Tectonic imprints within a granite exposed near Srinagar,Rajasthan, India

Partial melting in the middle to lower crustal level produces melts of granitic composition during orogeny. Thrusts play a vital role in their exhumation after consolidation of these granitic melts. In this paper we focus on one such granite along the eastern margin of the Delhi Fold Belt (DFB) rocks near Srinagar, Rajasthan, India. This is the first report of granite within the area and holds a key stratigraphic position in the entire rock package. The said granite is found to be intrusive to the DFB metasediments as well as their basement popularly known as the Banded Gneissic Complex (BGC). We disentangle the deformation fabrics seen within the granite and associated DFB metasediments, suggesting that subsequent to emplacement and consolidation, the granite has co-folded along with the country rocks. Three deformational events could be identified within the DFB metasediments namely, D_1D, D_2D and D_3D. The peak metamorphism was achieved in the D_1D event. The granite magma is generated and emplaced late syn-kinematic to D_1D and thereafter is deformed by D_2D and D_3D producing D_1G and D_2G structural fabrics. These compressive deformations resulted in the collapse of the basin; the combined package of DFB rocks and the granite was thrusted eastwards over the basement rocks. The tectonic transport direction during thrusting is suggested eastwards from our structural analysis. Transverse faults developed perpendicular to the length of the granite have led to partitioning of the strain thereby showing a heterogeneity in the development of fabric within it.     

Diurnal and seasonal variations of wind farm impacts on land surface temperature over western Texas

This paper analyzes seasonal and diurnal variations of MODerate resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) data at ~1.1 km for the period of 2003–2011 over a region in West-Central Texas, where four of the world’s largest wind farms are located. Seasonal anomalies are created from MODIS Terra (~10:30 a.m. and 10:30 p.m. local solar time) and Aqua (~1:30 a.m. and 1:30 p.m. local solar time) LSTs, and their spatiotemporal variability is analyzed by comparing the LST changes between wind farm pixels (WFPs) and nearby non wind farm pixels (NNWFPs) using different methods under different quality controls. Our analyses show consistently that there is a warming effect of 0.31–0.70 °C at nighttime for the nine-year period during which data was collected over WFPs relative to NNWFPs, in all seasons for both Terra and Aqua measurements, while the changes at daytime are much noisier. The nighttime warming effect is much larger in summer than winter and at ~10:30 p.m. than ~1:30 a.m. and hence the largest warming effect is observed at ~10:30 p.m. in summer. The spatial pattern and magnitude of this warming effect couple very well with the geographic distribution of wind turbines and such coupling is stronger at nighttime than daytime and in summer than winter. Together, these results suggest that the warming effect observed in MODIS over wind farms are very likely attributable to the development of wind farms. This inference is consistent with the increasing number of operational wind turbines with time during the study period, the diurnal and seasonal variations in the frequency of wind speed and direction distribution, and the changes in near-surface atmospheric boundary layer (ABL) conditions due to wind farm operations. The nocturnal ABL is typically stable and much thinner than the daytime ABL and hence the turbine enhanced vertical mixing produces a stronger nighttime effect. The stronger wind speed and the higher frequency of the wind speed within the optimal power generation range in summer than winter and at nighttime than daytime likely drives wind turbines to generate more electricity and turbulence and consequently results in the strongest warming effect at nighttime in summer. Similarly, the stronger wind speed and the higher frequency of optimal wind speed at ~10:30 p.m. than that at ~1:30 a.m. might help explain, to some extent, why the nighttime LST warming effect is slightly larger at ~10:30 p.m. than ~1:30 a.m. The nighttime warming effect seen in spring and fall are smaller than that in summer and can be explained similarly.     

Plasma clouds associated with Comet P/Borrelly dust impacts

The NASA DS1 spacecraft encountered Comet P/Borrelly on September 22, 2001 at a distance of ∼2171 km on the sunward side of the comet. The flyby speed was ∼16.5 km s⁻¹. Using high temporal resolution (50 μs) absolute electric field amplitude measurements from a ∼1 m dipole antenna, new features of plasma clouds created by cometary dust impacts have been detected. The pulses have 1/e exponential decays of ∼650 μs duration, exponentially shaped overshoots with rise times of ∼2 ms, and exponential-shaped overshoot decay times of ∼10 ms. Assuming a plasma temperature of 10⁴ K, these pulse features have been explained as plasma cloud space charge effects from the electron, proton and heavy ion portions of the clouds passing the antenna. Complex pulse shapes were also detected. These are believed to be due to either plasma cloud scattering off of the spacecraft, or to secondary impacts. Small electric pulses of duration 10-15 ms of cometary origin were detected but are presently unexplained. The electric component of the plasma wave spectra at closest approach had an f^−2.4 power law shape from 10 Hz to 1 kHz. The electron cyclotron frequency was approximately 1 kHz. One possible explanation of the wave spectrum is that whistler mode waves associated with phase steepened cometary plasma waves are dispersed, leading to the broad spectrum. Finally, based on the present results, a new type of low-cost, large-area dust detector is proposed.     

Exposure of developing countries to sea-level rise and storm surges

An increase in sea surface temperature is strongly evident at all latitudes and in all oceans. The scientific evidence to date suggests that increased sea surface temperature will intensify cyclone activity and heighten storm surges. The paper assesses the exposure of (coastal) developing countries to sea-level rise and the intensification of storm surges. Geographic Information System (GIS) software is used to overlay the best available, spatially-disaggregated global data on critical exposed elements (land, population, GDP, agricultural extent and wetlands) with the inundation zones projected with heightened storm surges and a 1 m sea-level rise. Country-level results indicate a significant increase in exposure of developing countries to these climate-induced changes.     

Mesoscale moisture transport effects on forest edges in a fragmented landscape in Amazonia

This work explores the dry season micrometeorology of fragmented forests in Amazonia. Numerical simulations with a coupled atmosphere-vegetation model show that mesoscale moisture transport leads to a significant drying and vegetation stress at the forest edges. Increased evaporation cannot fully compensate for the drying. Typical convective precipitation events that occur in the dry season have a localized impact and do not affect the drying trend in the long term. Availability of soil moisture can partially mitigate the drying effect and consequent vegetation stress. Edge effects can dominate the vegetation dynamics and fire susceptibility of forest fragments as a whole. Hence, understanding the dynamics and drivers of edge effects is crucial for understanding the ecology and future of tropical forests in a changing climate.     

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).