The 2023 Kahramanmaras, Turkey earthquake of Mw 7.8 that brought unparallel damage to the areas due to its widespread strong ground motion. The earthquake was caused by dynamic rupture of ~300 km in total involving three fault segments of the East Anatolian Fault (EAF). About nine hours after the mainshock, another Mw 7.5 earthquake ruptured ~160-km-long Surgu-Cardak fault that is a branch of the EAF. The epicenter of the M7.8 event locates ~20 km south of the center of the EAF rupture zone, which is indeed southern edge of the previously mapped small branch fault named Narli fault. The AFAD hypocenter catalog also demonstrates the seismicity rate near the epicenter has significantly risen since mid 2022 like a long-lasting seismic swarm, which enables us to consider active nucleation process to trigger the Narli fault rupture. This 20-km-long Narli fault rupture consequently led to a bilateral ~300-km-long faulting along the EAF (e.g., Melgar et al., 2023). The M7.8 rupture zone is composed of three distinctive segments, Amanos, Pazarcik, and Erkenek (Duman and Emre, 2013). Cumulative strain on the Pazarcik segment in particular was estimated to have been high due to the long-elapsed time since the last historical event of possibly 1513 A.D. Secular and transferred stress on the Pazarcik segment since 1822 modelled by Nalbant et al. (2002) also reached ~15 bar and regarded as the most hazardous fault segment along the EAF. To retrospectively evaluate whether the M7.8 mainoshock triggered the subsequent M7.5 earthquake, we calculated static Coulomb stress change on the Surgu-Cardak fault imparted by the M7.8 rupture using the USGS finite fault model. We found up to 3 bars of Coulomb stress were imparted to the central portion of the fault, which is roughly 10% of a typical stress drop in an earthquake, and sufficient to trigger an earthquake if the fault was already close to failure.

The 2023 Turkey earthquake occurred on February 6, 2023 with M_w 7.8. The rupture started on a branch of East Anatolian Fault (EAF) in Kahramanmaras province, southeastern Turkey. The rupture moved to the EAF and propagated bilaterally to the northeast and southwest. Surface ruptures with the range of 300 km were detected after the earthquake. Many strong ground motions were recorded along the EAF during the M_w 7.8 earthquake and aftershocks. These records are available from the website of AFAD. There are not many earthquakes with M_w 7.8 and many near-surface strong motion records available. Thus, analyzing the causes of strong ground motions is important for strong ground motion prediction of future large earthquakes.
In this study, strong ground motion simulations of the 2023 Turkey earthquake were conducted. The mechanisms of strong ground motion generation were investigated. The corrected empirical Green’s function method was used in the simulation. We first conducted spectral inversion analysis using aftershock data to evaluate empirical path and site amplification factors. Strong ground motion simulations were conducted using estimated path and site amplification factors. Rectangular asperities were used for the source. Simulations were conducted focusing on capturing the main phases of observed strong ground motions, thus parameters were not optimized. Target sites of the simulations were limited to the southwest side of the epicenter, where strong motions were densely recorded.
Surface ruptures can have strong effect on the near-fault strong ground motions as was observed in the 2016 Kumamoto earthquake. Near-fault strong motions of the 2016 Kumamoto earthquake can be characterized by the fault-parallel step-like displacement and strong velocity pulses. In addition, the directivity effect is another important factor to be considered. Observed strong ground motions of the 2023 Turkey earthquake showed both fault-parallel fault-normal strong velocity pulses, which exceeded 100 cm/s at some stations. Fault-normal pulse periods ranged from 3 s, which may be due to asperities, to 10 s, which may be due to the rupture propagation on the fault as a whole. Fault-normal fling-steps were confirmed by the opposite polarities of fault-normal component on both sides of the fault. Therefore, it is essential to appropriately combine both near-surface ruptures and asperities in the simulation. In this study, as a preliminary simulation, we used only asperities and aimed at capturing the main phases of observed strong ground motions assuming that high-frequency components were mainly generated by asperities. Modeling near-surface ruptures is one of the future tasks.
Empirical path and site amplification factors for the simulation were estimated by spectral inversion of small earthquake records. We used 736 records from 56 sites and 44 earthquakes. All the strong motions used were manually checked. A nonparametric inversion scheme was used. The source spectrum of the earthquake of 18:33, February 12, 2023 (M_w 4.6) was used as the constraint.
Strong ground motion simulations were conducted using the corrected empirical Green’s function method. Synthetic strong ground motions by this method consist of source, path, site amplification and site phase characteristics. Path and site amplification factors estimated by the inversion were used. Seven asperities were used in the simulation. Fault planes along the surface ruptures and the dip angle of 90° were assumed. Although the number of asperities and parameters can change in the future, the result suggests that strong motions were generated by continuous rupture propagation rather than by a small number of asperities. Good agreement was obtained in the acceleration time histories and Fourier spectra. Future tasks include the detailed modeling of strong pulses in fault-parallel and fault-normal components and adding near-surface ruptures.

On February 6, 2023, at 4:17 and 13:24 Turkey local time, two earthquakes of magnitudes 7.8 and 7.5 occurred successively in southeastern Turkey, which were called the Kahramanmaraş Earthquake. The two earthquakes, the largest ever recorded in Turkey, caused strong seismic motions that caused extensive damage in areas along the East Anatolian Fault and in northern Syria, and the number of victims reported at the end of February, over 50,000, was the largest in modern and contemporary Turkey. We attempted to analyze the earthquake ground motions and assess the damage based on information available on the Internet immediately after the earthquakes. The inverse analysis of long-period ground motions immediately after the earthquakes showed that the fault movement from the epicenter of the Kahramanmaras earthquake to the northwest along the East Anatolian Fault Zone was noteworthy, but the shaking from the epicenter to the south-southwest through the Hatay province was reflected in the seismic intensities based on the questionnaire to residents. AFAD in Turkey conducted strong-motion seismic observations and released the results immediately after the earthquake. The distribution of the maximum acceleration also showed large acceleration in the direction extending south-southwest from the epicenter, and there was concern that there would be more damage in the south-southwest direction from the epicenter. The results of the AFAD seismic motion analysis showed that some of the observation points had strong seismic pulse waves that were characteristic of the vicinity of the epicenter fault and have predominant periods from 1 to 3 seconds. It was necessary to observe the structural damage from the viewpoints of ground motion amplification and near-source pulse wave effects. The topography, geology, and ground conditions, which differ greatly from those in Japan, are also important perspectives when investigating and discussing structural damage. In Turkey, among the various types of structures, the main types are 1- and 2-story houses of masonry construction and mid- to high-rise reinforced concrete apartments (reinforced concrete (RC) frame structures with masonry infill walls). This RC construction type constitutes the bulk of the building stock in Europe. RC buildings in Turkey are designed according to the seismic design code, and this perspective is also essential in the damage analysis, as the building designed according to the code (AC) and not-according to the code (NAC) are the main indicators in past earthquake damage analysis studies. In the field survey, it is essential to observe the quality of the concrete and the details of the rebar system, such as the main bar and shear reinforcement bars. Satellite images and the results of damage detection based on these images were made public by many organizations immediately after the earthquakes. The field damage survey can be conducted efficiently and accurately by effectively referring to these images in advance. The authors prepared for the field survey by conducting various analyses immediately after the earthquake on February 6. For the field survey, Mori and Polat conducted the field survey from March 3 to March 7 in cooperation with JICA and in liaison with AFAD. Microtremor measurements and observations of building damage were conducted at AFAD seismograph sites in Gaziantep, Kahramanmaras, Hatay, and Adiyaman provinces and in areas of concentrated damage in those cities and towns. At the intersections of highways and roads, and surface fault ruptures (those previously detected by the USGS and those that could be determined in the field), the presence and status of highway damage and structural damage were confirmed. A lightweight small drone for structural inspection was used to determine the distribution of building damage around the seismographs and for detailed observation of damaged buildings that escaped collapse. In Antakya, the city with the highest concentration of collapsed buildings, we observed the damage concentration zone, which can be called the earthquake zone, and observed the damage around the seismographs from the sky. We infer a possible basin edge effect expected from the interaction of the basin structure of Antakya city.

On 6 February 2023, a local tsunami was recorded in the southeastern Mediterranean Sea following the Mw 7.8 Turkey–Syria inland strike-slip earthquake. Due to complexity of the earthquake source and lack of underwater observation, the physical mechanism of the tsunami generation remains mysterious. To understand the tsunami source mechanisms, we analyzed the tsunami waveforms recorded by four nearby tide gauges and located the possible sources using a backward tsunami ray tracing approach. We then conducted forward numerical modelings for a range of possible sources with parameters informed by both the periods and amplitudes of recorded tsunami waveforms. We show that there were probably two existing tsunami sources, inside the Iskenderun Bay and outside the Bay. The dominant period of the tsunami observed inside the Bay was 10–30 min with negative initial motion. It was generated by a source of 11 km in diameter with initial depression at the entrance of the Bay, where the large peak ground acceleration was recorded, hence probably generated by a landslide. Outside the Bay, tsunami mainly came with dominant periods of 2–20 min and positive initial motions. This was generated from an initial elevation of 6 km in diameter offshore the coast of Antakya, possibly related to liquefaction. The remarkably different wave properties and generation mechanisms raise our awareness of the underestimated tsunami hazards due to coastal strike-slip earthquakes.

Knowing the occurrences of various natural hazards, including earthquakes, flood, storms, and volcanic activities either in historic or prehistoric periods are crucial for future disaster mitigation, particularly in tectonically-active regions. However, because of the infrequency of such extreme events, historical records or people's memories of severe natural hazards often lack in middle east countries, including Turkey and Syria. It is therefore highly recommended to assess the past occurrences of hazardous phenomena associated with some archaeological records. Here we explore the geomorphological and geoarchaeological records in the Kayseri region, central Anatolia, where many prehistoric archaeological settlements are located in potentially hazardous environments with floodplains, volcanoes, and faults. We conducted field surveys to obtain detailed topographic data of the study sites using high-definition measurement methods such as laser range measurement, global navigation satellite system, and structure-from-motion multi-view stereo photogrammetry, as well as some subsurface information of geological and sedimentological records. From our investigations of landforms, including floodplain, alluvial fans, fault scarps, and debris avalanche deposits, several potential risks of natural hazards in the area were suggested regarding floods in basins, sector collapse of volcanic mountain bodies, and earthquakes by normal fault displacements in the late Pleistocene and Holocene periods, and some of them may have been associated with human activities that appear in archaeological records. Geomorphological and geological data, including a regional geomorphological map, will be further analyzed to explore spatiotemporal relationships between human settlements and landform developments. Also, disseminating these facts is crucial for mitigating future disasters by not only earthquakes but also multiple hazards. We promote the use of spatial data, including two-dimensional maps and three-dimensional models of landforms, for the effective dissemination of disaster risks in the regions so that residents can think of what to do in their daily life and urban planning.

Afghanistan is a mountainous country characterized by the Hindukush active tectonics uplifted by the India-Eurasia collision. Afghanistan is part of the Eurasian plate the most seismically hazardous region. Earthquake in Afghanistan is driven by the relative northward movements of the Arabian plate past western Afghanistan and of the Indian plate past eastern Afghanistan as both plates subduct under Eurasia. The Hindukush tectonic activities created several deep geological faults strong earthquake movement happened along them. Earthquake movements mostly occur around the northeastern part of the country because of the northward subduction of the Indian plate. Central and western Afghanistan is the least seismically active. Earthquakes cause the highest number of fatalities in the country, on June 22, 2022, a 6.1 magnitude earthquake struck the southeastern region of Afghanistan. The earthquake caused huge damage and casualties; over 1000 people died and 1500 were injured.
In this study, the geological structure and the tectonic earthquake in Afghanistan are explained. Afghanistan’s seismic region and active deep geological faults are illustrated using ArcGIS Pro. A historical review of the earthquake disaster and earthquake-vulnerable zones is conducted and conclude with a recommendation for earthquake risk reduction.