Tectonic implications of the February 2023 Earthquakes (Mw7.7, 7.6 and 6.3) in south-eastern Turkiye

The series of earthquakes that took place on February 6, 2023 caused one of the saddest major calamities in Turkiye. The first major earthquake of magnitude Mw7.7 broke the Pazarcik and Erkenek segments moving north on the East Anatolian Fault Zone (EAFZ) between Turkoglu and celikhan. According to the Coulomb failure criterion, the Pazarcik earthquake (Mw7.7) increased stress on the Surgu-cardak Fault, a segment on the north splay of the EAFZ, and nine hours later the Elbistan earthquake (Mw7.6) occurred. This great event ruptured the cardak Fault, the western part of the E-W trending Surgu-cardak Fault between Nurhak and Goksun. The Amanos Fault, which extends from Turkoglu south to Antakya, broke almost simultaneously to the first Pazarcik earthquake. Similarly, the earthquake that broke the Amanos Fault transferred increased stress to its southwestern neighbour, the Cyprus-Antakya Transform Fault, triggering the 6.3 magnitude Samandag earthquake 14 days later. The February 2023 earthquakes, which caused the collapse of >100,000 buildings and the death of >50,000 people, created surface ruptures hundreds of kilometres in length and caused different displacements on different faults, the two largest of which were 4.6 and 6.7 m. On all the faults where the deadly earthquakes occurred in February 2023, inversion of the focal mechanisms of the earthquakes (main shocks and their aftershocks) indicates a transtensional stress regime, or a change from strike-slip to normal slip. For all strike-slip inversions, the R values are <0.45 indicating transtension. The stress tensors obtained indicate left-lateral movement with normal component on all faults where the earthquakes occurred. The transtensional regime, which is thought to reflect regional tectonics, is the result of forces caused by relative movements of Arabia, eastern Mediterranean and Eurasia

Assessment of potential seismic hazard and site effect in Antakya (Hatay Province), SE Turkey

Antakya city is at risk because of strong earthquakes occurring in the area, and different soil conditions that can produce variation of the ground motion amplification. Microzonation of cities provides a basis for site-specific hazard analysis in urban settlements. In particular, seismic microzonation can be provided by means of detailed seismic assessment of the area, including earthquake recordings and geological studies. In this paper, we propose a preliminary microzonation map for the city of Antakya, based on the variation of the dominant periods and shear velocities of the sediments covering the area. The periods are retrieved from microtremor measurements conducted at 69 sites, using the horizontal-to-vertical spectral ratio technique. The results of microtremor analysis were compared with data obtained from refraction microtremor (ReMi) measurements at four profiles crossing the studied area. According to the classification of dominant periods, Antakya city can be divided into five zones, probably prone to different levels of seismic hazard. The shorter natural periods are in inner Antakya and both the sides of Asi River (i.e., northern and southern parts). The eastern and western parts of Antakya have maximum dominant periods. The V (s) (30) values were calculated by using the ReMi method along the profiles. Antakya city has V (s) (30) values in the range of category C of the national earthquake hazard reduction programme site classification.Mustafa Kemal University [05 D 0205]The authors thank the anonymous referee for her/his suggestions and corrections on the manuscript. This research was financially supported by the Mustafa Kemal University, Directorate of Research Fund (Project code: 05 D 0205). The authors thank to Mr. M. Ozgu Arisoy contribution to the project as a researcher

Late Cenozoic stress states around the Bolu Basin along the North Anatolian Fault, NW Turkey

This study defines the Late Cenozoic stress regimes acting around the Bolu Basin along the North Anatolian Fault in northwestern Turkey. The inferred regional stress regime, obtained from the inversion of measured fault-slip vectors as well as focal mechanism solutions, is significant and induces the right-lateral displacement of the North Anatolian Fault. The field observations have also revealed extensional structures in and around the Bolu Basin. These extensional structures can be interpreted as either a local effect of the regional trainstensional stress regime or as the result of the interaction of the fault geometries of the dextral Duzce Fault and the southern escarpment of the North Anatolian Fault, bordering the Bolu Basin in the north and in the south, respectively. The inversion of slip vectors measured on fault planes indicates that a strike-slip stress regime with consistent NW- and NE-trencling sigma(Hmax) (sigma(1)) and sigma(Hmin) (sigma(3)) axes is dominant. Stress ratio (R) values provided by inversion of slip vectors measured on both major and minor faults and field observations show significant variations of principal stress magnitudes within the strike-slip stress regime resulting in older transpression to younger transtension. These two stress states, producing dextral displacement along NAF, are coaxial with a consistent NE-trending sigma(3) axis. The earthquake focal mechanism inversions confirm that the transtensional stress regime has continued into recent times, having identical horizontal stress axis directions, characterized by NW and NE-trencling sigma(1) and sigma(3) axes, respectively. A locally consistent NE-trending extensional, normal faulting regime is also seen in the Bolu Basin. The stress-tensor change within the strike-slip stress regime can be explained by variations in horizontal stress magnitudes that probably occurred in Quaternary times as a result of the westward extrusion of the Anatolian block. (C) 2008 Elsevier Ltd. All rights reserved

Estimating shear wave velocity using acceleration data in Antakya (Turkey)

This manuscript presents a site response analysis and an estimation of S-wave velocity that are dependent on acceleration data. First, existing data, such as density, seismic wave velocity, and soil cross-sections, are obtained from previous seismic microzonation studies and used to prepare input data for a suite of MATLAB routines, which are referred to as SUA software. Acceleration data are obtained from four free-field strong-motion stations of the SERAMAR project, which was conducted between 2006 and 2009 in conjunction with a Turkish-German joint research project, and inputted into the software as basic data. The results include a 1D velocity cross-section versus depth and an amplification model of the site. Three different depth levels can be determined for the ranges of 0-5 m, 5-15 m and 15-25 m. The seismic velocities vary between 380 and 470 m s-1 for the first 5 m; 320 and 480 m s-1 for 5-15 m; and 470 and 750 m s-1 for 15-25 m. These results are comparable with the amplification values from the microtremor data from previous studies. The 1D velocity models are appropriate for the soil conditions. Resumen Este trabajo presenta el análisis a una respuesta de sitio y una estimación de la velocidad de la onda de corte que son dependientes de la información de aceleración. Los datos adicionales como la densidad, la velocidad de onda sísmica y los cortes transversales de suelo, se obtuvieron de estudios previos de microzonificación sísmica y se utilizaron para preparar el registro de datos en una plataforma de rutinas MATLAB, que se refieren al software SUA. Los datos de información de la aceleración se tomaron de cuatro estaciones de monitoreo de movimientos fuertes a campo abierto del proyecto SERAMAR, que se realizó entre 2006 y 2009 en una investigación conjunta turco-alemana, y se ingresaron en el programa como la información básica. Los resultados incluyen una sección cruzada de velocidad 1D versus profundidad y el modelo amplificado del sitio. Se pudieron determinar tres niveles diferentes a partir de los rangos de 0-5 m, 5-15 m y 15-25 m. Las velocidades sísmicas pueden variar entre 380 y 470 m s-1 para los primeros 5 metros; 320 y 480 m s-1 para el rango 5-15 m, y 450 y 750 m s-1 para el rango 15-25 m. Estos resultados son comparables con los valores de amplificación del perfil Microtemor de estudios previos. Los modelos de velocidad 1D son apropiados para las condiciones del suelo

Late cenozoic stress field in the Cameli Basin, SW Turkey

A history of deformation has been determined for the Cameli Basin located in the western part of the major Fethiye-Burdur Fault Zone, interpreted as the on-land continuation of Pliny-Strabo fault system (e.g., eastern boundary of the Hellenic Arc). Inversion of fault slip vectors affecting Mio-Pliocene to Quaternary formations in the Cameli Basin, in the southwestern segment of the transtensional Fethiye-Burdur Fault Zone, yields two different normal faulting stress regimes characterized by a roughly orthogonal set of extensional axes; a NW-SE (N129 +/- 19 degrees E) sigma(3) axis and a NE-SW (N50 +/- 16 degrees E) sigma(3) axis. The orientation of fault sets is predominantly around the NE-SW direction in the major Fethiye-Burdur Fault Zone, making the extension NW-SE. The mean R values are 0.74 and 0.69 for both extensions indicating a triaxial stress state, which is clearly different from radial extension and from transitional to strike-slip stress state. The NW-SE extension is probably responsible for the formation of the Cameli Basin during Mio-Pliocene time. In contrast, the inversion of focal mechanism solutions of shallow earthquakes occurring within the Cameli basin identifies a present-day, predominantly extensional stress regime, characterized by an approximately N-S (N184 degrees E) sigma(3) axis, which has an R value of 0.637 indicating a triaxial stress state. The nearly orthogonal extensional stress regimes seem to have been acting contemporaneously with each other at different intensities from the Mio-Pliocene onwards in SW Turkey. This may be attributed to the geodynamic effects related to the subduction of the African plate beneath Anatolia, diffusing along Hellenic and Cyprus arcs and in the west-southwestward extrusion of Anatolia. Our hypothesis is that the cause of the early NW-SE extension is the slab-pull force due to the subduction process along the Cyprus arc, considered to be dominant up to Plio-Quaternary. The later NE-SW to present-day similar to N-S extension, dominant since the Plio-Quaternary, is related to the combined forces of the Anatolian extrusion and the subduction process along the Hellenic arc. (C) 2010 Elsevier B.V. All rights reserved.TUBITAK-YDABAG [107Y321]This work was financially supported by TUBITAK-YDABAG (Project no: 107Y321). The authors thank also two anonymous reviewers for their contributions which improved the scientific quality of the paper. Also, the authors would like to thank Catherine Yigit for assistance with English exposition that improved recent version of the text

Plio-Quaternary Stress State in the Burdur Basin, SW-Turkey

This study defines the Plio-Quaternary to present day stress regime in the Burdur Basin, located at the northeastern end of the Fethiye-Burdur Fault Zone in SW Turkey. This fault length, which is considered the landward continuation of the Pliny-Strabo trench, is an important feature in SW Turkey. The inversion slip vectors measured on fault planes indicate a consistent normal faulting stress regime during Plio-Quaternary time, continuing into recent times as indicated by earthquake focal mechanism inversions. Both states have consistent NW-SE trending horizontal minimum stress axes (sigma(3)). The orientation of fault sets is predominantly around the NE-SW direction in the major Fethiye-Burdur Fault Zone, making the extension NW-SE. The mean stress ratio is 0.74 indicating a triaxial stress state, which is clearly different from radial extension. The NW-SE extension is probably responsible for the formation of the Burdur Basin during Plio-Quaternary time. This extension, which is probably caused by slab-pull force due to the subduction process along the Cyprus arc, produces a dominant normal motion along the FBFZ. (C) 2013 Elsevier B.V. All rights reserved.TUBITAK-CAYDAG [107Y321]This work was financially supported by TUBITAK-CAYDAG (Project no: 107Y321). The authors would like to thank Catherine Yigit for assistance with English exposition that improved recent version of the text. The authors are also grateful to the anonymous reviewers for their valuable comments and suggestions that greatly improved the quality of the manuscript

Estimating shear wave velocity using acceleration data in Antakya (Turkey)

This manuscript presents a site response analysis and an estimation of S-wave velocity that are dependent on acceleration data. First, existing data, such as density, seismic wave velocity, and soil cross-sections, are obtained from previous seismic microzonation studies and used to prepare input data for a suite of MATLAB routines, which are referred to as SUA software. Acceleration data are obtained from four free-field strong-motion stations of the SERAMAR project, which was conducted between 2006 and 2009 in conjunction with a Turkish-German joint research project, and inputted into the software as basic data. The results include a 1D velocity cross-section versus depth and an amplification model of the site. Three different depth levels can be determined for the ranges of 0-5 m, 5-15 m and 15-25 m. The seismic velocities vary between 380 and 470 m s-1 for the first 5 m; 320 and 480 m s-1 for 5-15 m; and 470 and 750 m s-1 for 15-25 m. These results are comparable with the amplification values from the microtremor data from previous studies. The 1D velocity models are appropriate for the soil conditions.Scientific and Technological Research Council of Turkey (TUBITAK) [106M420]The authors are grateful to Dr.-Ing. Jochen Schwarz and Dipl.-Ing. Lars Abrahamczyk from the Earthquake Damage Analysis Center (EDAC) of Bauhaus University in Weimar, Germany for the permission to use the recorded data provided by the collaborate SERAMAR project. The instruments donated by SYSCOM Inc., Switzerland and the financial support from The Scientific and Technological Research Council of Turkey (TUBITAK) under the project Grant No. 106M420 are also appreciated. This paper has been reviewed by Dr. Hakan Cinar of Karadeniz Technical University, Turkey, which has significantly improved its quality

Plio-Quaternary stress regime in Esen Cay Basin, SW Turkey

7th International Symposium on Eastern Mediterranean Geology -- OCT 18-22, 2010 -- Adana, TURKEYWOS: 000343703000020The Plio-Quaternary Esen Cay Basin is situated at the junction of Hellenic and Cyprus arcs in southwestern Turkey. The basin is important for understanding the tectonic evolution of the region in relation to the Hellenic and Cyprus arcs. Fault data from unconsolidated Pliocene and Quaternary deposits, as well as from pre-Pliocene lithologies, are analysed in order to reconstruct the evolution of the stress field evolution from Pliocene onwards. Inversion of measured fault slip vector data identifies two main stress states: extensional and strike-slip. Both states are characterized by a NE-SW-trending minimum horizontal stress axis (sigma(Hmin) = sigma(3)). The mean R value is 0.67, indicating a triaxial state of stress. The inversion also indicates the existence of extensional and strike-slip faulting characterized by a NW-SE-trending sigma(3) axis. This indicates a change in the direction of the minimum horizontal stress axis (sigma(3)) from a NW-SE-trending sigma(3) that dominated prior to Quaternary to a NE-SW-trending sigma(3) that dominated during Quaternary up to actual time