The earthquake activity and the state of stress in and around Egypt will provide an opportunity t... more The earthquake activity and the state of stress in and around Egypt will provide an opportunity to evaluate the seismic hazard. The seismicity data were compiled from the Egyptian National Seismological Network database during the period from 2004 to 2011 in an attempt to identify the different seismic source regions. Thirteen seismic source regions have been identified in this study. The focal mechanisms for 36 earthquakes in and around Egypt are constructed for the same period using the waveform data recorded by the Egyptian National Seismological Network (ENSN) and the International Data Center (IDC) of the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO). These solutions are computed by joining P, S H , S V polarities and S V /P, S H /P and S V / S H amplitude ratios where the quality of each solution is evaluated. This set of solutions is considered as a completion of the Egyptian focal mechanism catalogue. It will be helpful in understanding the spatial variation in the stress field within Egypt. At northern Egypt, the dominated mechanisms reflect a normal dip-slip, sometimes with strike component except in Dahshour region where strike–slip mechanism dominates. Toward the south, in Aswan source region, the strike–slip mechanism is dominated reflecting that the local tectonics is important characterized by a major strike slip component. The orientations of the T axes appear to be changed from NE-SW in the Gulf of Suez to ENE-WSW in the Gulf of Aqaba and NNE-SSW in the remains of the Egyptian territory. It is clear that Egypt is mainly controlled by extensional stress field.
The Cairo earthquake (12 October 1992; m b = 5.8) is still and after 25 years one of the most pai... more The Cairo earthquake (12 October 1992; m b = 5.8) is still and after 25 years one of the most painful events and is dug into the Egyptians memory.
This work presents new seismological and Global Positioning System (GPS) results aimed at underst... more This work presents new seismological and Global Positioning System (GPS) results aimed at understanding the nature and rate of strain associated with the opening of the Suez rift that separates the Sinai sub-plate from the African plate. The Sinai sub-plate has played a significant role in the tectonic evolution of the northern Red Sea and the Eastern Mediterranean region. Most small, moderate and large earthquakes occur within belts associated with the geologically documented borders of this sub-plate including the Dead Sea fault (DSF) system in the east, the Cyprian arc (CA) in the north, and the Suez rift (SR) to the southwest. The DSF and CA are well defined; however, the SR is only partially defined. Earthquake foci distribution supports the idea that the SR is seismically active, and this earthquake activity cannot be ignored throughout the kinematics evaluation of northern Red Sea region. The earthquake activity is relatively higher in the southern part of the SR and gradually decreases northward. The high seismicity is mainly attributed to the presence of the Sinai triple junction. Earthquake focal mechanisms in the SR are dominated by oblique normal faulting with left-lateral strike-slip components on NW trending fault planes consistent with regional kinematics. The extensional semi-principal stress axes derived from fault plane solutions are oriented NNE-SSW in good agreement with the current stress field obtained from borehole breakouts along the SR as well as results from GPS surveying. Recent survey-mode GPS observations provide evidence for coherent northerly motion of the Sinai sub-plate that varies between 2 and 5 mm/yr. Moreover, strain analysis indicates that the southern SR is dominated by extension while its northern segment is characterized by constriction, inconsistent with earthquake focal mechanisms and regional tectonic models. The overall northward motion of the Sinai sub-plate indicates that slab-pull rather than ridge-push is the dominant force controlling regional kinematics. Based on the low rate of extension and lack of oceanic crust, the SR can be considered an incipient plate boundary between the Sinai sub-plate and the Nubian plate. K e y w o r d s : earthquakes, focal mechanisms, GPS, Sinai sub-plate, Suez rift
—In the present study, a digital waveform dataset of 216 local earthquakes recorded by the Egypti... more —In the present study, a digital waveform dataset of 216 local earthquakes recorded by the Egyptian National Seismic Network (ENSN) was used to estimate the attenuation of seismic wave energy in the greater Cairo region. The quality factor and the frequency dependence for Coda waves and S-waves were estimated and clarified. The Coda waves (Q c) and S-waves (Q d) quality factor were estimated by applying the single scattering model and Coda Normalization method, respectively, to bandpass-filtered seismo-grams of frequency bands centering at 1.5, 3, 6, 12, 18 and 24 Hz. Lapse time dependence was also studied for the area, with the Coda waves analyzed through four lapse time windows (10, 20, 30 and 40 s). The average quality factor as function of frequency is found to be Q c = 35 ± 9f 0.9±0.02 and Q d = 10 ± 2f 0.9±0.02 for Coda and S-waves, respectively. This behavior is usually correlated with the degree of tectonic complexity and the presence of heteroge-neities at several scales. The variation of Q c with frequency and lapse time shows that the lithosphere becomes more homogeneous with depth. In fact, by using the Coda Normalization method we obtained low Q d values as expected for a heterogeneous and active zone. The intrinsic quality factor (Q i-1) was separated from the scattering quality factor (Q s-1) by applying the Multiple Lapse Time Domain Window Analysis (MLTWA) method under the assumption of multiple isotropic scattering with uniform distribution of scatters. The obtained results suggest that the contribution of the intrinsic attenuation (Q i-1) prevails on the scattering atten-uation (Q s-1) at frequencies higher than 3 Hz.
On 29–30 September 1996, an earthquake sequence occurred in the Füzesgyarmat region in eastern Hu... more On 29–30 September 1996, an earthquake sequence occurred in the Füzesgyarmat region in eastern Hungary. The main shock had a magnitude of M L = 3.2 and was felt with a maximum intensity 4 MSK. It was preceded by a foreshock with a magnitude of M L = 2.8 and was followed, within six hours, by five aftershocks with magnitudes 2.1≤M L ≤ 3.1. The dynamic source parameters of the Füzesgyarmat earthquake sequence have been derived from P-wave spectra of the Hungarian seismograph stations. The average of the obtained values at different stations shows that the main shock occurred on a fault length of 610 m, with relative displacement of 1.13 cm, stress drop of 7 bar and seismic moment of 3.96*10 21 dyne.cm. The main shock was small to yield data for a full mechanism solution and no reliable single fault plane solution could be obtained due to the low signal to noise ratio at the recording stations. The parameters of the foreshock are fault length of 560m, seismic moment of 2.09*10 21 dyne.cm, stress drop of 5.53 bar and relative displacement of 0.73 cm. The five aftershocks show source parameters similar to the foreshock stress drops (5.26≤ σ ≤ 5.76 bar), fault lengths (415 ≤ L ≤ 600 m), seismic moments (8.36*10 20 ≤M o ≤ 2.31*10 21 dyne.cm) and relative displacements (0.52 ≤ û ≤ 0.91 cm).
Egypt is recognized as a moderate seismic-ity region where earthquakes are distributed within sev... more Egypt is recognized as a moderate seismic-ity region where earthquakes are distributed within several active regions. Owing to sparse distribution of both seismicity and seismic stations, mostly moderate size Egyptian earthquakes were recorded by regional stations. One of such cases is the moderate-size earthquakes of moment magnitudes greater than 4.0 which struck the Western Desert of Egypt in 1998 and 1999. These events are the first instrumentally recorded earthquakes occurring in the area. In the present study, the source mechanism for these earthquakes was estimated using the waveform data recorded from one of the very broadband MedNet seismograph stations and polarities from the national short-period seismographs. An iterative technique was applied to find the best-fit double-couple mechanism by a grid search over strike, dip and rake. Regional synthetic seismograms were calculated by using f–k integration in the frequency range of 0.03–0.1 Hz. A crustal structure fitted to surface wave dispersion curves was used to compute Green's function. Focal depths were determined through the grid search method for a range of source depths. Our results show a normal faulting mechanism with minor strike-slip component. The NNW trend has been chosen as a preferred rupture plane in consistence with surface and subsurface faults and microearthquake seismicity in the epicenteral area as well.
In this study we investigate present-day seismicity and crustal deformation of Egypt based on a c... more In this study we investigate present-day seismicity and crustal deformation of Egypt based on a comprehensive earthquake catalog from 1900 to 2004 by focal mechanism stress inversion and by recent GPS observations. Spatial distribution of earthquake epicenters indicates that Egypt has been suffered from both interplate and intraplate earthquakes. Most earthquake activity (more than 70%) has been concentrated in northern Egypt along the geologically documented borders of Sinai subplate (northern Red Sea and its two branches Suez rift and Aqaba–Dead Sea transform). The majority of inland earthquake focal mechanisms in Egypt are normal with strike-slip component or strike-slip faulting events. Only a small minority, namely four events, exhibits reverse faulting. The inversion method of Gephart and Forsyth (1984) was applied to calculate the orientation of the principle stress axes and the shape of the stress tensor. The best fitting tensor in Egypt shows homogeneity stress field. The tension stress regime is dominant in northern Egypt. The stress directions are well resolved by the 95% confidence limits, the relative stress magnitude has a value of about 0.3. However, along southern Egypt the strike-slip regime is dominant. The shape factor (R-value) is 0.5, which means that the deviatoric components of σ 1 and σ 3 are of the same magnitude, but of opposite signs. The average horizontal velocity of GPS stations in Egypt is 5.15 ± 1.1 mm/year in mostly NNW direction. The results of deformation analysis indicate that the northern Egypt is deformed more than the southern part. Only the Egyptian-Mediterranean coastal–Nile Delta zone dominates as a compression deformation area. However, an extensional deformation has been observed throughout the rest of country. This means that the relative motion of African plate with respect to both Eurasian and Arabian has highly controlled the deformation processes in Egypt.
The rupture process of a moderate earthquake (ML∼4.9) occurred southeast Beni-Suef, northern Egyp... more The rupture process of a moderate earthquake (ML∼4.9) occurred southeast Beni-Suef, northern Egypt was analyzed. The characterization of the rupture process and source properties were extracted from studying the relative moment rate function (RMRF). RMRFs were retrieved by deconvolution of small aftershock records using an inversion procedure for only P-wave part of the records. Although, this event is a moderate earthquake, its RMRFs exhibited complexity and directivity of the rupture behavior. The deconvolution pulses reflect three subevents or more. The detailed analysis of the distinct subevents revealed gross temporal and spatial characteristics of the rupture propagation. The azimuthal variation in the time delay of the subevents with respect to the initiation rupture indicates that the subevents are located at 0.85±0.17 and 3.5±0.07 km in directions of 320 • ±45 • and 330 • ±15 • with rupture velocities 3.4±0.45 and 4.0±0.7 km/sec, respectively. This means that the rupture is predominately propagated toward the North. Estimation of the rupture direction was combined with P-wave focal mechanism to identify the fault plane for the initial rupture of mainshock. Source parameters were calculated for each distinct subevent, including seismic moments 8.53E14 to 6.80E15 Nm, fault radii 713 to 1800 m and stress drops 0.725 to 2.932 MPa. The large estimated stress drop for the main subevent reflects failure asperity.
Africa displays a variety of continental margin structures, tectonics and sedimentary records. Th... more Africa displays a variety of continental margin structures, tectonics and sedimentary records. The northern Egyptian continental margin represents the NE portion of the North African passive continental margin. Economically, this region is of great importance as a very rich and productive hydrocarbon zone in Egypt. Moreover, it is characterized by remarkable tectonic setting accompanied by active tectonic processes from the old Tethys to recent Mediterranean. In this article, seismicity of the northern Egyptian continental margin has been re-evaluated for more than 100-years and the source parameters of three recent earthquakes (October 2012, January 2013 and July 2013) have been estimated. Moment tensor inversions of 19th October 2012 and 17th January 2013 earthquakes reveal normal faulting mechanism with strike–slip component having seismic moment of 3.5E16 N m and 4.3E15 N m respectively. The operation of the Egyptian National Seismic Network (ENSN) since the end of 1997 has significantly enhanced the old picture of earthquake activity across northern Egyptian continental margin whereas; the record-ability (annual rate) has changed from 2-events/year to 54-event/year before and after ENSN respectively. The spatial distribution of earthquakes foci indicated that the activity tends to cluster at three zones: Mediterranean Ridge (MR), Nile Cone (NC) and Eratosthenes Seamount (ERS). However, two seismic gaps are reported along Levant Basin (LEV) and Herodotus Basin (HER).
In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of ... more In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of M L 4.1 has occurred at southeast Beni-Suef, approximately 160 km SEE of Cairo, northern Egypt. The quake has been felt as far as Cairo and its surroundings while no casualties were reported. The instrumental epicentre is located at 28.57°N and 31.55°E. Seismic moment is 1.76 E14 Nm, corresponding to a moment magnitude M w 3.5. Following a Brune model, the source radius is 0.3 km with an average dislocation of 1.8 cm and a 2.4 MPa stress drop. The source mechanism from a first motion fault plane solution shows a left-lateral strike-slip mechanism with a minor dip-slip component along fault NNW striking at 161°, dipping 52° to the west and rake À5°. Trend and plunging of the maximum and minimum principle axes P/T are 125°, 28°, 21°, and 23°, respectively. A comparison with the mechanism of the October, 1999 event shows similarities in faulting type and orientation of nodal planes. Eight small earthquakes (3.0 6 M L < 5.0) were also recorded by the Egyptian National Seismological Network (ENSN) from the same region. We estimate the source parameters and fault mechanism solutions (FMS) for these earthquakes using displacement spectra and P-wave polarities, respectively. The obtained source parameters including seismic moments of 4.9 Â 10 12 –5.04 Â 10 15 Nm, stress drops of 0.2–4.9 MPa and relative displacement of 0.1–9.1 cm. The azimuths of Taxes determined from FMS are oriented in NNE– SSW direction. This direction is consistent with the present-day stress field in Egypt and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS measurements.
On 11 October 1999, a moderate earthquake of local magnitude ML 4.9 hit northern Egypt. This even... more On 11 October 1999, a moderate earthquake of local magnitude ML 4.9 hit northern Egypt. This event shook the greater Cairo region and northern part of the Nile valley and was felt in much of northern Egypt with epicentral intensity of V (EMS). It was followed by eight aftershocks with local magnitude ranging from 1.6 to 3.2. A detailed analysis of this sequence, cross-correlation analysis, fault plane solutions and source parameter estimations is performed in the present article. A cross-correlation analysis allowed us to recognize a number of correlated events, which were used for earthquake ancestry using a master event technique. The focal mechanism solutions for the main-shock and the largest aftershock are moderately controlled and indicate strike-slip faulting with a dip-slip normal component. Rupture directivity, after-shock distributions and isoseismal lines were combined in an attempt to determine which of the two nodal planes is the fault plane. The dynamic source parameters of the southeast Beni-Suef earthquake sequence have been estimated from the P-wave spectra of the Egyptian National Seismograph Network (ENSN). The spectral amplitude of the main shock records displayed two distinct corner frequencies that reflect a complex rupture process. The averaging of the obtained values at different stations shows that the main shock occurred on a fault length of 1.5 km with relative displacement 9 cm, stress drop of 49 bar and seismic moment of 5Â10 22 dyn/cm. The aftershocks show a relatively similar source parameters fault length of 0.34L40.6 km, relative displacement of 0.054u40.2 cm, seismic moment of 2.3Â 10 19 4M 0 41.1Â10 20 dyn.cm and stress drop of 0.74Á44 bar. #
Although the precise boundaries and kinematics of the Sinai subplate are still doubtful\ it has a... more Although the precise boundaries and kinematics of the Sinai subplate are still doubtful\ it has a signi_cant role in the tectonic evolution of the northern Red Sea region[ On the basis of earthquake distribution\ the Sinai region can be considered as a subplate partially separated from the African plate by the Suez rift[ The relative motion between Africa\ Sinai and Arabia is the main source generating the present!day earthquake activity in the Gulf of Suez and the Gulf of Aqaba regions[ According to geological observations\ the southern segment of the Dead Sea fault system can be char! acterized by a left!lateral displacement of about 096 km since the Middle Miocene\ in contrast to the northern segment where only 14 to 24 km o}set can be inferred[ We think that along the southern segment the total displacement was 61 km until the late Miocene "09 Ma#[ The earthquake activity is strongly reduced along the northern segment of the Dead Sea fault system[ Therefore\ we suggest that the northern part "Yammouneh fault# evolves through initial cracking of the crust due to build!up of stress since the Pliocene time "4 Ma# and propagates northward into Lebanon and Syria[ This last 4 million years is the period when the southern and northern segments became linked and formed a single fault system with a new displacement of 24 km[ According to the proposed model the predicted opening pole of the Red Sea is near 23[9>N\ 11[9>E with an angle of total rotation of 2[3> since the early Miocene\ providing a 9[71 cm:a opening rate in the northern Red Sea[ We suggest that the Dead Sea strike!slip fault was active since Middle Miocene time "04 Ma# with a slip rate of 9[61 cm:a to provide a total displacement of about 096 km[ This strike!slip motion occurred about an Euler pole near 22[9>N\ 10[9>E with a rotation angle of 2[9>[ It can be inferred from the proximity of the pole and angle of rotations for the Red Sea and Dead Sea fault that more than 74) of the motion has been accommodated on the Gulf of Aqaba and the Dead Sea fault and less than 04) in the Gulf of Suez[ This model predicts a normal extensional motion in the Gulf of Suez with a minor left!lateral strike!slip component[ We expect the pole of this motion to be at 20[9>N\ 18[9>E\ o}shore of Alamein city about 219 km west of the Nile Delta[ The rate of motion through the last 04 Ma "Middle Miocene# is about 9[0 cm:a and the angle of rotation is 9[8>[ During this period the total opening of the Suez rift is 04 km\ while the rest
Based on historical and instrumental seismicity as well as recent GPS measurements, the seismicit... more Based on historical and instrumental seismicity as well as recent GPS measurements, the seismicity and kinematic evaluation of middle Egypt is presented. Middle Egypt suffered in historical times by six major earthquakes and the Ramses II temple on the west bank of the Nile in Luxor, was almost destroyed by an ancient event. The temporal distribution of recent earthquakes (1900–1997) is highly scattered with only nine events recorded. Only after the installation of the modern Egyptian national seismograph network (ENSN) the seismic record of middle Egypt increased with a total of 280 earthquakes from 1998 to 2004. Focal mechanism solutions of the largest five events during the ENSN's operation period reveal reverse faulting mechanism with minor strike-slip component on the west bank of the Nile, while a normal faulting mechanism dominate in the eastern side. The orientations of both P-and Taxes are consistent with the Red Sea-Gulf of Suez stress field. Dynamic source parameters of these five events were derived from P-wave spectra as well. Three campaigns of GPS measurements were carried out for the middle Egypt network that established after the first instrumental earthquake on 14 December 1998 in this area. The velocity vectors for each epoch of observations were calculated and deformation analysis was performed. The horizontal velocity varies between 1 and 4 mm/year across the network. The deformation pattern suggests significant contraction across the southeastern sector of the study area while, the northwestern part is characterized by an extension strain rates. High shear strain is observed along the epicenteral area of the M w = 4.0 June 2003 earthquake possibly reflecting the stress accumulation stage of a seismic cycle.
From January 1995 to December 1997, about 74 earthquakes were located in the Pannonian basin and ... more From January 1995 to December 1997, about 74 earthquakes were located in the Pannonian basin and digitally recorded by a recently established network of seismological stations in Hungary. On reviewing the notable events, about 12 earthquakes were reported as felt with maximum intensity varying between 4 and 6 MSK. The dynamic source parameters of these earthquakes have been derived from P-wave displacement spectra. The displacement source spectra obtained are characterised by relatively small values of corner frequency (f 0) ranging between 2.5 and 10 Hz. The seismic moments change from 1X48 Â 10 20 to 1X3 Â 10 23 dyne cm, stress drops from 0.25 to 76.75 bar, fault length from 0.42 to 1.7 km and relative displacement from 0.05 to 15.35 cm. The estimated source parameters suggest a good agreement with the scaling law for small earthquakes. The small values of stress drops in the studied earthquakes can be attributed to the low strength of crustal materials in the Pannonian basin. However, the values of stress drops are not dierent for earthquake with thrust or normal faulting focal mechanism solutions. It can be speculated that an increase of the seismic activity in the Pannonian basin can be predicted in the long run because extensional development ceased and structural inversion is in progress. Seismic hazard assessment is a delicate job due to the inadequate knowledge of the seismo-active faults, particularly in the interior part of the Pannonian basin. 7: S 0 2 6 4-3 7 0 7 (0 0) 0 0 0 2 0-X
The seismic activity of the Sinai subplate region on the basis of both historical "1199 B[C[Ð0899... more The seismic activity of the Sinai subplate region on the basis of both historical "1199 B[C[Ð0899 A[D[# and recent "0899Ð0884# earthquake catalogs have been evaluated[ Moderate and large earthquakes occurred mainly at the subplate boundaries\ Dead Sea Fault "DSF# system in the east\ Cyprean arc in the north\ and Suez rift in the southwest[ Along the Dead Sea Fault system the activity concentrated at the southern and central segments[ The earthquake distribution appears to have a tendency to cluster in time and space[ The swarms "February\ 0872^ April\ 0889^ August\ 0882 and November\ 0884# in the Gulf of Aqaba indicate that the southern segment of the Dead Sea Fault system is the most seismogenic through the last two decades[ North of the Dead Sea depression the seismic activity tends to have occurred with NW trend to extend under the Levantine Sea[ Although the northern segment of the Dead Sea Fault system is well de_ned from geological\ geophysical and historical earthquake activity recent seismic activity is practically absent especially north of Latitude 23>N[ In the eastern Mediterranean the seismicity is much higher in the area of the Hellenic arc than in the Cyprean arc[ Moreover\ the activity occurs in a wide belt suggesting that the plate boundary is a deformation zone instead of a single line[ The seismic activity in the Gulf of Suez is scattered and does not have any distinct trend[ However\ three active zones are delineated[ At the mouth of the gulf most of activity is concentrated where the Sinai triple junction "Africa\ Arabia\ Sinai# is situated[ The central part and the northern part of the gulf include the adjacent area as far as the river Nile[ Actually\ the activity is markedly decreased from south to north[ Although there is no seismological evidence that the Suez rift continues into the eastern Mediterranean\ the activity in the Gulf of Suez region cannot be ignored[ The parameters of magnitude!frequency relation "a\ b# indicate that the level of earthquake activity in the Sinai subplate region is generally moderate[ Moreover\ the energy release curve shows a regular trend and re~ects occasional high activity[ Þ
The earthquake activity and the state of stress in and around Egypt will provide an opportunity t... more The earthquake activity and the state of stress in and around Egypt will provide an opportunity to evaluate the seismic hazard. The seismicity data were compiled from the Egyptian National Seismological Network database during the period from 2004 to 2011 in an attempt to identify the different seismic source regions. Thirteen seismic source regions have been identified in this study. The focal mechanisms for 36 earthquakes in and around Egypt are constructed for the same period using the waveform data recorded by the Egyptian National Seismological Network (ENSN) and the International Data Center (IDC) of the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO). These solutions are computed by joining P, S H , S V polarities and S V /P, S H /P and S V / S H amplitude ratios where the quality of each solution is evaluated. This set of solutions is considered as a completion of the Egyptian focal mechanism catalogue. It will be helpful in understanding the spatial variation in the stress field within Egypt. At northern Egypt, the dominated mechanisms reflect a normal dip-slip, sometimes with strike component except in Dahshour region where strike–slip mechanism dominates. Toward the south, in Aswan source region, the strike–slip mechanism is dominated reflecting that the local tectonics is important characterized by a major strike slip component. The orientations of the T axes appear to be changed from NE-SW in the Gulf of Suez to ENE-WSW in the Gulf of Aqaba and NNE-SSW in the remains of the Egyptian territory. It is clear that Egypt is mainly controlled by extensional stress field.
The Cairo earthquake (12 October 1992; m b = 5.8) is still and after 25 years one of the most pai... more The Cairo earthquake (12 October 1992; m b = 5.8) is still and after 25 years one of the most painful events and is dug into the Egyptians memory.
This work presents new seismological and Global Positioning System (GPS) results aimed at underst... more This work presents new seismological and Global Positioning System (GPS) results aimed at understanding the nature and rate of strain associated with the opening of the Suez rift that separates the Sinai sub-plate from the African plate. The Sinai sub-plate has played a significant role in the tectonic evolution of the northern Red Sea and the Eastern Mediterranean region. Most small, moderate and large earthquakes occur within belts associated with the geologically documented borders of this sub-plate including the Dead Sea fault (DSF) system in the east, the Cyprian arc (CA) in the north, and the Suez rift (SR) to the southwest. The DSF and CA are well defined; however, the SR is only partially defined. Earthquake foci distribution supports the idea that the SR is seismically active, and this earthquake activity cannot be ignored throughout the kinematics evaluation of northern Red Sea region. The earthquake activity is relatively higher in the southern part of the SR and gradually decreases northward. The high seismicity is mainly attributed to the presence of the Sinai triple junction. Earthquake focal mechanisms in the SR are dominated by oblique normal faulting with left-lateral strike-slip components on NW trending fault planes consistent with regional kinematics. The extensional semi-principal stress axes derived from fault plane solutions are oriented NNE-SSW in good agreement with the current stress field obtained from borehole breakouts along the SR as well as results from GPS surveying. Recent survey-mode GPS observations provide evidence for coherent northerly motion of the Sinai sub-plate that varies between 2 and 5 mm/yr. Moreover, strain analysis indicates that the southern SR is dominated by extension while its northern segment is characterized by constriction, inconsistent with earthquake focal mechanisms and regional tectonic models. The overall northward motion of the Sinai sub-plate indicates that slab-pull rather than ridge-push is the dominant force controlling regional kinematics. Based on the low rate of extension and lack of oceanic crust, the SR can be considered an incipient plate boundary between the Sinai sub-plate and the Nubian plate. K e y w o r d s : earthquakes, focal mechanisms, GPS, Sinai sub-plate, Suez rift
—In the present study, a digital waveform dataset of 216 local earthquakes recorded by the Egypti... more —In the present study, a digital waveform dataset of 216 local earthquakes recorded by the Egyptian National Seismic Network (ENSN) was used to estimate the attenuation of seismic wave energy in the greater Cairo region. The quality factor and the frequency dependence for Coda waves and S-waves were estimated and clarified. The Coda waves (Q c) and S-waves (Q d) quality factor were estimated by applying the single scattering model and Coda Normalization method, respectively, to bandpass-filtered seismo-grams of frequency bands centering at 1.5, 3, 6, 12, 18 and 24 Hz. Lapse time dependence was also studied for the area, with the Coda waves analyzed through four lapse time windows (10, 20, 30 and 40 s). The average quality factor as function of frequency is found to be Q c = 35 ± 9f 0.9±0.02 and Q d = 10 ± 2f 0.9±0.02 for Coda and S-waves, respectively. This behavior is usually correlated with the degree of tectonic complexity and the presence of heteroge-neities at several scales. The variation of Q c with frequency and lapse time shows that the lithosphere becomes more homogeneous with depth. In fact, by using the Coda Normalization method we obtained low Q d values as expected for a heterogeneous and active zone. The intrinsic quality factor (Q i-1) was separated from the scattering quality factor (Q s-1) by applying the Multiple Lapse Time Domain Window Analysis (MLTWA) method under the assumption of multiple isotropic scattering with uniform distribution of scatters. The obtained results suggest that the contribution of the intrinsic attenuation (Q i-1) prevails on the scattering atten-uation (Q s-1) at frequencies higher than 3 Hz.
On 29–30 September 1996, an earthquake sequence occurred in the Füzesgyarmat region in eastern Hu... more On 29–30 September 1996, an earthquake sequence occurred in the Füzesgyarmat region in eastern Hungary. The main shock had a magnitude of M L = 3.2 and was felt with a maximum intensity 4 MSK. It was preceded by a foreshock with a magnitude of M L = 2.8 and was followed, within six hours, by five aftershocks with magnitudes 2.1≤M L ≤ 3.1. The dynamic source parameters of the Füzesgyarmat earthquake sequence have been derived from P-wave spectra of the Hungarian seismograph stations. The average of the obtained values at different stations shows that the main shock occurred on a fault length of 610 m, with relative displacement of 1.13 cm, stress drop of 7 bar and seismic moment of 3.96*10 21 dyne.cm. The main shock was small to yield data for a full mechanism solution and no reliable single fault plane solution could be obtained due to the low signal to noise ratio at the recording stations. The parameters of the foreshock are fault length of 560m, seismic moment of 2.09*10 21 dyne.cm, stress drop of 5.53 bar and relative displacement of 0.73 cm. The five aftershocks show source parameters similar to the foreshock stress drops (5.26≤ σ ≤ 5.76 bar), fault lengths (415 ≤ L ≤ 600 m), seismic moments (8.36*10 20 ≤M o ≤ 2.31*10 21 dyne.cm) and relative displacements (0.52 ≤ û ≤ 0.91 cm).
Egypt is recognized as a moderate seismic-ity region where earthquakes are distributed within sev... more Egypt is recognized as a moderate seismic-ity region where earthquakes are distributed within several active regions. Owing to sparse distribution of both seismicity and seismic stations, mostly moderate size Egyptian earthquakes were recorded by regional stations. One of such cases is the moderate-size earthquakes of moment magnitudes greater than 4.0 which struck the Western Desert of Egypt in 1998 and 1999. These events are the first instrumentally recorded earthquakes occurring in the area. In the present study, the source mechanism for these earthquakes was estimated using the waveform data recorded from one of the very broadband MedNet seismograph stations and polarities from the national short-period seismographs. An iterative technique was applied to find the best-fit double-couple mechanism by a grid search over strike, dip and rake. Regional synthetic seismograms were calculated by using f–k integration in the frequency range of 0.03–0.1 Hz. A crustal structure fitted to surface wave dispersion curves was used to compute Green's function. Focal depths were determined through the grid search method for a range of source depths. Our results show a normal faulting mechanism with minor strike-slip component. The NNW trend has been chosen as a preferred rupture plane in consistence with surface and subsurface faults and microearthquake seismicity in the epicenteral area as well.
In this study we investigate present-day seismicity and crustal deformation of Egypt based on a c... more In this study we investigate present-day seismicity and crustal deformation of Egypt based on a comprehensive earthquake catalog from 1900 to 2004 by focal mechanism stress inversion and by recent GPS observations. Spatial distribution of earthquake epicenters indicates that Egypt has been suffered from both interplate and intraplate earthquakes. Most earthquake activity (more than 70%) has been concentrated in northern Egypt along the geologically documented borders of Sinai subplate (northern Red Sea and its two branches Suez rift and Aqaba–Dead Sea transform). The majority of inland earthquake focal mechanisms in Egypt are normal with strike-slip component or strike-slip faulting events. Only a small minority, namely four events, exhibits reverse faulting. The inversion method of Gephart and Forsyth (1984) was applied to calculate the orientation of the principle stress axes and the shape of the stress tensor. The best fitting tensor in Egypt shows homogeneity stress field. The tension stress regime is dominant in northern Egypt. The stress directions are well resolved by the 95% confidence limits, the relative stress magnitude has a value of about 0.3. However, along southern Egypt the strike-slip regime is dominant. The shape factor (R-value) is 0.5, which means that the deviatoric components of σ 1 and σ 3 are of the same magnitude, but of opposite signs. The average horizontal velocity of GPS stations in Egypt is 5.15 ± 1.1 mm/year in mostly NNW direction. The results of deformation analysis indicate that the northern Egypt is deformed more than the southern part. Only the Egyptian-Mediterranean coastal–Nile Delta zone dominates as a compression deformation area. However, an extensional deformation has been observed throughout the rest of country. This means that the relative motion of African plate with respect to both Eurasian and Arabian has highly controlled the deformation processes in Egypt.
The rupture process of a moderate earthquake (ML∼4.9) occurred southeast Beni-Suef, northern Egyp... more The rupture process of a moderate earthquake (ML∼4.9) occurred southeast Beni-Suef, northern Egypt was analyzed. The characterization of the rupture process and source properties were extracted from studying the relative moment rate function (RMRF). RMRFs were retrieved by deconvolution of small aftershock records using an inversion procedure for only P-wave part of the records. Although, this event is a moderate earthquake, its RMRFs exhibited complexity and directivity of the rupture behavior. The deconvolution pulses reflect three subevents or more. The detailed analysis of the distinct subevents revealed gross temporal and spatial characteristics of the rupture propagation. The azimuthal variation in the time delay of the subevents with respect to the initiation rupture indicates that the subevents are located at 0.85±0.17 and 3.5±0.07 km in directions of 320 • ±45 • and 330 • ±15 • with rupture velocities 3.4±0.45 and 4.0±0.7 km/sec, respectively. This means that the rupture is predominately propagated toward the North. Estimation of the rupture direction was combined with P-wave focal mechanism to identify the fault plane for the initial rupture of mainshock. Source parameters were calculated for each distinct subevent, including seismic moments 8.53E14 to 6.80E15 Nm, fault radii 713 to 1800 m and stress drops 0.725 to 2.932 MPa. The large estimated stress drop for the main subevent reflects failure asperity.
Africa displays a variety of continental margin structures, tectonics and sedimentary records. Th... more Africa displays a variety of continental margin structures, tectonics and sedimentary records. The northern Egyptian continental margin represents the NE portion of the North African passive continental margin. Economically, this region is of great importance as a very rich and productive hydrocarbon zone in Egypt. Moreover, it is characterized by remarkable tectonic setting accompanied by active tectonic processes from the old Tethys to recent Mediterranean. In this article, seismicity of the northern Egyptian continental margin has been re-evaluated for more than 100-years and the source parameters of three recent earthquakes (October 2012, January 2013 and July 2013) have been estimated. Moment tensor inversions of 19th October 2012 and 17th January 2013 earthquakes reveal normal faulting mechanism with strike–slip component having seismic moment of 3.5E16 N m and 4.3E15 N m respectively. The operation of the Egyptian National Seismic Network (ENSN) since the end of 1997 has significantly enhanced the old picture of earthquake activity across northern Egyptian continental margin whereas; the record-ability (annual rate) has changed from 2-events/year to 54-event/year before and after ENSN respectively. The spatial distribution of earthquakes foci indicated that the activity tends to cluster at three zones: Mediterranean Ridge (MR), Nile Cone (NC) and Eratosthenes Seamount (ERS). However, two seismic gaps are reported along Levant Basin (LEV) and Herodotus Basin (HER).
In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of ... more In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of M L 4.1 has occurred at southeast Beni-Suef, approximately 160 km SEE of Cairo, northern Egypt. The quake has been felt as far as Cairo and its surroundings while no casualties were reported. The instrumental epicentre is located at 28.57°N and 31.55°E. Seismic moment is 1.76 E14 Nm, corresponding to a moment magnitude M w 3.5. Following a Brune model, the source radius is 0.3 km with an average dislocation of 1.8 cm and a 2.4 MPa stress drop. The source mechanism from a first motion fault plane solution shows a left-lateral strike-slip mechanism with a minor dip-slip component along fault NNW striking at 161°, dipping 52° to the west and rake À5°. Trend and plunging of the maximum and minimum principle axes P/T are 125°, 28°, 21°, and 23°, respectively. A comparison with the mechanism of the October, 1999 event shows similarities in faulting type and orientation of nodal planes. Eight small earthquakes (3.0 6 M L < 5.0) were also recorded by the Egyptian National Seismological Network (ENSN) from the same region. We estimate the source parameters and fault mechanism solutions (FMS) for these earthquakes using displacement spectra and P-wave polarities, respectively. The obtained source parameters including seismic moments of 4.9 Â 10 12 –5.04 Â 10 15 Nm, stress drops of 0.2–4.9 MPa and relative displacement of 0.1–9.1 cm. The azimuths of Taxes determined from FMS are oriented in NNE– SSW direction. This direction is consistent with the present-day stress field in Egypt and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS measurements.
On 11 October 1999, a moderate earthquake of local magnitude ML 4.9 hit northern Egypt. This even... more On 11 October 1999, a moderate earthquake of local magnitude ML 4.9 hit northern Egypt. This event shook the greater Cairo region and northern part of the Nile valley and was felt in much of northern Egypt with epicentral intensity of V (EMS). It was followed by eight aftershocks with local magnitude ranging from 1.6 to 3.2. A detailed analysis of this sequence, cross-correlation analysis, fault plane solutions and source parameter estimations is performed in the present article. A cross-correlation analysis allowed us to recognize a number of correlated events, which were used for earthquake ancestry using a master event technique. The focal mechanism solutions for the main-shock and the largest aftershock are moderately controlled and indicate strike-slip faulting with a dip-slip normal component. Rupture directivity, after-shock distributions and isoseismal lines were combined in an attempt to determine which of the two nodal planes is the fault plane. The dynamic source parameters of the southeast Beni-Suef earthquake sequence have been estimated from the P-wave spectra of the Egyptian National Seismograph Network (ENSN). The spectral amplitude of the main shock records displayed two distinct corner frequencies that reflect a complex rupture process. The averaging of the obtained values at different stations shows that the main shock occurred on a fault length of 1.5 km with relative displacement 9 cm, stress drop of 49 bar and seismic moment of 5Â10 22 dyn/cm. The aftershocks show a relatively similar source parameters fault length of 0.34L40.6 km, relative displacement of 0.054u40.2 cm, seismic moment of 2.3Â 10 19 4M 0 41.1Â10 20 dyn.cm and stress drop of 0.74Á44 bar. #
Although the precise boundaries and kinematics of the Sinai subplate are still doubtful\ it has a... more Although the precise boundaries and kinematics of the Sinai subplate are still doubtful\ it has a signi_cant role in the tectonic evolution of the northern Red Sea region[ On the basis of earthquake distribution\ the Sinai region can be considered as a subplate partially separated from the African plate by the Suez rift[ The relative motion between Africa\ Sinai and Arabia is the main source generating the present!day earthquake activity in the Gulf of Suez and the Gulf of Aqaba regions[ According to geological observations\ the southern segment of the Dead Sea fault system can be char! acterized by a left!lateral displacement of about 096 km since the Middle Miocene\ in contrast to the northern segment where only 14 to 24 km o}set can be inferred[ We think that along the southern segment the total displacement was 61 km until the late Miocene "09 Ma#[ The earthquake activity is strongly reduced along the northern segment of the Dead Sea fault system[ Therefore\ we suggest that the northern part "Yammouneh fault# evolves through initial cracking of the crust due to build!up of stress since the Pliocene time "4 Ma# and propagates northward into Lebanon and Syria[ This last 4 million years is the period when the southern and northern segments became linked and formed a single fault system with a new displacement of 24 km[ According to the proposed model the predicted opening pole of the Red Sea is near 23[9>N\ 11[9>E with an angle of total rotation of 2[3> since the early Miocene\ providing a 9[71 cm:a opening rate in the northern Red Sea[ We suggest that the Dead Sea strike!slip fault was active since Middle Miocene time "04 Ma# with a slip rate of 9[61 cm:a to provide a total displacement of about 096 km[ This strike!slip motion occurred about an Euler pole near 22[9>N\ 10[9>E with a rotation angle of 2[9>[ It can be inferred from the proximity of the pole and angle of rotations for the Red Sea and Dead Sea fault that more than 74) of the motion has been accommodated on the Gulf of Aqaba and the Dead Sea fault and less than 04) in the Gulf of Suez[ This model predicts a normal extensional motion in the Gulf of Suez with a minor left!lateral strike!slip component[ We expect the pole of this motion to be at 20[9>N\ 18[9>E\ o}shore of Alamein city about 219 km west of the Nile Delta[ The rate of motion through the last 04 Ma "Middle Miocene# is about 9[0 cm:a and the angle of rotation is 9[8>[ During this period the total opening of the Suez rift is 04 km\ while the rest
Based on historical and instrumental seismicity as well as recent GPS measurements, the seismicit... more Based on historical and instrumental seismicity as well as recent GPS measurements, the seismicity and kinematic evaluation of middle Egypt is presented. Middle Egypt suffered in historical times by six major earthquakes and the Ramses II temple on the west bank of the Nile in Luxor, was almost destroyed by an ancient event. The temporal distribution of recent earthquakes (1900–1997) is highly scattered with only nine events recorded. Only after the installation of the modern Egyptian national seismograph network (ENSN) the seismic record of middle Egypt increased with a total of 280 earthquakes from 1998 to 2004. Focal mechanism solutions of the largest five events during the ENSN's operation period reveal reverse faulting mechanism with minor strike-slip component on the west bank of the Nile, while a normal faulting mechanism dominate in the eastern side. The orientations of both P-and Taxes are consistent with the Red Sea-Gulf of Suez stress field. Dynamic source parameters of these five events were derived from P-wave spectra as well. Three campaigns of GPS measurements were carried out for the middle Egypt network that established after the first instrumental earthquake on 14 December 1998 in this area. The velocity vectors for each epoch of observations were calculated and deformation analysis was performed. The horizontal velocity varies between 1 and 4 mm/year across the network. The deformation pattern suggests significant contraction across the southeastern sector of the study area while, the northwestern part is characterized by an extension strain rates. High shear strain is observed along the epicenteral area of the M w = 4.0 June 2003 earthquake possibly reflecting the stress accumulation stage of a seismic cycle.
From January 1995 to December 1997, about 74 earthquakes were located in the Pannonian basin and ... more From January 1995 to December 1997, about 74 earthquakes were located in the Pannonian basin and digitally recorded by a recently established network of seismological stations in Hungary. On reviewing the notable events, about 12 earthquakes were reported as felt with maximum intensity varying between 4 and 6 MSK. The dynamic source parameters of these earthquakes have been derived from P-wave displacement spectra. The displacement source spectra obtained are characterised by relatively small values of corner frequency (f 0) ranging between 2.5 and 10 Hz. The seismic moments change from 1X48 Â 10 20 to 1X3 Â 10 23 dyne cm, stress drops from 0.25 to 76.75 bar, fault length from 0.42 to 1.7 km and relative displacement from 0.05 to 15.35 cm. The estimated source parameters suggest a good agreement with the scaling law for small earthquakes. The small values of stress drops in the studied earthquakes can be attributed to the low strength of crustal materials in the Pannonian basin. However, the values of stress drops are not dierent for earthquake with thrust or normal faulting focal mechanism solutions. It can be speculated that an increase of the seismic activity in the Pannonian basin can be predicted in the long run because extensional development ceased and structural inversion is in progress. Seismic hazard assessment is a delicate job due to the inadequate knowledge of the seismo-active faults, particularly in the interior part of the Pannonian basin. 7: S 0 2 6 4-3 7 0 7 (0 0) 0 0 0 2 0-X
The seismic activity of the Sinai subplate region on the basis of both historical "1199 B[C[Ð0899... more The seismic activity of the Sinai subplate region on the basis of both historical "1199 B[C[Ð0899 A[D[# and recent "0899Ð0884# earthquake catalogs have been evaluated[ Moderate and large earthquakes occurred mainly at the subplate boundaries\ Dead Sea Fault "DSF# system in the east\ Cyprean arc in the north\ and Suez rift in the southwest[ Along the Dead Sea Fault system the activity concentrated at the southern and central segments[ The earthquake distribution appears to have a tendency to cluster in time and space[ The swarms "February\ 0872^ April\ 0889^ August\ 0882 and November\ 0884# in the Gulf of Aqaba indicate that the southern segment of the Dead Sea Fault system is the most seismogenic through the last two decades[ North of the Dead Sea depression the seismic activity tends to have occurred with NW trend to extend under the Levantine Sea[ Although the northern segment of the Dead Sea Fault system is well de_ned from geological\ geophysical and historical earthquake activity recent seismic activity is practically absent especially north of Latitude 23>N[ In the eastern Mediterranean the seismicity is much higher in the area of the Hellenic arc than in the Cyprean arc[ Moreover\ the activity occurs in a wide belt suggesting that the plate boundary is a deformation zone instead of a single line[ The seismic activity in the Gulf of Suez is scattered and does not have any distinct trend[ However\ three active zones are delineated[ At the mouth of the gulf most of activity is concentrated where the Sinai triple junction "Africa\ Arabia\ Sinai# is situated[ The central part and the northern part of the gulf include the adjacent area as far as the river Nile[ Actually\ the activity is markedly decreased from south to north[ Although there is no seismological evidence that the Suez rift continues into the eastern Mediterranean\ the activity in the Gulf of Suez region cannot be ignored[ The parameters of magnitude!frequency relation "a\ b# indicate that the level of earthquake activity in the Sinai subplate region is generally moderate[ Moreover\ the energy release curve shows a regular trend and re~ects occasional high activity[ Þ
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