Mohammed Shokry Farag

The 19 October 2012 earthquake (M L = 5.1) occurred in the northern continental margin of Egypt within the Nile Cone at latitude 32.35° N and longitude 31.27° E. The quake was felt over a wide area in north Egypt and East Mediterranean countries, but no casualties have been reported. This area had experienced the large earthquake (Ms = 6.7) of 12 September 1955. The fault plane solution of the 19 October 2012 earthquake is here presented based on the digital seismograms recorded by the Egyptian National Seismological Network (ENSN) and other regional seismic stations. The analysis is carried out using the well-known techniques of first motion polarities of P-wave and the amplitude ratios of P-, SH-, and SV-waves with lower hemisphere projection. The fault plane solution based on the first P-wave onset demonstrates a left lateral strike-slip faulting mechanism , while the solution based on both P-wave polarities and amplitude ratios of P-, SH-, and SV-waves reveals a reverse fault with strike-slip component trending NW–SE to NE–SW, in conformity with the N–S compression along the Hellenic Arc convergence zone. Following the Brune's model, the source dynamic parameters for the 19 October 2012 earthquake are estimated as corner frequency = 1.47 Hz, fault radius = 0.7 km, stress drop = 22.1 MPa, seismic moment = 2.80E + 16 Nm, and moment magnitude M w = 4.9. These parameters may provide important quantitative information for the seismic hazard assessment studies.

Keywords: H/V spectral ratio Shear wave velocity Multichannel analysis of surface wave Site classification Microtremor data a b s t r a c t The soft sediments are one of the most important factors responsible for the amplification of the seismic ground motion in an area of study. Three components, single-station microtremor measurements were performed at 61 sites along the Suez Canal to estimate the fundamental frequencies of the soil and corresponding H/V amplitude ratios by using the horizontal-to-vertical spectral ratio (HVSR) method. We have applied the investigations of the shear wave velocity for supplementing the existing seismic microzonation of the Suez Canal. The multichannel analysis of surface wave (MASW) tests were done along the Suez Canal in the three cities, Suez, Ismailia, and Port Said using 24 channels digital engineering seismograph with 4.5 Hz geophones from September 2014 to January 2015 to get the shear wave velocity V S30. The SeisImager/SW software was used for analyzing the data, and 1D-shear wave velocity model have achieved for each site. The HVSR curves show that the fundamental frequency values are ranging from 0.57 to 1.08 Hz, and H/V amplitude ratios are ranging from 4.05 to 6.46. The average values of V S30 are (548, 301), (241, 319), (194, 110, 238) for Suez, Ismailia, and Port Said respectively. The average of shear wave velocity up to 30 m depth is estimated and used for site classification based on the National Earthquake Hazard Reduction Program (NEHRP) classification. The majority of the sites was classified as Class D (stiff soil) except one site at Port Said city is classified as Class E (soft soils), and another site in the Suez city is classified as Class C (hard rock).

The objective of this study is to evaluate the seismic hazard at the northwestern Egypt using the probabilistic seismic hazard assessment approach. The Probabilistic approach was carried out based on a recent data set to take into account the historic seismicity and updated instrumental seismicity. A homogenous earthquake catalogue was compiled and a proposed seismic sources model was presented. The doubly-truncated exponential model was adopted for calculations of the recurrence parameters. Ground-motion prediction equations that recently recommended by experts and developed based upon earthquake data obtained from tectonic environments similar to those in and around the studied area were weighted and used for assessment of seismic hazard in the frame of logic tree approach. Considering a grid of 0.2 Â 0.2 covering the study area, seismic hazard curves for every node were calculated. Hazard maps at bedrock conditions were produced for peak ground acceleration, in addition to six spectral periods (0.1, 0.2, 0.3, 1.0, 2.0 and 3.0 s) for return periods of 72, 475 and 2475 years. The unified hazard spectra of two selected rock sites at Alexandria and Mersa Matruh Cities were provided. Finally, the hazard curves were de-aggregated to determine the sources that contribute most of hazard level of 10% probability of exceedance in 50 years for the mentioned selected sites.

The effects of the near-surface geology on the ground-motion at New Borg El-Arab City were evaluated in the current work based on the analysis of the ambient noise records (microtre-mor). Sixty-nine microtremor measurements have been done in the studied area. The dataset was processed using horizontal-to-vertical-spectral ratio (HVSR) technique to estimate the fundamental frequencies corresponding to the ground-motion amplification due to the soil deposits. By spatial interpolation of the resulted fundamental frequencies (f 0) of all the measured sites, the zonation map was produced. This map was correlated with the geological features of the study area and demonstrated that the fundamental frequency ranges between 5.8 Hz and 7 Hz were corresponding to the sites located over Quaternary deposit. However, the fundamental frequencies (f 0) increased in the middle of the study area due to presence of parallel Alexandria limestone ridge. Finally, site effect was highlighted by performing a site response analysis. It indicated that, the PGA at surface of the analyzed site is 0.047 g and the maximum spectral acceleration (SA) is 0.157 g. It was also found that, the maximum spectral period from site response analysis is in a good agreement with that one from HVSR technique. This confirmed the robustness of HVSR for determination of fundamental period or frequency.

15th May City, 12 km to the southeast of Helwan city, is one of promised cities planned in 1986 by the Egyptian government through its program to withdraw the population from the condensed central Nile valley to the side parts of the Nile valley Egypt. The present study runs on the famous and known place of the city that is called ''the cave''. The main target of this study is to detect the nearly shape of this cave and estimate its extension and dimension parameters. This study embraces, two dimension electrical resistivity, and shallow seismic refraction surveys. The two dimension electrical imaging technique was interpreted in terms of depths and thicknesses of the geoelectric layers, on this regard, it suggests a succession of one to two layers, and in addition, the boundaries of the cave could be sensed. The shallow seismic refraction technique results revealed a succession of one to two seismic layers. These layers illustrated from both techniques are limestone ''calcite to dolomite'' layer, and the second layer ''fractured limestone''. On the other hand, these parameters allow for separating the area into parts of different competence nature and consequently different appropriateness, and stand to detect and draw the boundaries of the cave underground. Finally, it is outstanding to mention that, within the investigated depth of seismic profiles, their interpreted layers are in close agreement with both shape and thickness of the interpreted layers from the R2D sections and this chains the results obtained from both techniques especially in the geotechnical survey.

The 19 October 2012 earthquake (M L = 5.1) occurred in the northern continental margin of Egypt within the Nile Cone at latitude 32.35° N and longitude 31.27° E. The quake was felt over a wide area in north Egypt and East Mediterranean countries, but no casualties have been reported. This area had experienced the large earthquake (Ms = 6.7) of 12 September 1955. The fault plane solution of the 19 October 2012 earthquake is here presented based on the digital seismograms recorded by the Egyptian National Seismological Network (ENSN) and other regional seismic stations. The analysis is carried out using the well-known techniques of first motion polarities of P-wave and the amplitude ratios of P-, SH-, and SV-waves with lower hemisphere projection. The fault plane solution based on the first P-wave onset demonstrates a left lateral strike-slip faulting mechanism , while the solution based on both P-wave polarities and amplitude ratios of P-, SH-, and SV-waves reveals a reverse fault with strike-slip component trending NW–SE to NE–SW, in conformity with the N–S compression along the Hellenic Arc convergence zone. Following the Brune's model, the source dynamic parameters for the 19 October 2012 earthquake are estimated as corner frequency = 1.47 Hz, fault radius = 0.7 km, stress drop = 22.1 MPa, seismic moment = 2.80E + 16 Nm, and moment magnitude M w = 4.9. These parameters may provide important quantitative information for the seismic hazard assessment studies.