الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Chapter 1: discusses a general overview about the seismic activity in the Central Egypt study area, its location map, aims of study, source of data and methodology.
The study area covers the central part of Egypt. It is located between latitudes 25° and 29° N and longitude 29° E till the eastern Red sea and Gulf of Suez shore line. This area represents one of the most important and promising areas, where it has many strategic and developmental projects besides the most valuable historical archeological sites. The central part of Egypt constitutes a very large area as well as a highly populated zone. Furthermore, it includes a number of new developmental communities such as the new branch of Gulf of Suez and its global port, El-Galala, new Beni Sueif and new Teba sites. Due to the cultivated soil extends along both sides of the River Nile amplify the earthquake ground motion, and this- in turn- may cause a damage for the structures and buildings in future especially in some areas that are close to earthquake source zones, consequently not only the present but also the planned projects should be protected against the expected earthquake hazards and risks. Hence, this study represents one step in this direction for the earthquake hazard and risk mitigation. The obtained results from the present work are very useful for the planners before establishing new projects and new urban communities within this area.
Egypt is considered to be the link between two massive plate movements; the African plate and the Arabian plate, causing a series of compressional and extensional events along the history of Egypt that play an important role in the deformation of the Unstable Shelf and reactivation and propagation of pre-existing faults in the Stable Shelf.
Chapter 2: throws a more light on the reactivated faults in the study area along the geological time scale. The start of extension began during Early Cretaceous, in some areas reactivating E-W Jurassic basins as in the Sarir, Troughs, Faghur and Abu Gharadig Basins that formed new NW-SE-trending rifts. During Early Cretaceous the extension direction rotated clockwise toward the NE-SW direction. Closing of the Neo-Tethys, during the Santonian (Late Cretaceous); the motion between Africa and Eurasia was changed dramatically from sinitral divergence to dextral convergence resulting E-W and NE-SW-directed compressional waves.
During Early Cenozoic the E-W oriented structures were reactivated as small graben and horst structures. Paleocene, Eocene tectonics are characterized by active subsidence that affected most of the Sirt troughs, Abu Gharadiq Basin and the Gindi Basin of northern Egypt. Along river Nile, Qena bend is considered to be the most complicated area in the Egyptian course of the Nile, which believed to be the result of rejuvenation of the NE fault system superimposed on NW and N-S trends. The predominant structural direction of the Nile Valley is NW, this direction is observed mainly north of Idfu. Direction of rifting was continued changing from NE-SW to NW-SE. By Early Quaternary the general and dominant extension direction was NE-SW, which agrees with the present-day stress field directions across most of Africa that will be explained in details in chapters four and five.
In this study, seismological data from the Egyptian National Seismic Network (ENSN) were used for the period from 1997 to 2018. About two thousand seed format events recorded and analyzed by Atlas Nanometrics program in the ENSN main center in (NRIAG) Helwan have been used. Data has been chosen according to their locations and purposes: 878 events (Abu Dabbab), 181 events (East Beni Suef), 105 events (Hurghada) and 152 events (Asyut) for relocation in Chapter 3 and 9 events (Central Egypt) for focal mechanism in Chapter 4, 376 events (Edfu) for discrimination in Chapter 6, and finally, 317 events (Aswan) for magnitude estimation in Chapter 7.
Chapter 3 starts with evaluating the detectability of the recording systems in Central Egypt followed by event relocations. About 21 ENSN stations lay in Central Egypt were used in this study, with varying sensors types and components. from all 21 stations 8 were not working right now, leaving the study area with only13 working stations without covering the southern part of Nile Valley and only North Abu Dabbab and Abu Ghson in southern Red Sea shore line and Bernes station in the center of southern Eastern Dessert.
After quantitative evaluation for the used recording stations, we were able to enhance and detect the Central Egypt seismic sources by relocated seismic events using different techniques such as absolute and relative relocation methods. Plotting all the seismicity of Central Egypt; five main clusters have been found that are concentrated in Beni-Suef, Northern Hurghada, Eastern Asyut, Northwest Idfu and Abu Dabbab areas.
The relocation starts using modified joint hypocenter determination (MJHD). This method makes it possible to process large number of events in a time comparable to that required for the single-event location of the same events, thereby removing the effects of lateral heterogeneity within the Earth. According to the output results of MJHD, station correction map for Central Egypt had been established.
MJHD method has been applied for Beni-Suef and Abu Dabbab clustered areas, showing very good results and small residuals, while for other clusters this method was tested showing very high residuals and inconsistence results. That is –in turn- leads us to try other techniques like Double-Difference HypoDD.
After re-plotting the relocated events on surface structure lineaments map; the clusters show a good matching with surface fault zones.
from the fact that, the seismic activity in a region is not independent phenomena, but it depends greatly on the structures present within the region and the situation of the region within the framework of new tectonics. We investigated those structures in detailed by focal mechanisms at Chapter 4 which has dialed with the focal mechanisms solutions for 60 significant events in the study area. The results matched the fact of present-day stress field across most of Africa that delineate NE-SW trending of Gulf of Aqaba.
In order to clarify the structural main trend in Central Egypt; Seis-Pc program has been used showing that:
Central part of Egypt is characterized by normal with strike-slip mechanisms that are mainly trending NE–SW and NW–SW.
At Central Egypt it is very difficult to see pure reveres faults, but some minor events are seen as oblique reverse type.
The main trend of T-axis is NE-SW which is consistent with the dominant extensional stresses along the Gulf of Suez and Northern Red Sea.
The major P and T axes are enormously plunging with 50° and 10° to 20°, respectively, which mean that T axes are semi-horizontal, while P axes are semi-vertical.
Chapter 5 clarifies the subsurface lineaments in Central Egypt due to aero magnetic data field. The qualitative output results shown in the reduced to the pole (RTP) map, note that the magnetic field of the area has a maximum relief of about 144 nT nearly in the southeastern and central parts and minimum relief of about -155 nT in the northeastern part of the studied area. These anomalies have different reliefs, polarities and shapes. The general magnetic trends patterns of this field are NW-SE, NE-SW, and E-W. The detected structural pattern deduced from the RTP magnetic anomaly map was constructed by tracing a total of 63 faults or lineaments of different trends all over the study area. from the analysis of these faults, it has been shown that, there are three different major structural trends which can be delineated as the follows:
1) NW-SE (Gulf of Suez and Red Sea trend): The faults of this trend are characterized by their regional nature and great intensity. This trend is clearly dominant in the central, eastern and western parts of the study area.
2) NE-SW (Aqaba trend): Also this trend is a regional trend which distributed all over the study area.
3) N-S trend: this trend is represented in the study area along six faults.
The directions of faults are represented in the rose diagram shows the major lineaments directions are at NW-SE (parallel to Gulf of Suez direction), and NE-SW (parallel to Gulf of Aqaba direction) while N–S lineament direction was minor direction.
By the end of that chapter, we found that trends deduced from potential field data are matching the seismic trends (deduced from fault plane solutions) and the geographical distribution of seismicity of relocated central Egypt data.
Chapter 6: deals with the contamination of the local earthquake catalogue at Idfu area with mining explosions which leads to a mis-interpretation for activity of seismic sources. That causes false result for any seismic studies for such area besides miss-interpretation for activity of seismic sources. Therefore, decontamination using different discrimination criteria’s is necessary to be done in order to determine the real seismicity of the region that aids the seismic hazard assessment studies. The different methods applied to discriminate earthquakes and quarry blasts in this study were:
Daytime and nighttime (qualitative discrimination). Since the quarry blasts commonly occur during the daytime especially at working hours (8 a.m. and 3 p.m.), while earthquakes could occur any time during the day, a simple histogram relation shows that the number of events has been rising during the daytime between 08 a.m. and 01 p.m. Among 381 events recorded at northeast of Idfu region, 109 events were recorded in only one hour between 10 a. m. - 11 a. m.
Frequency Bands: MATLAB program code used Fourier analysis to convert a signal from the time domain to frequency domain (FFT) in order to calculate and observe spectral modulation on the seismograms of earthquake and quarry blasts. As a result of using this method about 85% of all events have been discriminated as a quarry that shows lower-frequency contents, while earthquakes shown high frequency bands.
Complexity (C) and Spectral Amplitude Ratio Analysis (Sr) (quantitative analysis). The seismic events could be classified according to their degree of spectral complexity and richness of different types of waves and amplitudes. After applying the two methods using a MATLAB coded program, it has been concluded that Time-of-day is not the sole criterion for discrimination, though it can be utilized in conjunction with satellite imagery and waveform analysis in time-frequency domain to further provide constraints on anomalously timed events Therefore, data sets were used with different methodologies for the discrimination analysis of quarry blasts from natural seismicity such as frequencies bands, depths range and correlation between the complexity (C) and spectral ratio (Sr) of both mining blasts and earthquakes in Idfu region where we were able to show that the time-frequency discriminate separated about 90% of mining blasts from only 10% of the earthquake. Also, we concluded that the natural activities in this area seem to be recent and it could be induced from the artificial explosions in that area.
Chapter 7: This is the main target in the present study, concerns with the estimation of a new local magnitude equation applied in Central Egypt. Twenty three stations equipped by 3-components (E-W, N-S, and Z) as well as the epicentral of the 317 events with the magnitude range of 1.8 to 4.6 ML through the time period (2009- 2018) for Aswan area have been used for this study for estimating local magnitude equation in Central and Southern Egypt.
Based on Richters (1935 and 1958) definitions of ML, source code for analysis was written using ObsPy toolbox and Matlab under python in order to read and handle of the observed data of earthquakes to estimate the local magnitude scale (ML) for the area under study. The output results of auto-picking the maximum amplitude are printed out in the format of Comma separated values (CSV). According to wave dispersion and attenuation with respect to simple geometrical spreading an amplitude-distance relation has been plotted for some events to display the attenuation attributes, confirming the decay of amplitude with distance.
The resultant distance correction model for the area of study is given as:
-log (Ao) = 1.7481* log 10 (R) - 0.0056 * (R) + 0.0625
-log (Ao) = -0.1216 * log 10 (R) - 2.1084e-5* (R) + 3.2411.
Finally, the local magnitude ML for Central and Southern Egypt is deduced from the following equations:
M_L={█(〖log 〗_10 (A)+1.7481*〖log 〗_10 (R)-0.0056* (R)+0.0625 &R<100 Km@@@〖log 〗_10 (A)-0.1216*〖log 〗_10 (R)+2.1084 e^(-5)* (R)+3.2411 500≥ &R≥100 Km)┤
A comparison between the obtained new local magnitude ML equation with the standard local magnitude equation of IASPEI (2011) has been carried out and approved to be reliable for ML estimation with slight differences.