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Article

Soil Amplification and Code Compliance: A Case Study of the 2023 Kahramanmaraş Earthquakes in Hayrullah Neighborhood

by
Eyübhan Avcı
1,
Kamil Bekir Afacan
2,*,
Emre Deveci
1,
Melih Uysal
1,
Suna Altundaş
3 and
Mehmet Can Balcı
4
1
Department of Civil Engineering, Bursa Technical University, 16330 Bursa, Türkiye
2
Department of Civil Engineering, Eskişehir Osmangazi University, 26000 Eskişehir, Türkiye
3
Department of Geophysics, Gümüşhane University, 29000 Gümüşhane, Türkiye
4
Department of Civil Engineering, Batman University, 72000 Batman, Türkiye
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(15), 2746; https://doi.org/10.3390/buildings15152746
Submission received: 27 June 2025 / Revised: 15 July 2025 / Accepted: 30 July 2025 / Published: 4 August 2025
(This article belongs to the Section Building Structures)
Browse Figures
Versions Notes

Abstract

In the earthquakes that occurred in the Pazarcık (Mw = 7.7) and Elbistan (Mw = 7.6) districts of Kahramanmaraş Province on 6 February 2023, many buildings collapsed in the Hayrullah neighborhood of the Onikişubat district. In this study, we investigated whether there was a soil amplification effect on the damage occurring in the Hayrullah neighborhood of the Onikişubat district of Kahramanmaraş Province. Firstly, borehole, SPT, MASW (multi-channel surface wave analysis), microtremor, electrical resistivity tomography (ERT), and vertical electrical sounding (VES) tests were carried out in the field to determine the engineering properties and behavior of soil. Laboratory tests were also conducted using samples obtained from bore holes and field tests. Then, an idealized soil profile was created using the laboratory and field test results, and site dynamic soil behavior analyses were performed on the extracted profile. According to The Turkish Building Code (TBC 2018), the earthquake level DD-2 design spectra of the project site were determined and the average design spectrum was created. Considering the seismicity of the project site and TBC (2018) criteria (according to site-specific faulting, distance, and average shear wave velocity), 11 earthquake ground motion sets were selected and harmonized with DD-2 spectra in short, medium, and long periods. Using scaled motions, the soil profile was excited with 22 different earthquake scenarios and the results were obtained for the equivalent and non-linear models. The analysis showed that the soft soil conditions in the area amplified ground shaking by up to 2.8 times, especially for longer periods (1.0–2.5 s). This level of amplification was consistent with the damage observed in mid- to high-rise buildings, highlighting the important role of local site effects in the structural losses seen during the Kahramanmaraş earthquakes.

1. Introduction

Türkiye’s location makes it one of the most significant earthquake zones [1]. Two major fault zones (North Anatolian Fault Zone and East Anatolian Fault Zone) and many active faults, which have very important significance in the world’s literature, are known as important seismic sources within the country. The country’s active tectonics are mostly caused by the North Anatolian Fault Zone (NAFZ) and East Anatolian Fault Zone (EAFZ) [2,3,4,5,6,7]. These strike–slip faults are the source of frequent earthquakes in Türkiye due to their high seismic activity [8]. The intense seismic activity in the country has caused many major earthquakes throughout the historical period. It is possible to list the earthquakes that caused large amounts of fatalities and structural damage in Turkey due to high seismic activity as follows: 1939 Erzincan (Ms = 7.9), 1944 Bolu (Ms = 7.2), 1953 Çanakkale (Ms = 7.2), 1999 İzmit (Mw = 7.4), 1999 Düzce (Mw = 7.2), 2011 Van (Mw = 7.2), and Kahramanmaraş (Mw = 7.7 and Mw = 7.6) [9].
In Turkey, where many major earthquakes have occurred, the area affected and the earthquakes with the highest loss of life are the Kahramanmaraş earthquakes that occurred on 6 February 2023. These earthquakes are recognized as among the most devastating of the 21st century [8,10,11]. The focal depths were recorded at 8.6 km and 7 km, respectively. These seismic events resulted in significant damage and extensive destruction across 11 provinces: Adana, Adıyaman, Diyarbakır, Elazığ, Gaziantep, Hatay, Kahramanmaraş, Kilis, Malatya, Osmaniye, and Şanlıurfa. The affected area covered around 110,000 km2, constituting 14% of the country’s total land area, directly impacting more than 14 million people, which is about 16.5% of the total population residing in the region. Additionally, these 11 provinces contribute approximately 10% to the country’s gross domestic product. Both earthquakes occurred in the EAFZ and its adjacent segments. Over half a million buildings were affected, with nearly 54,000 classified as either severely damaged or destroyed [12,13,14].
In order to determine the earthquake characteristics at the surface of the local soil layers, soil amplification analyses are performed in accordance with local seismic hazard findings. Soil amplification, a well-established concept in seismology, plays a significant role in determining the extent and spatial variation of building damage during earthquakes [15,16]. Seismic motions are generated for different reasons and change during the movement from the bedrock to the surface by being affected by local soil conditions, and depending on the soil type and dynamic properties, they are dampened or amplified and transmitted to the surface. This increase in the amplitude of earthquake waves passing through the soil layers is defined as soil amplification in the literature [17]. The magnified earthquake motion transmitted to the foundation of the structure increases the deformation levels on the structural elements, resulting in possible local collapse or structural collapse. Bedrock accelerations with very small values can be magnified several times in some regions by the effect of local conditions and can cause very severe damage [18].
Incorporating local site effects is essential when designing earthquake-resistant infrastructure and conducting seismic hazard assessments for a region [19]. Numerous studies have demonstrated that local soil conditions significantly influence key aspects of earthquake motion, including frequency content, amplitude, and duration [20,21]. Moreover, it has been noted that seismic waves can amplify substantially, leading to high acceleration values, particularly in the presence of soft alluvial soils [9,22,23].
In the analysis of the amplification effect of soils, it is important to know the properties of the earthquake, as well as the soil characteristics. In site-specific analyses, earthquakes are selected and analyzed according to the characteristics of the region, such as fault type and local soil conditions, for the analysis and design of structures according to earthquakes. In the codes determined by the countries, the selection and scaling of earthquake acceleration records and obtaining design spectrum curves are specified [24]. Another concept that needs to be determined in site-specific analyses is the response spectra. Acceleration spectra are accepted as parameters reflecting earthquake characteristics and used in the design of structures [25]. Studies to evaluate the performance of the analyzes with the regulations are still in progress and are still being developed today [26,27,28].
In order to reduce the damage caused by earthquakes and to build reliable structures against earthquakes, it is necessary to determine the behavior of the soil layers under seismic loads and to design the superstructure. Design spectrum values specified in earthquake codes are used to determine soil motions. With these values, the natural vibration periods of the structures are taken into account and the horizontal and vertical loads that will affect the structure are determined. Design spectra consist of the maximum values of the response to different earthquake forces, taking into account the seismic characteristics of the site and soil conditions [29].
Soil amplification plays a key role in the experience of ground shaking due to an earthquake. When seismic waves pass through soft/loose soils, they tend to slow down and increase in amplitude, which can significantly intensify surface excitation. Over the years, many studies have highlighted how local site conditions can amplify shaking and contribute to more severe damage. While early observations came mainly from field damage reports after major earthquakes, more recent research has focused on using geotechnical and geophysical data to model site responses in greater detail. Techniques like equivalent linear (EL) and nonlinear analyses (NL) are now commonly used to simulate how soils behave during strong shaking, though challenges remain—particularly when dealing with soft clays, where traditional methods may not fully capture the effects of high strain levels.
In this study, we investigate the role of soil amplification in the damage observed during the 6 February 2023 earthquakes in Kahramanmaraş—a city largely built on alluvial ground and located near active fault zones. Site investigations and subsurface data collected from the area were used to build a representative soil profile. To simulate earthquake shaking, 11 real ground motion records were scaled to reflect the seismic characteristics of the region. The analyses were carried out using DeepSoil v7.0 with a focus on equivalent linear and non-linear approaches [30]. The goal was to assess whether current code provisions adequately capture the level of amplification observed in this type of soil environment. Ultimately, the obtained results were compared with the Turkey Building Code, 2018.

2. Investigation Area

Following the earthquake, the study area was designated as a disaster-prone area, since it had the highest number of building collapses in the area. In order to decide what remediations should be made in the event that development is possible, scientists will examine the site and provide insight into the future.

2.1. Tectonic Characteristics

The most important fault zones in Türkiye are the NAFZ and the EAFZ, which have strike–slip characteristics (Figure 1). Research in the region using GPS data has shown that the EAFZ is moving westward with slip rates of 6 mm/yr to the NE and 10 mm/yr to the SW of Kahramanmaraş, and the total displacement is about 20–30 km [4,5]. These fault zones cause the westward movement of the Anatolian plate, and this movement generates very destructive earthquakes in Anatolia and its immediate vicinity [31,32]. The right-lateralized NAFZ spans approximately 1500 km, whereas the left-lateralized EAFZ covers a length of around 550 km [6,33,34]. In the literature, there are two prevailing perspectives on the age of formation of the EAFZ. One of them is Late Pliocene [6,35,36,37,38,39] and the other is Late Pliocene–Pleistocene [40]. The most important tectonic structures that are effective in morphologic shaping are the faults belonging to the northern and southern branches of the Eastern Anatolia Fault, Ölü Deniz Fault Zone, Engizek Fault Zone, Andırın Fault Zone, and Kahramanmaraş Fault Zone. It can be said that these faults are active or potentially active and therefore have the potential to generate earthquakes [41].
Kahramanmaraş is located in a region that is quite complex in terms of its geological evolution and structural features, where different tectonic units meet. The province of Kahramanmaraş lies within the Orogenic Belt and the Edge Fold Belt [43]. The highly complex structural features of the region, consisting of thrusts and faults, are related to the closure of the southern branch of the Neotetis Ocean [38]. Regarding the geodynamic evolution of Kahramanmaraş and its surroundings, it can be said that there are many faults and thrusts in Kahramanmaraş Province and its surroundings due to many deformation phases.
The last earthquakes in the southern branch of the EAFZ occurred on 6 February 2023, in Pazarcık (Mw = 7.7) and Elbistan (Mw = 7.6). The first earthquake in Pazarcık occurred in the Narlı segment at the northern end of the Dead Sea Fault Zone, while the second earthquake occurred in the Çardak fault, a branch of the Eastern Anatolian Fault Zone [44]. Surface fractures exceeding 4.7 m in the Amanos segment, 3.2 m in the Pazarcık segment, and 8 m in the Çardak fault were observed [45].

2.2. Geology of the Region

Kahramanmaraş Province, which is located in the zone where the Anatolian, African and Arabian plates intersect with each other and is affected by the movements of these plates, has a highly complex geological structure [38,46]. Units belonging to the Taurus Orogenic Belt, Southeastern Anatolian autochthon, and cover rocks surface the city center of Kahramanmaraş and its nearby areas. Upon examining geological units of Kahramanmaraş city center and its nearby surroundings, Quaternary alluviums are observed in the areas over the Maraş Plain in the city center and south. It is seen that most of the city center of Kahramanmaraş is located on these alluvial deposits. Ahır Mountain is located in the north of the city. On the slopes of this mountain, Middle Miocene conglomerates and Quaternary depositional cones as well as slope materials are located. The summits of Ahır Mountain are observed to be entirely formed by clayey limestones of Eocene age. Eocene clayey limestones are the dominant formation where many streams reaching the city center originate. Toward the northeast, Middle-Miocene-aged sandstone, mudstone, and conglomerate units are located in the basin of Peynirdere Stream. In the southeastern parts, mélange units consisting of Mesozoic aged ophiolitic rocks are encountered [47]. A geological map of Kahramanmaraş city center and its close surroundings is given in Figure 2.

2.3. 6 February 2023 Kahramanmaraş Earthquakes

Based on the analysis of earthquakes in the historical and instrumental periods up to 6 February 2023, it is clear that the seismic activity in Kahramanmaraş and its immediate vicinity is quite high. In the historical period, Kahramanmaraş was affected by many earthquakes with intensities between VI and IX (according to the Mercalli–Sieberg intensity scale). On 10.08.1114, a magnitude IX earthquake occurred off Karataş, which is the westernmost end of the East Anatolian Fault, affecting Ceyhan, Adana, Antakya, Kahramanmaraş, and Lebanon. On 29.11.1114, a magnitude VIII earthquake occurred in Kahramanmaraş, affecting Kahramanmaraş, Urfa, and Harran. Earthquakes of intensity VIII also occurred in the Turkoglu region of the East Anatolian Fault in 1513 and 1874 [49,50].
During the instrumental period (1900–), many earthquakes occurred in Kahramanmaras and its immediate surroundings. Although the region seems to have entered a quieter period after the 1905 Malatya earthquake, the 1971 Bingöl (Ms = 6.8) and 1986 Doğanşehir (Ms = 5.8 and Ms = 5.6) earthquakes were recorded as moderate earthquakes by the EAFZ in the last century. The last earthquakes on the southern branch of the EAFZ in the study area were the Pazarcık and Elbistan earthquakes on 6 February 2023. When the epicenters and aftershock distributions of the earthquakes were analyzed, the epicenter of the Pazarcık earthquake was thought to have ruptured a line between Çelikhan and Pötürge in the NE, including the Erkenek, Gölbaşı, and Amanos segments of the EAFZ and the Narlı segment at the northern end of the Ölüdeniz Fault Zone. The second earthquake, with its epicenter in Elbistan, was thought to be related to the Çardak fault and the Doğanşehir fault zone [44]. The two earthquakes that occurred on 6 February 2023, with epicenters in the Kahramanmaraş districts of Pazarcık and Elbistan, are referred as “shallow earthquakes” and the damage caused by such earthquakes is relatively higher because they are close to the surface.
The first earthquake occurred on the main fault zone and the triggered earthquake occurred on a secondary segment that separated from the main segment. The magnitude 7.6 earthquake occurred about 90 km north of the first earthquake. However, it shook the northern areas affected by the first earthquake quite violently. The Pazarcık earthquake (Mw = 7.7) struck the Narlı Segment at the northern end of the left-lateral strike–slip Dead Sea Fault Zone, while the Elbistan earthquake (Mw = 7.6) struck the Çardak Fault, a branch of the East Anatolian Fault. Nearly 1300 earthquakes were recorded within three days after the main shock (Figure 3) [44]. The ground acceleration and spectral accelerations measured in the Kahramanmaraş earthquake show that the earthquake had a much higher intensity than the estimated intensity, and this was one of the important factors in the earthquake being very destructive. In conclusion, when both earthquakes are analyzed, it is seen that the Pazarcık earthquake (Mw = 7.7) was more effective and produced more energy than the Elbistan earthquake (Mw = 7.6). In addition, as can be seen from the earthquake acceleration records, the catastrophic effects of the earthquake increased, especially in the central and Pazarcık districts of Kahramanmaraş, due to the close fault effect and soil type.

2.4. Location

The study area comprises a 10-hectare area located in the Onikişubat district of Kahramanmaraş Province (Figure 4). Following the earthquakes centered in Kahramanmaraş Pazarcık (Mw = 7.7) and Elbistan (Mw = 7.6) on 6 February 2023, some structures in the study area were destroyed, while others remained standing.
Figure 5 provides information about the buildings in the study area, sourced from the Kahramanmaraş Metropolitan Municipality. The significance of earthquake-resistant structural design and building codes becomes evident through the occurrence of destructive earthquakes and subsequent structural damage. The necessity for regular updates and revisions of the building codes arises due to advancements in scientific understanding, innovations in construction technologies, and developments in building materials.
Turkey, being a highly seismic region, has continually adapted to these changes over time [51]. The most recent three building codes (1998, 2007, and 2018) were taken as limit value in the categorization process of damaged buildings. The standing structures were categorized as undamaged, slightly damaged, moderately damaged, or heavily damaged. The examination revealed that 74% of the collapsed and heavily damaged buildings were constructed before 1999, with 91% of the structures built before 1999 being heavily damaged or collapsed (Figure 6). Notably, most slightly damaged and undamaged buildings were found to have basements, few floors, and had received thorough engineering services. In addition, the year of construction and the building code under which it was made were also effective in causing damage.

3. Field Tests Results

3.1. Geophysical Tests

Within the scope of the study, microtremor at eight points, seismic refraction–MASW on eight profiles, vertical electrical sounding (VES) at one point, and electrical resistivity tomography (ERT) studies on three profiles were carried out at the predetermined locations on the existing maps (Figure 7). From the measurements obtained from the field study, calculating the dynamic–elastic parameters of the soil, layer thicknesses, soil amplification, predominant period, and frequency, soil classification was conducted according to the earthquake regulations.

3.1.1. Single Station Microtremor Measurements

Microtremor measurements were taken at 8 points corresponding to the locations of each seismic refraction–MASW profile in the study area. In the this, three-component recordings of 30 min (vertical (Z), N–S, and E–W) were taken with an Ambregeo brand Echo Tromo model seismograph and the recordings were evaluated with the Geopsy program. As a result of the evaluation, the soil predominant period and frequency and H/V ratios were obtained and soil classification was conducted according to the TBC [24]. Due to the ongoing debris removal works in the study area and the lack of a suitable ground layer to take measurements, although the measurements were taken at night, quality records could not be obtained. Due to the high noise content of the measurements taken, accurate amplification values could not be obtained as no distinct peaks could be observed on the H/V curves. At this stage, spectral amplification values were calculated using MASW data.
Based on the frequency, the predominant period was found from the formula T0 = 1/F0. To obtain the upper and lower vibration periods Ta and Tb from the predominant period of the ground, the upper and lower period values were calculated using the relations Ta = 0.67 × T0 and Tb = 1.50 × T0 (Table 1) [52].
It is observed that the predominant period (T0) of the ground varied between 0.20 and 0.61 s and the spectral amplification values (A0) varied between 0.60 and 1.39. Ansal et al. categorizes this as low degree [53].
While the frequency values obtained in the study area showed alluvial soil characteristics, spectral amplification values indicated solid rock. This was due to both the measured points and the gravelly unit at these points. In general terms, areas with high T0 values are defined as softer, less compacted, and less cemented areas compared with areas with low T0 values. In short, areas with high T0 values are loose poor soils. T0 avoids resonance, Ta ≤ T0 ≤ Tb.

3.1.2. Seismic Refraction–MASW (Multi-Channel Surface Wave Analysis) Studies

Seismic refraction–MASW measurements were performed using a Seistronix RAS-24 seismograph system (Seistronics Inc., Berthoud, CO, USA) with 24 channels and signal accumulation (enhancement) and 4.5 Hz vertical geophones. MASW measurements were conducted on eight profiles of 75 m each with an offset of 6 m and geophone spacing of 3 m in the study area. In MASW measurements, the sampling interval was chosen to be 0.5 ms, the recording length was 2 ms. and average shear wave velocity values (Vs30) were calculated for 30 m depth. In addition, P-wave velocities (Vp) were determined by performing seismic refraction measurements on the same lines as the MASW profiles with a geophone spacing and offset distance of 3 m and a profile length of 72 m. In the seismic refraction–MASW study, straight and reverse shots were taken and records were taken by applying three stack operations. Seismic refraction–MASW measurements were performed using Seisimager Ver. 2.8.0.1 software and the results are presented in Table 2. All the profiles are classified as ZD according to the new building earthquake regulations of Turkey [24].
The dynamic and elastic parameters of the soil were calculated by using P and S wave velocities obtained from seismic refraction–MASW data and lithological classification with thickness information of the layers, and the results are presented in Table 2 and Table 3. In addition, spectral amplification coefficients for the study area were calculated using the relation of Midorikawa [54] Ak = 68. Vs30 (−0.6) (Vs30 < 1100) using Vs30 values obtained from MASW measurements in the study area [54].
In the seismic refraction–MASW study performed on the same profiles, the first layers were defined as gravelly clay units up to 6 m (Vs: 188–269 m/s, Vp: 377–621 m/s), while the second layers corresponded to a firmer hard gravelly clay unit after 6 m (Vs: 274–414 m/s, Vp: 1117–1391 m/s). Seismic refraction–MASW, microtremor, and ERT measurements were taken close to boreholes in the study area. The boreholes and geophysical measurements were evaluated together and both the boreholes and the MASW measurements showed eartfill, gravelly clay, and rubble piles in the first 6 m of the descent, while after this depth, the soil showed a firmer hard gravelly clay unit. The Vs velocity values obtained in the alluvium unit in the study area indicated a gravelly clay unit in the drilling study and Vs30 values varied between 251 and 374 m/s.

3.1.3. Vertical Electrical Sounding (VES) Technique

A VES study was conducted at one point in the study area using a Schlumberger electrode array. Measurements were conducted with a maximum AB/2 strike length of 100 m and the data were evaluated as 1D with IP2WIN (Version 3.0.1) software (Figure 8).
As a result of the evaluation, a three-layered structure was obtained, while the resistivity values of the first two layers were very close and continued to a depth of approximately 7.5 m. At the end of the investigation, it was seen that the resistivity value of the soil varied between 45.2 and 206 ohm-m. The areas with low resistivity values can be considered as gravelly and poorly cemented units containing water. The decrease in resistivity indicated high moisture content and wetness. In these areas where there was a transition to low resistivity; it is possible to talk about a possible groundwater level or dampness. The possible lithology corresponding to the resistivity changes obtained from the VES measurement is also consistent with the data obtained from the drilling studies in the study area. The VES-1 point approximately coincided with the middle of the BH-1 well and the resistivity values obtained in the wells coincided with the eartfill up to about 2 m, a clayey gravelly unit was observed after this depth.

3.2. Boreholes and Standard Penetration Tests

Standard penetration tests (SPTs) and multi-channel analysis of surface waves (MASW) measurements were conducted at eight borehole locations. Six of these boreholes were drilled to a depth of 30 m, while the remaining two extended to 50 m to investigate the deeper, stiffer soil layers. The water table was observed at approximately 4.5 m below the surface, and the soil profiles derived from the borehole data are presented in Figure 9. Based on the data obtained from both the field and laboratory tests, alongside the drilling program and field observations, the comprehensive soil profile of the study area was identified as consisting primarily of clay units from Quaternary-aged alluvial soils.
As shown in Figure 9, the shallow soil profile was characterized by generally low SPT-N values, suggesting soft clayey material. However, a few higher N-value readings—likely indicating gravelly layers—were interspersed within the otherwise uniform profile. The shear wave velocity (Vs) measurements for the top 6 m ranged between 185 and 270 m/s, whereas values in the deeper layers ranged from 270–390 m/s, resulting in an average shear wave velocity of less than 360 m/s, which classified the soil as ZD (according to seismic classification standards). This variation is not unexpected given the natural heterogeneity in near-surface materials and limitations inherent to surface wave methods, such as noise, limited depth penetration, and inversion non-uniqueness. However, multiple MASW lines were interpreted to reduce the bias. Another point is that microtremor measurements at a couple of locations were inconclusive due to extensive surface debris and noise following the earthquake,. In future studies, these limitations could be addressed by using array-based microtremor techniques that are less sensitive to localized disturbances, and/or by deploying downhole or borehole-based geophysical methods.
The soil consists of both low- and high-plasticity clays, with the index properties summarized in Figure 10. The idealized soil profile is also provided in Figure 11. Laboratory testing revealed that the CH-CL (clay of high and low plasticity) unit exhibited an average swelling percentage of 1.64%, with a swelling pressure value of 26.28 kPa. the results of unconsolidated undrained (UU) triaxial tests on CH-CL soils show cohesion intercepts ranging from 50 kPa to 60 kPa, and internal friction angles between 2° and 5°.
The idealized soil profile was determined based on data from several boreholes and MASW surveys conducted across the Hayrullah neighborhood. Overall, the subsurface conditions showed a fairly consistent strata. The way to choose the profile is to represent the average conditions in the area, especially in zones where earthquake damage is the most concentrated. Local variations in soil properties can exist and may influence how the ground responds during shaking, and this is well recognized. While this study focused on one-dimensional analysis assuming uniform layering, incorporating multiple profiles or exploring two- or three-dimensional effects could provide a more detailed understanding of how site conditions vary across the neighborhood.

4. Site Specific Analysis Results

This section presents the results of site-specific seismic analyses, carried out in accordance with the Turkish Building Code (TBC) published in 2018. As outlined in the TBC (2018), the earthquake level corresponding to a rare event, with a 10% probability of exceeding the spectral magnitudes in 50 years and a recurrence period of 475 years, was determined for the site. Based on the seismic characteristics of the region (including site-specific faulting, distance to fault, and average shear wave velocity), a set of 11 earthquake ground motion records were selected for analysis.
The selection and scaling of the earthquake records were performed according to the guidelines set forth in Articles 2.5.1 and 2.5.3 of the TBC [24]. Additionally, a second scaling procedure was applied to match the maximum ground acceleration (PGA) as stipulated by the regulation for the site, and the results were subsequently compared. Earthquake data were sourced from the Peer Ground Motion Database, and the corresponding record properties are summarized in Table 4. The time histories of the selected motions are shown in Figure 12.
The earthquake records selected for the site were scaled in two distinct ways: (1) to match the design spectrum for short, medium, and long periods (T < 3.0), and (2) to match the peak ground acceleration (PGA). The design spectrum and the scaled versions are presented in Figure 13a,b. The building code suggests a PGA of 0.374 g for the studied area. The recorded ground motions were scaled to ensure the compatibility with both the design spectrum and target PGA. While this method controls overall spectral shape, it is acknowledged that it can introduce minor distortions in the frequency content or alter characteristics such as the duration or peak acceleration sequence. In order to overcome this, only records with source and site characteristics broadly consistent with regional conditions were selected.

4.1. Site Response Using the Base Motions That Compatible with the Design Spectrum

The nonlinear site response analysis was conducted using DeepSoil v7.0, employing the general quadratic model (GQ) to simulate the stress–strain behavior of soils under cyclic loading. The Darendeli (2001) modulus reduction and damping curves were adopted, as they have previously shown strong agreement with cyclic test results from similar local clayey soils [56]. The peak shear strains reached during shaking exceeded the linear threshold (typically > 0.1%), validating the necessity of a nonlinear framework. However, both EL and NL models were established in order to determine the capacity of EL models to estimate the site response.
Using the scaled motions, the soil profile was excited with 22 different earthquake scenarios and the results were obtained for the equivalent and non-linear models. For brevity, only spectral accelerations for different cases are presented here, along with the amplification at varying periods. Figure 14 shows the observations from the two different analysis approaches.
The most important outcome from the results is if the building code fails to match the site response at longer periods, regardless of the analysis type. Although non-linear site response seems more conservative compared with the equivalent linear analyses, the amplification for medium to longer periods is almost 3. For short periods, there is a fundamental difference between the models in that one overestimates the peak ground acceleration (equivalent linear analyses) and the other underestimates in comparison with the building code estimation.

4.2. Site Response Using the Base Motions That Compatible with the Pga

This part conveys another discussion about the design spectrum of the building code. The previous section proved the parameters of the design spectrum in terms of the corner frequencies and spectral acceleration for short periods, but how did the building code do for the estimation of the site-specific peak ground acceleration? The results for the models that used the PGA-matched base motions are presented in Figure 15.
One notable observation is the increased scatter in the data compared with previous analyses, as the frequency content of the motions was held constant, with only the PGA being scaled. The results align with those from the previous section, further illustrating that the design spectrum provided by the building code is accurate for periods up to approximately 0.3–0.4 s, but underestimates the ground response at longer periods. Additionally, the frequency content of the selected motions results in differing amplification behaviors between the equivalent linear and non-linear analyses. A fundamental conclusion from the results is that the building code’s design spectrum does not accurately predict the site response for longer periods. Although the non-linear analysis appears more conservative, amplification factors for medium to longer periods are still close to 3, and for shorter periods, the models diverge significantly, with equivalent linear analyses overestimating and non-linear analyses underestimating the PGA in comparison with the building code estimate.
The amplification factors approaching 3 at longer periods are notably higher than those typically prescribed in empirical models. In terms of the Turkish Building Code (TBC 2018) and Eurocode 8, they generally predict lower amplification at long periods for sites classified as ZD or equivalent (around 1.5–2.0). The elevated values are the reflection of the influence of soft, deeper clay layers and possible resonance effects that are not fully captured by generic code-based curves. This is one of the reasons for the mass destruction of the high-rise buildings. Notably, areas with higher predicted amplification for long periods corresponded to zones where mid- to high-rise reinforced concrete buildings suffered significant damage. Local site effects may have contributed to their poor performance, since these structures are more sensitive to long-period motions. Studies from the Düzce basin reported amplification factors of 2–3 at periods above 1 s—values consistent with those obtained in our analysis. These parallels suggest that deep sedimentary basins and soft soil conditions tend to produce similar amplification behavior in seismically active regions of Turkey. As such, we recommend applying an amplification factor of 1.5–2.0 to the long-period portion of the design spectrum for deep, soft clay sites in similar tectonic settings, unless site-specific response analysis is performed. This adjustment could help to reduce the underestimation of seismic demand in high-rise buildings and improve the safety margins in performance-based design.
Regarding the observation of the divergence in short-period PGA values between EL and NL analyses, it reflects the inherent differences in how each method models soil behavior under cyclic loading. For soft clayey soils, nonlinear analysis is generally considered more reliable, specifically under strong ground motions because it well captures strain-dependent stiffness degradation along with the energy dissipation through hysteresis. On the other hand, equivalent linear methods tend to overestimate short-period accelerations due to their limitations in simulating large-strain, cyclic soil behavior.

5. Conclusions

This study aimed to evaluate the role of local soil conditions—particularly soil amplification—in the structural damage observed during the 6 February 2023 earthquakes in Kahramanmaraş, with a focus on the Hayrullah neighborhood of the Onikişubat district, which sustained heavy damage whereas others remained largely intact. Using borehole data, MASW profiles, and dynamic ground response analyses (both equivalent linear and nonlinear), we assessed how soft clayey soils influenced seismic wave propagation and surface ground motions. It was observed that structures with basements, fewer floors, and those designed with comprehensive engineering services were less affected. Additionally, the year of construction and the building code under which the structures were designed played an important role in determining the extent of the damage.
In the course of this study, six boreholes were drilled to a depth of 30 m, and two boreholes were extended to 50 m. The soil profile revealed that the predominant soil type in the study area was clay (CH-CL). Bedrock was not encountered in any of the boreholes. The results from the standard penetration tests (SPTs) indicated that the soil exhibited soft clay characteristics, particularly near the surface.
Based on the Vs30 values derived from multi-channel analysis of surface waves (MASW), the soil in the study area was classified as ZD-type soil according to the Turkish Building Code (TBC 2018). A comparison of the results from MASW, vertical electrical sounding (VES), and single-station microtremor measurements confirmed that the borehole data and the regional geological structure were closely correlated.
When conducting microzonation for the region, it is essential to consider factors such as local ground conditions, construction quality, environmental and geological factors, regional seismicity, and the history of seismic disasters. This study is expected to contribute valuable insights into safe construction practices for the region, particularly for the new settlement process in Kahramanmaraş, by providing preliminary data on the soil–structure interaction in the central district.
Dynamic analysis under both equivalent linear and non-linear models demonstrated that the soft soil significantly amplified seismic motions for medium to high periods, contributing to the destruction of medium to high-rise buildings in the affected areas.
The analysis revealed that the Turkish Building Code (TBC 2018) does not adequately account for site-specific responses, particularly in terms of corner frequencies and spectral acceleration for short periods, which were not accurately estimated for this region. Site observations highlighted that many of the affected buildings were old, with static and dynamic load designs that did not meet contemporary engineering standards. Furthermore, the execution of construction work did not always adhere strictly to the approved design projects, which contributed to the vulnerabilities observed.
The combined effects of inadequate design, suboptimal construction practices, soil amplification, and the failure of the building code to account for site-specific seismic responses were identified as key contributors to the extent of the damage. The dynamic analysis confirmed that soil amplification played a significant role in the structural damage observed during the seismic events.
In conclusion, this study underscores the importance of considering both geotechnical and structural factors in earthquake risk assessment and highlights the need for improved seismic design standards, including site-specific considerations, to enhance the resilience of buildings in seismic regions. This study contributes to the ongoing development of microzonation in Kahramanmaraş Province, but further research is needed to refine the zoning criteria, taking into account the heterogeneity of local soil conditions and building practices. High-resolution seismic hazard maps based on more extensive seismic and geotechnical data will be vital for informed urban planning and disaster mitigation efforts. As demonstrated by the limitations of the current building code (TBC 2018), further studies should focus on the development of updated seismic design guidelines that incorporate site-specific conditions, such as soil amplification and local geological factors. Policy recommendations for integrating these findings into construction standards could lead to safer building practices and improved earthquake resilience in the region.
While the findings highlight the critical role of soil amplification in the observed damage patterns, this study does not capture possible 2D/3D basin effects. Additionally, although strong correlations were noted between amplification zones and areas of structural failure, limited access to detailed structural inventory and fragility data constrained the depth of damage correlation analysis. Future work should incorporate more extensive geotechnical coverage, building data, and multi-dimensional modeling to enhance microzonation and hazard assessment.

Author Contributions

Methodology, E.A., K.B.A., E.D. and M.U.; Validation, S.A.; Formal analysis, E.D. and S.A.; Investigation, E.A., M.U. and M.C.B.; Resources, M.C.B.; Data curation, K.B.A.; Writing—original draft, K.B.A.; Writing—review & editing, E.A. and K.B.A.; Supervision, E.A. and K.B.A.; Project administration, E.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

We wish to confirm that there are no known conflicts of interest associated with this publication. The authors have no relevant financial or non-financial interests to disclose.

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Buildings 15 02746 g001
Figure 1. Major tectonic units around the region (modified from USGS) [42].
Figure 1. Major tectonic units around the region (modified from USGS) [42].
Buildings 15 02746 g001
Buildings 15 02746 g002
Figure 2. Geological map of Kahramanmaraş and its surroundings (modified from MTA) [48].
Figure 2. Geological map of Kahramanmaraş and its surroundings (modified from MTA) [48].
Buildings 15 02746 g002
Buildings 15 02746 g003
Figure 3. Pazarcık (Mw = 7.7) and Elbistan (Mw = 7.6) earthquakes and aftershock activity (modified from AFAD 2023b) [44].
Figure 3. Pazarcık (Mw = 7.7) and Elbistan (Mw = 7.6) earthquakes and aftershock activity (modified from AFAD 2023b) [44].
Buildings 15 02746 g003
Buildings 15 02746 g004
Figure 4. Location map of investigation area.
Figure 4. Location map of investigation area.
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Buildings 15 02746 g005
Figure 5. Damaged or collapsed building in the study area.
Figure 5. Damaged or collapsed building in the study area.
Buildings 15 02746 g005
Buildings 15 02746 g006
Figure 6. (a) The damage statuses of buildings by year, (b) the damage statuses of buildings by floors.
Figure 6. (a) The damage statuses of buildings by year, (b) the damage statuses of buildings by floors.
Buildings 15 02746 g006
Buildings 15 02746 g007
Figure 7. Location of seismic refraction, MASW, ERT, VES, microtremor measurements, and borehole points in the study area.
Figure 7. Location of seismic refraction, MASW, ERT, VES, microtremor measurements, and borehole points in the study area.
Buildings 15 02746 g007
Buildings 15 02746 g008
Figure 8. VES-1 resistivity curve.
Figure 8. VES-1 resistivity curve.
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Buildings 15 02746 g009
Figure 9. Soil profile of the site.
Figure 9. Soil profile of the site.
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Buildings 15 02746 g010
Figure 10. Index properties of the soil profile.
Figure 10. Index properties of the soil profile.
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Buildings 15 02746 g011
Figure 11. Idealized soil profile.
Figure 11. Idealized soil profile.
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Buildings 15 02746 g012
Figure 12. Earthquake data used in the site response analyses.
Figure 12. Earthquake data used in the site response analyses.
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Buildings 15 02746 g013
Figure 13. Response spectra of the scaled motions compatible with (a) design spectrum and (b) PGA.
Figure 13. Response spectra of the scaled motions compatible with (a) design spectrum and (b) PGA.
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Buildings 15 02746 g014
Figure 14. Results from the models that use the base motions compatible with the design spectrum. (a) equivalent linear analyses and (b) non-linear analyses.
Figure 14. Results from the models that use the base motions compatible with the design spectrum. (a) equivalent linear analyses and (b) non-linear analyses.
Buildings 15 02746 g014
Buildings 15 02746 g015
Figure 15. Results from the models that use the base motions compatible with PGA. (a) Equivalent linear analyses and (b) non-linear analyses.
Figure 15. Results from the models that use the base motions compatible with PGA. (a) Equivalent linear analyses and (b) non-linear analyses.
Buildings 15 02746 g015
Table 1. F0, T0, Ta, Tb, and A0 values obtained from microtremor measurements.
Table 1. F0, T0, Ta, Tb, and A0 values obtained from microtremor measurements.
NoF0 (Hz)H/V (A0)Window Length (s)Number of WindowT0Ta (0.67 T0)Tb (1.5 T0)Record Length (s)Formation
M14.871.3925340.200.140.311800Alluvium
M22.631.3025250.380.250.571800
M33.631.1325320.270.180.411800
M42.700.8520150.370.250.551800
M52.140.9225490.470.310.701800
M62.451.2125410.410.270.611800
M73.690.6025390.270.180.411800
M81.640.9525300.610.410.911800
Table 2. Lithological classification, P and S velocities, and layer thicknesses obtained by MASW–seismic refraction measurements.
Table 2. Lithological classification, P and S velocities, and layer thicknesses obtained by MASW–seismic refraction measurements.
Profile No.Layer NoVp (m/sn)Vs (m/sn)H (m)Vs30 (m/sn)Litology Formation
MASW–Seismic refraction 114862696374Earthfill/Low-gravel clay
21126414 Low-gravel clayAlluvial
MASW–Seismic refraction 216051886251Sandy gravel rubble
21391274 Sandy gravel clay
MASW–Seismic refraction 316212116282Earthfill/gravelly silty clay
21297308 Gravelly clay
MASW–Seismic refraction 413772526336Silty clay
21117366 Hard silty clay
MASW–Seismic refraction 514052426334Coarse gravel clay
21162369 Gravelly silty clay
MASW–Seismic refraction 614392186306Earthfill
21149341 Gravelly clay
MASW–Seismic refraction 715612326316Earthfill/gravelly clay
21262347 Gravelly silty clay
MASW–Seismic refraction 814222156304Earthfill/gravelly clay
21307339 Gravelly silty clay
Table 3. Dynamic–elastic parameters of the study area.
Table 3. Dynamic–elastic parameters of the study area.
Profile No.Layer Noh (m)d (gr/cm3)Vp/VsρGmax (kg/cm2)E (kg/cm2)K (kg/cm2)Ak
MASW–Seismic refraction 1161.451.810.281052269020301.9
2---1.792.720.423073873918,636
MASW–Seismic refraction 2161.543.220.45543157048952.5
2---1.895.080.481419420034,683
MASW–Seismic refraction 3161.552.940.43688197450412.3
2---1.864.210.471762518128,898
MASW–Seismic refraction 4161.361.500.1086618997842.1
2---1.793.050.442397690319,130
MASW–Seismic refraction 5161.391.670.22813198811932.1
2---1.813.150.442461710621,120
MASW–Seismic refraction 6161.422.010.34673180018332.2
2---1.803.370.452095608420,997
MASW–Seismic refraction 7161.512.420.40811226536602.2
2---1.843.640.462221648226,420
MASW–Seismic refraction 8161.401.960.32648171816342.2
2---1.863.860.462139626228,940
Table 4. Selected motions (PEER) [55].
Table 4. Selected motions (PEER) [55].
IDRSNEarthquakeComponentYearPGA
(g)		MwRjb
(km)		Rrup
(km)		Vs30
(m/s)
D1292Irpinia_ Italy-01ITALY_A-STU27019800.3216.96.7810.84382
D2313Corinth_ GreeceCORINTH_COR--T19810.2966.610.2710.27361.4
D3727Superstition Hills-02SUPER.B_B-SUP04519870.5826.545.615.61362.38
D4811Loma PrietaLOMAP_WAH00019890.3736.9311.0317.47388.33
D5821Erzincan_ TurkeyERZINCAN_ERZ-EW19920.4966.6904.38352.05
D6848LandersLANDERS_CLW-TR19920.4177.2819.7419.74352.98
D71119Kobe_ JapanKOBE_TAZ00019950.6976.900.27312
D81615Düzce_ TurkeyDUZCE_1062-E19990.2597.149.149.14338
D93748Cape MendocinoCAPEMEND_FFS27019920.3767.0116.6419.32387.95
D104847Chuetsu-oki_ JapanCHUETSU_65010EW20070.4566.89.4311.94383.43
D114866Chuetsu-oki_ JapanCHUETSU_65039EW20070.3236.8011.75338.32
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Avcı, E.; Afacan, K.B.; Deveci, E.; Uysal, M.; Altundaş, S.; Balcı, M.C. Soil Amplification and Code Compliance: A Case Study of the 2023 Kahramanmaraş Earthquakes in Hayrullah Neighborhood. Buildings 2025, 15, 2746. https://doi.org/10.3390/buildings15152746

AMA Style

Avcı E, Afacan KB, Deveci E, Uysal M, Altundaş S, Balcı MC. Soil Amplification and Code Compliance: A Case Study of the 2023 Kahramanmaraş Earthquakes in Hayrullah Neighborhood. Buildings. 2025; 15(15):2746. https://doi.org/10.3390/buildings15152746

Chicago/Turabian Style

Avcı, Eyübhan, Kamil Bekir Afacan, Emre Deveci, Melih Uysal, Suna Altundaş, and Mehmet Can Balcı. 2025. "Soil Amplification and Code Compliance: A Case Study of the 2023 Kahramanmaraş Earthquakes in Hayrullah Neighborhood" Buildings 15, no. 15: 2746. https://doi.org/10.3390/buildings15152746

APA Style

Avcı, E., Afacan, K. B., Deveci, E., Uysal, M., Altundaş, S., & Balcı, M. C. (2025). Soil Amplification and Code Compliance: A Case Study of the 2023 Kahramanmaraş Earthquakes in Hayrullah Neighborhood. Buildings, 15(15), 2746. https://doi.org/10.3390/buildings15152746

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