Microzonation map of the Abbottabad basin and immediate surroundings

Abstract

This study presents seismic hazard and seismic microzonation maps for the Abbottabad basin and surroundings, which are used in assessment and seismic design of buildings and bridges and other infrastructures. This research work determines microzonation parameters (shear wave velocity, fundamental frequency, and acceleration on ground surface) using geotechnical and geophysical testing procedures. Standard penetration test (SPT) and H/V methods are used to characterize the soils by estimating shear wave velocity at different locations. Microzonation maps for Abbottabad are developed in terms of acceleration parameter for 10% and 2% probability of exceedances in 50 years return period. These maps have been obtained based on the mean of average spectral acceleration values between 0.10 and 1.00 s following the Borcherdt (1994) recommendations. Based on H/V data (using Tromino Engy Plus instrument), it has been observed that the study area has average fundamental frequency range from 1 to 5 Hz, which represents the deposition of alluvial sediments (i.e., stiff and dense soil). Site characterization based on shear wave velocity indicated that soil in the study area consists of categories C and D. For the return period (Tr) of 475 years, the surface acceleration values ranges from 0.623 to 0.673 g, and for Tr = 2475 years, the area ranges from 1.007 to 1.107 g. These results show that soils in the Abbottabad basin will amplify 0.540 and 0.548 time respectively for Tr = 475 and 2475 against bed rock ground motions. Microzonation maps for Abbottabad basin do not exist; the maps produced in this study will be the basic input for carrying out the earthquake resistant design of the structures in Abbottabad.