This paper presents the findings of field observations conducted in the aftermath of the earthquakes that struck the Pazarcik (Mw7.7) and Elbistan (Mw7.6) in Kahramanmaras province, Turkey on February 6th, 2023. The earthquakes, occurring on the East Anatolian Fault Zone (EAFZ), resulted in more than 50,000 losses of life and damage of more than 1.5 million properties across 11 provinces in Turkey. Field observations presented herein encompass seismological and strong ground motion data, geotechnical observations, as well as damage assessments of underground and above ground structures in various provinces and districts. The types and reasons of the structural damages were discussed. The study also examined the effects of high acceleration values and distribution of strong ground motions on the performance of structures. Soil liquefaction problems were observed in many locations such as Golbasi and Iskenderun. The paper highlights the geology, tectonics, strong motion characteristics, surface deformations, geotechnical and structural aspects, and the evaluation of lifelines in the affected area. Furthermore, the authors provide initial recommendations for improving disaster management, evaluating building stock, prioritizing urban transformation, strengthening infrastructure systems, addressing soil-building interaction issues, ensuring security measures during search and rescue efforts, utilizing satellite imagery effectively, considering seismic effects on water infrastructure, and taking a holistic approach to earthquake effects in industrial facilities.

Local site conditions may pose a significant influence on the seismic responses of submarine pipelines by altering both the offshore motion propagation and soil-structure interaction (SSI). This paper aims to provide an in-depth understanding of the influence regularity of local site conditions on the seismic performance of free-spanning submarine pipelines (FSSPs). For this purpose, a suite of underwater shaking table tests were performed to investigate the seismic responses of FSSP subjected to the offshore spatial motions at three site categories. Response comparison factor (chi R.ij${\chi }_{R.ij}$) is defined to quantify the structural response discrepancies caused by the seismic inputs at different sites. The test results indicate that responses of the studied model FSSP gradually increase as spatial offshore motions at softer soil sites are employed as inputs; and the values of chi R.ij${\chi }_{R.ij}$ vary with a maximum magnitude of up to 40%-60% for different response indices when the site soil changes from fine sand to clay. Subsequently, the corresponding numerical simulations are carried out to reproduce the seismic responses of the test model. The experimental and numerical results meet a good agreement, indicating that the developed numerical modeling method can accurately predict the seismic responses of FSSPs. Following this verified modeling method and using the p-y approach to address the SSI effect, fragility surfaces of the studied FSSP are derived in terms of PGA and site parameter VS30${V}_{S30}$ (shear-wave velocity in the top 30 m of the soil profile) via probabilistic seismic demand analyses. The impact of local site conditions on the seismic performance of the FSSP is quantitatively examined by comparing the fragility curves corresponding to various VS30${V}_{S30}$. Furthermore, a fast seismic damage assessment method is proposed for efficiently evaluating the performance of FSSPs buried in various offshore soil conditions. This approach proves beneficial for designers and decision-makers, enabling accurate estimation of seismic damage and facilitating the implementation of post-earthquake maintenance measures for FSSPs.

Base-isolation systems applied in building structures and infrastructures often suffer from damage even failure during strong earthquakes. The adaptability of isolators to local sites is a main concern for the robust design of base-isolation systems. In this study, seismic mitigation analysis of base-isolated structure with newly-developed sliding hydro-magnetic bearing (HMB) and sliding implant-magnetic bearing (IMB) considering local-site conditions is carried out. Extension of modeling of sliding magnetic bearings is first conducted based on the data of shaking-table tests of a reduced-scale base-isolated structure. To assess the instantaneous frequency for quantifying sliding magnetic bearings' resisting force, the Hilbert-Huang transform (HHT) is applied. The influences of local-site conditions upon mitigation performance of the sliding magnetic bearings are then addressed, including far-field and near-field, ground motions with and without velocity pulses, and hard-soil and soft-soil. For comparison purposes, the seismic mitigation analysis of the base-isolated structure attached with lead rubber bearing (LRB) and curved surface slider (CSS) is carried out as well. Numerical results show that the sliding magnetic bearings outperform the state-of-the-art seismic isolators in both seismic mitigation and deformation constraint, and the IMB has excellent applicability for engineering since its perfect adaptability to local sites. However, the LRB cannot achieve the desired seismic mitigation under near-field pulse-like ground motions.

Sea-crossing bridges face complex site environments compared to onshore bridges, with the marine environment significantly influencing seismic responses. Despite this, current seismic design for these bridges relies on onshore earthquake records. Therefore, investigating the impact of seawater layers and site conditions on seacrossing bridge seismic performance is crucial. This paper investigates the influence of characteristics of offshore ground motion, site conditions, and hydrodynamic effect on the seismic performance of piers. Initially, based on the validated finite element model, 5 offshore and onshore strong ground motion records from K-NET were selected for assessing the seismic performance of piers. Subsequently, the effects of the water depth and site conditions on the seismic responses of piers were investigated. Finally, the effects of the size, shape, and boundary conditions on the piers were investigated. The result shows that the seismic response of piers under offshore ground motion exceeds that under onshore ground motion. In addition, the seismic response of the pier increases with greater water depth, while they exhibit a slight decrease with increasing soil depth. Notably, the larger the size, result in higher the hydrodynamic pressure, and square piers experience greater hydrodynamic pressure compared to circular piers.