1 Introduction

One of the numerous new cities being built in Egypt is New Aswan City. It was established in 1999 and built to address the issue of insufficient accommodations. The location under study is on the western riverbank of the Nile, between latitudes 24°09′20″ and 24°13′07″N and longitudes 32°50′18″ and 32°52′08″E. The recent study conducted the seismic survey for the non-studied extension of New Aswan City (Fig. 1). The aims of the current study are to apply shallow seismic refraction and MASW technique to estimate the compressional and shear wave velocities for geotechnical parameters estimation and Vs30 computation to determine site class and to estimate the soil amplification and site natural periods of the study area, according to the National Earthquake Hazards Reduction Program Provisions (NEHRP, 2003) and ECP-201 (2012), to avoid any probable soil-building interaction effects throughout the construction in the extension of New Aswan City.

Fig. 1
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Location of the study area with SSR and MASW profiles

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The assessment of ground response is one of the most important and often encountered issues in geotechnical earthquake engineering. It is well known that any probable damage to buildings by earthquakes is significantly related to the subsoil conditions (Kanai, 1952; Ooba, 1957). Therefore, the obtained data on the regional soil conditions will be crucial for risk evaluation and establishing mitigation strategies. To assess the essential building characteristics and clarify issues regarding underlying rocks and soils, the shallow seismic refraction and Multi-Channel Analysis of Surface Wave (MASW) techniques are employed for geotechnical site investigation purpose (Park et al., 1999). Rayleigh wave analysis of seismic signal recordings yields shear wave values for the surface/subsurface soils (Miller et al., 1999; Mohammed et al., 2020; Xia et al., 2000). Practically, these geophysical methods may precisely identify a subsurface bedrock as well as lateral and vertical soil property variations (Whiteley, 1994).

There are various case studies where collaborative geophysical approaches have been used such as refraction, MASW, and ERT for geotechnical site evaluation (Abudeif et al., 2017; El-Moghazy, 2017; Fat-Helbary et al, 2019a, 2019b; Hamed, 2019; Mohammed et al., 2018) and landslide detection (Grit & Kanli, 2016) in addition to dam safety research (Hodgkinson & Brown, 2005; Lankston, 1989; Yilmaz et al., 2006).

2 Overview of Geology and Earthquake Activity

Numerous authors have examined the overall geologic framework of the studied area and its environs, including Issawi et al., (2009a, b), El Bastawesy et al. (2010), and Yousif (2019). Outcropping Precambrian crystalline hard igneous and metamorphic rocks are predominant in the geology of the Aswan area, and these rocks are overlain by a Cretaceous Nubian Sandstone deposit (EGSMA, 2002).

Basement rocks and subsequent weathering products form the bottom of the stratigraphic succession. Most of these are covered by sandstone formations. The Aswan area has a sandstone sequence that is anywhere from 70 to 162 m thick. Based on the existence of oolitic iron ore deposits, it has been classified into three distinct layers (Attia, 1955; Youssef, 2003). The Abu Aggag Formation, dating back to the Turonian period, is the oldest depositional layer and is composed of coarse sandstone with mudstone interbeds. The Timsah Formation consists of siltstone, sandstone, shales, and an iron ore deposit; it dates to the Coniacian to Santonian periods and is situated above the Abu Aggag Formation. The Um Barmil Formation, made up of moderate-sized sandstone with claystone intercalations and dating back to the Campanian period, lies northeast of the research area. The Nubian Sandstone is covered by Quaternary sediments, including Darb El Gallaba gravel, conglomerates, playa, alluvium-eluvium, and surficial sediments that are primarily alluvium (Fig. 2).

Fig. 2
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Geologic map of study area (a); the main geologic cross-section shows the lithologic succession (b) (after EGSMA, 2002)

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Fat-Helbary et al. (2006) used geophysical and geotechnical data to study the initial section of New Aswan City located directly along the riverbank. They concluded that there are two to three underlying layers in the studied region; the first layer is fine sand intercalated with fragments of clay. The second stratum is mostly formed of fragments of fracture of sandstone intercalated with gravel. Finally, the third layer is composed mainly of sandstone. In addition, the structural trend analysis technique for the acquired magnetic data is utilized to determine the location of the tectonic lines for the area. The results indicate that there are two major faults more or less in the N–S to NW–SE directions, in addition to minor faults with various trends (Fat-Helbary et al., 2004).

Regional basement rock uplift and regional faulting govern the structural layout of the Aswan region (Issawi, 1968). In the Aswan highlands, Precambrian basement granite has been exposed as a consequence of the structural high that has developed east of the Nile Valley. The Nubia Formation and underlying stratigraphic units have been gradually tilted toward the west and northwest. These units often experience regional dips of 1° to 2° (WCC, 1985). Local faults are overlaid on the largely horizontally structure of the Nubian Plain, Sinn El-Kaddab Plateau, and Aswan Hills to the east of Lake Nasser. The region of Lake Nasser, which hosts multiple notable faults inside the Western Desert fault networks, was divided into several categories according to the faults' patterns. The east-west trend (Kalabsha and Seiyal fault) and north-south trend (Khor El Ramla, Kurkur, Gebel El-Barqa, Gazelle, and Abu Dirwa fault) are the two most significant faults among them. The spillway fault is one of several dispersed faults (El Bohoty et al., 2023) found in the region (Fig. 3).

Fig. 3
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Active and inactive fault system map of the study area (after Conoco, 1987)

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The earthquake coverage of the Upper Egypt region grew more consistent with the beginning of worldwide seismograph operation and data analysis in 1900, but it is still at the threshold value of magnitude 4.5 attributed mostly to the distance from seismic stations. Seismographs at Aswan and Abu Simbel were added by the Helwan Observatory in 1975, enabling identification of the epicenters of the seismic events that were too minor to be felt. After the earthquake of November 14, 1981, a radio-telemetry network of 13 stations was set up to monitor micro-seismic events in the northern half of the Nasser Lake. According to Simpson et al. (1986), the earthquake activity in and around the Kalabsha fault is centered on two separate clusters in the Aswan region. Several scientists and researchers have studied the Aswan area's seismic activity (e.g., El-Khashab et al., 1991; Kebeasy et al., 1987; Simpson et al., 1986). The seismic activity map surrounding the study region is constructed using the new earthquake data catalog for the years 1981–2021 (Fig. 4). The catalog's analysis reveals that seismic activity is localized at the point where the N–S and E–W fault networks intersect. The spillway fault region, contrarily, is near the research area and has experienced a significant rise in microearthquake activity (El-Bohoty et al., 2023). The yearly rise in lake water level, which exceeded 180 m and reached its highest level (181.6 m) in 1999, has been ascribed to the abrupt increase in seismicity in the spillway region from 1999 to 2002. After the lake's water level reached 180.11 m in October 2007, the earthquake of 2010 and its aftershocks occurred.

Fig. 4
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Seismicity map of the study area for 1981–2021

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3 Geophysical Measurements

By establishing an acquisition mechanism for forwarding, mid-point, and reverse P-wave shoots (Hamed, 2019; Hamed et al., 2023; Fat-Helbary et al., 2019b), as well as a forward system for surface wave shootings, 21 profiles for both shallow seismic refraction and MASW techniques were established to calculate the Vp and Vs of the subsurface soil in the region. Each measured location has two types of profiles. These profiles were oriented according to the topography of each site.

In this study, the shallow seismic refraction (SSR) data were collected utilizing a 48-channel signal geometrics seismograph; therefore, seismic waves were generated using a 15-kg sledgehammer and recorded by vertical geophones (40 Hz), which had to be used and firmly fastened to the ground for good ground coupling (Fat-Helbary et al., 2019b; Luna & Jadi, 2000; Mohammed et al., 2020). All of the profiles were constructed with 115 m length with 5-m geophone spacings. Three shots were carried out: two at the terminals of each profile and the third one in the midpoint (Fig. 5). The sample interval and total recording length were 0.25 ms and 0.75 s, respectively.

Fig. 5
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Refraction survey with shot location and geophone spreading

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Using the 1D MASW approach, S-waves were produced (Park et al., 1999, Abbas et al., 2023). Hence, MASW profiles were performed along the same profiles of seismic refraction lines (P-wave). Consequently, the surface wave survey was done using a low-frequency (4.5 Hz) vertical geophone (Stokoe et al., 1994), utilizing a seismic array with length of 46 m and 2 m offset distance. It was suggested to use a 15-kg sledgehammer to create seismic energy for active source surface wave studies. To prevent near- and far-field effects, two shoots were conducted at distances of 5 and 10 m before the first geophone with vertical stacking from three to five shoots to considerably reduce ambient noise (Fig. 6). Consequently, a 1-ms sampling interval with a 2-s total recording length (T = 2 s) is the most typical parameter adopted here.

Fig. 6
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Active MASW data acquisition field setup for generating 1D-Vs model

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4 Data Processing

To analyze the obtained refraction data (forward, middle, and reverse) (Fig. 7a), the SeisImager/2D software package (2019) is utilized. As seen in Fig. 7b, the travel-time curves are produced by considering the survey line's length, space between receivers (geophones), source position, and initial arrival time (Veezhinathan & Wagner, 1990). Travel-time curves are corrected and checked to provide an accurate approximation of the P-wave velocity structure (Sheehan et al., 2005). The ultimate depth-velocity models are represented in two dimensions (Fig. 7c). Depending on the numbers of layers, which rely on how much the slope of the travel-time curve varies (Ellefsen, 2009), two- or three-layered models have been implemented in the processing. The travel-time dispersion curve, on the other hand, clearly indicates a slight change and reveals three layers. The third layer has a slightly different velocity value and has been regarded as a transition zone between the over- and underlaid strata. Due to its small thickness, it is simply considered as two layers (Fig. 7c).

Fig. 7
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Steps of shallow seismic refraction processing a forward, middle, and reverse shootings; b travel-time curve, and c 2D velocity model

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To compute the 1D-MASW velocity model, SeisImager/SW software (SeisImager, 2009; Underwood, 2007) was utilized. The MASW data processing passed through converting of the recorded signals from time domain (Fig. 8a) to frequency domain (Fig. 8b), followed by creating dispersion curves (Fig. 8c). The frequency range of 5–42 Hz has been selected for the frequency-phase velocity image. Finally, a profile of the shear wave velocity has been generated (Fig. 8d).

Fig. 8
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Procedure of MASW data processing using SeisImager software (ex. Profile No. 8)

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5 Results and Data Interpretation

The description of seismic refraction records is often applied to compute the correct velocities for each investigation layer as well as to determine the depth under the shot point and each geophone. The interpretation of the data is based on an iterative ray-tracing approach, and the final 2D velocity-depth models for subsurface in form of Vp were generated (Fig. 7e). For the same site, S-wave dispersion curves and corresponding shear wave 1D-velocity models have also been constructed (Fig. 8). The ultimate seismic velocities of many strata were calculated for each observed location.

Typically, we chose a two-layered model because of two considerations. The very little variations in seismic velocities caused us to define it as two different strata. The second hypothesis is that, in accordance with the geologic map and lithological cross-section shown in Fig. 2, the measured points are located in either the Abu Aggag Formation or Timsah Formation, both of which often have a few meters of Quaternary deposits on the top. In addition, the rocks exposed in the work area support our explanation.

Therefore, two layers in the seismic cross-sections of subsurface strata are produced. According to the distinct variation in shear wave velocities, a surface layer made up of friable sand and gravel particles constitutes the first geoseismic zone, which ranges in thickness between 0.5 and 5 m, with P-wave velocities from 927 and 1900 m/s and shear wave velocities (Vs) between 260 and 630 m/s. The second geoseismic layer has maximum seismic wave velocities (Vp), which vary from 2000 to 3300 m/s and Vs from 520 to 1150 m/s, and comprises intercalations of sandstone with shale and clay. The results of Vp, Vs, and the corresponding geotechnical parameters calculated for all investigated profiles are summarized in Figs. 9, 10, and 11 and Table 5.

Fig. 9
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P and S  seismic wave velocity distribution for the first (a, c) and second (b, d) geoseismic layers along the study area

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Fig. 10
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Selected elastic and geotechnical parameters for the surface layer: a density, b Poisson’s ratio, c N-value, d material index

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Fig. 11
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Selected elastic and geotechnical parameters for the second layer: a density, b Poisson’s ratio, c N-value, d material index

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5.1 Elastic and Geotechnical Parameters

The geotechnical site characteristics are crucial in the calculations of intensity distribution since rock sites regularly provide lower ground-motion intensities than less stiff areas (Dutta, 1984). A limited number of geotechnical criteria were chosen to assess whether subsurface materials were suitable for construction or not. In the current study, the calculated Vp and Vs were utilized to assess the elastic and geotechnical characteristics. Tables 1 and 5 provide an overview of the empirical equations of elastic, geotechnical, and petrophysical parameters used in the current study in addition to the estimated values of those parameters. Currently, four geotechnical parameters have been selected to be discussed briefly here.

Table 1 Definition of elastic and geotechnical parameters used in this work
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Density is one of the essential parameters that demonstrates how density causes the P-wave velocity to rise (Gardner et al., 1974). According to Keceli (2009), density values for the first and second layers range from 1.8 to 2.2 and 2.1 to 2.6 g/cm3, respectively (Figs. 10a, 11a). The second layer is distinguished by considerably large values; this significant increase in calculated values is indicative of a rather high competent rock composition that characterizes the second stratum.

Furthermore, referring to the equation of Telford et al. (1976) and Kearey et al. (2002), Poisson's ratio (σ) shows the relative expansion strain to the relative compression strain under the given load (De Beer & Maina, 2008). Telford et al. (1976) classified the value as being 0.5 for fluids or friable sediments and approaching zero for tough rocks, typically zero for hard rocks, 0.25 for hard soil, and 0.5 for loose soil (Table 2). This parameter's values in this study area are close to each other for the first and second layers (Figs. 10b, 11b). As a result, the sediments in the first and second strata range from being incompetent to significantly competent.

Table 2 Description of soil according to Poisson's ratio and material index (Birch, 1966; Mohammed et al., 2020; Sheriff & Geldart, 1995; Tatham, 1982)
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On the other hand, N-value according to Table 3 is a parameter used in geophysical evaluation to describe the material resistance to penetration by normalized cylindrical pointed bars under a load effect (Stümpel et al., 1984). Hence, the values fluctuated between 22.52 and 301.79 for the first layer (Fig. 10c) and between 171.92 and 1762.59 for the second layer (Fig. 11c), both of which are made up of extremely thick and very dense materials (Bowles, 1984).

Table 3 Relationship between both N-values and type of soil (Bowles, 1984)
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Material index (Mi) is one of the geotechnical parameters that relates to the content of the entire material, the amount of consolidation, and whether or not fluids are contained inside the pore spaces, all of which have an impact on the wave velocities as a result of the medium of the materials (Abd El-Rahman, 1989). According to Sheriff and Geldart (1995), the derived material index values were divided into four major groups for foundational considerations. The two layers' values fall within the group (I) of incompetent to moderately competent soils (Figs. 10d, 11d), which mostly refers to soft to competent deposits for the first and second layers, respectively.

5.2 Vs30 and Site Classification

The microzonation map of any city must be created in accordance with the soil characteristics of that city to construct the optimal master plan. All technical challenges in building originate from disturbances of ground motion, which are controlled by subsurface geology. Therefore, knowledge of near-surface soil parameters, such as their elastic properties and how they affect the propagated seismic wave, is essential for engineering and environmental applications (Mohammed et al., 2020).

Multichannel analysis of surface waves (MASW), which calculates shear wave velocities at shallow depths, is widely used because it makes determining the parameters much simpler and less expensive (Park et al., 1998). Therefore, in the current study, the Vs30 is suggested for examining the amplification factor and site effects on seismic waves propagating in the upper 30 m following data processing, as demonstrated in the previous section. Different velocity distribution maps were created at six different depths, 5, 10, 15, 20, 25, and 30 m, respectively, to determine the mean shear wave velocity variation with depth (Fig. 12). The top 5 m of soil's average velocity distribution (the effective thickness close to structure basements) is crucial, and in some instances, a direct association may be observed between such a high amount of probable damage and low velocity. Two significant zones in the research region's center have low Vs values of around 360 m/s, but when we descend into deeper strata, the value rises to > 760 m/s in the majority of the area, indicating the presence of highly compacted rocks.

Fig. 12
figure 12

Average shear wave velocity distribution maps of the study area down to 5, 10, 15, 20, 25, and 30 m depth, respectively

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Borcherdt (1994) first proposed a site classification depending on Vs30 parameter, which represents travel times from the ground's surface to the topmost 30 m of depth. Subsequently, numerous contemporary seismic codes, including NEHRP, UBC97, IBC2000, and Eurocode8, were developed, using Vs30 to characterize the site (Dobry et al., 2000; Kanli et al., 2006). NEHRP site classification has been adopted in this study (Table 4). Vs30 is calculated using the following equation (CEN, 2004).

$$Vs^{30} = \frac{30}{{\sum_{i = 1}^N {\frac{hi}{{Vi}}} }}$$

where Vi and hi represent the thickness (m) and the VS of ith layer, in a total of N, present in the upper 30 m.

Table 4 Site classification using NEHRP (2003)
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The Vs30 values typically range from 450.8 to 935.4 m/s (Fig. 13); depending on NEHRP guidelines, the region is divided into two classes: class B (Rock) sites are found at the NE, SE, and middle portions of the studied area's western edge, while Class C, which comprises the majority of the interested region, is characterized by very thick soil and soft rock (Fig. 14).

Fig. 13
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Vs30 of the study area based on MASW measurement

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Fig. 14
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Site classification map of the study area based on NEHRP classification

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The Vs30 values of the Dinar area in Turkey are compared to the Vs30 values presented here based on the soil thickness of New Aswan City, Egypt. According to El Bastawesy et al. (2010) and Yousif (2019), New Aswan City is situated on compacted sandstone, shale, and siltstone covered with shallow Quaternary deposits. In certain locations on the surface, compacted sandstone is visible. The estimated Vs30 values range from 450 to 935 m/s according on the soil thickness. The Turkish town of Dinar is situated on a tiny alluvial basin. The Quaternary soft soils throughout the basin's center are over 30 m thick (Kanli et al., 2008). The calculated Vs30 ranges from 160 to 240 m/s in the basin's middle region (Kanli et al., 2006). It is observed that the Vs30 values of both areas are different because of geologic condition (soil compaction and Quaternary deposit thickness) variation in both areas (Kanli 2010) (Table 5).

Table 5 Elastic, geotechnical parameters, Vs30 values, and site classification at the study area
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5.3 Soil Amplification and Site Natural Period

The estimation of site amplification values utilizing Vs30 has been shown to be one of the easiest methods for primarily estimating the amplification factor of seismic ground motion (Dobry et al., 2000; Kanli et al., 2006). Soft soils contribute significantly to earthquake damage and boost the intensity of the shaking that occurs during an earthquake. The shear wave velocity is a well-known index characteristic used to assess soil properties (e.g., soil amplification). Consequently, the Vs data acquired by the MASW technique are employed in the current work to primarily and simply estimate the soil amplification of the site soil in the western extension of New Aswan City. The following equations provide the Vs30 and soil amplification (A) relationships (Midorikawa, 1987):

$$\begin{aligned} A & = 68 Vs^{ - 0.6} \left( {Vs < 1100\,{\text{m}}/{\text{s}}} \right) \\ A & = 1 \left( {Vs > 1100 \,{\text{m}}/{\text{s}}} \right) \\ \end{aligned}$$

The soil amplification map, shown in Fig. 15, displays a qualitative evaluation of the soil's sensitivity to amplification. The resulting soil amplification value varied from 1.1 to 1.7, with high amplification in two central zones and at the southwest regions, where the layers were primarily loose deposits from the alluvial plain (Table 6).

Fig. 15
figure 15

Amplification susceptibility map: amplification values (colored) plotted with Vs30 (solid contour lines) for the study area

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Table 6 Amplification and site natural period for each point in the study area
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Therefore, places with soft sediments in the soil, such as loose sands, silty clay, and gravels, are much more vulnerable to amplification. Lower shear wave velocities near 400 m/s are correlated with the outcrop of poorly consolidated Quaternary sediments in the work area when the amplification susceptibility map and Vs30 results are combined. Additionally, regions that are thought to be more prone to soil amplification based on the overlay approach correspond with areas of calculated lower shear wave velocities (Vs30 ≤ 440 m/s).

The fundamental site period (Ts) constitutes one of the significant indications for seismic hazard assessment, which is used to represent the initial phase of vibrating in soils. The following equation is used to compute it, which is determined by the thickness and Vs of the underlying soil (Kramer, 1995).

$$Ts = \frac{4H}{{Vs}}$$

where Vs is the average shear wave velocity of the overburden soil, and H is the overall thickness of the alluvium deposits. In the current study the depth (H) in the equation above is set to 30 m, since the depth of 30 m below the surface is crucial for the construction of building foundations and is vulnerable to amplification of seismic ground motion (Boore, 2003; Boore et al., 2011). In addition, this assumption was obtained by Kramer's suggested quarter wavelength approximation (1995).

The projected natural period for each chosen location in the research region is displayed in Table 6. Figure 16 is the map of the natural site period that was created to show that there are three areas, two at the center and the third one in the southwest portion of the research region, where the soils are primarily soft deposits (Table 6), due to the lowest Vs30 values of the alluvium deposits. The locations in the study area where the soils are composed of soft sediments, such as loose sands, silty clay, and gravels, are much more prone to amplification with higher site periods ranging from 0.199 to 0.27 s.

Fig. 16
figure 16

Natural site periods for the study area

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A number of soil properties, such as the lateral variation, soil type (sand, silt, clay), shear modulus, and damping ratio, have an impact on soil amplification and site natural periods estimation (Midorikawa, 1987). Consequently, in this study, the utilized empirical relationships were employed in the current research and only used to calculate the region's initial soil amplification and resonance frequency from the Vs30 value, since it is the easiest and cheapest way to do that. Therefore, the obtained results have to be used as a guide and first step specially for the natural periods of the site because of the importance to avoid the destructive effect of any probable seismic activity that could happen in proximity to the study area (see Fig. 4). Therefore, the Nakamura technique (the Horizontal to Vertical Spectral Ratio method) is recommended for use for microtremor measurements to accurately estimate the value of resonance frequencies, which represent the real and direct measured natural periods for the site, as a result of the impedance contrast between the soil and the underlying bedrock.

5.4 Soil-Structure Interaction (Dynamic Interaction Problem)

The estimated natural period is especially high because of the clay and clayey sand sediments scattered over much of the area and typically has a lower Vs30 value. Because of the greater Vs30 values of the terrace and colluvial sediments, the other sites in the area have natural periods ranging from 0.13 to 0.19 s. The damage to the structures will often be particularly severe if the fundamental site period of the sediments at such places approaches the natural period of the buildings.

The research region was divided into two zones according to their periods since the period estimated by the empirical equation will be restricted to 0.12 and 0.27 s, which does not vary significantly. This was done to identify which buildings should be avoided in every zone. The first zone's periods range from 0.12 to 0.19 s, and the second zone's periods range from 0.19 to 0.27 s (Fig. 16).

Indeed, calculating the seismic loads according to design codes like NEHRP (2003), EC8, ASCE7-10, UBC 97, and ECP-201 (2012) necessitates estimating the building's fundamental period. The basic period could be calculated using a variety of techniques. To predict the period of the buildings, however, design regulations advise using simplified empirical formulas as a preliminary stage. The kind and height of buildings that should be avoided in these two districts are identified using the techniques proposed by ECP-201 (2012) and NEHRP (2003). Table 7 lists the calculations in the cited codes as well as the building height restrictions of each zone. In particular, the severity of the destruction to the buildings increases as the fundamental frequency (natural period) of the strata matches that of the building.

Table 7 Equations for determination of buildings period by ECP-201 (2012) and NEHRP (2003) and height limitations in study area
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In principle, it is necessary to accept a defined period within every zone for the construction of safe buildings if somehow the buildings are divided into three categories of 1–3, 4–10, and 10–15 story buildings (typical building height in Egypt). Due to the exactly equal values of the periods among both buildings and soil, Table 8 demonstrates that one- to two-story buildings are much more particularly prone to seismic risk in the majority of the study region; in addition, one- to three-story buildings are more susceptible to damage in three other areas in the study region.

Table 8 Natural period of building with different stories (Kramer, 1995)
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Consequently, the soil characteristics of New Aswan City's western extension frequently provide a possible risk of damage, particularly to one- to three-story structures during an earthquake. Table 9 lists the applicable requirements for structures based on ECP 201 (2012) and NEHRP (2003). There would be no restrictions for such buildings if their period did not fall between 0.12 and 0.19s in zone 1 and between 0.19 and 0.27s in zone 2; therefore, Table 9 presents them  correctly.

Table 9 Classification of buildings based on their height in study area
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6 Discussion

Generally, the study area is composed of two layers, according to the lithologic cross-section (Fig. 2), and the seismic cross-sections of the surface/subsurface strata that are obtained from the shallow seismic refraction data. The surface layer has Vp 927–1900 m/s and shear wave velocities (Vs) around 260–630 m/s to a depth of approximately 5 m. The second layer extends from 5 to 20 m depth; it has Vs range values between 520 and 1150 m/s and corresponding Vp values between 2000 and 3300 m/s. The higher compressional and shear wave velocity values could be related to the consolidated sandstone mainly occurring in the study area.

Since bedrock site frequently produces lower ground-motion intensities than less rigid places, the geotechnical engineering properties are critical for any future infrastructure development project. The elastic properties of rocks that are close to the Earth's surface including their impact on wave propagation are critical in seismic design. To determine whether subsurface materials are acceptable for construction, some selected geotechnical parameters have been chosen to be estimated for the purpose. As a result, estimations were made for the soil's dynamic characteristics, including density, Poisson's ratio, rigidity modulus, Young's modulus, bulk modulus, allowable maximum bearing capacity, and ultimate bearing capacity. Those factors, which depended on Vs and Vp, are acquired through compressional waves created using shallow seismic refraction's 2D profiles and from 1D-Vs models generated from the MASW approach. For instance, it has been calculated that the first- and second layer's densities vary between 1.8 and 2.2 g/cm3 and 2.1 and 2.6 g/cm3, respectively. A significant increase in calculated values is an indication of a rather high competent rock composition that characterizes the second stratum.

The generated Vs models were used to calculate the Vs30. Utilizing the NEHRP site classification for earthquake resistance design, it can be shown that the Vs30 values almost fall between 450 and 935 m/s. Consequently, the area is split into two groups, in accordance with NEHRP standards: The western edge of the investigated region has Class B (Rock) sites (North-East, South-East) and central parts; however, Class C makes up the rest of the research area and is distinguished by incredibly thick soil with soft rock. In addition, the soil amplification map derived from MASW technique displays values between 1.1 and 1.7, with high amplification in the same three zones which existed in Vs30 map. Additionally, according to the produced site natural period map, the three zones mentioned above, in which the soils are composed of soft sediments (such as loose sands, and gravels), are more prone to amplification with significantly higher site periods. However, the natural periods at the other sites in the city are lower. So, we could say, the research area is separated into two zones according to the calculated natural periods. If the structures are divided into three categories of 1–3, 4–10, and 10–15 story buildings based on the typical construction heightening in Egypt, one- to three-story structures seem to be more susceptible to earthquakes in most of the study region since the periods between the structure and the soil are identical in value.

In general, the higher values of soil amplification and natural periods have mostly been interpreted based on the sediment content of the soft alluvial plain as well as some river terraces. Accordingly, places with soft sediments, such as unconsolidated Quaternary deposits, are much more vulnerable to amplification. The geologic features observed in the field work and deduced from the scientific literature indicate that the moderate to compacted sandstone which may intercalate with shale is dominant and plays an essential role in the geotechnical parameter's high values, with exception of the three previously mentioned zones, which may suffer from higher soil amplification.

7 Conclusion

In the western extension of New Aswan City, we conducted 21 pairs of profiles of shallow seismic refraction and MASW to measure the compressional and shear wave velocity. The sedimentary rocks in the study area are distinguished into two layers, the first of which could be made up of loose sand and clay, while the second layer represents the bedrock, which has relatively high values of both Vp and Vs. Based on these geophysical characteristics and geologic evidence, we have deduced that the foundation layer is made up of compacted strata of sandstone. Additionally, the geotechnical parameters have been estimated for site effect evaluation. The NEHRP classification system has been applied, which reveals that the majority of the study area is classified as type C. Empirical equations have also been used to obtain the site amplification factor and the soil's natural period. We could conclude that the geologic features and compactness level of the rocks in the study area play an essential role in the compressional, shear wave, geotechnical parameter, amplification and site natural period values. All of these obtained geophysical criteria will help in establishing the suitable and safe design for the study area.

8 Recommendations

Due to the limitations of financial support, we could state that the data collected provide a broad perspective of the geotechnical features for the research region. A condensed study must be conducted to track any potential minor lateral variations in the soil's characteristics. In addition, we recommend using other geophysical tools such as the Nakamura technique to assess the accurate natural period for the site.