Seismic Site Specific Study for Seismic Microzonation: A Way Forward for Risk Resiliency of Vital Infrastructure in Sikkim, India

Seismic Microzonation comprising study of site specific seismic Microtremor (H/V ratio) is deployed to generate seismological parameters (Peak Frequency, Peak Amplification, Site Vulnerability Index) that may help estimate requisite factors for sound building design codes that can be used to construct risk resilient infrastructures. In this paper the site of Pakyong, Sikkim, India has been investigated by dividing it into three differed zones (Zone 1, Zone II, Zone III). The study area is associated with site amplification factor varying from 1.47 to 11.49 with corresponding frequency variations from 0.5 Hz - 12.5 Hz in which site vulnerability index found varied from 0.2 to 220.6. The anomalous subsurface formation with its high amplification corresponds to the centre of the Pakyong sites having conspicuous trend in NW-SE direction suggesting the existence of geological formations of Chlorite, Phyllite with intercalations of Quartzite beneath the centre of Pakyong site. The risk associated with vulnerability index for different zones maintains its variability as Zone I > Zone II > Zone III, indicating the low vulnerability index values are attributed to compact parts of the sub-surface materials with less amplifications whilst high vulnerability index of the site corresponds to relatively lower strength of the sub-surface materials and soft sediments underlying the Pakyong site which can be used for constructing risk resilient structure by enhancing the stiffness coefficient of the sub-surface by providing plausible engineering solutions for the purpose.

Seismic Microzonation Study of South Asian Cities and Its Implications to Urban Risk Resiliency under Climate Change Scenario

In this study, an attempt has been made to review the existing framework of earthquake risk resiliency for the urban agglomerates of South Asian earthquake-prone countries (Afghanistan;Bangladesh;Bhutan, India, and Pakistan) with aim of suggesting a plausible model for earthquake risk resiliency for urban agglomerates of the region under the influence of uncontrollable climate change scenario. We demonstrated that the existing infrastructures can be retrofitted to mitigate and reduce the nature and extent of damages to structures to the greater extent whilst site response based comprehensive seismic microzonation is very much required for new settlements and for long-term sustainable urban planning by adopting multi-disciplinary investigations using integrated tools consisted of geophysical, geological, and geotechnical methodologies, which in turn help understand how and why underneath sub-surface layers get amplified to cause destruction of buildings and severe damages to critical infrastructures of South Asian Cities. It is inferred that implementation of fourth level comprehensive seismic Micro, Nano, Pico and Femto zonation study for almost all strategic cities of South Asia is a need of an hour in particular, and of the seismically prone regions of the world, in general, which would be helpful for generating a series of new parameters for development of multi-dimensional risk resilient building design codes for the safer and sustainable infrastructures of urban settlement. The methodology has wide-scale applicability to different kinds of structures and typology of the buildings.

Test of Strain Behavior Model with Radon Anomaly in Seismogenic Area: A Bayesian Melding Approach

Mathematical models in seismo-geochemical monitoring offer powerful tools for the study and exploration of complex dynamics associated with discharge of radon as the indicator of change of intense-deformed conditions of seismogenic layers or blocks within the lithosphere. Seismic precursory model of radon gas emanation in the process of earthquake prediction research aims to find out the distinct anomaly variation necessary to correlate radon gas with processes of preparation and realization of tectonic earthquakes in long-term and short-term forecasts tectonic earthquakes. The study involves a radon gas volume analytic model to find the correlation of radon fluctuations to stress drop under compression and dilatation strain condition. Here, we present a mathematical inference by observing radon gas emanation prior to the occurrence of earthquake that may reduce the uncertainties in models and updating their probability distributions in a Bayesian deterministic model. Using Bayesian melding theorem, we implement an inferential framework to understand the process of preparation of tectonic earthquake and concurrent occurrence of radon discharge during a tectonic earthquake phenomena. Bayesian melding for deterministic simulation models was augmented to make use of prior knowledge on correlations between model inputs. The background porosity is used as a priori information for analyzing the block subjected to inelastic strain. It can be inferred that use of probabilistic framework involving exhalation of radon may provide a scenario of earthquake occurrences on recession of the curve that represents a qualitative pattern of radon activity concentration drop, indicating associated stress change within the causative seismogenic fault. Using evidence analysis, we propose a joint conditional probability framework model simulation to understand how a single fracture may be affected in response to an external load and radon anomaly change that can be used to detect the slip, a predictable nature of the causative fault in the subsurface rock.