1 Introduction

The Egyptian north-western coastal region is among the most hopeful areas for future development, the establishment of new cities with a global stamp, and the creation of new projects that provide additional opportunities for economic development and face the population increase. One of these projects is a hotel building, where our study lies, in El-Alamein new city on the Mediterranean coast covering about one square kilometer. It lies between latitudes 30° 58′ 15.18′′ N–30° 58′ 28.27′′ N and between longitudes 28° 45′ 23.87′′ E–28° 45′ 23.87′′ E (Fig. 1). Any new project requires site investigation, which consists of obtaining information that may impact the project's construction (Clayton et al. 1995; Baniela et al. 2021). Nowadays, geophysical methods come into play as efficient tools that precede the construction process for studying rock succession, existing structures, saltwater intrusion, cavities, …. etc. Among all geophysical techniques required to image the near surface, both ERT and SSR represent an excellent modern technique used for environmental, engineering, geotechnical, groundwater, and saltwater intrusion investigations (Basheer et al. 2013; Hewaidy et al. 2015; Ma and Zhang 2015; Kazakis et al. 2016; Mohamaden et al. 2016; Goebel et al. 2017; Alabjah et al. 2018).

Fig. 1
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a The location of our study area, b Digital elevation model, c Locations of ERT and SSR profiles

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In ERT method, the subsurface layer’s resistivities are highly affected by the presence of water, which directly affects the measured resistivity values (El-sayed and Mohamaden 2018). Our area under investigation lies on the shoreline, so it is essential to study the intrusion of water in the layers and any abnormal changes in the homogeneous layers that reflect clay lenses to avoid them (Alshehri et al. 2021; Satheeskumar et al. 2021; Basheer and Salama 2022). In SSR method, the velocity provides a mechanism for measuring the strength and evaluating the quality of rock materials, since it depends on the density and elasticity of the material through, which the energy is passed (Almalki et al. 2011; Comina et al. 2021; Ray et al. 2021). Because beach sand makes up the surface of the study area, it is crucial to understand the geotechnical properties of the various strata and how they affect the height of structures that are planned to be built (Sakr et al. 2021; Basheer and Salama 2022).

The results from the two applied methods will be integrated to accomplish the primary objectives of our current study which are the delineation of the shallow subsurface layering, the detection of seawater intrusion and its effects on the foundation layers, and the determination of the geotechnical characteristics of the rocks that make up the area and its relationship to the types of buildings that can be constructed.

2 Geological settings

Two geomorphic units make up Egypt's north-western coast, which runs parallel to the shoreline. It is arranged with a northward sloping piedmont zone between the southern tableland and the northern coastal region (Shata 1957; Hammad 1972; Misak 1974; Raslan 1995; Massoud et al. 2015). The top-most surface deposits of the coastal region, where our area under investigation lies, are covered by sedimentary rocks belonging to the Tertiary and Quaternary ages as shown in Figs. 2 and 3 (Shukri et al. 1956; Butzer 1960; Said 1962, 1990; Atwa 1979). The coastal region is made up primarily of oolitic limestone of varying degrees of hardness that was formed during the Pleistocene period but is occasionally missed or deformed due to local structures and/or erosion effects. It is characterized by two elongated foreshore and inland ridges and shallow depressions (Hammad 1966; Shata 1971). Sand dunes, sand beaches, and marches are some of the additional features that may be found in the coastal region (Massoud et al. 2015; Basheer and Salama 2022). The Pliocene Hagif and Middle Miocene Marmarica formations, that made mostly of fissured limestone, are the primary Tertiary deposits covering the southern tableland (Yousif et al. 2013).

Fig. 2
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Geology of the study area (modified after Basheer and Salama 2022)

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Fig. 3
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Stratigraphy of the study area (modified after Hilmy et al. 1978; El-Sharabi 2000; El-Sayed et al. 2021)

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Tectonically, “The unstable shelf” is occupying most of northern Egypt (Said 1990) including the area under investigation. Since the Precambrian until the present, the study area and its environs have been affected by various tectonic events. Three tectonic trends can be seen in the basement rocks, including the Red Sea (NNW), Tibesti (NE), and Nubian (N-S) trends (BAPETCO 2007). Additional E-W tectonic patterns developed from the Late Paleozoic to the Late Jurassic (Sultan and Halim 1988). An oceanic trench that contains the Hellenic subduction zone (HSZ), which is the nearby boundary between the African plate and the Eurasian plate, has another tectonic effect on the Mediterranean (Gordon et al. 2003; Royden and Papanikolaou 2011; Le Pichon et al. 2019; Basheer and Salama 2022).

3 Methodology

3.1 Electric resistivity tomography (ERT) measurement

In ERT survey, two electrodes (current, or A–B) are used for current injection into the earth and another two electrodes (potential, or M–N) are used to measure the potential drop between potential electrodes caused by the injecting current on the ground. Then, by dividing the measured potential difference (∆V) by the input current (I) and multiplying the result by a geometrical factor (K), where (a) represents the radius or the distance from the reference point to the measurement point, we got the apparent resistivity (ρapparent), (Loke and Barker 1996; Xayavong et al. 2022).

$${\uprho }_{{{\text{apparent}}}} = \left( {\frac{{\Delta {\text{v}}}}{{\text{I}}}} \right){\text{K}}$$
(1)
$$K\, = \,2\pi a$$
(2)

In this study, the multi-electrode technique is used which consists of a 48-electrodes on a multi-core cable implanted into the ground at a fixed spacing every six-meter using a Wenner array (Fig. 4a), and the data was obtained along nine profiles distributed over the area under investigation directed from NW to SE (Fig. 1). This array is advantageous because it offers a high signal-to-noise ratio, which is typically employed for strong vertical resolution and a clear image of the subsurface (Baharuddin et al. 2011; Eissa et al. 2016; Sakanann et al. 2020). In the IRIS Syscal Pro resistivity meter used in this study, the relays are located which enable the selection of any four of those electrodes two for (A, B) current injection and two (M, N) for potential measurement for each measurement by a sequence of readings established and recorded in the equipment's internal memory. A laptop connected to a resistivity meter checks that all the electrodes are connected and properly grounded before measurements start (Fig. 4b).

Fig. 4
figure 4

a The Wenner electrode array (modified after Xayavong et al. 2022), b Create a pseudo section using a series of measurements (modified after Rai et al. 2013)

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3.2 Shallow seismic refraction (SSR) measurement

The seismic wave moves down and along the various boundaries of refractors. The critical angle (θc) -the angle of incidence at which the refraction angle is 90 degrees- occurs when the velocity in the deeper layer (V2) is higher and increases with depth (Sjogren 1984; Kearey et al. 2002; Lowrie 2007). This results in the creation of a refracted ray with (θc) that moves along the interface with a high velocity (V2). The wave's interaction with the interface results in a secondary source that creates upgoing wavefronts that emerge at θc, or what Huygen's principle refers to as a head wave. Only critically refracted waves are concerned in seismic refraction surveys. If falls at an angle less than θc, part of it is reflected and the other remaining portion is refracted at a lower angle while if it falls at an angle higher than θc, all the energy is reflected with no refraction ray (Milsom 2003). Only the first arrival of these energies is detected by the geophones that are arranged along the ground from the source and these arrivals represent a direct ray or a refracted ray (Fig. 5). To store them in the stacking memory, it is first transformed to digital signals. The electrical signal is amplified by the seismograph from several thousand to several ten thousand times and the results are recorded as waveform data (Telford et al. 1990a, b; Reynolds 2011). Nine seismic profiles are aligned along the NW–SE direction parallel to the coast of the Mediterranean Sea (Fig. 1) to record compressional (primary or P-) waves (Fig. 6a) and shear (or S-) waves (Fig. 6b). The geophones and shot points are in-line with three different relative positions of the shot point. In the first (Normal) arrangement the shot point is placed 5 m from geophone 1, in the second (Middle) arrangement, the shot point is placed in the intermediate point between geophone 24 and 25, and in the third (Reverse) arrangement the shot point is placed 5 m from the last geophone (Fig. 7). The seismograph, which has been used in this study, is “Geometrics, Smartseis”. The distribution of the ERT profiles is placed in the same sites of SSR (Fig. 1) to give a good correlation between them and to prevent ambiguity in the measurements of one of the two methods.

Fig. 5
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Seismic ray path of direct, reflected, and refracted waves (modified after Reynolds 2011)

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Fig. 6
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a Ground particle movements and elastic deformations caused by the passage of P-wave by a sequence of rarefactions (R) and compressions (C), b Ground particle movements and elastic deformations caused by S-wave (modified after Bolt 1982; Lowrie 2007)

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Fig. 7
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The location of shot points for the seismic refraction survey profiles (modified after Xayavong et al. 2022)

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4 Results and discussion

4.1 Electric resistivity tomography (ERT) results

The Res2dinv resistivity inversion software edited in 1998 is used to produce a two-dimensional resistivity model by automatically inverting the data that has been collected (Edwards and Hillel 1977; Griffiths and Barker 1993). Using the least square inversion by Jacobian matrix calculation, a representation of the true resistivity distribution as a function of depth was created (Loke 2001) to locate the high resistivity zones and the low resistivity zones that attributed to water-saturated layers. Saline water typically has an extremely low resistivity, averaging around 0.2 Ohms.m (Nowroozi et al. 1999; Rao et al. 2011), whereas the resistivities of sand saturated with a saltwater range from 8 to 50 Ω.m (Adepelumi et al. 2009; Kouzana and Benassi 2010; McInnis et al. 2013; Basheer et al. 2014; Basheer and Salama 2022). Silty sand that is a mixture of both granular and fine particles has lower electrical resistivity than dry sand that has exceedingly high resistivity (Fukue et al. 1999; Munoz-Castelblanco et al. 2012) because the grain size fraction can affect the ease of current propagation inside each geomaterial, with fine particles allowing current to flow easily and producing low resistivity values and coarse grains providing high resistivity values due to the difficulty of current propagation (Abidin et al. 2012). Consequently, the resistivity shows a sharp reduction even with a little raise in water content (Archie 1942; Gupta and Hanks 1972; McCarter 1984; Kalinski and Kelly 1993; Yan et al. 2012). The inverted data clearly show that three layers can be observed in the area under investigation along profiles 1 (P1) and 5 (P5) while defined two layers along profile 9 (P9). Profile 9 is closest to the Mediterranean Sea, so the water interference appears at a high level (Fig. 8c). This level decreases as we move far from the seacoast until profile 5 (Fig. 8b) and decreases further until reaching profile 1 (Fig. 8a) (the farthest from the sea).

Fig. 8
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2-D electrical resistivity along profile a 1, b 5, c 9

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The top layer, which is noticed along all profiles, has high values for resistivity from about 500 Ω m to 800 Ω m in profile 1 with depth from the surface to about 13 m, between 500 and 750 Ω.m in profile 5 with depth from the surface about 10.5 m, and between about 200–720 Ω m in profiles 9 with depth from the surface to about 8.5 m. The second layer, observed along profiles 1 and 5, is distinguished by moderate values from 200 to 500 Ω m from a depth of 13 to about 18 m as observed in profile 1 and from 10.5 to 14 m as observed in profile 5. The third layer, observed along profiles 1, 5, and 9, is distinguished by low resistivity values ranging between 0.1 to about 200 Ω m. These low values exist at different depths from less than about 8.5 m (as in P9), below about 14 m (as in Profile 5), and below 18 m (as in Profile 1). This reflects the seawater intrusion in the sand layer (sand saturated layer).

4.2 Shallow seismic refraction (SSR) result

The times of the first arrival measured at geophones located at varying distances from the source make up the data obtained from a refraction survey. When the data are displayed on a graph with vertical time axes and horizontal geophones offset axes, the time-distance curve is obtained. Any line that fits the plotted data has a slope whose reciprocal equals the velocity. For simplicity and similarity between the nine profiles, only 3 seismic profiles of 1, 5, and 9 will be used as an example in the present study, and when there is a noticeable difference in seismic velocities, a comparison with the other six profiles will be made. The time distance curve for P1 (Fig. 9 a and b), P5 (Fig. 10a and b), and P9 (Fig. 11a and b). Then, to create geo-seismic cross-sections, the layer's depth, thickness, and velocities under each geophone were determined using Seisimager software. By linking to nine test wells with this information, accurate and integrated information can be obtained. It is clear from the interpreted data that there are three layers along profile 5 while there are two layers along profiles 1 and 9.

Fig. 9
figure 9

a Time-distance curve of P-waves, b Time-distance curve of S-waves, c Vertical distribution of Vp waves, d Vertical distribution of Vs waves of profile 1

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Fig. 10
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a Time-distance curve of P-waves, b Time-distance curve of S-waves, c Vertical distribution of Vp waves, d Vertical distribution of Vs waves of profile 5

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Fig. 11
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a Time- distance curve of P-waves, b Time- distance curve of S-waves, c Vertical distribution of Vp waves, d Vertical distribution of Vs waves of profile 9

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The top layer (beach sand) consists of beach sand which has P-wave velocities ranging between 400 and more than 950 m/sec (Figs. 9c, 10c, 11c), S-wave velocities ranging between 150 and 330 m/sec (Figs. 9d, 10d, 11d), and the thickness varies from 10.08 m (as shown in well 4 along P5) to 16.1 m (as shown in well 3 along profile 1). The horizontal variations of both waves’ values are high in the southwestern corner and gradually decrease toward the northeast direction of the area under investigation (Fig. 12a and b).

Fig. 12
figure 12

a Vp for layer 1, b Vs for layer 1, c Vp for layer 2, d Vs for layer 2, e Vp for layer 3, f Vs for layer 3

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Layer two consists of fine sorted sand (Silty sand) and its P-wave velocities change with the depth and ranging between 700 and 1300 m/sec (Fig. 9c, 10c), S-wave velocities ranging between 230 and 430 m/sec (Fig. 9d, 10d), thickness varies from 2.32 to 8.99 m, and depth to the top of this layer varies from 13.8 m (as shown in well 1 along profile 1) to 16.1 m (as shown in well 3 along profile 1). For the horizontal variations in P- and S- waves (Fig. 12c and d), it is observed that the velocity values are high in the northwestern, western, and southwestern parts of our area under investigation and decrease in the northeast direction.

Layer three consists of sand saturated with seawater which has P-wave velocities ranging between 700 and more than 1200 m/sec (Fig. 10c, 11c), S-wave velocities ranging between 170 and 390 m/sec (Fig. 10d, 11d), and thickness varies from 18.2 to 25.4 m and depth to top of this layer varies from 6.89 m (in well 7 along profile 9) to 14.05 m (in well 6 along profile 5). The highest values of both P- and S- waves are observed in northwestern, western, and southwestern parts of our area under investigation and decrease toward the northeast and southeast directions (Fig. 12e and f).

4.3 Evaluation of geotechnical properties

To compute these properties, the compressional wave velocity (VP) and shear wave velocity (VS) from SSR profiles with density (\(\rho\)) values are required. When these properties are integrated, it is possible to better understand the engineering condition of the underlying rocks in our area under investigation, which enables us to divide the area into separate zones based on how suitable the subsurface soils and rocks are for construction activities.

4.3.1 Poisson’s ratio (σ)

It is defined as the product of dividing the contraction strain in the lateral direction per unit width divided by longitudinally extension strain per unit length with dimensionless units (Sheriff 1991). When the rocks have σ of 0.5, they behave like fluids and for extremely hard indurate rocks, it is almost zero (Salem 1990; Telford et al. 1990a, b; Gretener 2003). The more competent (hard) material is, the smaller the values of σ are, and vice versa (Telford et al. 1990a, b).

$${\upsigma } = \left( {1 - 2\left( {\frac{{{\text{V}}_{{\text{s}}} }}{{{\text{V}}_{{\text{p}}} }}} \right)^{2} } \right)/\left( {2 - 2\left( {\frac{{{\text{V}}_{{\text{s}}} }}{{{\text{V}}_{{\text{p}}} }}} \right)^{2} } \right)$$
(3)

where, (\({\upsigma }\)) is Poisson’s Ratio, (\({\text{V}}_{{\text{s}}}\)) is shear velocity, (\({\text{V}}_{{\text{p}}}\)) is primary velocity. The distributions of this ratio for the three layers are shown in Figs. 13a, b, and c. The lowest values for the three layers are observed in the northeastern part and increase gradually toward the southwest direction. All three layers are characterized by a relatively high Poisson’s ratio, which indicates incompetent to slightly competent soil/rock.

Fig. 13
figure 13

Poisson’s ratio (σ) of a layer one, b layer two, c layer three

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4.3.2 The N value

It is known as the number of blows required to penetrate the soil by using a cylindrical bar under a standard load. It is geotechnically known as the SPT (Standard Penetration Test) (Meyerhof 1956; Seed and Idriss 1982; Seed and De Alba 1986). Additionally, bearing capabilities can be calculated using the N-values (Othman 2005). These values are computed using Imai's (1975) equation that was modified by Stumpel et al. (1984):

$${\text{V}}_{{\text{s}}} = 89.9{\text{ N}}^{0.341}$$
(4)

Where, (\({\text{N}}\)) is the number value of SPT and (\({\text{V}}_{{\text{s}}}\)) is the shear velocity. Table 1 shows the values of N-values and what this reflects according to Bowles (1984) classification. Generally, for the three layers in our area, these values are low in the northeastern, eastern, and southeastern corners and increase gradually toward the southwestern, western, and northwestern parts and the middle values in between them as shown in Figs. 14a, b, and c.

Table 1 The study area's distribution of N-Value
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Fig. 14
figure 14

N-value for a layer one, b layer two, c layer three

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4.3.3 Concentration index (Ci)

It is a parameter used in engineering that explains the level of material compaction or concentration for foundation purposes. The depth-pressure distribution and materials’ elastic moduli are the key variables that affect the concentration index. The larger the values, the more competent materials are, and vice versa. The following formula is used to calculate the concentration index (Ci) in terms of (\({\upsigma }\)) Poisson’s ratio (Bowles 1982):

$${\text{C}}_{{\text{i}}} = \frac{{\left( {1 + {\upsigma }} \right)}}{{\upsigma }}$$
(5)

The following equation of Abd Elrahman (1991) is applied to calculate this value:

$${\text{C}}_{i} = \left[ {3 - 4\left( {\frac{{V_{s}^{2} }}{{V_{p}^{2} }}} \right)} \right]/\left[ {1 - 2\left( {\frac{{V_{s}^{2} }}{{V_{p}^{2} }}} \right)} \right]$$
(6)

where \(\left( {\frac{{V_{s}^{2} }}{{V_{p}^{2} }}} \right)\) is the result of division the square of the shear velocity of layer by the primary velocity of the same layer. The distribution values of this index are shown in Figs. 15a, b, and c. The values are low in the southwestern, western, and northwestern parts of the area under investigation and increase gradually to the middle part until reaching maximum values in the east and the northeastern portions of the area under investigation, this indicates a less competent material. The same nature of the majority of the components that make up the sand layers could account for the values' close proximity (Shipton and Coop 2015) and the minor variations result from the simple proportional overlap of other components like clay and silt, a change in sand grain size, or a rise in the vertical load on the lower strata (Basu et al. 2008; Gupta and Basu 2017; Basheer and Salama 2022).

Fig. 15
figure 15

The distribution of concentration index (Ci) in a layer one, b layer two, c layer three

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4.3.4 Stress ratio index (Si)

It can be achieved by dividing the pore-filling fluids’ stress or horizontal and vertical stress at a specific depth. Bowles (1982) noted that the behavior of this ratio is like that of Poisson's ratio, where its value increases for the less hard (competent) and cohesive materials with high water content (Al-Fahdawi and Salah 2000). The following relationship was given by Bowles (1982) and Thomsen (1986) to calculate this stress ratio index (Si) in terms of Poisson’s ratio (\({\upsigma }\)):

$${\text{S}}_{{\text{i}}} = \frac{{\text{Horizontal Stress }}}{{\text{Vertical Stress }}} = \frac{{\upsigma }}{{1 - {\upsigma }}}$$
(7)

Abd Elrahman (1991) expressed other relations to calculate this ratio:

$${\text{S}}_{{\text{i}}} = 1 - 2\left( {\frac{{{\text{V}}_{{\text{s}}}^{2} }}{{{\text{V}}_{{\text{p}}}^{2} }}} \right)$$
(8)

where \(\left( {\frac{{{\text{V}}_{{\text{s}}}^{2} }}{{{\text{V}}_{{\text{p}}}^{2} }}} \right)\) is the outcome of dividing the square of the shear velocity of layer by the primary velocity of the same layer. The distribution values of this index are shown in Figs. 16a, b, and c. The low values are observed in the northeastern corners of the three layers and the eastern, and southeastern edges of the third layer in our area under investigation. These values gradually increase toward the southwest, west, and northwest directions reaching the maximum values in the southwestern part. According to the classification scale of Abd Elrahman (1989), the three layers indicate a less competent material. The three layers in the area under investigation are similar in that they are sandy which accounts for the uniformity in values (Massarsch et al. 2021) and the small variance is due to the accumulating vertical weight change particularly on the bottom of each layer (Stapelfeldt et al. 2021; Basheer and Salama 2022).

Fig. 16
figure 16

Stress ratio index (Si) in a layer one, b layer two, c layer three

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4.3.5 Foundation material bearing capacity

In Geotechnics, it is the rock, soil, or foundation material capacity to safely support loads without shearing (Terzaghi 1943). It is divided into ultimate bearing capacity (Qult) which is the maximum vertical pressure that can be sustained without failing and allowable bearing capacity (Qa) which is obtained by reducing Qult by a factor of safety (FS) (Abd Elrahman et al. 1992). The shear strength of the soil beneath the foundation load predominantly determines Qult and is expressed in terms of the N-values as shown by Parry’s formula (1977):

$${\text{Q}}_{{{\text{ult}}}} = 30{\text{N}}$$
(9)

where ultimate bearing capacity (Qult) and (N) is the value of SPT.

The allowable bearing capacity can be calculated according to Parry (1977) and Abd Elrahman (1989):

$${\text{Q}}_{{\text{a}}} = \frac{{{\text{Q}}_{{{\text{ult}}}} }}{{{\text{FS}}}}.$$
(10)

where (FS) is the factor of safety, which is a multiplier applied to the ultimate load to ensure a sufficient margin of safety in the design. In the case of cohesive soil, FS equals (3), while in the case of cohesionless soil, it equals (2) For the three layers, the relatively low Qult and Qa (Figs. 17 and 18, respectively) values are observed in the northeastern, eastern, and southeastern parts, and increasing toward the southwest, west, and northwest directions reflect the high bearing capacity materials (Table 2).

Fig. 17
figure 17

Ultimate bearing capacity (Qult) in a layer one, b layer two, c layer three

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Fig. 18
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The allowable bearing capacity (Qa) in a layer one, b layer two, c layer three

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Table 2 Qult and Qa distribution in our area of study
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Using the geotechnical parameters that were calculated from interpreted data of Shallow Seismic Refraction (SSR), the area under investigation will be divided into 2 zones (Fig. 19) but in general, it is a low competent area suitable for low buildings with a very small variation and seawater intrusion. Zone (A) occupies the north-western, western, and southwestern parts to about the middle part of our area under investigation. In it, the top layer is beach sand composed of soft loose material with low bearing capacity. The second layer is composed of fine sorted, nearly wet silty sand with a medium bearing capacity and a good hardness with slightly competent materials. It is suggested to take this layer (2nd) as a foundation layer after removing the top layer and it is suitable for light buildings.

Fig. 19
figure 19

Zoning map of the study area

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Zone (B) occupies the middle part of our area under investigation to northeast, east, and southeast seaward directions. The top layer is like that of zone (A), but its thickness gradually decreases in the direction of the sea. Also, the second layer is an extension of the second layer in zone (A). This layer appears at the middle part of zone (B) with a thickness that decreases until disappears at the end of the area near the sea. The third layer is sand saturated with seawater. The intrusion of seawater will increase the soil particle disintegration and increases the porosity and permeability and because of the impacts of tidal motions during hurricane seasons, the stability of the soil will be impacted by this intrusion, and seawater may rise to the surface.

5 Conclusion and recommendation

The geophysical investigation has fed worthy insights and crucial and significant information pertaining to the subsurface characteristics and geological attributes of the area under investigation. Based on the ERT data, we found that there are three layers; two of them were observed at profiles near the sea while we observed that there are three layers as the profiles become farther from the sea due to the low level of seawater intrusion and thus the exposure of the layers to become from saturated with water to nearly wet. This intrusion begins to appear at the seashore in the north-eastern, eastern, and south-eastern parts of our area under investigation at a depth of about 8.5 m and decreases gradually to a depth of 14 m in the middle of our area under investigation and it further decreases to a depth of 18 m at the northwest, west, and southwest direction of the area under investigation. All layers are consistent layers without any horizontal variation that indicates the absence of clay lenses but the resistivity varies vertically due to the seawater intrusion into the third layer (saturated sand).

SSR data compared with drilled wells in our area under investigation was used to delineate the shallow subsurface layers and determine the geotechnical characteristics of the rocks. We found that three layers also characterize our area under investigation; two of them are observed along profiles 1 and 9, and three of them are observed in the middle part of the area. This difference is due to the various physical characteristics that each method depends on. The top layer (beach sand) has P-wave velocities ranging between 400 and more than 950 m/sec and S-wave velocities ranging between 150 and 330 m/sec. The second layer (Silty sand) has P-wave velocities change from between 700 and 1300 m/sec and S-wave velocities change from 230 and 430 m/sec. The third layer (sand saturated with seawater) has P-wave velocities change from 700 and more than 1200 m/sec and S-wave velocities change from 170 and 390 m/sec.

From the calculation and integration of geotechnical parameters such as Poisson’s ratio, N values, stress ratio, concentration index, and bearing capacities, our area under investigation is divided into two zones with low bearing capacities. Zone B is affected by seawater intrusion. Because of erosion of the iron utilized in building foundations by this intrusion, it is advised to keep this zone without any buildings or improve the durability of concrete exposed to seawater to be suitable also for light building.