Effect of earthquakes liquefaction on the ground water hydraulic heads and changes in hydrogeological features in Potwar and alluvial deposits

Zulfiqar Ahmad 1 and Iftikhar Ahmad 2

1Department of Earth Sciences, Quaid-i-Azam University, Islamabad, Pakistan
2College of Earth and Environmental Sciences, Punjab University, Lahore, Pakistan

Earthquake liquefaction is a major contributor to urban seismic risk. The shaking causes increased pore water pressure which reduces the effective stress, and therefore reduces the shear strength of the sand. If there is a dry soil crust or impermeable cap, the excess water will sometimes come to the surface through cracks in the confining layer, bringing liquefied sand with it, creating sand boils, colloquially called "sand volcanoes".

Earthquakes produce changes in the hydraulic heads, porosity and permeability of the underlying aquifers of all types, and reduces the ultimate well discharge, sand blowing, muddy water and even abandonment of water wells. This phenomenon of abundance changes in the hydrogeological features are much pronounced in the alluvial deposits conforming unconfined aquifers in the vicinity of floodplains of Punjab. In Rawalpindi City, about 300 tube-wells being used to supply water to the community are also prone to meet the hazardous changes in the hydrogeology of the Potwar stratified aquifers connected in series isolated by the clayey lenses of variable thicknesses.  

Recent study implemented using Visual Modflow indicates that the potentiometric surfaces are constantly declining in the Rawalpindi city and any abandonment of water wells in future due to Earthquakes Liquefaction, changes in porosity and permeability and hydraulic heads would be considered as a sheer loss.