عنوان مقاله [English]
The occurrence of groundwater in hard rocks is very much different from that in granular
media, being highly irregular due to varriable subsurface geology and hydrogeology. The
accumulation and movement of water in such an area, are governed by primary and secondary
porosity (mainly due to weathering, jointing and fracturing). It is cleafly known that the potential
water may reside preferentially in those regions where either weathering zone attains considerable thickness or where the fracturing, jointing is intense.
The square array technique is used to throw some light on this problem. The objective of this study is to apply the square array resistivity and chargeability techniques to aid the understanding
of the fracture behaviour of hard rocks in detph. Work by several researchers in square array resistivity show the usefulness of the techniques in such investigations. In this study we add the
square array chargeability to these methods, which have been conducted at Shahran in north-west of Tehran, Iran. The area have an undulating topography.
A useful parameter of anisotropic medium, known as the coefficient of anisotropy and the
mean resistivity indicates whether fractures are water saturated or not. The square array
technique having a profile with a station interval of 20 m and survey line vertical to the fault direction with a square length of 200 m were applied in the site. The profile at Shahran in
north-west of Tehran has survey line of 300 m long. The discharge rate of 13.5 m "3/hr for the exisiting well is consistent with our data.
The definitions for coefficient of anisotropy and mean resistivity were applied to the induced polarisation technique. Saturated fractures are indicated by high mean chargeability and high
coefficient of anisotropy in chargeability.
The square array resistivity and chargeability techniques made at Shahran show that
significant joints and fractures occur in these area which are saturated with water. These studies
further indicate that the intensity of fracturing may differ considerably both in the horizontal and
vertical directions in hard rock terrains.