ORIGINAL PAPER Near-surface seismic refraction applied to exploring subsurface clay layer at a new mining area in southeast Cairo, Egypt A. K. Abd El-Aal & A. A. Mohamed Received: 10 September 2008 / Accepted: 20 January 2009 / Published online: 7 March 2009 # Saudi Society for Geosciences 2009 Abstract A near-surface seismic refraction survey was conducted at a new mining area located in southeast Cairo, Egypt, to explore the subsurface clay layer for future economic use in mining and cement industry. The purpose of the survey has been to provide geological and geophys- ical information because no borehole was existent in the area under investigation. The aim of study had been to explain the main characteristics of the subsurface layers. For this purpose, a new technique has been used to acquire and process the data. This technique provides critical information to determine the depth of the subsurface layers, as well as morphology, stratigraphy, and potential locations of the clay layer for future economic use. The thickness and general shape of the clay layer in the whole area were determined and are illustrated in maps. Keywords Shallow seismic refraction . P-wave seismic profiles . Stratigraphy Introduction The shallow seismic refraction techniques is considered one of the most effective methods for determining the depth of the bedrock and the ground water, the lithology type, the lateral and vertical changes in lithology, and investigating the structural features such as micro faults. The evaluated seismic velocities can be used in the interpretation of lithology, structural features and the zones of solution cavities. Shallow seismic refraction has been widely applied to detect and resolve many complicated problems within the subsurface layers. From the engineering vantage point, shallow seismic refraction has been used to study bedrock foundation properties in road tunneling, dam sites, quarries, hydroelectric power plants, subway constructions, nuclear power plants, and many other facilities. P and S-wave velocities obtained from shallow seismic refraction surveys are used to evaluate the bedrock and determine its elastic properties. Today, the shallow geophysical techniques have been used to study the physical and dynamic characteristics of soil and bedrock. Many researchers have used the seismic refraction technique to determine the characteristics of the site (Helfrich et al. 1970; Gregory 1976; Sjogren and Sandberg 1979; Dutta 1984; Kilty et al. 1986; Hatherly and Neville 1986). On the other hand, there are some precautions which must be taken into consideration when using shallow seismic refraction technique such as profile length and source energy which limits the depth penetration of the refraction method. Typically, a profile can only detect features at a depth of one- fifth of the survey length. Another significant limitation to the refraction method is the so-called hidden layer problem. The seismic refraction method requires the increase of seismic velocity with depth. It is difficult to resolve a thin, low-velocity sand/gravel bed beneath a high-velocity clay layer which is a typical case for velocity inversion. The seismograms require careful analysis to pick the first arrival times of layers. If a thin layer produces first arrivals, which cannot be easily identified on a seismogram, the layer may never be identified. Thus, another layer may be misinter- preted as incorporating the hidden layer. As a result, the layer thickness may increase. In the present study, the shallow seismic refraction method is applied to investigate the depth and the subsurface geological Arab J Geosci (2010) 3:105–112 DOI 10.1007/s12517-009-0036-2 A. K. Abd El-Aal (*) : A. A. Mohamed National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt e-mail: dewaky@nriag.sci.eg