Assessment of Seismic Local Hazard of Agartala town based on Nonlinear Site Response Analysis

Acharya Vedatri, Bashir Khalid and Saha Rajib*

Assessment of local site effect on seismic ground motion is of great importance and recognized on the nature of earthquake damage. Local site conditions influence most of the important characteristics mainly the acceleration amplitude and frequency characteristics of ground motion during an earthquake. The extent of this modification depends on geometry of the soil profile, thickness and properties of the soil profile and characteristics of the input motion. Present study is an effort to carry out 2D ground response analysis for bore-hole deposits at different locations of Agartala Town which is capital of Tripura situated in north-eastern part of India and categorized as seismic zone V, the highest level of seismic hazard potential as per BIS (2002).

Further, the study outlines a methodology to generate synthetic earthquake motions where limited amount of past strong motion data is available. The results presented in the form of Peak Ground Acceleration PGA at ground surface, amplification factor and generated response spectra for the site give significant input pertaining to sustainable design of future structures and retrofitting the existing ones in order to reduce the seismic vulnerability of Agartala town. However, the present study may be help for the local planners/designers for future planning and designing the structures.

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Estimation and Analysis of Possible Flood for the Silchar city- A Case Study

Annayat Wajahat and Sil Briti Sundar*

Recently it has been observed that Silchar city located in North East India, is receiving maximum amount of rainfall, though Cherrapunji has a record of receiving maximum rainfall every year. This variation may be because of some climate change or hydrological change. As because Silchar city is a very old, thickly populated, diversified rich cultural and important in respect of trade and business, therefore it is intended to carry out a flood analysis study which may help the planners to get rid of or minimize the flood related disasters. Surface run-off is very important for Silchar city as it is lying at the downstream section of the catchment. Therefore, due to its own location it receives maximum discharge from the catchment. For a given rainfall event, to predict the direct runoff volume, Soil conservation Service Curve Number (SCS-CN) approach is used. In this paper surface runoff has been estimated considering the rainfall events of monsoon period.

The city receives runoff from both of the tributaries of Barak river Basin namely Katakhal and Sonai. The area is most flood affected region resulting in various types of erosion. The results showed moderately high, positive, correlation between the estimated and measured values with coefficient of regression of R2 = 0.947. Rainfall data, soil map, land use/land cover map were collected from various sources and processed.

Land use/land cover mapping has been carried out using thematic map (0.5 km) MODIS- based Global Land Cover Climatology (MCD12Q1) for the year 2012. The daily rainfall data of 4 rain gauge stations (2012) was collected and then average of all the stations was taken using Theisen Polygon Method. Weighted curve numbers were determined considering the antecedent moisture conditions, soil groups and land use/ land cover.

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Research on Seismic Risk and Traffic Capacity of Bridges Based on Bayesian Network

Wu Fengying, Wang Wei* and Liu Xiao-ran

According to the bridge damage information, identifications are random and the Bayesian network analysis expresses information potential probability relationship as flexible. Based on Bayesian network and seismic theory, the method of bridge seismic hazard grade identification is established. Based on the complete investigation data of the Wenchuan earthquake bridges, eight representative factors such as PGA etc. are selected. The influence of bridge seismic vulnerability classification variables and discrete quantization value, parameters learning using the maximum likelihood (MLE) method is to get the nodes probability table. The grade of bridge seismic is identified by using BN reverse reasoning technology and it has good prediction accuracy of 95.5% and can identify the reasons for damaging.

Through the model validation of the Baihua Bridge and 10 typical bridges, the classification imbalance of the sample data had impacts on the model prediction. There is a deviation between the damage states of the bridge with the survey data, the results verify the feasibility and effectiveness of the proposed method. The traffic capacity of the bridge after the earthquake the traffic flow changes and the transit time in the Lishui Bay Bridge are evaluated. The results show that the evaluation results provide some reference values for post-earthquake disaster reduction.

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Stochastic Simulation of Rock Level Motion for Indo- Bangladesh Border Earthquake (1988) of Magnitude (Mw 5.9) in North East India

Sil Arjun

The study presents the selection of appropriate model for synthetic simulation of acceleration time history at rock level of Northeast India. A code is developed using point source seismological model concept where source, path and site parameters are taken into account. The code has been validated with the actual (rock level) ground motion records obtained from the ground motion monitoring network (Cosmos Virtual Data Centre and PESMOS) operated by Shillong array of NE India for Bangladesh Boarder earthquake occurred on 6th Feb 1988 and compared with the available programming codes such as, EXSIM and Strong ground motion simulation (SGMS). However, results are presented in their corresponding acceleration time histories and response spectra (5% damping). The simulated acceleration time histories using developed code have a close agreement with the actual ground motion for all the stations.

The simulated Peak ground acceleration (PGA) for Shillong, Pynursla and Mawphlang are found 0.048g, 0.052g and 0.059g whereas their actual PGA at rock surfaces were recorded as 0.048g,0.05g and 0.081g respectively. The EXSIM, SGMS models have completely under estimated all responses of the stations (Shillong, Pynursla, Mawphlang). This may be because of large distances from source to site (>50km).

Therefore, developed code could be used for further extended studies such as site response, attenuation model and other necessary studies required for the urban cities which are located at moderate/far distances from controlling seismic sources in Northeast India, especially for Microzonation purposes.

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Dynamic Evaluation on Road's Evacuation Capability under the Influence of Post-Earthquake Fire in Urban Seismic Weak Area

Liu Xiaoran1, Wang Wei*, Dong Tingting and Yang Zhun

The relations between crowd flow, evacuation space on road and post-earthquake fire were researched to solve the problem about road's evacuation under the influence of post-earthquake fire in urban seismic weak area. The flow model of road's evacuation with the post-earthquake fire influence was established based on system dynamics theory. The building height and wind speed were selected as sensitive factors to simulate under two states of certain assumptions. The results show that the different values of building height and wind speed will affect the spread speed of post-earthquake fire differently.

Reasonable parameters were selected for the system dynamics model under certain acceptable levels. Corresponding counter-measures were put forward to improve the evacuation capability and some references about specific implementations for urban planning on earthquake resistance and hazardous prevention were provided according to the simulation.

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