Planning n Mitigation | VOL. 11, ISSUE 64, January-February 2010

Seismic Microzonation of Dehradun

The unconsolidated materials of young sedimentary basins can have a profound effect on the spatial distribution of earthquake ground motion amplification, resulting in a large variation in the severity of damage to buildings, transportation corridors and other lifeline infrastructures. To be able to carry out a seismic microzonation study for such sedimentary basins a large amount of input data is required on the three dimensional structure of the basin, the stratigraphy of the unconsolidated deposits and their geotechnical and geophysical characteristics. The city of Dehradun - located on unconsolidated sediments (Doon gravels) underlain by Siwalik sediments in the broad intermontane depression known as the Doon valley within the Siwalik foreland basin of Garhwal Himalaya (Fig 1), has been chosen for this study. [caption id="attachment_3600" align="aligncenter" width="852"] Fig 1. Location map with regional geology and tectonics of Dehradun region[/caption] The Doon valley is a crescent shaped, longitudinal, synclinal valley bounded on the north by the Main Boundary Thrust (MBT), where pre-tertiary rocks of the Lesser Himalayan zone override the tertiary rocks from the Siwalik Group. The southern margin of the Doon valley is marked by a sudden break in topography defined by the Himalayan Frontal Thrust (HFT), locally known as the Mohand Thrust where the rocks from the Siwalik Group are overriding the recent alluvial sediments towards the south. On the seismic hazard map of India,...

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