Regions with high wind resources, which are suitable for the operation of wind turbines, often coincide with earthquake-prone areas. So far, the design of wind turbines in earthquake-risk regions is carried out by simulations only. There is no data from full-scale operating wind turbines for validation purposes available. By conducting a long-term field study in a high-risk seismic area on full-scale running wind turbines, this research project intends to change the current state of the art and provide relevant data, which can be used for the improvement of design guidelines and the setup of structural health monitoring systems contributing to the development of digital twins. To ensure the structural integrity of wind turbines under high loads, modal parameters can be tracked over time. A shift in these parameters can provide insight into potential damages. These parameters can be determined using operational modal analysis, which is applied to an operating wind turbine in an earthquake-prone area. From this preliminary study, the challenge dealing with the harmonic response signal arises. The harmonics, present in the system, are very strong and overlap with the structural properties. Suitable measures have to be taken and appropriate techniques have to be applied to eliminate the harmonic influence in the data for reliable modal identification. Preliminary data from a wind turbine operated in Chile, located in the south-central area, is available for this study, and will be analyzed and discussed in detail. An emphasis is placed on demonstrating the influence and impact of harmonics in the ambient vibration test data. Different timefrequency analysis techniques are applied to the described data set to understand the role of harmonics and their superimposing character on the ambient vibration data. A comparison can be drawn between the results from the data in operation and the ones from standstill measurements. One main parameter of interest is the damping ratio, which is highly dependent on the operating point and loading condition. The insights of this study represent a first step towards the future of structural health monitoring for wind turbines in earthquake-prone areas.