Chandrani Singh

Fractal and b-Value Mapping in Eastern Himalaya and Southern Tibet

Abstract Fractal (correlation) dimension and b -value are determined from ∼1300 well-located earthquakes recorded at 32 seismic stations in eastern Himalaya and southern Tibet during 1993–2003. The spatial correlation of 0.9 is indicative of more clustered events in the region, while a b -value of 1.02 implies a highly active seismic region. A detailed study of the frequency–magnitude distribution and fractal dimension as a function of depth is also made. The results suggest structural variability at different depth levels in the Tibet–Himalaya collision zone that reflects highly heterogeneous and high-grade metamorphism in the region.

Effect of Sheet Resistance and Morphology of ITO Thin Films on Polymer Solar Cell Characteristics

Solar cell fabrication on flexible thin plastic sheets needs deposition of transparent conducting anode layers at low temperatures. ITO thin films are deposited on glass by RF sputtering at substrate temperature of 70∘C and compare their phase, morphology, optical, and electrical properties with commercial ITO. The films contain smaller nanocrystallites in (222) preferred orientation and exhibit comparable optical transmittance (~95%) in the wavelength range of 550–650 nm, but high sheet resistance of ~103 Ω/□ (the value being ~36 Ω/□ for commercial ITO).The polymer solar cells with PEDOT: PSS and P3HT: PCBM layers realized on RF sputtered vis-a-vis commercial ITO thin films are shown to display a marginal difference in power conversion efficiency, low fill factor, and low open-circuit voltage but increased short-circuit current density. The decrease in fill factor, open-circuit voltage is compensated by increased short-circuit current. Detailed study is made of increased short-circuit current density.

Spatial variation of coda wave attenuation in the Southern Indian Shield and its implications

During the recent past the Indian peninsular shield has experienced six damaging earthquakes of M 5.4-7.7 and compelled to readdress our understanding of the seismic attenuation characteristics for better evaluation of the seismic hazards in the so-called stable shield. We have performed the seismic attenuation study using coda waves of the broadband network from 1995 to 2009 for the shield region. About 400 local earthquakes M 2.5-4.0 within an epicentral distance of 250km are used in this study. The broadband seismic stations established are in different geological provinces, such as the Archaean Dharwar craton, the southern granulite terrain, the Proterozoic Cuddapah basin, the Godavari graben, the Cretaceous-Eocene Deccan volcanic province and in the Cambay basin. This allows us to understand the fluctuation of Q 0 in terms of spatial variations in the geologic and tectonic provinces. The results reflect a ubiquitous observation of frequency dependence of Q c in the different geologic provinces. The rift basins exhibit lower Q 0 , which suggests higher attenuation due to a more heterogeneous structure. Higher Q 0 in the western Dharwar craton infers lower attenuation. Similarly the Deccan volcanic province is characterized by significantly higher Q 0 . The results show a good correlation with the observed heat flow. The study fills an important gap in knowledge about the Q factor as well as of crustal attenuation conditions in the whole southern peninsular shield of India.

Spatial variation of seismic b-values across the NW Himalaya

The frequency–magnitude distribution is investigated along the entire north-western Himalaya (28°–36°N; 72°–81°E). The analysis includes a complete set of 1819 earthquakes of Mb ≥ 2.9 taken from the International Seismological Catalogue (ISC) bulletin which occurred between 1964 and 2010. The study area has been divided into three blocks (A, B and C) that include the Kashmir, Kangra–Chamba and Garhwal–Kumaun segments, respectively. The b-value of each block has been determined to see the disparity among the different segments. A comprehensive study of the spatial mapping of frequency–magnitude distribution is also made for the whole area. Significant variations in the b-value are detected with b ranging from b ≈ 0.6 to 1.3. The study shows that the accumulated stresses are high at the Kumaun as well as in the Kangra–Chamba region which may indicate the possibility of future large earthquakes at these locations.

Frequency and lapse time dependent seismic attenuation in eastern Himalaya and southern Tibet

We have studied the attenuation characteristics of eastern Himalaya and southern Tibet by using local earthquake data set that consists of 123 well-located events, recorded by the Himalayan Nepal Tibet Seismic Experiment operated during 2001–2003. We have used single backscattering model to calculate frequency-dependent values of coda Q (

A review of crust and upper mantle structure beneath the Indian subcontinent

Q_\mathrm{c}

Frequency-dependent body wave attenuation characteristics in the Kumaun Himalaya

Qc). The estimation of