###### Abstract  
Structural health monitoring is vital for the safety and longevity of infrastructure, particularly in seismic zones. This study focuses on identifying the dynamic properties of a reinforced concrete building in Chile's Valparaiso region. Using an experimental approach, the study compares ambient vibration records, seismic events (moment magnitude > 4), and data collected during adjacent construction activities. Force-balanced accelerometers were used for vibration measurements. The analysis employs the Stochastic Subspace Identification with Covariances (SSI-COV) method within an operational modal analysis framework to extract the building's modal parameters without requiring artificial excitations. This technique effectively identifies modal characteristics under different vibration sources, making it suitable for evaluating the structural condition under diverse loading conditions. The findings reveal the building's modes and frequencies, offering critical insights for maintenance and management of infrastructure. Little to no variations were observed in the identified frequencies of the building when working with different types of input data. These data support the integration of real-time IoT systems for continuous monitoring, providing a foundation for future digital twin applications. These advancements facilitate early deterioration detection, enhancing resilience in seismic environments. structural health monitoring; ambient vibration; SSI-COV method +
Footnote †: journal: Applied Sciences  
0000-0001-5000-0000-0000-0000-0000-0000-0000-00000-0000-00000-00000-00000-00000-00000-00000-000000-00000-000000-000000-000000-000000-000000-000000-000000-000000-000000-0000000-0000000-0 identification of potential deterioration or anomalies in buildings [5; 6]. Among these technologies, the use of accelerometers to record vibrations has been widely used in the past for assessing a structure's health, as they capture the dynamic response of a system subjected to environmental excitations without the need for additional loads (e.g., artificially applied forces or controlled vibrations). This technique, known as operational modal analysis, is based on observing structures under their normal operating conditions, utilizing vibrations generated by wind, traffic, or seismic activity [7]. In this study, ambient vibrations, vibrations from adjacent construction, and seismic events were recorded, with data collected during the years 2022, 2023, and 2024. Output-only or operational modal analysis (OMA) has become very popular, as no artificial vibration source is needed, which is anyhow impossible in many cases. Time domain system identification algorithms like Stochastic Subspace Iteration (SSI) have replaced the obsolete \"peak-picking\" method [8]. Using an OMA procedure, one can identify the system eigenfrequencies and mode shapes of typical structures excited by unmeasured ambient (broadband) loads. This is beneficial, since the operation of the structure is not obstructed, as it would be in the case of forced vibration testing [9]. The term structural health evaluation is directly focused on verifying the presence of damage in structures [10; 11]. Damage can be defined as changes introduced into a system that adversely affect its current or future state. In general, the definition of what is considered damage is limited to changes in the material and/or geometric properties of a system and does not necessarily imply a total loss of system functionality, but rather that the system no longer operates optimally, highlighting the importance of detecting and quantifying any deterioration to maintain structural integrity. Changes in the dynamic properties of structures are linked to changes in modal parameters, which depend on the stiffness of the structures, a property influenced by the material composition of the structure. Changes in natural frequencies, damping ratios, and mode shapes can therefore be used as features to detect and to identify damage [12].