الفهرس 
Seismicity and Tectonic SettingOnly 14 pages are availabe for public view
 |  | from | 137 |  |  |
| | | from | 137 | | |
Abstract
Abstract
The area of study is considered an important area due to the Aswan High Dam, the most important project of Egypt for social, agricultural and electrical energy production. After the occurrence of Nov. 14, 1981 earthquake in the southwest of the High Dam, The seismicity of this area is studied by many authors. The seismic activity is low compared with other zones as the Gulf of Suez and Gulf of Aqaba. The activity appears to be cluster at the intersections of the E-W and N-S trending faults.
In this study, the digital waveform data were extracted from the database of the Egyptian National Seismological Network (ENSN). This data includes earthquakes that occurred in the Aswan area during the period from 2014 to 2018 with local magnitude (Ml) ≥ 2.08 to construct focal mechanism solutions. Two programs are used; the first one (PMAN) is based on the first onset of P- wave and the other one is FOCMEC, which used the polarities of P, SH, SV and their amplitude ratios in solution. The result of the two programs are identical and shows two types of motion as an oblique mechanism of strike-slip with minor normal dip-slip component or normal with minor strike-slip component, and pure strike-slip solutions. The nodal planes have the trend of ENE-WSW and NNW-SSE, and WNW-ESE and NS which compatible with the surface geology of this area. The stress tensor inversion technique is carried out to obtain the best fitting stress model from the inversion of the focal mechanism data set compiled from previous studies and that constructed herein. This model represents the stress regime of the area. The obtained model shows that the maximum stress σ1, minimum stress σ3, are horizontal while the intermediate σ2 is nearly vertical, indicating strike-slip stress regime. The plunge/ azimuth for σ1, σ2 and σ3 are respectively 07o/29o, 82 o/77o and 05o/204o. This is well with that of the previous studies that also reveals the dominant stress in which the tension has a direction of N 24o-28oE. The source parameters of eight events are estimated. The parameters are hypocenter location, fault rupture mechanism, differential displacement, seismic moment, corner frequency and stress DROP which are used in identifying whether these earthquakes are of tectonic origin or induced seismicity due to the Nasser Lake. The Seismic Analysis Code (SAC) and MATLAB programs are used for the analysis of data. The main results of source parameters are as follow; corner frequency has range (3.5-6.8) Hz, stress DROP ranged between 0.02 and 3.56 MPa, source radius varied from (393-783) m and seismic moment varied from (2.23E+19 to 1.48E+21) dyne-cm. Standard deviation and a multiplicative error factor are calculated.
The estimated stress DROP doesn’t show any distinct relation with depth but the higher stress DROP is sometimes obtained at the intersection between the N-S and E-W trend fault system. The obtained stress DROP is small (0.02-3.56) MPa, coincides with the reservoir induced activity that reveals low-stress DROP if comparing with the earthquakes of tectonic origin. Scaling relations between different source parameters are constructed using all compiled data set to enhance and upgrade the empirical relationships between these parameters which, can help obtain the source parameters to any area faster without running programs.