Structural mapping from high resolution aeromagnetic data in west central Arabian Shield, Saudi Arabia using normalized derivatives

Aeromagnetic data covering an area of about 40,000 km² at the west central Arabian Shield, Saudi Arabia has been collected and interpreted to provide structural map of the area. A number of normalized derivatives were used to help interpret the signature of magnetic data so that weak and small amplitude anomalies can be amplified relative to the stronger and larger amplitude anomalies. The interpretations obtained from these geophysical techniques of the field data demonstrated a strong correlation between magnetic anomalies and mapped subsurface geology. Based upon the variation in magnetic lineaments, shape amplitude, and trend structural map of the west central Arabian Shield on Saudi Arabia were obtained.     

Source parameters of March 10 and September 13, 2007, United Arab Emirates earthquakes

On March 10 and September 13, 2007 two earthquakes with moment magnitudes 3.66 and 3.94, respectively, occurred in the eastern part of the United Arab Emirates (UAE). The two events were widely felt in the northern Emirates and Oman and were accompanied by a few aftershocks. Ground motions from these events were well recorded by the broadband stations of Dubai (UAE) and Oman seismological networks and provide an excellent opportunity to study the tectonic process and present day stress field acting in this area. In this study, we report the focal mechanisms of the two main shocks by two methods: first motion polarities and regional waveform moment tensor inversion. Our results indicate nearly pure normal faulting mechanisms with a slight strike slip component. We associated the fault plane trending NNE–SSW with a suggested fault along the extension of the faults bounded Bani Hamid area. The seismicity distribution between two earthquake sequences reveals a noticeable gap that may be a site of a future event. The source parameters (seismic moment, moment magnitude, fault radius, stress drop and displacement across the fault) were also estimated from displacement spectra. The moment magnitudes were very consistent with waveform inversion. The recent deployment of seismic networks in Dubai and Oman reveals tectonic activity in the northern Oman Mountains that was previously unknown. Continued observation and analysis will allow for characterization of seismicity and assessment of seismic hazard in the region.     

Determination of Phosphate in Saudi Arabian Waters

The procedures for the determination of phosphate are based on the reduction of molybdophosphoric heteropoly acids using ascorbic acid. Measurements of the complex products formed with rhodamine B and chlorophenol red dyes and the reduced molybdophosphoric acid are made at 490 and 510 nm with molar absorptivities of 28571 and 20949 l/mol. cm with each dye, respectively. Phosphate could be determined in the concentration ranges of 0.44 to 1.21 and 0.44 to 1.32 μg/l PO₄-P with rhodamine B and chlorophenol red dyes, respectively. The results obtained are compared with those of molybdophosphoric acid with rhodamine B and chlorophenol red using stannous chloride as reducing agent. These procedures are used for the determination of phosphate in the Kingdom of Saudi Arabia.     

The distribution and growth of urban settlements in Saudi Arabia

This paper examines the distribution characteristics of urban settlements in the Kingdom of Saudi Arabia through major dimensions such as settlement regularly, degree of primacy and polarisation at the national and geographic regional levels. The paper points out that the settlement pattern at the national level has transformed from a primate distribution during the pre-plan period (< 1970) to an intermediary distribution during the period of development planning (1970 >). At the geographical regional level the settlement distribution, however, has shown diverse pattern. While the regional settlement distribution of Western and Eastern Region have shown trends of increasing polarisation, settlements in the Northern and Southern Regions are more log-normal in character. This is explained by the increasing growth of small and intermediary towns in the Northern and Southern Regions. The paper concludes that the national trend of decreasing urban primacy, induced by the decentralised national development strategies, is less pronounced due to the absence of a balanced regional investment policy. Since the government expenditure and settlement population growth rates are not related, slow growing primate cities continue to receive a larger share of public expenditure, enabling them to retain their primacy. This calls for a balanced regional investment policy to fully realise the national strategy of regional balance and multi-polar settlement pattern.     

Isoprenoid alkanes with irregular “head-to-head” linkages

A lightly biodegraded crude oil from the Tolkinsk field (Upper Jurassic), situated in north-west Siberia, was found to contain a series of C₂₈–C₃₉ isoprenoid alkanes. Most of these components contain a pristane unit linked head-to-head with other isoprenoid units. The structures of these components were elucidated by mass spectral interpretations, comparisons with a synthesised standard and by reference to data published previously in the literature. These results extend the carbon number range, the variety of structural types, and the number of reported occurrences of these compounds in geological samples. These results provide further evidence for a contribution of bacterial cell-wall lipids to crude oils.     

Kinematics of the bottom of the Eurasia Basin near the Spitsbergen domain

Prior to extension of the lithosphere in the Eurasia Basin, the Yermak Plateau was an element of the Eurasian Arctic margin. Extension of the Barents Sea shelf culminated gradually in rifting of the continental crust with separation of this block from the continent during Chrons C25r?C26n (57.656?59.237 Ma ago) and emplacement of numerous basic dikes, which could be responsible for the formation of high-amplitude magnetic anomalies on the Yermak Plateau. The investigation included reconstruction of axes in the breakup zones along peripheral continental fragments of Spitsbergen with determination of the Euler poles and angles of rotation, which describe the kinematics of this process. It is revealed that the difference between depths of conjugate isobaths can be as large as many tens of meters, which reflects the nonuniformly scaled slide of peripheral areas of the continental crust along the plane of the crustal-penetrating fault and, correspondingly, their different subsidence during rifting.     

Ionized gas in the circumgalactic vicinity of the M81 galaxy group

The dynamics of the dust and gas in the tidal region of the M81 galaxy group have been analyzed, and the drift of the dust relative to the gas has been estimated, including the drift due to the action of radiation pressure from stars in M81. It is concluded that a large fraction of the gas in the tidal region is in the form of ionized hydrogen HII that shields the observedHI gas from the extragalactic Lyman continuum: the observed atomic gas could be only 10% of the total mass of gas. Only then it is possible to satisfactorily explain the excess dust abundance, which exceeds the Galactic value by a factor of six. By analogy, extended HI disks in galaxies with sizes appreciably larger than the stellar disks could be surrounded by HII envelopes with a comparable or greater mass. Such disks could play an important role in supporting prolonged star formation in galaxies with extended HI disks. Associated observational manifestations are discussed. Such HII envelopes outside HI disks could be detectable in absorption in Ly α and lines of ions of heavy elements.     

Transtension of the Romanche transform fault

Areas of transtension are discovered in the western part of the Romanche transform fault. Geodynamical parameters of the transtension are calculated on the basis of three-dimensional modeling of the inversive magnetic layer using survey data. The interval spreading rates calculated on this basis appeared to be smaller (1.65 cm/y for paleoanomalies C1-C5E on the northern side of the fault and 1.56 cm/y for paleoanomalies C6–C24 on the southern side) than those derived from the theoretical concepts based on the NUVEL-1 and NUVEL-1A models.