Geotechnical and Structural Damages Caused by the 2023 Kahramanmaraş Earthquakes in Gölbaşı (Adıyaman)

Abstract

On 6 February 2023, two independent earthquake pairs on the East Anatolian Fault Zone, with epicenters in Pazarcık (Mw = 7.7) and Elbistan (Mw = 7.6) districts of Kahramanmaraş province, caused great destruction. Adıyaman and Gölbaşı districts of this city are among the settlements most affected by the earthquake. Especially in the district where geotechnical damages are most observed, the destructive effects of earthquakes have been clearly observed in buildings with different structural systems. In this study, information is given about the earthquakes that hit the region and the fault zone where the earthquakes occur. Geotechnical and structural damages occurring in the villages and center of the district were evaluated within the scope of earthquakes and structural engineering. It can be stated that damages observed in the district center are generally caused by soil–structure interaction problems. The fact that masonry structures, which are widely used in rural areas, do not benefit from any engineering services has an impact on the level of damage. The main reason for the damages occurring in the reinforced concrete structures in the district is the reinforced concrete system that is not designed properly or not built in accordance with the design. This case study demonstrated the importance of earthquake–soil–structure interactions in line with earthquake-resistant building design principles.

1. Introduction

Studies and evaluations to be carried out after the destructive effects of earthquakes on the completed environment are important in order to realistically reveal the earthquake hazard of that region, as well as to reveal the factors that negatively affect the earthquake performance of the existing building stock. Assessment of post-disaster structural damage, which is a fundamental part of modern disaster management, is necessary both for the development of earthquake-resistant building design principles and for spatial planning and urban transformation. One of the main tectonic elements that stands out within the complex tectonic structure of Türkiye, which has a very high seismic risk, is the East Anatolian Fault Zone (EAFZ). The last couple of Kahramanmaraş earthquakes, which occurred on 6 February 2023, caused great geotechnical and structural damage in 11 different provinces on and near this fault zone and caused over 50,000 deaths. The 1939 Erzincan earthquake caused the highest loss of life among instrumental earthquakes in Türkiye and 33,000 people lost their lives. The earthquakes of 6 February 2023, which caused the highest loss of life in Türkiye, were the disaster of the century for the country.

Türkiye, which is frequently affected by devastating earthquakes, is located in the Alpine–Himalayan earthquake zone, one of the most active earthquake zones in the world. The three main tectonic elements active in the country, where a very complex tectonic system exists, are the North Anatolian Fault Zone (NAFZ), the East Anatolian Fault Zone (EAFZ), and the Aegean Graben System. Earthquakes constantly happen on all three main tectonic elements, and as a result, large-scale losses of life and property occur. The dominant movements that stand out within this complex tectonic element of the country reveal the definition of tectonism in Anatolia. When explaining tectonism, the most common method is to look at plate movements and follow the movements of the plates. The Anatolian Block is basically under the influence of two important plate movements. The first and most effective of these is that the African Plate pushes the Arab Block northwards due to its counterclockwise rotation. This thrust event also pushes the Southeastern part of the Anatolian Block towards the north. Another important movement is the clockwise movement of the Europe–Asia, commonly known as the Eurasian Plate. Under the influence of this movement, the Anatolian Block is being pushed towards the south. Therefore, the Anatolian Block is under the influence of these two important compressions and is displaced in the west-southwest direction. The effects observed in the Anatolian Block are observed as a shear effect between Erzincan and Karlıova, and earthquakes occur from time to time when the stress resulting from the movement breaks. On the other hand, in the west of the Anatolian Block, due to the southeast direction movement, the south of western Anatolia opens to the south and the north to the north (Figure 1).

EAFZ, which has been the source of many big earthquakes in historical periods, was very active in the 19th century. It created an earthquake series that started with the 1822 Antakya earthquake, continued with the 1866, 1872, 1874, 1875, and 1893 earthquakes, and eventually ended with the 1905 Malatya earthquake. After this earthquake, it entered a relatively calmer period and did not produce an earthquake large enough to cause a surface rupture. It has been stated in some studies that this silence is temporary and significant stresses accumulate [2,3,4]. The 2020 Elazığ (Sivrice) earthquake broke this silence and was felt in many residential areas. This earthquake has become one of the most important earthquakes in the EAFZ earthquake history with the loss of life, injuries, structural damage, and economic losses in the region where many aftershocks occurred after the main earthquake. Finally, the 6 February 2023 Kahramanmaraş earthquakes once again demonstrated that this fault zone is active. The earthquake couple caused significant structural damage in Hatay, Kahramanmaraş, and Adıyaman provinces, as well as Adana, Osmaniye, Gaziantep, Kilis, Şanlıurfa, Diyarbakır, Elazığ, and Malatya provinces. Ground- and soil-related structural damages were observed in Hatay (İskenderun) and Adıyaman (Gölbaşı) districts. Within the scope of this study, Gölbaşı district of Adıyaman province, one of these two districts, was taken into consideration.

Many studies in the literature discuss post-earthquake damage in Türkiye and the world. Field observations are conducted after an earthquake for a variety of structures, including bridges, historical structures, masonry, reinforced concrete, and industrial buildings, etc. [5,6,7,8,9,10,11,12,13,14,15,16].

Especially after the Kahramanmaraş earthquakes, there are many case studies examining the effects of earthquakes and damage on structural systems within the framework of cause and effect. Some of these are as follows: Avcil et al. [17] examined the effects of earthquakes on all structures in Kahramanmaraş province. Ivanov and Chow [18] evaluated the effects of earthquakes on reinforced concrete structures in Adıyaman province. Işık et al. [19,20] revealed the effects of earthquakes on masonry structures, mosques, and minarets in Adıyaman province as a result of field investigations. Ince [21] evaluated the structural damages caused by earthquakes in reinforced concrete structures in Adıyaman province. Avcil [22] examined the damages caused by earthquakes on prefabricated structures. Zengin and Aydın [23] examined the effect of material properties on earthquake damage in the case of Elbistan. Karaşin [24] evaluated the effects of the earthquake in Diyarbakır province, especially taking into account the reinforcement effect. Işık [25] examined the structural damages in adobe buildings located in the earthquake zone within the framework of a cause–effect relationship. Yıldız and Kına [26] examined in detail the geotechnical and structural damages caused by the earthquake couple in Malatya province. Öztürk et al. [27] considered the entire earthquake region to reveal the effects of earthquakes on reinforced concrete structures. Öztürk et al. [28] evaluated the effects of earthquakes on schools within the scope of the earthquake and civil engineering. Karataş and Bayhan [29] revealed the effects of earthquakes on Diyarbakır Walls. Altınsu et al. [30] examined the damage to the structures in Hatay, one of the provinces most affected by a pair of independent earthquakes. Mavroulis es al. [31] evaluated debris management and environmental risks in the affected provinces after earthquakes. Kahya et al. [32] examined the structural damages in masonry buildings in Hatay province. Wan et al. [33] analyzed the peak ground acceleration decrease characteristics for Pazarcık (Kahramanmaraş), which was the first earthquake.

Within the scope of this study, the Gölbaşı district of Adıyaman province, where the most ground and ground-related structural damages were observed, was chosen as an example. The failures that occurred during the 6 February Kahramanmaraş earthquake in the district center and villages were evaluated in terms of structural and earthquake engineering in geotechnical and structural contexts. Ground-related damages in particular constitute the main theme of this study. This case study, which aims to present the main reasons for the damages occurring in different structural systems in Gölbaşı district, also draws attention to the negative features of the structures. While the dominant urban building stock in the district is reinforced concrete, the dominant building stock in rural areas is masonry buildings. In this study, in addition to the damages that occur in the case of insufficient earthquake–soil–structure interactions, the damages that occur in reinforced concrete, masonry, and prefabricated structures are examined within the framework of cause and effect. This study also mentions the damages observed in mosques and minarets. In general, failure to implement earthquake-resistant building design rules has negatively affected the structural damage that occurred. Additionally, information is given about the fault zone where earthquakes occur. The study includes information about the general tectonic and geological structure of the region, geotechnical observations and evaluations, observations and evaluations regarding building materials, and structural performance-based observations and evaluations.

The organization of the paper is as follows: Section 2 introduces the characteristics of the East Anatolian Fault Zone, Section 3 describes the Kahramanmaraş earthquakes and explains the seismicity and seismo-tectonics of the region, Section 4 describes the seismicity of Adıyaman and the surrounding areas, Section 5 presents the geotechnical findings, Section 6 discusses the structural damages, and at the end, Section 7 covers the main conclusion of the study.

2. East Anatolian Fault Zone (EAFZ)

The East Anatolian Fault (EAF) creates a NE-SW left-lateral strike-slip transform boundary between the northward-moving Arabian Plate and the westward-moving Anatolian Block, with an average width of 30 km and a length of 580 km. It merges with the Ölüdeniz Fault around Türkoğlu and with the NAFZ around Karlıova. The zone between Karlıova and Antakya, consisting of many left-lateral strike-slip faults with different characteristics and complementing each other, is called the East Anatolian Fault Zone (EAFZ) [34]. Different researchers have evaluated EAFZ as consisting of different numbers of segments. Şaroğlu et al. [35] stated that it was divided into six segments based on the fault traces on the surface. Hempton et al. [36] divided the fault into five segments in terms of changes in geometry and orientation. Barka and Kadinsky-Code [37] divided it into 14 segments according to geometric discontinuities, surface fractures, and seismicity features. Duman and Emre [38] divided the EAFZ into five segments for similar reasons. These faults are expressed as Karlıova–Bingöl, Palu–Hazar, Hazar Lake–Sincik, Çelikhan–Erkenek, Gölbaşı–Türkoğlu and Türkoğlu–Antakya segments. Syria–Latakia earthquakes further south are also included in this zone. EAF, which is one of the most active fault systems in Türkiye and forms the border between the Anatolian and Arabian Plates, meets the westward movement of the Anatolian block together with the North Anatolian Fault Zone (NAFZ). Current GPS data give today’s slip rate in the 11 ± 2 mm/year range. The closest settlements to this fault zone are Hatay, Osmaniye, Kahramanmaraş, Adıyaman, Malatya, Elazığ, Bingöl and their affiliated centers. A representation of these settlements on the map is shown in Figure 2.

Important historical and instrumental period earthquakes that occurred on the EAFZ are shown in

Table 1. Earthquakes that occurred on the EAFZ AFAD 2020; [40,41,42,43,44,45,46,47].

No	Date	Region	Intensity	Magnitude
Historical Period
1	148 BC	Antakya	VIII
2	69 BC	Antakya	IX
3	37 BC	Antakya	VIII
4	53	Lazkiye–Antakya	VIII
5	220	Antakya	VII
6	396	Antakya	VIII
7	526	Antakya	IX
8	529	Antakya and its region	IX
9	1544	Elbistan	VIII
10	1568	Lazkiye	VIII	Ms = 6.0
11	1626	Halep	IX	Ms = 7.3
12	1726	Harim	VIII	Ms = 6.1
13	1738	Amik Lake	VIII	Ms = 6.2
14	1789	Elazığ	VIII
15	1796	Lazkiye	VIII-IX	Ms = 6.8
16	1822	Antakya	IX	Ms = 7.0
17	1866	Karlıova, Bingöl		Ms = 6.8
18	1872	Hatay (Amik Lake)	VIII-IX	Ms = 7.2
19	1874	Elazığ	IX	Ms = 7.1
20	1875	Elazığ	VI	Ms = 6.7
21	1875	Palu		Ms = 6.1
22	1893	Malatya	IX
Instrumental Period
1	4 December 1905	Pütürge (Malatya)		Ms = 6.8
2	20 March 1945	Ceyhan (Adana)		Ms = 6.0
3	22 October 1952	Misis (Adana)		Ms = 5.6
4	14 June 1964	Sincik (Adıyaman)		Ms = 6.0
5	22 May 1971	Bingöl		Ms = 6.8
6	6 September 1975	Lice (Diyarbakır)		M = 6.6
7	1979	Adana-Kozan		Ms = 5.1
8	5 May 1986	Sürgü (Malatya)		Mw = 6.0
9	1986	Gaziantep		Ms = 5.0
10	1989	İskenderun		Ms = 4.9
11	1991	Kadirli		Ms = 5.2
12	1994	Ceyhan		Ms = 5.0
13	22 January 1997	Samandağ (Hatay)		Mw = 5.7
14	27 June 1998	Yüreğir (Adana)		Mw = 6.2
15	1 May 2003	Bingöl		Mw = 6.3
16	11 August 2004	Sivrice–Elazığ		Mw = 5.6
17	9 February 2007	Sivrice (Elazığ)		Mw = 5.5
18	21 February 2007	Sivrice (Elazığ)		Mw = 5.7
19	8 March 2010	Kovancılar (Elazığ)		Mw = 6.1
20	24 January 2020	Sivrice (Elazığ)		Mw = 6.8

. Here, earthquakes are discussed in two groups, historical and instrumental earthquakes. It is seen that both historical and instrumental period earthquakes are generally more severe in the central and northeastern parts of the EAFZ. On the other hand, it is understood that no destructive earthquake has occurred in the last 500 years, especially in the Gölbaşı–Türkoğlu segment [39,40].

3. 2023 Kahramanmaraş Earthquakes

The earthquake series that occurred on 6 February 2023 started with an earthquake on the Pazarcık Narlı fault at 01:47 with a focal depth of 8.6 km and a magnitude of Mw = 7.7. The moment tensor solution of the earthquake reveals an almost entirely left-lateral strike-slip movement on NE-SW trending faults. This mainshock, which started in the south of the EAFZ, caused a rare rapid stress transfer in the north and the successive rupture of the Pazarcık–Erkenek fault section in the northeast and the Amanos section in the southeast. The Kahramanmaraş–Pazarcık earthquake shows complex rupture, showing directionality effects at both ends of the rupture zone and discontinuous time evolution along multiple fault sections, and in this sense, it is a unique example of a complex earthquake structure containing multiple ruptures. The total length of the rupture formed by the main shock is around 300 km. Ten min after the main shock, a large aftershock with a magnitude of Mw = 6.8 occurred just west of the focus of the main shock. Approximately 9 h later, a second earthquake occurred in Elbistan Ekinözü with a focal depth of 10 km and a magnitude of Mw = 7.6, and a surface rupture occurred along the Çardak–Sürgü fault section. The moment tensor solution of this earthquake also shows an almost entirely left-lateral strike-slip movement. The total length of the rupture formed during this earthquake is approximately 160 km. The main shocks and aftershocks of the February 2023 Mw = 7.7 Kahramanmaras–Pazarcık and Mw = 7.6 Elbistan earthquakes were recorded by stations located in a wide area in the National Strong Motion Network operated by AFAD. The acceleration values of these earthquakes measured at stations in Adıyaman district are shown in

Table 2. Accelerometer stations and measured accelerations of earthquakes in Adıyaman province [39].

Pazarcık (Kahramanmaraş) Mw = 7.7
Code	Longitude	Latitude	District	PGA_NS (cm/s2)	PGA_EW (cm/s2)	PGA_UD (cm/s2)	Refi (km)
0201	37.76121	38.26742	Center	474.12	879.95	318.97	120.12
0208	37.78694	37.65275	Gölbaşı	30.20	14.00	16.97	77.26
0210	37.7672	38.2866	Center	65.91	61.37	42.13	121.92
0213	37.79667	37.92957	Tut	242.28	171.69	291.29	96.48
0214	38.028298	38.22594	Çelikhan	61.68	54.38	69.91	132.74
Elbistan (Kahramanmaraş) Mw = 7.6
0205	37.79177	38.61597	Kahta	44.88	54.66	32.94	125.19
0213	37.79667	37.92957	Tut	121.30	126.62	71.35	68.73

. The earthquakes that occurred on 6 February 2023 also affected Syria. According to official data, 53,537 people lost their lives in Türkiye and 8476 people in Syria. More than 100 thousand people were injured in Türkiye and over 20 thousand people in Syria.

The largest earthquake acceleration values for the first earthquake were measured at Adıyaman (Center-0201) station. The highest acceleration value was measured in the E-W direction as 879.95 cm/s². The lowest values were measured at Gölbaşı (0208) station. However, probably due to instrumental error, no measurement data were available in Gölbaşı district for the second earthquake.

Calculations were made for the earthquake stations where measurements were made within the scope of the study. A representation of the considered stations on a map is given in Figure 3.

In the paper, earthquake parameters were also obtained by taking into account the geographical locations of the earthquake stations in Adıyaman province. In this context, peak ground accelerations (PGA) and peak ground velocities (PGV), which are the most commonly used intensity measures, were attained separately for the locations of the accelerometer in Adıyaman province. PGA and PGV values predicted in the current earthquake hazard map for different ground motion levels were obtained. Ground motion levels were selected according to current earthquake regulations. In the Türkiye Building Earthquake Regulation [48], earthquake ground motion level is expressed in four various ways, unlike previous codes. Earthquake ground motion levels used within the scope of the paper are given in

Table 3. Earthquake ground motion levels [48].

Ground Motion	Probability of Exceedance (in 50 Years)	Repetition Period	Definition
DD-1	0.02	2475	Largest earthquake ground motion
DD-2	0.1	475	Standard design earthquake ground motion
DD-3	0.5	72	Frequent earthquake ground motion
DD-4	0.68	43	Service earthquake ground motion

.

PGA and PGV values obtained according to different exceedance probabilities are shown in

Table 4. PGA and PGV values obtained for the locations of accelerometers in Adıyaman province.

No	Location	PGA (g)				PGV (cm/s)
		2%	10%	50%	68%	2%	10%	50%	68%
1	Center	0.426	0.245	0.099	0.066	29.538	16.359	6.254	4.070
2	Gölbaşı	0.953	0.510	0.170	0.111	63.873	32.755	9.814	6.088
3	Center	0.427	0.246	0.100	0.066	29.576	16.388	6.284	4.090
4	Tut	0.809	0.440	0.147	0.094	51.958	27.343	8.670	5.318
5	Çelikhan	1.063	0.593	0.209	0.126	77.674	41.883	11.326	6.388
6	Kahta	0.427	0.244	0.099	0.068	27.922	15.582	6.079	4.050

.

For Adıyaman province, PGA values for earthquakes with a 10% probability of being exceeded in 50 years are predicted to be in the range of 0.24–0.6 g. The predicted PGA value for DD-2 for Adıyaman city center is well below the measured acceleration value. It can be stated that the value recommended for Gölbaşı district is higher than the PGA value of the earthquake measured in the district; therefore, the ground motion level is adequately represented for the standard design earthquake.

Table 5. Comparing the results within the parameters of the previous two regulations [48,49].

No	Station Code	TEC-2007 Seismic Zone	TEC-2007 PGA (g)	TBEC-2018 PGA (g)	PGA
					2018/2007
1	0201 (Center)	2	0.300	0.245	0.82
2	0205 (Kahta)	2	0.300	0.244	0.82
3	0208 (Gölbaşı)	1	0.400	0.510	1.28
4	0210 (Center)	2	0.300	0.246	0.82
5	0213 (Tut)	1	0.400	0.440	1.10
6	0214 (Çelikhan)	1	0.400	0.593	1.48

presents a comparison of the values acquired for the last two earthquake maps with the Turkish regulations for the locations of all accelerometers in the Adıyaman province. As a point of reference, both earthquake maps and regulations considered the typical earthquake ground motion level with a recurrence period of 475 years.

When the last two earthquake hazards are compared, the earthquake hazard in the locations of the accelerometers in Gölbaşı, Tut, and Çelikhan districts has increased with the current map. The biggest increase was in Çelikhan district. However, there was a decrease in the Center and Kahta districts. Taking these earthquakes into account, realistically presenting the seismic hazard on a micro scale for Adıyaman will enable a more accurate determination of the behavior of structures under earthquake effects.

For the geographical location of the earthquake station located in Gölbaşı district of Adıyaman province, which is the subject of the study, maximum and minimum values were obtained by taking into account the soil class (ZA), which is the strongest soil class, and the soil class (ZE), which is expressed as the least resistant soil class. Calculations were made for the short-period map spectral acceleration coefficient, design spectral acceleration coefficients, local ground effect coefficients, peak ground acceleration, peak ground velocity, and horizontal and vertical elastic spectrum curves for the selected location. The earthquake parameters obtained for Gölbaşı station due to different earthquake ground motions for the best and worst soil classes are shown in

Table 6. Comparison of earthquake parameter values for the epicenter of the earthquake.

Parameter	ZA				ZE
	DD1	DD2	DD3	DD4	DD1	DD2	DD3	DD4
SS	2.363	1.218	0.394	0.253	2.363	1.218	0.394	0.253
S1	0.680	0.327	0.095	0.059	0.680	0.327	0.095	0.059
FS	0.800	0.800	0.800	0.800	0.800	0.926	1.997	2.392
F1	0.800	0.800	0.800	0.800	2.000	2.692	4.200	4.200
SDS	1.890	0.974	0.315	0.202	1.890	1.127	0.787	0.605
SD1	0.544	0.262	0.076	0.047	1.360	0.880	0.399	0.248
TA (s)	0.058	0.054	0.048	0.047	0.144	0.156	0.101	0.082
TB (s)	0.288	0.268	0.241	0.233	0.719	0.781	0.507	0.410
TAD (s)	0.019	0.018	0.016	0.016	0.048	0.052	0.034	0.027
TBD (s)	0.096	0.089	0.080	0.078	0.240	0.260	0.169	0.137

. As stated in TBEC-2018, the parameter “S_S” refers to the short-period map spectral acceleration coefficient, “S₁” refers to the map spectral acceleration coefficient for the 1.0 s period, “F_S” and “F₁” refer to the local ground effect coefficients, and “S_DS”, and “S_D1” refer to the design spectral acceleration coefficients. Also, “T_A” and “T_B” mean the corner period of the horizontal elastic design acceleration spectrum, and “T_AD”, “T_BD” mean the corner period of the vertical elastic design acceleration spectrum.

A comparison of design spectral acceleration coefficients for the location of the earthquake station in Gölbaşı district within the scope of the last two regulations is given in

Table 7. Comparison of spectral acceleration coefficients.

Station	TEC-2007	ZA (2018)	ZE (2018)	2018/2007 (ZA)	2018/2007 (ZE)
208 Gölbaşı	1	0.974	1.127	0.97	1.13

.

In TEC-2007, the design spectral acceleration coefficients take constant values for different soil classes in the same earthquake zone. However, local ground effect coefficients, which started to be used with the current earthquake regulations, mean that different spectral acceleration coefficients are obtained for each soil class. With the current regulation, the spectral acceleration coefficient has increased in the case of poor ground conditions in Gölbaşı.

While the PGA and S_DS values suggested in the previous map decreased in the Adıyaman/Center and Kahta districts with the current map, they increased in Gölbaşı. A large part of Adıyaman province is located on the East Anatolian Fault Zone, one of the most important tectonic elements of the country. Palu–Sincik (145 km), Çelikhan–Erkenek (45 km) and Gölbaşı–Türkoğlu (90 km) segments of the East Anatolian Fault Zone pass through Adıyaman province. In the instrumental period, no damaging earthquake was recorded except the Çelikhan earthquake with Mw = 5.1 in 2004 (Adıyaman-IRAP).

4. Seismicity of Adıyaman Province and General Geology of the Study Area

On a macro scale, in Gölbaşı and its surroundings, sedimentary rocks of the Southeast Anatolian autochthonous, developed from the Paleozoic to Tertiary periods, and allochthonous masses related to the Karadut complex from the Koçali–Karadut nappes settled in the region at the end of the Upper Cretaceous are observed. Although it is located on the Southeastern Anatolian autochthonous, volcanic rocks consisting mostly of basalt and pyroclastics in the Late Miocene–Early Pliocene age range are exposed in the study area [50].

In the region located at the northern end of the Southeastern Anatolia autochthonous, the oldest rock units belonging to the autochthonous are the Kestel formation, consisting of late Campanian–Maastrichtian sandstone, shale, and marls. At the top, the Midyat group, which consists of Eocene–Oligocene aged carbonates, unconformably covers the sequence. In the lower part of the Midyat group, there is the Gercüş formation, consisting of Early Eocene-aged continental crumbs. Above the Gercüş formation is the Hoya formation, consisting of Eocene-aged limestone, and above it is the Gaziantep formation, consisting of Late Eocene–Oligocene aged limestone, clayey limestone, and chert limestone. The Fırat formation, consisting of Early Miocene-aged limestones, and the Şelmo formation, consisting of Middle–Late Miocene-aged conglomerate, sandstone, siltstone, shale, and mudstones, are observed unconformably above the Midyat group. The Karadut complex, consisting of Cretaceous-aged siliceous shale, clayey limestone, limestone, and chert belonging to the allochthonous Koçali–Karadut nappes in the region, was settled in the region at the end of the Upper Cretaceous. All rock units are covered with Pliocene–Quaternary unnamed terrestrial sediments and Quaternary alluviums [51].

On a smaller scale, the local geology of the study area consists of Quaternary-aged Alluvium (Qal), residual (Kkad) units belonging to the Upper Cretaceous-aged Black Mulberry Complex, and units belonging to the Black Mulberry Complex (Kkad). Alluvium (Qal) units are in the form of gray, greenish-gray, light brown-cream colored, and reddish-brown colored, gravel, sand, silt, and clay, which are transitional with each other, and these units are low–medium–high-plasticity clay, well–poorly graded sand, it were observed in the form of clayey sand, gravelly sand, clayey gravel, silty gravel, sandy gravel, and occasionally blocks.

The residual units belonging to the Black Mulberry Complex (Kkad) were observed as reddish-brown-colored low-plasticity clay, clayey sand, and clayey gravel. A general geological map of Gölbaşı and its surroundings is shown in Figure 4.

Like the whole of Southeastern Anatolia, two main tectonic faults are observed in the area where Adıyaman is located. The first of these tectonic phases is the compressional regime that took effect during the Upper Campanian–Lower Maestristian period and resulted in the settlement of allochthonous units in the Kastel basin and occurred due to the subduction of the Arabian plate under the Anatolian plate. This compression regime caused the Koçali and Karadut Complexes, which form allochthonous units in the northern areas, to drift southwards and settle on the platform with thrusts in the north, while in the southern parts (Kastel basin), they settled into the basin with gravity shifts. The compression that caused these events caused deformations (folding and fracture) in the southern parts of the platform, the effect of which gradually decreased towards the south. While this compression is observed in a northwest-southeast direction in the project area, it has created northeast-southwest folds and structures limited by reverse faults in the south. Such structures formed by Cretaceous tectonics cannot be observed on the surface due to the masking of deformations formed by Miocene tectonics but can be monitored through seismic sections [53].

On the other hand, allochthonous units coming onto the plate with thrusts in the northern parts caused a great load to be applied on the crust, in addition to compression and deformation. This load showed an elastic reaction due to the viscoelastic property of the crust and caused collapse following the isostasy principle and the formation of a front depression (Kestel Basin) and a front rise right in front of it. While the effects of this north-south oriented event are observed in the form of thrusts and drifts from north to south, this event shows its effect decreasingly towards the south. As a result, folding, asymmetrical structures towards the south, reverse faults and associated east-west trending, asymmetrical anticlines form the dominant topography (Figure 4).

Instrumental period earthquakes (Mw > 3.0) and historical period earthquakes affecting Gölbaşı and its surroundings are shown in Figure 5. It is seen that the earthquakes are especially concentrated in the north and east of Gölbaşı, in the section between the Çardak Segment of the East Anatolian Fault Zone and the Adıyaman Fault Zone and Pazarcık Segment.

5. Geotechnical Findings

Increases in pore water pressure due to earthquakes can cause liquefaction in sand and silt soils. Ground liquefaction is when the layers below the groundwater level temporarily lose their strength and behave like a viscous liquid instead of a solid. Liquefaction is a phenomenon that occurs in loose-grained soils (sandy-silty soils) under dynamic loading such as earthquakes. It occurs when the structure of the water-saturated granular soil deteriorates as a result of sudden loading, the contact force between the separated grains decreases, the pore water pressure increases, and the soil loses its resistance. Liquefaction is shown schematically in Figure 6.

During the 6 February 2023 Kahramanmaraş earthquakes, structural damages caused by liquefaction were widely observed, especially in Hatay’s İskenderun and Adıyaman’s Gölbaşı districts. After an earthquake, the boiling of water and fine sand trapped under pressure in the underlying sand layer on the ground surface is a very common observation that indicates liquefaction. Sand boils observed in Gölbaşı district are shown in Figure 7.

Lateral spreads on the ground surface have been widely observed in Gölbaşı district, on the ground with low or nearly flat slopes after the earthquake. Depending on the earthquake’s magnitude and local soil conditions, large depressions, separations, and wide cracks formed on the ground surface, as shown in Figure 8. These cracks tend to be parallel to each other on the ground surface.

Due to lateral spread, transportation structures such as vehicle and pedestrian roads, infrastructure systems such as sewage and drinking water, and various types of buildings have also been affected. Examples of such damage are shown in Figure 9.

The lateral spreads that occurred on the ground clearly affected the surrounding walls. Examples of damage to surrounding walls are shown in Figure 10.

As a result of lateral spreading on the ground, small or large ground collapses have occurred in many parts of the district. Some examples of collapse are shown in Figure 11.

The loss of bearing capacity and settlement damages occurring in the buildings in Gölbaşı district as a result of ground liquefaction are shown in Figure 12.

Since the bearing capacity of the ground, whose shear strength decreases as a result of liquefaction, will decrease, the structures on this ground may suffer damage in the form of foundation settlements as well as the structure shifting from the foundation and toppling over. In addition, improper design of the structure–soil interaction or lack of sufficient foundation depth can be considered among the causes of such damages. A building on the main street in Gölbaşı district collapsed and fell onto a building at the rear. There was no structural damage to the load-bearing system of the building and it remained mostly intact. Images taken from different facades of the building are shown in Figure 13.

6. Structural Findings

6.1. Damages Observed in Reinforced Concrete Structures

Figure 14 shows examples of collapsed reinforced concrete structures with an inadequate frame made of reinforced concrete and plastic hinges produced mostly at the bottom ends of the ground floor columns.

The main reasons for this are the inadequate reinforced concrete frame, the weak column–beam connection, the column dimensions being smaller than the beam dimensions, and the building floors piling up on top of each other and collapsing altogether. Examples of this type of damage, called pancake, are shown in Figure 15.

Partial and complete collapses occurred on the ground floors due to stiffness differences between floors. Especially in buildings where the ground floors are used as workplaces and the upper floors are used as residences, the number of infill walls varies between floors. Examples of partial or total collapse that occurred on the ground floors as a result of this are shown in Figure 16.

In RC structures, changes in column lengths within the floor or structure due to different reasons cause the formation of short columns, and plastic hinges form in these columns during an earthquake. Examples of structural damage occurring in short columns created from sloping ground and band-type windows are shown in Figure 17.

Reinforced concrete structures built adjacent to each other may cause different damages to neighboring structures by causing a pounding effect during an earthquake. Different floor levels negatively affect the damage that may occur due to collision. Additional shear forces resulting from the pounding effect, which is not taken into account in the design, cause significant damage, especially to the columns that will be subjected to the impact of the collision. The damages that occur if the floor levels are not the same are shown in Figure 18.

The fact that the floor levels of adjacent buildings are the same prevented the damage from increasing. Examples of damage to neighboring structures with floors at the same level are shown in Figure 19.

Column and beam connection regions are stressed the most in reinforced concrete structures under earthquake loads. When appropriate joint design and manufacturing are not carried out, plastic deformations occur at these joints in a severe earthquake. One of the typical damage examples seen in the region is the plastic hinge that occurs in the column end regions, as shown in Figure 20.

Various levels of damage occurred in the structures due to the low-strength concrete, inadequate concrete cover, insufficient amount of transverse reinforcement and crossties, poor workmanship, and connections details. Examples of such damage are shown in Figure 21.

The low strength of the infill wall materials used in reinforced concrete structures and poor workmanship have created X-shaped shear cracks in these walls. Examples of damage caused by shear force are shown in Figure 22.

Many of the reinforced concrete buildings in the district have closed heavy overhangs that extend beyond the floor area. These heavy overhangs, as well as the damage to the gable walls of the roof, also caused damage in some places due to the application of strong beams and weak columns. Examples of heavy overhang, gable wall, and strong beam-weak column damage are shown in Figure 23.

6.2. Damages Observed in Masonry Buildings in Gölbaşı

Masonry structures, which have been built since the beginning of humanity and generally do not receive engineering services, are built by local craftsmen and workers using local materials and are common in rural areas. The seismic behavior of such structures is quite low. This situation caused significant damage to masonry buildings in the rural areas of Gölbaşı district, which was affected by the Kahramanmaraş earthquakes, due to the lack of application of earthquake-resistant building design rules. The masonry structures in this region were generally made of stone or adobe, and either soil mortar or, rarely, cement mortar was used as a structural member connection.

Damage to masonry structures generally occurs in the form of cracks in the walls, settlements in the foundation, and deterioration or deformation of the material used. The tensile strength of the wall material generally used in masonry structures is low, and the shear strength of the mortar is low. In order to ensure efficient load transfer, adherence must be ensured between the materials [54,55,56]. The most important cause of structural damage observed in the region is cracks, separation, and out-of-plane failure caused by shear stresses in the walls due to the earthquake effect. Within the scope of this study, masonry structures in the villages of Gölbaşı district were taken into consideration.

In rural areas susceptible to earthquakes, masonry buildings make up a significant portion of the stock of existing structures, and earthen roofs are the typical roofing system utilized in these buildings. There have been varying degrees of damage to the load-bearing masonry walls and roof floors as a result of heavy earthen roofs. Examples of damage to heavy earthen roofs in the Gölbaşı are shown in Figure 24.

Structural damage at different levels occurred in the structures built as a result of the use of different types of wall materials, inconsistencies in material dimensions, and poor workmanship in the load-bearing walls and between floors. Some examples are shown in Figure 25.

The most common damage caused by an earthquake is the out-of-plane collapse of load-bearing walls. The most important reason for this is inadequate connections between external walls that intersect at right angles to each other, or between external walls and internal walls that meet perpendicularly to them. Examples of out-of-plane failures in structures are shown in Figure 26.

While the closeness of doors and windows to wall corners and/or large door and window openings cause shear cracks, different ground settlements on the ground where the building sits and the excess of the door and window openings cause settlement cracks. Examples of damage occurring in door and window openings as a result of the moment occurring in these gaps are shown in Figure 27.

The insufficient connection between the layers forming the load-bearing walls caused these layers to split from each other during the earthquake. These damage examples are shown in Figure 28.

The coverings used on the load-bearing walls, which were observed in many slightly damaged buildings, were separated from the walls during the earthquake. These damage examples are shown in Figure 29.

In masonry constructions, separation damage at the corner points has been caused by inadequate interlocking at the corners where the load-bearing walls are connected in both directions. Furthermore, the wall’s improper support on the structural part to which it was attached in all three directions resulted in these damages, as shown in Figure 30.

6.3. Damages Observed in Mosques and Minarets

Mosques are wide-open structures built to bring crowds together for worship. Mosques, which are generally built as two floors, have service areas (ablution room, ghusl room, Quran course, tea house, etc.) on the lower floor. The upper floor contains the main place of worship (Harim) and the dikka (mahfil) floor is built as a mezzanine. The floors are kept high to provide a spacious place for the crowds coming to worship.

Another important part of mosques is the minarets. They are high slender structures onto which the muezzin (the person who calls the believers to worship) climbs and reads the call called adhan. Although this function is performed through speakers today, they are still the highest and most spectacular parts of mosques, making them landmarks in terms of their symbolic value. Minarets, built at different heights with the materials and techniques used, have a structure consisting of various sections where static requirements are prioritized. At the bottom, there is a square prismatic pulpit section that continues after the foundation. There is a prismatic transition segment in the transition from this section, which is built with a solid body, except for the stair shaft, to the circular section body. One or more balconies can be attached to the body. After the last balcony, there is no staircase in the circular section upper part of the body, and its outer radius (wall thickness is less) is smaller. There is a spire section above this section, usually conical and sometimes domed. Although there are parts of this section made of the same material as the minaret, most of them are hollow with wooden or steel construction and lead metal coating. There is a metal end ornament at the top.

Mosques received little damage in the earthquake due to their low-rise structural features in terms of their main structures. In addition, as they are public buildings capable of gathering large crowds, they became the priority buildings used for temporary shelter after the earthquake. This situation made it necessary to consider mosques as a separate section. The damages of the mosques, whose damages mostly originated from the minaret sections, are handled as minaret-related.

Table 8. Failure mechanism and damages of some mosques and minarets in Gölbaşı.

Mosque Name	Failure Mechanism	Existing Damage
Yeni Mosque	Incorrect design damage	As a result of the lack of a suitable transition segment in the transition from a square planned section to a circular planned section, the minaret collapsed from this section and fell onto the neighboring structure.
Ulu Mosque	Rigidity differentiation and additional shear force damages	Due to the rigidity created by the shadirvan space built around the pulpit section, the minaret fell onto the shadirvan from the transition segment zone.
Erek Baba Mosque	Spire damage	The spire area collapsed as a result of displacement, causing damage to the cloistered narthex of the mosque and the courtyard wall of the neighboring building.
Hacı Gani Diler Mosque	Reinforcement mistakes in RC minarets, poor workmanship, low-strength material	The minaret, which was damaged by earthquakes, collapsed on the neighboring structure 26 days after the main earthquake.
Abdullah Günaydın Mosque	Reinforcement mistakes in RC minarets	The cylindrical body of the minaret was damaged and collapsed and fell onto the neighboring building.
Karadoğan Mosque	Incorrect design damage	Since there is no transition segment, the minaret collapsed at the center of rigidity. The collapsed masonry minaret fell on the mosque and caused damage to the mosque’s roof.

explains the failure mechanism and damages of some mosques and minarets in Gölbaşı. Pictures of the mosque and minaret in Gölbaşı before and after the earthquake are shown in Figure 31.

6.4. Damages Observed in Precast Buildings

One of the most frequent failures of prefabricated reinforced concrete structures in earthquake regions is the loss of support at the beam-to-column connections. Even though the column and gutter beams were undamaged, the roof beam lost support and collapsed completely along with the roof parts because of the weak column–beam connection, as shown in Figure 32.

Double steel bars are used to tie the prefabricated reinforced concrete columns and beams. The roof beam separated from the joint because of the insufficiency of the column beam connection during the earthquake, and a significant portion of the structure, including the roof coverings and purlin beams, collapsed, as shown in Figure 33.

Figure 34 shows a single-span reinforced concrete industrial structure in Gölbaşı. It is understood that the structure collapsed completely during the earthquake, as the roof beams were separated from the column connections. There are deviations in the axes of the middle columns. Moreover, the shear force from the different members of the contact with the masonry walls also caused damage to the precast columns.

7. Results and Conclusions

Two major Kahramanmaraş earthquakes that occurred on 6 February 2023, in the East Anatolian Fault Zone, one of the main tectonic elements of Türkiye, resulted in great losses of life and property in 11 different provinces. One of the provinces significantly affected by the earthquake was Adıyaman. It caused great destruction in Adıyaman province, especially in Gölbaşı district. What makes Gölbaşı district special is the high level of damage, especially due to ground liquefaction. Following the earthquake couple, Gölbaşı district was one of the two districts where ground-related damage was most observed. In this context, this study particularly focused on ground-related damages. The study also gave information about the damages occurring in reinforced concrete, masonry, and precast structures in the district center and rural areas. In addition, the damage to mosques and minarets in the district, which were damaged at different levels, was also mentioned. All damages considered in the study were examined within the framework of cause and effect in the context of earthquakes and civil engineering.

The main reason for the damage was the low strength of the wall materials used in masonry structures. Heavy earthen roofs, poor masonry, the use of different types of wall materials, and inadequate wall interlocks were the main causes of damage. It is necessary to provide engineering services for masonry buildings, which constitute the majority of the building stock in rural areas. Such structures are generally constructed unconsciously, without taking into account earthquake forces and paying attention to the necessary details. Corner connections on the walls must be constructed properly. Care should be taken not to deviate from the symmetry of the wall layout in the plan, and the required constructive rules should be followed. Demolition of very old masonry structures, in any case of their damage, and renovation of them with projects that provide optimum design principles specific to each rural area will be one of the damage reducing strategies due to new earthquakes.

It was determined that most of the damaged reinforced concrete buildings examined were built in accordance with the 1975 earthquake regulation or the previous regulation. The general cause of damage to reinforced concrete structures is the reinforced concrete system that is not designed properly or not built in accordance with the design. The reasons the authors investigated are as follows: inadequate confinement reinforcement that causes longitudinal reinforcement to buckle; using plain reinforcement rebar as reinforcement in general old-type structures; using unprocessed aggregate; excessive segregation in concrete; using low-strength concrete; failing to bend confinement bar by 135°; not using the RC shear-wall; not using confining reinforcement in column–beam joint areas, etc. All these issues are included in the earthquake-resistant building design rules. In this context, it is important to obtain the necessary engineering services in the implementation of structures designed in accordance with earthquake-resistant building design rules. Under the effect of this earthquake, the significance of the concepts of strength and size for RC buildings has emerged once again.

Türkiye is located in a seismically active region due to its location between the African and Eurasian tectonic plates. This geological environment leads to interaction between these two major tectonic plates, creating significant seismotectonic stress that results in large earthquakes. More than 95% of the country has the potential to be affected by earthquakes, and most of them are settlements directly affected by faults such as NAFZ and EAFZ. The vulnerability of buildings and infrastructure to strong ground movements is a major concern, especially in areas with high seismic risk. Some old buildings are designed to have lower earthquake resistance, but efforts are being made to improve building regulations and strengthen existing buildings with constantly updated regulations. In this study, Gölbaşı district of Adıyaman, which is located in the EAFZ and suffered significant damage after two major earthquakes centered in Kahramanmaraş on 6 February September 2023, was discussed. The main problem observed in Gölbaşı during the earthquake was liquefaction. Although the ground structure consists of very fine-grained lacustrine material, the observation of liquefaction effects is considered a very interesting behavior. The old settlement in Gölbaşı was mostly built on the ground formed as a result of the lake receding. The structures here begin at a certain distance from the lake, after a protection zone to take precautions against water rise. No significant damage was observed in these buildings, which were mostly built as two stories. However, over time, some of these buildings were converted into multi-story buildings, and if a basement was not built, these structures suffered significant damage. On the other hand, the damage extent of 4–5 story buildings with basements is much less. Of course, these damages were caused by the very loose soil layer near the surface and the effect of shallow groundwater. Most of the damage to buildings occurred in the form of tilting, and the tilting decreased with aftershocks and returned to its previous position with partial deformations over time. Some buildings have experienced excessive buckling due to the very low shear strength of the ground, causing large deformations in their column–beam systems. The fact that Gölbaşı is very close to the EAFZ has naturally increased the damage caused by the close fault effect. Extremely low damages are observed, especially on the slopes, as we move away from the lake, leading to the conclusion that the damage in the Gölbaşı was significantly caused by the ground and occurred in conditions where there was no suitable construction for the type of soil.