Modelling for Science, for a better future - some recent outcomes
Crustal Structure beneath the Kashmir Basin Adjoining the Western Himalayan Syntaxis
by Ramees R. Mir, Imtiyaz A. Parvez, Vinod K. Gaur, Ashish, Rakesh Chandra and Shakil A. Romshoo
We present a crustal shear‐wave velocity model for the intermontane Kashmir valley derived from eight broadband seismic stations located on hard‐rock sites surrounding and within the valley. Receiver functions at these sites were calculated using the iterative time‐domain deconvolution method of Ligorria and Ammon (1999) jointly inverted with fundamental‐mode Rayleigh‐wave group velocity dispersion data to estimate the underlying shear‐wave velocity structure. The inverted Moho depths were further constrained within ±2 km by forward modeling and conform to those independently estimated using H‐κ(crustal thickness vs. VP/VS) stacks. The Moho descends steeply (>15° NE) beneath the Pir Panjal range from a depth of ∼40 km south of the Main Central thrust to ∼58 km on the southwestern flank of the valley and undergoes an ∼4 km upwarp beneath the valley, thinning the overlying crust. Further northeast (NE) of the valley, the Moho dips gently ( ∼3°) beneath the Zanskar range. A persistent low‐velocity zone at a depth of ∼12–16 km is interpreted as a sheared zone associated with the décollement separating Himalayan rocks from the Indian plate. Relocated seismicity from the International Seismological Centre (ISC, 2013) catalog (1964–2013), together with a small number of local earthquakes recorded by our network, is apparently confined south of the NE edge of the valley, suggesting that the transition of the Indian plate from locked décollement to aseismic creep lies near here. This result is consistent with the geodetic findings that a broad zone of partial seismic coupling exists beneath the Kashmir valley.
Source: https://pubs.geoscienceworld.org/bssa/article-abstract/107/5/2443/506668/crustal-structure-beneath-the-kashmir-basin?redirectedFrom=fulltext
Identifying the Transition Zone Between East and West Dharwar Craton by Seismic Imaging
by Ashish and Imtiyaz A. Parvez
The data from 12 temporary broadband seismic stations operated across east–west corridor in Dharwar region of Indian Peninsula along with ten other seismic stations operated by CSIR National Geophysical Research Institute (NGRI) in the region have been analysed that provide high-resolution image of southern Dharwar crust. Crust along the corridor is imaged by receiver function H−kH−k stacking, common conversion point stacking using data from 22 sites in combination with joint inversion modeling of receiver functions and Rayleigh wave group velocity dispersion curves. The velocity image reveals thinner crust (36–38 km) except one site (coinciding with Cuddapah basin on the surface) in East Dharwar Craton (EDC), while crust beneath the West Dharwar Craton (WDC) is thicker (46–50 km). This study also observed a transition zone between EDC and WDC starting west of Closepet granite to the east of Chitradurga Schist Belt (CSB), which shows diffused Moho with a thickness of 40–44 km. Chitradurga Schist Belt is identified as the contact between Mesoarchean (WDC) and Neoarchean (EDC) crustal blocks. The lowermost part of the crust ( Vs>4.0Vs>4.0 ) is thin (2–6 km) beneath EDC, intermediate (6–8 km) beneath transition zone and thicker (14–30 km) beneath WDC across the profile.
Source: https://link.springer.com/article/10.1007/s00024-017-1657-0
Neo-deterministic seismic hazard scenarios for India - a preventive tool for disaster mitigation
by Imtiyaz A. Parvez, Andrea Magrin, Franco Vaccari, Ashish, Ramees R. Mir, Antonella Peresan and Giuliano Francesco Panza
Current computational resources and physical knowledge of the seismic wave generation and propagation processes allow for reliable numerical and analytical models of waveform generation and propagation. From the simulation of ground motion, it is easy to extract the desired earthquake hazard parameters. Accordingly, a scenario-based approach to seismic hazard assessment has been developed, namely the neo-deterministic seismic hazard assessment (NDSHA), which allows for a wide range of possible seismic sources to be used in the definition of reliable scenarios by means of realistic waveforms modelling. Such reliable and comprehensive characterization of expected earthquake ground motion is essential to improve building codes, particularly for the protection of critical infrastructures and for land use planning. Parvez et al. (Geophys J Int 155:489–508, 2003) published the first ever neo-deterministic seismic hazard map of India by computing synthetic seismograms with input data set consisting of structural models, seismogenic zones, focal mechanisms and earthquake catalogues. As described in Panza et al. (Adv Geophys 53:93–165, 2012), the NDSHA methodology evolved with respect to the original formulation used by Parvez et al. (Geophys J Int 155:489–508, 2003): the computer codes were improved to better fit the need of producing realistic ground shaking maps and ground shaking scenarios, at different scale levels, exploiting the most significant pertinent progresses in data acquisition and modelling. Accordingly, the present study supplies a revised NDSHA map for India. The seismic hazard, expressed in terms of maximum displacement (Dmax), maximum velocity (Vmax) and design ground acceleration (DGA), has been extracted from the synthetic signals and mapped on a regular grid over the studied territory.
Source: https://link.springer.com/article/10.1007/s10950-017-9682-0
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