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51.
The lithospheric structure of the Sinai Peninsula is shown by means of nine shear velocity profiles for depths ranging from
zero to 50 km, determined from the Rayleigh wave analysis. The traces of 30 earthquakes, which occurred from 1992 to 1999
in and around the study area, have been used to obtain Rayleigh wave dispersion. These earthquakes were registered by a broadband
station located in Egypt (KEG station). The dispersion curves were obtained for periods between 3 and 40 s, by digital filtering
with a combination of MFT and TVF filtering techniques. After that, all seismic events were grouped in source zones to obtain
a dispersion curve for each source-station path. These dispersion curves were inverted according to generalized inversion
theory, to obtain shear wave velocity models for each source-station path, which is the main goal of this study. The shear
velocity structure obtained for the Sinai Peninsula is shown through the shear velocity distributions with depth. These results
agree well with the geology and other geophysical results, previously obtained from seismic and gravity data. The obtained
velocity models suggest the existence of lateral and vertical heterogeneity. The shear velocity increases generally with depth
for all paths analyzed in the study area. Nevertheless, in some paths a small low velocity channel in the upper or lower crust
occurs. Along these profiles, it is found that the crustal structure of the Sinai Peninsula consists of three principal layers:
upper crust with a sedimentary layer and lower crust. The upper crust has a sedimentary cover of 2 km thick with an average
S-velocity of 2.53 km/s. This upper crust has a variable thickness ranging from 12 to 18 km, with S-wave velocity ranging
from 3.24 to 3.69 km/s. The Moho discontinuity is located at a depth of 30 km, which is reflected by a sharp increase in the
S-velocity values that jump from 3.70–4.12 to 4.33–4.61 km/s. 相似文献
52.
Source mechanisms of the June 2004 Tabuk earthquake sequence, Eastern Red Sea margin, Kingdom of Saudi Arabia 总被引:1,自引:0,他引:1
K. S. Aldamegh K. M. Abou Elenean H. M. Hussein A. J. Rodgers 《Journal of Seismology》2009,13(4):561-576
A sequence of earthquakes took place in June 2004 approximately 60 km southeast of Tabuk, Saudi Arabia. The first felt event
(M
W = 3.9) occurred on June 9 and caused minor damage in the epicentral area according to the National Earthquake Information
Center and the local reports. Another moderate size event occurred on June 22 (M
W = 5.1) and was followed by a few felt aftershocks without any reported damage. This earthquake sequence caused considerable
alarm at Tabuk and highlights the fact that damaging earthquakes can occur in this region away from the major plate boundary
in the Red Sea. Being the largest well-recorded event in the area for which the digital and broadband records from Saudi Arabia,
Egypt, Israel, Jordan, Turkey, Cyprus, and Kuwait are available, it provides an excellent opportunity to study the tectonic
process and present day stress field acting on this area. The digital records from these regional networks were used to relocate
the largest three events of this sequence. Focal mechanisms were obtained from full waveform inversion and indicate normal
faulting mechanisms with two nodal planes oriented NW–SE in parallel to the faults bounding the Tabuk graben and the Red Sea
rift axis. These events originated at shallow focal depths of 4–5 km, possibly contributing to the widely felt ground motions.
These events offer a unique opportunity to study the active tectonics of the region as well as inform future studies of seismic
hazard in northwestern Saudi Arabia, the Gulf of Aqaba, and eastern Egypt. 相似文献
53.
Hussein R. Sayani Kim M. Cobb W. Crawford Elliott Robert B. Dunbar Laura K. Zaunbrecher 《Geochimica et cosmochimica acta》2011,75(21):6361-6373
The integrity of coral-based reconstructions of past climate variability depends on a comprehensive knowledge of the effects of post-depositional alteration on coral skeletal geochemistry. Here we combine millimeter-scale and micro-scale coral Sr/Ca data, scanning electron microscopy (SEM) images, and X-ray diffraction with previously published δ18O records to investigate the effects of submarine and subaerial diagenesis on paleoclimate reconstructions in modern and young sub-fossil corals from the central tropical Pacific. In a 40-year-old modern coral, we find secondary aragonite is associated with relatively high coral δ18O and Sr/Ca, equivalent to sea-surface temperature (SST) artifacts as large as −3 and −5 °C, respectively. Secondary aragonite observed in a 350-year-old fossil coral is associated with relatively high δ18O and Sr/Ca, resulting in apparent paleo-SST offsets of up to −2 and −4 °C, respectively. Secondary Ion Mass Spectrometry (SIMS) analyses of secondary aragonite yield Sr/Ca ratios ranging from 10.78 to 12.39 mmol/mol, significantly higher compared to 9.15 ± 0.37 mmol/mol measured in more pristine sections of the same fossil coral. Widespread dissolution and secondary calcite observed in a 750-year-old fossil coral is associated with relatively low δ18O and Sr/Ca. SIMS Sr/Ca measurements of the secondary calcite (1.96-9.74 mmol/mol) are significantly lower and more variable than Sr/Ca values from more pristine portions of the same fossil coral (8.22 ± 0.13 mmol/mol). Our results indicate that while diagenesis has a much larger impact on Sr/Ca-based paleoclimate reconstructions than δ18O-based reconstructions at our site, SIMS analyses of relatively pristine skeletal elements in an altered coral may provide robust estimates of Sr/Ca which can be used to derive paleo-SSTs. 相似文献
54.
Two felt moderate-sized earthquakes with local magnitudes of 4.9 on October 11, 1999 and 4.3 on November 08, 2006 occurred
southeast of Beni Suef and Cairo cities. Being well recorded by the digital Egyptian National Seismic Network (ENSN) and some
regional broadband stations, they provided us with a unique opportunity to study the tectonic process and present-day stress
field acting on the northern part of the Eastern Desert of Egypt. In this study, we analyze the main shocks of these earthquakes
and present 15 well recorded aftershocks (0.9 ≤ ML ≤ 3.3) which have small errors on both horizontal and vertical axes. The
relocation analysis using the double difference algorithm clearly reveals a NW trending fault for the 1999 earthquake. The
spatial distribution of its aftershocks indicates a propagation of rupture from the SW towards the NW along a fault length
~5 km dipping nearly ~40°SW. We also determined the focal mechanisms of the two main shocks by two methods (polarities and
amplitudes ratios of P, SV and SH and regional waveform inversion). Our results indicate a normal faulting mechanism with a slight shear component for the
first event, while pure normal faulting for the second one. The spatial distribution of the 1999 aftershocks sequence along
with the retrieved focal mechanism confirmed the NW plane as the true fault plane. While for the 2006 event, the few aftershocks
do not reveal any fault geometry; its focal mechanism indicated a pure normal fault nearly trending WNW-ESE that corresponds
more likely to the extension of the 1999 earthquake fault. The seismicity distribution between the two earthquake sequences
reveals a noticeable gap that may be a site of a future event. The NNE-SSW extensional stress indicated by the mechanisms
of these events is in agreement with the regional stress field and the rifting of the northern Red Sea in its northern branches
(Gulf of Suez and Gulf of Aqaba). The source parameters (seismic moment, moment magnitude, fault radius, stress drop and displacement
across the fault) were also estimated and compared based on both the regional waveform inversion and the displacement spectra
and interpreted in the context of the tectonic setting. The obtained results imply a reactivation of the pre-exiting NW-SE
faults as a result of extensional deformation from the northern Red Sea-Gulf of Suez rifts. 相似文献
55.
Another look at the 1993 and 1995 Gulf of Aqaba earthquakes from the analysis of teleseismic waveforms 总被引:3,自引:0,他引:3
In this work we estimated the source process and the source parameters of the 1993 and 1995 Gulf of Aqaba earthquakes. To
investigate the source process of both events, we inverted the teleseismic P- and SH-waveform data using an iterative technique in which the rupture is modeled as a series of point source subevents with varying
mechanisms. The main source process of the 1993 event can be explained by two subevents with essentially the same mechanism.
These two subevents had different focal depths. The second subevent was about 5 s later than the first one and about 70% of
the moment rate released with the second one. The total rupture duration time was about 12 s. Our solution for the 1995 Gulf
of Aqaba earthquake indicated that the event consists of three subevents with various fault geometries and about 60% of the
moment released by the second subevent. The first subevent occurred at a depth of 13 km, and was followed after 9 s by the
second one at a depth of 11 km; the third subevent, at a depth of 9 km occurred 19 s after the second one. The total duration
of the earthquake rupture process was about 18.7 s. The obtained mechanisms for the 1993 and 1995 Gulf of Aqaba earthquakes
are well correlated with the structural setting of the Gulf of Aqaba. 相似文献
56.
In this paper we study shape-preserving formations of three spacecraft, where the formation keeping forces arise from the electric charges deposed on each craft. Inspired by Lagrange’s 3-body problem, the general conditions that guarantee preservation of the geometric shape of the electrically charged formation are derived. While the classical collinear configuration is a solution to the problem, the equilateral triangle configuration is found to only occur with unbounded relative motion. The three collinear spacecraft problem is analyzed and the possible solutions are categorized based on the spacecraft mass–charge ratio. Precise statements on the number of solutions associated with each category are provided. Finally, a methodology is proposed to study boundedness of the collinear solution that is inspired by past understanding and results for the 3-body problem. Given the initial position and the velocity vectors of each craft along with the charges, analytical solutions are provided describing the resulting relative motion. 相似文献
57.
Majdi Al-Mahasneh Mohamad Al-Widyan Hussein Ababneh Taha Rababah Khalil Ereifej 《Natural Resources Research》2008,17(1):13-20
Grain dust is a by-product produced in large quantities from grain storage and milling facilities but as of yet is treated
as waste locally and regionally. Based on the conviction that material properties determination is a necessary first step
for the efficient handling, processing, and use of materials, this work was initiated with the purpose of characterizing grain
dust in terms of its physicochemical and thermal properties.
Grain dust as a special waste material is a complex, dry, grey powder, composed mainly of grain chips, soil, whole wheat and
barley seeds, and straw. The material was found to have a bulk density of 362 kg/m3, specific heat, thermal conductivity, and gross calorific value were 1540 J/kg K, 0.27 W/m K, and 4120 kJ/kg, respectively.
Nutritional composition showed low concentrations of protein, and ether extract, and high concentrations of carbohydrates,
ash, and crude fiber. Mineral analysis showed that Ca, Fe, and K were available in significant amounts ranging from 30 to
135 ppm.
The as-received material is dry enough to be stored very safely and burned for energy production in either its loose form
or as pellets. Moreover, adjustments to the ash content and C:N ratio of the material deems it a promising candidate as an
animal feed and as a substrate for composting and biogasification. 相似文献
58.
Faisal Rehman Abdullah M. Alamri Sherif M. El-Hady Hussein M. Harbi Ali H. Atef 《Arabian Journal of Geosciences》2017,10(24):540
A probabilistic approach is used to evaluate the seismic hazard for 12 strategic cities in Saudi Arabia along the eastern coast of Red Sea. The focal depth variations controlled by rheological characteristics are taken into account for hazard calculations, and its creditability is tested through sensitivity analysis for hazard results. This study presents a neo-probabilistic seismic hazard assessment methodology in which the focal depth distribution of earthquakes within seismogenic layer is divided into three depth slices. These depth slices are based upon rheological characteristic of seismogenic layer. The hazard results are obtained using this depth-slice methodology and conventional approach in which uniform distribution of seismicity within seismogenic layer is assumed. The sensitivity analysis culminated in underestimation of hazard values in higher frequencies for uniform distribution of seismicity within seismogenic layer. Foregoing the observations recorded above, it can be concluded that the exploitation of depth-slices biased by the rheology to calculate hazard is relatively preferable in the situations demanding safety measures. 相似文献
59.
Mansour S. Alhumimidi Hussein M. Harbi Mohammed S. Alfarhan Kamal Abdelrahman Carlos L.V. Aiken 《Arabian Journal of Geosciences》2017,10(14):306
Khuff Formation is of utmost importance in Saudi Arabia for oil and gas reservoir although it is composed mainly of limestone. This reason refers to the existence of intensive fractures which play a vital role in the increase in porosity and permeability of this formation. The fracture pattern in the study area was verified through 2D and 3D ground penetrating radar (GPR)-defined and electrical resistivity tomography (ERT)-defined surveys. In this respect, ten of 2D GPR surveys were collected along an intersected grid of profiles covering the study area while ERT data were collected along three profiles of the GPR grid. The results were interpreted in light of the field-based structural and stratigraphic assessment of the outcropping rocks. The analysis of the inverted ERT and filtered GPR sections revealed the presence of fractures. Several resistivity and electromagnetic reflection anomalies were laterally and vertically identified across the measured sections clarifying fractures that extend to a depth of 24 m in the limestone. Most fractures are oriented vertical to sub-vertical dipping both east-west and north-south. 相似文献
60.
The groundwater reserves in Kharga Oases have been studied for the long-term socioeconomic development in the area. The Nubian Sandstone, which consists of a thick sequence of coarse clastic sediments of sandstone, sandy clay interbedded with shale, and clay beds, forms a complex aquifer system. The Nubian Aquifer has been providing water to artesian wells and springs in the Kharga Oases for several thousand years. Groundwater in the Kharga Oases is withdrawn from springs and shallow and deep artesian wells Nearly all the wells originally flowed, but with the exploitation of ground-water from deep wells for irrigation beginning about 1959. the natural flows declined as more and more closely spaced deep wells were drilled By 1975 many deep wells had ceased to flow The water demand in the area has been met by pumping both shallow and deep wells The total annual extraction from deep wells has fluctuated over the year, however, the annual withdrawal from deep wells has exceeded extraction from shallow wells About 17 billion m3 of water was withdrawn from the combination of shallow and deep wells during the period 1960–1980 The Nubian complex aquifer in the Kharga Oases has a very large groundwater potential that could be exploited and beneficially used for a long-term agricultural development in the area, provided proper well spacing and management are implemented Other major environmental considerations for which precise hydrogeologic data are needed include
- Determination of the long-term yield available from properly constructed and producing artesian wells that will support a planned migration of population from the overcrowded Nile delta and flood plain areas
- Development of an effective management program and adequate staff to maintain groundwater production over an extended period of years
- The impact on climate caused by extensive irrigation in the oases of the Western Desert of Egypt
- Protection against water logging of soils from irrigation practices
- Protection against salinization of soils from irrigation practices
- Development of effective surface and subsurface drainage practices
- The impact of farming and pest control practices on the shallow groundwater of the oases
- Determination of the long-term development of the artesian water on the quality of the water from the aquiter systems in the Western Desert