Table of contents

This study is based on a site survey carried out in the capital city of Morocco, Rabat. For this aim, we used a technique based on the recording and processing of seismic ambient noise to characterize local geological conditions in terms of the dynamic response of soil during earthquakes. This technique consists of an assessment of the spectral ratio of the horizontal to vertical components of microtremors recorded at the surface during a few minutes, and allows determination of the fundamental period and the maximum amplification factor at the site of measurement. We applied this technique in the city of Rabat to obtain distribution maps of dominant periods and amplification factors assessed in more than 250 sites. In order to discuss the results of this study, we used the information available in this zone about the lithology and topography to correlate the obtained values of dominant periods and amplification factors with the ground conditions. Finally, we established a microzoning map of the city of Rabat based on the contours of dominant periods. The microzoning map established in this study can be used by engineers and decision makers for urban and land use planning and also as a guide in reduction of the seismic vulnerability of buildings.

Coal fires represent a major problem in most coal producing countries. The Jharia coal field (JCF) has been affected by surface and sub-surface coal fires since the beginning of mining in the region in the mid 1800s. Currently research is focused on using freely available satellite data such as NOAA/AVHRR, MODIS (moderate resolution imaging spectrometer) etc for various applications. The potential of National Oceanographic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) images for detecting coal fires and monitoring their progress and associated environmental hazards and risks to the local communities in the JCF has been reviewed. Three models, namely the thresholding model, the contextual model and the fuel mask model have been used to determine the potential fire pixels. Due to the coarse resolution of the NOAA/AVHRR data it was essential to determine sub-pixel fires as well. Results of this study have been verified using the MODIS active fires product, MOD14 (Terra). We have used ten images of NOAA/AVHRR for the year 2004 in this study, and the results are in broad agreement with the ground truth data.

Evaluating the uncertainty in fracture connectivity and its effect on the flow behaviour of natural fracture networks formed under in situ conditions is an extremely difficult task. One widely used probabilistic approach is to use percolation theory, which is well adapted to estimate the connectivity and conductivity of geometrical objects near the percolation threshold. In this paper, we apply scaling laws from percolation theory to predict the connectivity of vein sets exposed on the southern margin of the Bristol Channel Basin. Two vein sets in a limestone bed interbedded with shales on the limb of a rollover fold were analysed for length, spacing and aperture distributions. Eight scan lines, low-level aerial photographs and mosaics of photographs taken with a tripod were used. The analysed veins formed contemporaneously with the rollover fold during basin subsidence on the hanging wall of a listric normal fault. The first vein set, V₁, is fold axis-parallel (i.e. striking ∼100°) and normal to bedding. The second vein set, V₂, strikes 140° and crosscuts V₁. We find a close agreement in connectivity between our predictions using the percolation approach and the field data. The implication is that reasonable predictions of vein connectivity can be made from sparse data obtained from boreholes or (limited) sporadic outcrop.

This paper deals with the use of QuickBird images for the identification of features linked to ancient transformations, the landscape induced by human activities. The methodological approach adopted for the identification of these features is mainly based on the use of data fusion and edge detection. The data fusion enabled the integration of the high spatial resolution of the panchromatic image with the spectral capability of multispectral images, thus allowing us to achieve improved capabilities that are not possible solely using the individual datasets. The use of edge detection enhanced the spatial feature, thus facilitating their identification. The investigation was performed on Metaponto, one of the most important archaeological sites in the south of Italy. The analysis focused on the identification of ancient land divisions related to the Greek colonization age. The obtained results showed that the use of QuickBird images enables the detection of the archaeological features linked to buried remains with a high level of detail.

In conventional vibroseis signal processing, algorithms including cross correlation and deconvolution are applied to convert the raw trace data into a seismic section. However, their performance deteriorates when the trace data are corrupted by the ambient noise, so the mathematical tool for time–frequency analysis and wavelet transform is applied in this paper to overcome the difficulty. A time–frequency cross correlation (TFCC) algorithm based on wavelet transform is proposed to extract the reflection from the trace data by detecting the reflected sweeps and estimating their time delay. The source signal and the trace data are transformed into time–frequency domain with respect to a same wavelet basis function; then time–frequency cross correlation is performed between the source signal and the trace data. The reflected sweeps are converted into time–frequency correlation wavelets in the result; meanwhile, the trace data are converted into seismic section. In wavelet decomposition, the high-frequency noise can be suppressed automatically. In the time–frequency representation of the trace data, the ambient noise and the reflected sweeps can be separated from each other. So in the TFCC algorithm, the interference of the ambient noise can be decreased considerably, and the weak reflections can be extracted clearly. Real vibroseis trace data were processed with the TFCC algorithm and the conventional cross correlation. The results showed the superiority of the proposed new algorithm in vibroseis signal processing.

A direct current (dc) resistivity geoelectric technique is applied in the Abu Zenima area, West Sinai, Egypt to delineate salt water intrusion from the Gulf of Suez and evaluate the quality and some of the petrophysical parameters of the aquifer. Sixteen Schlumberger vertical electrical soundings (VES) with maximum AB/2 = 3000 m are conducted. The interpretation of the one-dimensional (1D) inversion of the acquired resistivity data could map the fresh to slightly brackish aquifer (true resistivity = 52–71 Ω m, thickness = 17–66 m), which floats on denser, more saline, deeper water (<5 Ω m). A number of water samples of the fresh aquifer are analysed to determine the total dissolved solids (TDS) concentrations (ppm). A good agreement is observed between the resistivity boundaries and the borehole data. The mutual relations between the aquifer layering, the direction of the groundwater flow and the hydrogeophysical conditions of the aquifer are investigated. The geoelectric (Dar-Zarrouk) parameters are determined and interpreted in terms of the hydraulic conductivity, transimissivity, clay content, grain size distribution and potentiality of the aquifer. The integration of the results indicates a high potentiality and a relatively good quality of the fresh to slightly brackish aquifer in the north-eastern part of the study area.

In this paper, we have developed a least-squares analysis method to estimate not only the depth and shape but also to determine the horizontal position of a buried structure from the residual SP anomaly profile. The method is based on normalizing the residual SP anomaly using three characteristic points and their corresponding distances on the anomaly profile and then determining the depth for each horizontal position of the buried structure using the least-squares method. The computed depths are plotted against the assumed horizontal positions on a graph. The solution for the depth and the horizontal position of the buried structure is read at the common intersection of the curves. Knowing the depth and the horizontal position and applying the least-squares method, the shape factor is determined using a simple linear equation. Procedures are also formulated to estimate the polarization angle and the electric dipole moment. The method is semi-automatic and it can be applied to short or long residual SP anomaly profiles. The method is applied to synthetic data with and without random noise. The validity of the method is tested on a field example from Turkey. In all cases, the model parameters obtained are in good agreement with the actual ones.

Rock typing in modelling and simulation studies is usually based on two techniques; routinely defined rock types and those defined by special core analysis (SCAL). The challenge in these techniques is that it is frequently assumed that these two are the same to assign, but in practice static rock-types (routinely defined) are not always representative of dynamic rock-types (SCAL defined) in the reservoir. There is also no significant link between these two. To fill this gap, we propose a method for the combination of core description data with well log data for identification of the optimal number of static rock-types, and SCAL data with its high interpretive potential for identifying effective dynamic rock-types within determined static rock-types in a given reservoir zonation. In this paper, the proposed method was applied for two new exploration wells in one of the southern carbonate reservoirs in Iran with the lowest number of available data. First, with the integration of well logs and core description data using multivariate statistical methods, seven static rock-types were identified. Next, in these static rock-types the values of the permeability and reservoir quality index were predicted using neural networks with matching of core and log data. Then, based on the correlation of static rock-types and reservoir quality index a reservoir zonation consisting of nine zones was determined. Finally, with interpretation of SCAL data in the different positions of static rock-types for each zone, six different dynamic rock-types with distinct flow behaviour above the oil water contact were identified. This method can be used for the development of rock-type characterization in any heterogonous reservoir and it is a workable solution as input for saturation functions to the simulation model.

Seismic reflection travel time–offset curves are complicated, and depend on many parameters. There is a need for simplified equations involving a reduced number of parameters that can be estimated from data and used for moveout correction and a simplified velocity model of the Earth. Many authors have derived explicit equations for travel time as a function of offset, involving several parameters which depend on velocity. Some authors have applied the approach in which velocity varies with offset (velocity with high-order terms or anisotropic properties). Here we present a new approach in which we employ velocity variation with depth instead of offset. A simple linear variation of velocity is used to derive expressions for travel time and offset as a function of ray parameter, from which the variation of travel time with offset can be obtained. Only two parameters are involved in defining the velocity–depth profile, but the resulting travel time–offset curves are good approximations. Two-parameter linear variations of slowness with depth, and velocity and slowness with depth and zero-offset travel time, have also been derived and the relationships between them are described. Comparison of the new approximations with those of Taner and Koehler (1969 Geophysics34 859–81), and the large-offset approximations of Causse et al (2000 Geophys. Prospect.48 763–78) was performed using 1D plane-layered models with different velocity profiles. Taner and Koehler and Causse et al approximations are inaccurate for large and small offsets respectively, while the new approximations show improved accuracy and can be applied over the whole range of offsets. The velocity and slowness expressions can also be used for moveout correction. Synthetic and real records are used to demonstrate their effectiveness.

The pre-stack time migration and velocity analysis methods on common scatter-point (CSP) gathers are based on pre-stack Kirchhoff time migration. The concept of equivalent offset provides a new idea for the research of seismic pre-stack migration and velocity estimation. In this paper, according to the theory of the equivalent offset, we derive the travel-time equation of CSP gathers, introduce the related pre-stack time migration method and discuss velocity analysis methods based on the CSP gathers, and point out the advantages of CSP methods over conventional methods. Processing of a model example and field seismic data show the validity of CSP pre-stack time migration and the velocity analysis methods based on it.