Modelling for Science, for a better future - some recent outcomes
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
Urban extreme rainfall events: categorical skill of WRF model simulations for localized and non-localized events
by G. N. Mohapatra, V. Rakesh and K. V. Ramesh
An objective method is used for determining the rainfall threshold for identifying extreme rainfall events (EREs) over the urban city, Bangalore, using observed rainfall data for a period of 35 years (1971–2005). Using this threshold, 52 EREs were identified during the period 2010–2014 using high-resolution rain-gauge observations. From these EREs, 15 localized and non-localized events were chosen based on spatial distribution to examine the forecast skill of the Weather Research and Forecasting (WRF) model. Apart from the conventional verification methods, a number of skill scores and indices were defined for a comprehensive evaluation of rainfall model skill. In general, the forecast underpredicted the magnitude of localized and non-localized EREs for the majority of cases; however, the model overpredicted light rainfall (≤10 mm day−1). The model showed a success rate of 59% in simulating light rainfall for localized EREs while 12% of events were missed and 29% were wrongly predicted. The success rate was significantly reduced at higher rainfall categories for localized and non-localized EREs, where the forecast missed the majority of rainfall events. The Reliability Index (RI) computed clearly showed that model skill is relatively higher for non-localized EREs compared to localized EREs. The average forecast reliability for non-localized and localized EREs were 74 and 51%, respectively. For localized EREs, model skill is relatively higher in rainfall location prediction (61%) compared to area (44%) and intensity (46%) prediction; while in the case of non-localized EREs, model skill is similar for location, intensity and area prediction. It is found that coupling an urban canopy model with WRF reduces the model errors particularly for lower rainfall thresholds.
Source: http://onlinelibrary.wiley.com/doi/10.1002/qj.3087/full
Subsurface profiling along Banni Plains and bounding faults, Kachchh, Western India using microtremors method
by Dhananjay A. Sant, Imtiyaz A. Parvez, Govindan Rangarajan, Satish J. Patel, Madhuri N. Bhatt and T.A. Sanoop Salam
The present article is a maiden attempt to map shallow subsurface rheological interfaces laterally across the Banni Plains and to decode geometry of the antecedent faults associated with the Kachchh Mainland Fault using the microtremor method. We conducted microtremor data acquisition for thirty-one sites along N-S transect from Loriya in Mainland Kachchh to Bhirandiara towards Patcham Island. Results from H/V spectral ratio technique show presence of two distinct rheological interfaces characterised by the resonant frequency (fr) ranges 0.23–0.27 Hz and 0.8252–1.5931 Hz respectively. The above frequency ranges are correlated with the depths of the Mesozoic-Basement (M-B) interface and the Quaternary-Tertiary (Q-T) interface. Using either the velocity (Vs) of seismic waves at the M-B and Q-T interfaces (calculated as 1830 m/s and 411 m/s respectively) or the standard non-linear regression relationship derived for the Banni Plains (h = 110.18fr−1.97) we estimate the depth range for M-B interface to be 1442–1965 m and for Q-T interface to be 44–160 m. The subsurface profile across the Banni Plains educe cluster of four faults that develop an array of imbricate faults at the forefront of the Kachchh Mainland Fault within the Banni Footwall Syncline. The geometry of the faults suggests a ‘positive flower structure’ indicating step-overs and strain restraining bends displaying push-ups resulting from localized shortening between converging bends of Kachchh Mainland Fault and the South Wagad Fault. The Banni Footwall Syncline preserves evidence of two episodes of deformations. The initial deformation event led to subsidence within the Kachchh Mainland Fault Zone bringing Mesozoic sequence juxtaposed to the basement rocks, whereas the later event is dominated by an uplift developing a positive flower structure in the Kachchh Mainland Fault Zone. Finally, the present study provides a mechanism to investigate faults and fault geometries correlating surface structural grains with subsurface structures.
Source: http://www.sciencedirect.com/science/article/pii/S1367912017303085
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