No abstract

No abstract

The phonon spectra of diamond, Si, Ge, and ␣-Sn are systematically investigated by using real-space interatomic force constants ͑IFC's͒ up to the 25th shell. The calculations are performed employing density functional perturbation theory, a pseudopotential plane-wave approach, and the local density approximation for the exchange-correlation potential. Moreover, analytical expressions are derived for the phonon frequencies at some high-symmetry points, in terms of the IFC's up to second nearest neighbors. Compared to those of Si, Ge, and ␣-Sn, the IFC's of diamond are found to be larger in magnitude and those of the first and second shells show significantly different relative strengths. The reasons behind the peculiar features of the phonon spectra of diamond are identified. Contrary to a common belief, the flatness of some transverse acoustical phonon branches ͑of Si, Ge, and ␣-Sn͒ appears only after including IFC's up to the eighth shell. The calculated phonon spectra are in good agreement with the available experimental data, for the four considered systems.

Gravity data were used to investigate subsurface geology in the Ariana region from the Diapir Zone in Tunisia. Our study area is located in the north‐eastern part of the Maghrebides affected by the Alpine orogeny. Despite the smooth topography and the low density of the Quaternary series, integrated geological data and gravity responses (Bouguer anomaly and derivative mapping) help decipher the geological heterogeneities beneath the Quaternary overburden. The interpretation of the gravity data points to alignments of positive anomalies delineating two major orthogonal features that are thought to characterize the subsurface deep structures: 1) a lineament striking north‐west at the emplacement of an actual horst bordered by a buried fault‐system directed N140 and 2) a second counterpart striking north‐east, and is clearly expressed in the surface outcrops. These principal structural features were described as the result of a regional tectonic, compressive phase dating the Miocene. This phase was marked by reactivation and oblique‐slip displacements of regional faults; some of which (N070) are reverse and south‐east vergent. Further faulting enhanced the ascension of Triassic evaporites in diapir structures. This tectonic evolution may be integrated in the regional tectonic scheme of Alpine orogeny induced by a collision between African and European plates.

Often systems are described in a play for a region and stated as a conceptual model for a specific hydrocarbon accumulation style and implemented in order to develop geological targets. The recognition of each systemelement involves the deployment of geological and geophysical studies and evaluation techniques to identify delineate and locate subsurface prospects. Each geological model is identified through its geophysical signature pattern. The latter becomes particularly important as exploration moves to detect smaller, more complex, and more remote targets. Although targets are getting smaller, exploration and appraisal wells can be sited more accurately allowing greater chance of success through the use of multi-source information. One of the successful tools of choice to assist with this endeavour has been the usage of Gravity data. This paper reports the results using gravity data for hydrocarbon exploration in central Tunisia. Gravity was used to define structural elements which constitute important aspects in the identification and definition of hydrocarbon plays.