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61.
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
62.
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
63.
Hussein A. Abd-Elmotaal 《Studia Geophysica et Geodaetica》2017,61(4):657-674
The aim of this paper is to investigate the effect of implementing the experimentally determined GEMMA Moho depths (GOCE Exploitation for Moho Modeling and Applications), which are partly seismically estimated, in gravimetric geoid computation in Egypt. The window remove-restore technique has been proposed to avoid the double consideration of the topographic-isostatic masses in the neighbourhood of the computational point. The plate loading theory has been used to model the seismically determined Moho depths. A constant density contrast between the lower crust and the upper mantle has been postulated. The tailored geopotential model EGTGM2014 has been used for the long wavelength contributions of the Earth’s gravity field. A comparison with a geoid computed using the EGM2008 and Airy floating hypothesis has been made. For all cases, a gravimetric geoid for Egypt has been computed using Stokes’ integral in the frequency domain by 1-D FFT technique. The computed geoids are fitted to the GPS-levelling derived geoid using an optimum geoid fitting technique for Egypt introduced by the author. The results show that using the seismically determined Moho depths within the plate loading theory and the EGTGM2014 tailored geopotential model gives a geoid with external accuracy of about 16 cm. 相似文献
64.
Khalid S. Aldamegh Hesham Hussein Moussa S. Nasser Al-Arifi Sayed S. R. Moustafa Moustafa Hemeda Moustafa 《Arabian Journal of Geosciences》2012,5(4):599-606
Focal mechanism solution of the 27th August 2009 earthquake (mb?=?4.0) that occurred in the Badr area, northwest of Saudi Arabia, approximately 50?km from the Red Sea has been determined from the P-wave first motion polarities. Results show normal faulting mechanism with a negligible component of strike-slip motion with NE T-axis direction. This type of mechanism is common with other earthquakes of the northwestern Saudi Arabia and is considered to present the tectonic movement of the region. The dominantly extensional tectonic regime in this province demonstrates the influence of NE extension in the Red Sea. The strikes of the solution are consistent with those of the main faults near the epicenter. Hypocentral location of this earthquake was carried out using the data from the King Abdulaziz City of Science and Technology Seismic Network, Saudi Arabia, and the Egyptian National Seismological Network, Egypt. The horizontal and vertical confidence estimates are 0.5?km for both. The local magnitude, M L, following the Richter??s original definition was also derived from ten digital three-component broadband seismograms. The average local magnitude determined in this study is 3.8?±?0.17. The estimated seismic moment of this event is $ {3}.{\hbox{7e}} + {14}\,{\hbox{Nm}}\left( {{M_{\rm{W}}} = {3}.{66}\pm 0.0{7}} \right) $ . 相似文献
65.
Snehamoy Chatterjee Roussos Dimitrakopoulos Hussein Mustapha 《Mathematical Geosciences》2012,44(3):343-374
A pattern-based simulation technique using wavelet analysis is proposed for the simulation (wavesim) of categorical and continuous variables. Patterns are extracted by scanning a training image with a template and then storing
them in a pattern database. The dimension reduction of patterns in the pattern database is performed by wavelet decomposition
at certain scale and the approximate sub-band is used for pattern database classification. The pattern database classification
is performed by the k-means clustering algorithm and classes are represented by a class prototype. For the simulation of categorical variables,
the conditional cumulative density function (ccdf) for each class is generated based on the frequency of the individual categories at the central node of the template. During
the simulation process, the similarity of the conditioning data event with the class prototypes is measured using the L
2-norm. When simulating categorical variables, the ccdf of the best matched class is used to draw a pattern from a class. When continuous variables are simulated, a random pattern
is drawn from the best matched class. Several examples of conditional and unconditional simulation with two- and three- dimensional
data sets show that the spatial continuity of geometric features and shapes is well reproduced. A comparative study with the
filtersim algorithm shows that the wavesim performs better than filtersim in all examples. A full-field case study at the Olympic Dam base metals deposit, South Australia, simulates the lithological
rock-type units as categorical variables. Results show that the proportions of various rock-type units in the hard data are
well reproduced when similar to those in the training image; when rock-type proportions between the training image and hard
data differ, the results show a compromise between the two. 相似文献
66.
67.
68.
Alaa I. Ibrahim William C. Parke Jean H. Swank Hisham Anwer Roberto Turolla Silvia Zane M. T. Hussein T. El-Sherbini 《Astrophysics and Space Science》2007,308(1-4):43-50
The defining property of Soft Gamma Repeaters is the emission of short, bright bursts of X-rays and soft γ-rays. Here we present the continuum and line spectral properties of a large sample of bursts from SGR 1806-20, observed with
the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE). Using 10 trail spectral models (5 single
and 5 two component models), we find that the burst continua are best fitted by the single component models: cutoff power-law,
optically thin bremsstrahlung, and simple power-law. Time resolved spectroscopy show that there are two absorption lines at
∼5 keV and 20 keV in some bursts. The lines are relatively narrow with 90% upper limit on the line widths of 0.5–1.5 keV for
the 5 keV feature and 1–3 keV for the 20 keV feature. Both lines have considerable equivalent width of 330–850 eV for the
5 keV feature and 780–2590 eV for the 20 keV feature. We examined whether theses spectral lines are dependent upon the choice
of a particular continuum model and find no such dependence. Besides, we find that the 5 keV feature is pronounced with high
confidence in the cumulative joint spectrum of the entire burst sample, both in the individual detectors of the PCA and in
the co-added detectors spectrum. We confront the features against possible instrumental effects and find that none can account
for the observed line properties. The two features do not seem to be connected to the same physical mechanism because (1)
they do not always occur simultaneously, (2) while the 5 keV feature occurs at about the same energy, the 20 keV line centroid
varies significantly from burst to burst over the range 18–22 keV, and (3) the centroid of the lines shows anti-correlated
red/blue shifts. The transient appearance of the features in the individual bursts and in portions of the same burst, together
with the spectral evolution seen in some bursts point to a complex emission mechanism that requires further investigation.
相似文献
69.
70.
This paper presents a three‐dimensional finite element analysis of the response of battered piles to the combined lateral and vertical pullout loads. Analyses are carried out using an elastoplastic constitutive law based on the non‐associated Mohr–Coulomb criterion. The influence of the contact condition at the pile–soil interface is also investigated. Analyses show that the load's inclination with regard to the pile's axis affects both the lateral and axial response of the battered piles. Analyses also show that the pullout capacity of battered piles is affected by the pile's inclination regarding the vertical axis as well as the load's inclination regarding the pile's axis. The investigation of the influence of the contact condition at the soil–pile interface shows that the possibility of sliding at the soil–pile interface affects the response of battered piles subjected to loads with low inclination regarding the pile's axis. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献