The frequency–magnitude statistics of 6527 earthquakes with 1.0 ≤ ml ≤ 5.7 and focal depths betwe... more The frequency–magnitude statistics of 6527 earthquakes with 1.0 ≤ ml ≤ 5.7 and focal depths between 0 and 49 km in the Red Sea region between 1980 and 2021 show that the threshold magnitude, above which most of the Red Sea earthquakes are precisely located, is 1.5. The b-value, which identifies regional stress situations and associated energy release modalities, has a value of 0.75, less than in historical data, and averages between 0.4 and 0.85 as it varies over time, indicating modest stress accumulation. We utilised these instrumental data to examine dynamic stress patterns in the Red Sea region, shedding light on the region’s geodynamics and providing a foundation for estimating the region’s seismic hazard. The computed fractal dimension (Dc) has a relatively high value of 2.3, which is significant for the Red Sea’s geological complexity and structural diversity. This result indicates the regular distribution of Red Sea earthquakes, which occur in clusters or along fault lines. ...
Tectonic stress regime and stress patterns from the inversion of earthquake focal mechanisms in NW Himalaya and
Because the impact of earthquake effects can extend over great distances from their origin, stres... more Because the impact of earthquake effects can extend over great distances from their origin, stress field inversion was performed for 440 earthquake focal mechanisms from the northwest Himalayas and surrounding regions compiled from the data bulletins of international seismological institutions. Earthquakes between November 1976 and April 2019 in the depth range of 10-258 km with moment magnitudes between 4.6 and 7.9 were selected. High-quality solutions were inverted to locate the best fitting stress tensor. Most of the earthquake fault plane solutions indicated thrust faulting, confirming northward underthrusting of the Indian plate along the Main Boundary Thrust and the Main Central Thrust systems and eastward underthrusting along the Burmese Arc. The focal mechanisms indicated right-lateral motion along the Karakoram Fault and left-lateral motion along the Kirthar-Sulaiman Range, which agrees with the expected sense of the lateral mass movement of the continental collision model. The present-day stress regimes obtained from the earthquake focal mechanism inversions indicated a predominantly compressional stress regime represented by NNE-SSW trending normal fault mechanisms in northwest India and Nepal and NNW-SSE trending normal fault mechanisms in Pakistan and Hindukush. These are consistent with the direction of the ongoing India-Eurasia plate collision and the extensional stress of WNW-ESE trending thrust faulting in the Xizang and Kashmir regions.
ABSTRACT The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occ... more ABSTRACT The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occurred on the Kalabsha fault at the Aswan area are analyzed. The derived focal mechanisms of this event and other two aftershocks using polarities of P, SV, and SH waves show strike-slip fault with minor vertical movement of normal type. The solutions give two nodal planes trending ENE–WSW and NNW–SSE in close agreement with the surface traces of the faults crossing the area. The movement is right lateral along the first plane while left lateral along the second one. The rupture process characterization of this event has been investigated by using the empirical Green’s function deconvolution method. By inversion only for the P wave part of the records of these three events (main and other two aftershocks), the source time function for the master events and the azimuthally variations in the (RSTF) pulse amplitude are retrieved for estimating the rupture directivities. The estimated rupture direction is combined with the P-wave focal mechanisms for the three events to identify the fault plane solution for these earthquakes. Based on the width, amplitudes, and numbers of the isolated source time functions, a complex bi-lateral rupture of the studied earthquake is delineated. The source parameters of the master event is calculated and the derived corner frequencies f o for P-wave spectra show a value of 6.6 Hz; the seismic moment (M o ) is 4.2 × 1022 Nm; the average displacement (U) is 0.5 m; fault radius (r) 40 m; the average value of the stress drops (Δσ) is 0.6 Mpa, and the moment magnitude (M w ) is 4.4.
ABSTRACT The present day tectonic deformation within Egypt is related to the regional tectonic fo... more ABSTRACT The present day tectonic deformation within Egypt is related to the regional tectonic forces of the surrounding plate boundaries including the African–Eurasian plate margin, the Red Sea plate margin and the Levant transform fault in addition to the local tectonics of Egypt. Based on the spatial distribution of earthquake epicenters in Egypt, the most seismically active areas are located in the Northern Red Sea, Gulf of Suez, Gulf of Aqaba and Mediterranean coastal zone. On 30 January 2012, a moderate earthquake of local magnitude ML 4.6 struck the northeast part of Egypt, at the entrance of Gulf of Suez. This event was felt in many areas surrounding the epicenter with low damage recorded. To understand the mechanism and the reflected irregularity of the evolved stress field concerning the Gulf of Suez area, calculation of source parameters and source mechanisms of this event are necessary. Moment tensor inversion is used to retrieve the fault plain solutions and the seismic moment by using waveforms recorded by the Egyptian National Seismic Network. The fit between observed and synthetic seismograms was computed for an elastic layered media and minimized using a least squares algorithm. The derived source mechanism indicates normal faulting along NNW–SSE trending faults, in agreement with the rifting of the northern Red Sea in its northern branches (Gulf of Suez and Gulf of Aqaba). The source parameters are estimated and the derived corner frequency f o for the P-wave spectra shows a value of 3.00 Hz. The seismic moment M o is 1.278 × 1023 Nm, the fault length r is 0.8 km, the average displacement D 0 is 0.023 m, and the value of the stress drop Δσ is 1.10 MPa. The source mechanism and source parameters imply the continuous activity of the Red Sea rift system at the Gulf of Suez opening.
ABSTRACT We have relocated 259 inland earthquakes in northern Egypt using the double-difference h... more ABSTRACT We have relocated 259 inland earthquakes in northern Egypt using the double-difference hypocenter technique. Among this dataset we are able to determine source mechanisms of 200 events using P-wave polarities and amplitude ratios as well. The studied earthquakes have been recorded by the Egyptian National Seismological Network from October 1997 to December 2006 with local magnitude (ML) varies between 1.5 and 5.0. Three earthquake dislocations have been defined namely: Dahshour, southeast Beni-Suef, and Cairo-Suez district. Earthquake activities tend to occur in clusters along the first dislocation (Dahshour) however, relatively scattered along the second (southeast Beni-Suef) and the third (Cairo-Suez district) dislocations. At Dahshour dislocation three distinct clusters have been distinguished. Source mechanism solutions of Dahshour earthquakes displayed normal faulting with a strike-slip component to strike-slip faulting with a minor normal dip-slip component. Most of earthquake focal mechanism orientations are varying from NE-SW to NW-SE. The fault plane solutions of Beni-Suef earthquakes represented normal faulting with a strike-slip component. If the NNW-SSE striking plane has been chosen to be the actual fault plane, some solutions would indicated normal faulting with a sinistral strike-slip motion and other reflect normal faulting with a dextral strike-slip component. The fault plane solutions of Cairo-Suez district earthquakes are compatible with E-W to ENE-WSW striking normal fault with a dextral strike-slip motion.
ABSTRACT The present day tectonic deformation within Egypt is related to the regional tectonic fo... more ABSTRACT The present day tectonic deformation within Egypt is related to the regional tectonic forces of the surrounding plate boundaries including the African–Eurasian plate margin, the Red Sea plate margin and the Levant transform fault in addition to the local tectonics of Egypt. Based on the spatial distribution of earthquake epicenters in Egypt, the most seismically active areas are located in the Northern Red Sea, Gulf of Suez, Gulf of Aqaba and Mediterranean coastal zone. On 30 January 2012, a moderate earthquake of local magnitude ML 4.6 struck the northeast part of Egypt, at the entrance of Gulf of Suez. This event was felt in many areas surrounding the epicenter with low damage recorded. To understand the mechanism and the reflected irregularity of the evolved stress field concerning the Gulf of Suez area, calculation of source parameters and source mechanisms of this event are necessary. Moment tensor inversion is used to retrieve the fault plain solutions and the seismic moment by using waveforms recorded by the Egyptian National Seismic Network. The fit between observed and synthetic seismograms was computed for an elastic layered media and minimized using a least squares algorithm. The derived source mechanism indicates normal faulting along NNW–SSE trending faults, in agreement with the rifting of the northern Red Sea in its northern branches (Gulf of Suez and Gulf of Aqaba). The source parameters are estimated and the derived corner frequency f o for the P-wave spectra shows a value of 3.00 Hz. The seismic moment M o is 1.278 × 1023 Nm, the fault length r is 0.8 km, the average displacement D 0 is 0.023 m, and the value of the stress drop Δσ is 1.10 MPa. The source mechanism and source parameters imply the continuous activity of the Red Sea rift system at the Gulf of Suez opening.
ABSTRACT The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occ... more ABSTRACT The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occurred on the Kalabsha fault at the Aswan area are analyzed. The derived focal mechanisms of this event and other two aftershocks using polarities of P, SV, and SH waves show strike-slip fault with minor vertical movement of normal type. The solutions give two nodal planes trending ENE–WSW and NNW–SSE in close agreement with the surface traces of the faults crossing the area. The movement is right lateral along the first plane while left lateral along the second one. The rupture process characterization of this event has been investigated by using the empirical Green’s function deconvolution method. By inversion only for the P wave part of the records of these three events (main and other two aftershocks), the source time function for the master events and the azimuthally variations in the (RSTF) pulse amplitude are retrieved for estimating the rupture directivities. The estimated rupture direction is combined with the P-wave focal mechanisms for the three events to identify the fault plane solution for these earthquakes. Based on the width, amplitudes, and numbers of the isolated source time functions, a complex bi-lateral rupture of the studied earthquake is delineated. The source parameters of the master event is calculated and the derived corner frequencies f o for P-wave spectra show a value of 6.6 Hz; the seismic moment (M o ) is 4.2 × 1022 Nm; the average displacement (U) is 0.5 m; fault radius (r) 40 m; the average value of the stress drops (Δσ) is 0.6 Mpa, and the moment magnitude (M w ) is 4.4.
The frequency–magnitude statistics of 6527 earthquakes with 1.0 ≤ ml ≤ 5.7 and focal depths betwe... more The frequency–magnitude statistics of 6527 earthquakes with 1.0 ≤ ml ≤ 5.7 and focal depths between 0 and 49 km in the Red Sea region between 1980 and 2021 show that the threshold magnitude, above which most of the Red Sea earthquakes are precisely located, is 1.5. The b-value, which identifies regional stress situations and associated energy release modalities, has a value of 0.75, less than in historical data, and averages between 0.4 and 0.85 as it varies over time, indicating modest stress accumulation. We utilised these instrumental data to examine dynamic stress patterns in the Red Sea region, shedding light on the region’s geodynamics and providing a foundation for estimating the region’s seismic hazard. The computed fractal dimension (Dc) has a relatively high value of 2.3, which is significant for the Red Sea’s geological complexity and structural diversity. This result indicates the regular distribution of Red Sea earthquakes, which occur in clusters or along fault lines. ...
Tectonic stress regime and stress patterns from the inversion of earthquake focal mechanisms in NW Himalaya and
Because the impact of earthquake effects can extend over great distances from their origin, stres... more Because the impact of earthquake effects can extend over great distances from their origin, stress field inversion was performed for 440 earthquake focal mechanisms from the northwest Himalayas and surrounding regions compiled from the data bulletins of international seismological institutions. Earthquakes between November 1976 and April 2019 in the depth range of 10-258 km with moment magnitudes between 4.6 and 7.9 were selected. High-quality solutions were inverted to locate the best fitting stress tensor. Most of the earthquake fault plane solutions indicated thrust faulting, confirming northward underthrusting of the Indian plate along the Main Boundary Thrust and the Main Central Thrust systems and eastward underthrusting along the Burmese Arc. The focal mechanisms indicated right-lateral motion along the Karakoram Fault and left-lateral motion along the Kirthar-Sulaiman Range, which agrees with the expected sense of the lateral mass movement of the continental collision model. The present-day stress regimes obtained from the earthquake focal mechanism inversions indicated a predominantly compressional stress regime represented by NNE-SSW trending normal fault mechanisms in northwest India and Nepal and NNW-SSE trending normal fault mechanisms in Pakistan and Hindukush. These are consistent with the direction of the ongoing India-Eurasia plate collision and the extensional stress of WNW-ESE trending thrust faulting in the Xizang and Kashmir regions.
ABSTRACT The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occ... more ABSTRACT The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occurred on the Kalabsha fault at the Aswan area are analyzed. The derived focal mechanisms of this event and other two aftershocks using polarities of P, SV, and SH waves show strike-slip fault with minor vertical movement of normal type. The solutions give two nodal planes trending ENE–WSW and NNW–SSE in close agreement with the surface traces of the faults crossing the area. The movement is right lateral along the first plane while left lateral along the second one. The rupture process characterization of this event has been investigated by using the empirical Green’s function deconvolution method. By inversion only for the P wave part of the records of these three events (main and other two aftershocks), the source time function for the master events and the azimuthally variations in the (RSTF) pulse amplitude are retrieved for estimating the rupture directivities. The estimated rupture direction is combined with the P-wave focal mechanisms for the three events to identify the fault plane solution for these earthquakes. Based on the width, amplitudes, and numbers of the isolated source time functions, a complex bi-lateral rupture of the studied earthquake is delineated. The source parameters of the master event is calculated and the derived corner frequencies f o for P-wave spectra show a value of 6.6 Hz; the seismic moment (M o ) is 4.2 × 1022 Nm; the average displacement (U) is 0.5 m; fault radius (r) 40 m; the average value of the stress drops (Δσ) is 0.6 Mpa, and the moment magnitude (M w ) is 4.4.
ABSTRACT The present day tectonic deformation within Egypt is related to the regional tectonic fo... more ABSTRACT The present day tectonic deformation within Egypt is related to the regional tectonic forces of the surrounding plate boundaries including the African–Eurasian plate margin, the Red Sea plate margin and the Levant transform fault in addition to the local tectonics of Egypt. Based on the spatial distribution of earthquake epicenters in Egypt, the most seismically active areas are located in the Northern Red Sea, Gulf of Suez, Gulf of Aqaba and Mediterranean coastal zone. On 30 January 2012, a moderate earthquake of local magnitude ML 4.6 struck the northeast part of Egypt, at the entrance of Gulf of Suez. This event was felt in many areas surrounding the epicenter with low damage recorded. To understand the mechanism and the reflected irregularity of the evolved stress field concerning the Gulf of Suez area, calculation of source parameters and source mechanisms of this event are necessary. Moment tensor inversion is used to retrieve the fault plain solutions and the seismic moment by using waveforms recorded by the Egyptian National Seismic Network. The fit between observed and synthetic seismograms was computed for an elastic layered media and minimized using a least squares algorithm. The derived source mechanism indicates normal faulting along NNW–SSE trending faults, in agreement with the rifting of the northern Red Sea in its northern branches (Gulf of Suez and Gulf of Aqaba). The source parameters are estimated and the derived corner frequency f o for the P-wave spectra shows a value of 3.00 Hz. The seismic moment M o is 1.278 × 1023 Nm, the fault length r is 0.8 km, the average displacement D 0 is 0.023 m, and the value of the stress drop Δσ is 1.10 MPa. The source mechanism and source parameters imply the continuous activity of the Red Sea rift system at the Gulf of Suez opening.
ABSTRACT We have relocated 259 inland earthquakes in northern Egypt using the double-difference h... more ABSTRACT We have relocated 259 inland earthquakes in northern Egypt using the double-difference hypocenter technique. Among this dataset we are able to determine source mechanisms of 200 events using P-wave polarities and amplitude ratios as well. The studied earthquakes have been recorded by the Egyptian National Seismological Network from October 1997 to December 2006 with local magnitude (ML) varies between 1.5 and 5.0. Three earthquake dislocations have been defined namely: Dahshour, southeast Beni-Suef, and Cairo-Suez district. Earthquake activities tend to occur in clusters along the first dislocation (Dahshour) however, relatively scattered along the second (southeast Beni-Suef) and the third (Cairo-Suez district) dislocations. At Dahshour dislocation three distinct clusters have been distinguished. Source mechanism solutions of Dahshour earthquakes displayed normal faulting with a strike-slip component to strike-slip faulting with a minor normal dip-slip component. Most of earthquake focal mechanism orientations are varying from NE-SW to NW-SE. The fault plane solutions of Beni-Suef earthquakes represented normal faulting with a strike-slip component. If the NNW-SSE striking plane has been chosen to be the actual fault plane, some solutions would indicated normal faulting with a sinistral strike-slip motion and other reflect normal faulting with a dextral strike-slip component. The fault plane solutions of Cairo-Suez district earthquakes are compatible with E-W to ENE-WSW striking normal fault with a dextral strike-slip motion.
ABSTRACT The present day tectonic deformation within Egypt is related to the regional tectonic fo... more ABSTRACT The present day tectonic deformation within Egypt is related to the regional tectonic forces of the surrounding plate boundaries including the African–Eurasian plate margin, the Red Sea plate margin and the Levant transform fault in addition to the local tectonics of Egypt. Based on the spatial distribution of earthquake epicenters in Egypt, the most seismically active areas are located in the Northern Red Sea, Gulf of Suez, Gulf of Aqaba and Mediterranean coastal zone. On 30 January 2012, a moderate earthquake of local magnitude ML 4.6 struck the northeast part of Egypt, at the entrance of Gulf of Suez. This event was felt in many areas surrounding the epicenter with low damage recorded. To understand the mechanism and the reflected irregularity of the evolved stress field concerning the Gulf of Suez area, calculation of source parameters and source mechanisms of this event are necessary. Moment tensor inversion is used to retrieve the fault plain solutions and the seismic moment by using waveforms recorded by the Egyptian National Seismic Network. The fit between observed and synthetic seismograms was computed for an elastic layered media and minimized using a least squares algorithm. The derived source mechanism indicates normal faulting along NNW–SSE trending faults, in agreement with the rifting of the northern Red Sea in its northern branches (Gulf of Suez and Gulf of Aqaba). The source parameters are estimated and the derived corner frequency f o for the P-wave spectra shows a value of 3.00 Hz. The seismic moment M o is 1.278 × 1023 Nm, the fault length r is 0.8 km, the average displacement D 0 is 0.023 m, and the value of the stress drop Δσ is 1.10 MPa. The source mechanism and source parameters imply the continuous activity of the Red Sea rift system at the Gulf of Suez opening.
ABSTRACT The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occ... more ABSTRACT The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occurred on the Kalabsha fault at the Aswan area are analyzed. The derived focal mechanisms of this event and other two aftershocks using polarities of P, SV, and SH waves show strike-slip fault with minor vertical movement of normal type. The solutions give two nodal planes trending ENE–WSW and NNW–SSE in close agreement with the surface traces of the faults crossing the area. The movement is right lateral along the first plane while left lateral along the second one. The rupture process characterization of this event has been investigated by using the empirical Green’s function deconvolution method. By inversion only for the P wave part of the records of these three events (main and other two aftershocks), the source time function for the master events and the azimuthally variations in the (RSTF) pulse amplitude are retrieved for estimating the rupture directivities. The estimated rupture direction is combined with the P-wave focal mechanisms for the three events to identify the fault plane solution for these earthquakes. Based on the width, amplitudes, and numbers of the isolated source time functions, a complex bi-lateral rupture of the studied earthquake is delineated. The source parameters of the master event is calculated and the derived corner frequencies f o for P-wave spectra show a value of 6.6 Hz; the seismic moment (M o ) is 4.2 × 1022 Nm; the average displacement (U) is 0.5 m; fault radius (r) 40 m; the average value of the stress drops (Δσ) is 0.6 Mpa, and the moment magnitude (M w ) is 4.4.
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