock sequence is investigated here from the viewpoint of pore fluid diffusion process. The Sumatra earthquake created a regionally extensive crustal rupture plane exceeding 1,200 km length below the Andaman Sea. The r–t plots (Shapiro et al. 1997) are constructed for these aftershocks in order to examine the role of poroelastic effects as rupturing progressed with time. Their main results are as follows: the r–t plot corresponding to first 3 h of aftershock activity (when only 44 events of mb ≥ 4.5 originated) reveals that 95% of the data points occurred below the modelled parabola with relatively high D value of 20 m²/s, whereas a significantly low D value of 3.5 m²/s characterises the aftershock activity for the first 24 h (when 420 events of mb ≥ 4.0 occurred). Here, the Coulomb stress was transferred from the main shock with a rapid imposition of normal stress, thus inducing the pore-pressure change that started diminishing almost immediately by fluid diffusion, at a rate, defined by the diminishing D value. The modelling results for fault seismicity at far off distances from the main epicentre are interpreted here as potential indicators for large-scale sub-seabed rupturing—consequent to stress changes induced by bending of the Indian Ocean plate. Bathymetric slopes under the Andaman subduction zone are particularly amenable to sub-marine slides where crustal E–W hinge faults inferred seismically cut across the N–S trending regional thrust and strike-slip faults. Seabed rupturing appears to allow deep-slab hydration in these areas, producing pressure gradients along the normal faults. These features are important since they can herald marine geohazards in the Andaman region.     

Role of transverse tectonics in the Himalayan collision: Further evidences from two contemporary earthquakes

Two contemporary earthquakes originating in the central Himalayan arc and its foredeep (Sikkim earthquake of 18.09.2011, M_w 6.9, h: 10–60 (?) km and Bihar-Nepal earthquake of 20.08.1988, Mw 6.8, h: 57 km) are commonly associated with transverse lineaments/faults traversing the region. Such lineaments/faults form active seismic blocks defining promontories for the advancing Indian Craton. These actually produce conjugate shear faulting pattern suggestive of pervasive crustal interplay deep inside the mountains. Focal mechanism solutions allow inferring that large part of the current convergence across the central Himalayan arc is accommodated by lateral slip. Similar slip also continues unabated in the densely populated foredeep for distances up to several tens of kilometers south of the Main Boundary Thrust (MBT).     

Turbulent unsteady flow profiles over an adverse slope

When an unsteady free surface flow encounters an adverse slope, it results in a decelerating flow up the adverse slope. The time dependent turbulent flow is treated here by appropriately reducing the two-dimensional Reynolds averaged Navier-Stokes equation along with the equation of continuity considering turbulence closure. With suitable choice of parameters, the resulting differential equations are numerically solved to compute free surface and streamwise velocity profiles with time. It is found that initially the advancing free surface is convex upwards for a short time, followed by a jump of the free surface with a negative streamwise velocity that is a backwater rolling breaker due to deceleration of flow. At later time, however, the velocity becomes positive, that is, the breakers roll forward. This dual feature of motion, that is a surge followed by rolling breakers, is repeated for sometime before the jumps stop. The theoretical analysis presented here is motivated by tidal bores propagating upstream in an estuarine river.     

Geophysical Characterization of the Salna Sinking Zone, Garhwal Himalaya, India

Infrastructure and communication facilities are repeatedly affected by ground deformation in Gharwal Himalaya, India; for effective remediation measures, a thorough understanding of the real reasons for these movements is needed. In this regard, we undertook an integrated geophysical and geotechnical study of the Salna sinking zone close to the Main Central Thrust in Garhwal Himalaya. Our geophysical data include eight combined electrical resistivity tomography (ERT) and induced polarization imaging (IPI) profiles spanning 144–600 m, with 3–10 m electrode separation in the Wenner–Schlumberger configuration, and five micro-gravity profiles with 10–30 m station spacing covering the study region. The ERT sections clearly outline the heterogeneity in the subsurface lithology. Further, the ERT, IPI, and shaliness (shaleyness) sections infer the absence of clayey horizons and slip surfaces at depth. However, the Bouguer gravity analysis has revealed the existence of several faults in the subsurface, much beyond the reach of the majority of ERT sections. These inferred vertical to subvertical faults run parallel to the existing major lineaments and tectonic elements of the study region. The crisscross network of inferred faults has divided the entire study region into several blocks in the subsurface. Our studies stress that the sinking of the Salna village area is presently taking place along these inferred vertical to subvertical faults. The Chamoli earthquake in March 1999 probably triggered seismically induced ground movements in this region. The absence of few gravity-inferred faults in shallow ERT sections may hint at blind faults, which could serve as future source(s) for geohazards in the study region. Soil samples at two sites of study region were studied in a geotechnical laboratory. These, along with stability studies along four slope sections, have indicated the critical state of the study region. Thus, our integrated studies emphasize the crucial role of micro-gravity in finding fine subsurface structure at deeper depth level; supported by ERT and IPI at shallow depth intervals, they can satisfactorily explain the Salna sinking zone close to Lesser Himalaya. The geotechnical studies also lend support to these findings. These integrated studies have yielded a better understanding of the mass-wasting mechanism for the study region.     

Detection of ionospheric perturbation due to a soft gamma ray repeater SGR J1550-5418 by very low frequency radio waves

The properties of cylindrical and spherical dust acoustic (DA) solitary and shock waves in an unmagnetized electron depleted dusty plasma consisting of inertial dust fluid and ions featuring Tsallis statistics are investigated by employing the reductive perturbation technique. A Korteweg-de Vries Burgers (KdVB) equation is derived and its numerical solution is obtained. The effects of ion nonextensivity and dust kinematic viscosity on the basic features of DA solitary and shock waves are discussed in nonplanar geometry. It is found that nonextensive nonplanar DA waves behave quite differently from their one-dimensional planar counterpart.     

Unique Observation of a Solar Flare by Lunar Occultation During the 2010 Annular Solar Eclipse Through Ionospheric Disturbances of VLF Signals

Very Low Frequency (VLF) radio waves propagate through the Earth-ionosphere waveguide. Irregularities caused by excess or deficient extreme ultra-violet and X-rays, which otherwise sustain the ionosphere, change the waveguide properties and hence the signals are modified. We report the results of monitoring of the NWC transmitter (19.8?kHz) by a receiver placed at Khukurdaha (22°27′N, 87°45′E) during the partial solar eclipse (75?%) of 15th January, 2010. The propagation path from the transmitter to the receiver crosses the annular eclipse belt. We got a clear depression in the data during the period of the eclipse. Most interestingly, there was also a X-ray flaring activity in the sun on that day which reached its peak (C-type) right after the time when the eclipse reached its maximum. We saw the effects of the occultation of this flare in our VLF signal since a part of the X-ray active region was clearly blocked by the moon. We quantitatively compared by using analogies with previous observations and found best fitting parameters for the time when the flare was occulted. We then reconstructed the VLF signal in the absence of the occulted flare. To our knowledge, this is the first such incident where the solar flare was observed through lunar occultation and that too during a partial eclipse.