On the automatic interpretation of direct current resistivity soundings

A method for the automatic inversion of resistivity soundings is presented. The procedure consists of two main stages. First, application of linear filters which transforms the apparent resistivity curve into the kernel function, and vice versa. In the second stage the first and second derivatives of the kernel function are calculated and used in a second-order modified Newton-Raphson iterative fitting procedure. The model obtained is optimal in the least squares sense. The method has been tried on some field examples and produced resistivity models which show a good agreement with the geological well logs.     

The extreme well-loss component of drawdown in two deep artesian wells in Israel

Hydrogeology Journal - The water-level drawdown in pumping wells is the sum of two components: aquifer loss and well loss. The latter results from mostly turbulent and nonlaminar flow in and around...     

The structure of the crust and upper mantle in the Dead Sea rift

The previously published results of a deep seismic refraction study of the Dead Sea—Gulf of Elat rift show crustal thinning underneath the rift and the presence of a 5 km thick velocity transition zone in the lower crust along the rift. The structural interpretation of the first-arrival data was revised using the detailed velocity-depth distribution.The revised crustal thicknesses are 35 km near Elat and 27 km, 160 km south of Elat.The crustal thinning and the presence of the velocity transition zone are interpreted as being the result of intrusion of upper mantle material into the lower crust, possibly representing the initial shape of the processes which have been active further south in the Red Sea since earlier times.     

Seismic investigation of crust-mantle transition in continental rift systems - Jordan-Dead Sea rift and Rhinegraben

The recent acquisition of high-quality seismic refraction data in the Jordan—Dead Sea rift and adjacent areas has made possible the investigation of the dynamic properties of seismic P-waves refracted and reflected at the crust—upper mantle boundary.

These waves cause high-amplitude arrivals near the outer cusp of the travel-time curve which are followed by an abrupt decrease in amplitudes at increasing distances beyond the cusp.

It has been shown that such amplitude distributions can only be the result of a smooth rapid increase of velocity with depth. In the case of the Jordan—Dead Sea rift the amplitude distribution indicates the presence of a transition zone between the lower crust and upper mantle in which the velocity increases smoothly. The interpretation of seismic refraction data in the Rhinegraben indicates the existence of a similar transition zone. In both rifts the crust—mantle boundary outside the rift is represented by sharp velocity discontinuity.

The comparison of the velocity structure of the crust—upper mantle boundary suggests that a smooth transition zone at the base of the lower crust is a characteristic property of continental rifts which could be interpreted in terms of crust—mantle interaction.     

Seismic reflection and refraction investigations of Lake Kinneret - central Jordan Valley, Israel

Seismic reflection and refraction studies in Lake Kinneret, which is located in the northern part of the Dead Sea Rift have been carried out. In the seismic reflection work several instruments including sparker, boomer and air guns were used. The acoustic penetration was limited, giving information on the uppermost sediments only. In the seismic refraction study the energy source was seismic explosives charges placed below the water table in shotholes located onshore at either end of two lines. The seismic signals were picked up by hydrophones and transmitted to the shore-based recording stations by special radio transmitters.

The seismic refraction profiles show different sedimentary structures at various parts of the lake. The layer underlying the top sedimentary sequence is of higher seismic velocity in the northern section than in the southern section. This suggests a difference in the stratigraphic section between the two parts. Unconformities and faults which account for the structures observed here probably exist under the lake.

The shallow reflection data indicate active tectonic processes in this area. Folds and faults have been observed in the uppermost sediments. The most deformed areas are along the margins but some deformation also occurs at the center of the lake in its deepest portion. The area is also seismically active.     

Resistivity surveying

This paper reviews the principles and applications of the resistivity method of geophysical prospecting. Topics covered are physical principles, instrumentation, field techniques, interpretation procedures, and their recent development. The applications are illustrated by selected case histories of engineering studies, hydrology, structural mapping, and crustal structure.     

Crustal structure of the Levant Basin, eastern Mediterranean

A seismic refraction/wide-angle reflection experiment was undertaken in the Levant Basin, eastern Mediterranean. Two roughly east–west profiles extend from the continental shelf of Israel toward the Levant Basin. The northern profile crosses the Eratosthenes Seamount and the southern profile crosses several distinct magnetic anomalies. The marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources. The results of this study strongly suggest the existence of oceanic crust under portions of the Levant Basin and continental crust under the Eratosthenes Seamount. The seismic refraction data also indicate a large sedimentary sequence, 10–14 km thick, in the Levant Basin and below the Levant continental margin. Assuming the crust is of Cretaceous age, this gives a fairly high sedimentation rate. The sequence can be divided into several units. A prominent unit is the 4.2 km/s layer, which is probably composed of the Messinian evaporites. Overlying the evaporitic layer are layers composed of Plio–Pleistocene sediments, whose velocity is 2.0 km/s. The refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single-layer oceanic crust takes place along the Levant margin. The transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual. The northern profile, north of the Carmel structure, presents a different structure. The continental crust is much thinner there and the transition in the crustal structure is more rapid. The crustal thinning begins under western Galilee and terminates at the continental slope. The results of the present study indicate that the Levant Basin is composed of distinct crustal units and that the Levant continental margin is divided into at least two provinces of different crustal structure.     

Three-dimensional configuration and dynamics of the fresh–saline water interface near two saline lakes with different levels (Middle East)

A typical fresh–saline water interface in a coastal aquifer is characterized by saline-water circulation below the interface and freshwater flow above. Both flows are perpendicular to the shoreline. The flow pattern near two separated saline lakes is more complicated. For example, in the Middle East, the Dead Sea northern basin and the evaporation ponds of the Dead Sea Works are adjacent to each other but separated. The northern basin level is dropping by 1.1 m/year and the evaporation ponds’ levels are increasing by 0.2 m/year. The fresh–saline water interface in such situation is numerically simulated. Streamlines parallel or semiparallel to the shoreline are significant. Moreover, the fresh–saline water interface intrudes landward adjacent to the higher saline lake and is pushed lakeward adjacent to the lower saline lake. The simulation results support field observations showing that the interface migrates vertically at a faster rate relative to the changes in the water table and the lake levels.