Local Site Effects Investigation in Durres City (Albania) Using Ambient Noise, after the 26 November 2019 (M6.4) Destructive Earthquake  
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1 Institute of Engineering Seismology and Earthquake Engineering, 55535 Thessaloniki, Greece 1  
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2 Department of Seismology, Institute of Geosciences, Polytechnic University Trinna, 1000 Tirana, Albania 2  
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2 Department of Seismology, Institute of Geosciences, Polytechnic University Trinna, 1000 Tirana, Albania 2  
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1 Institute of Engineering Seismology and Earthquake Engineering, 55535 Thessaloniki, Greece 1  
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3 Department of Geophysics, Aristotle University Thessaloniki, 54124 Thessaloniki, Greece 3  
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4 GeGeos-IT Consulting, London N14 6 JF, UK 4  
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2 Department of Seismology, Institute of Geosciences, Polytechnic University Trinna, 1000 Tirana, Albania 2  
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and especially difficult, due to the time period required to compile a statistically significant number of seismic records in order to produce results using traditional methods (e.g., Standard Spectral Ratio; [3]). In the last three decades, ambient noise recordings have been extensively employed and have proven to be a useful tool in determining local site effects. Ambient noise is defined as the constant vibration of the Earth's surface, generated either by human activities (e.g., machinery, traffic, pedestrians) in high frequency ranges (f > \(\sim\)1 Hz) or by natural phenomena (e.g., wind, variations in atmospheric pressure, sea waves) in low frequency ranges (f < \(\sim\)1 Hz). It is often assumed that ambient noise recordings are dominated by Rayleigh and Love waves at more than one wavelength from the source [4]. The most common technique, routinely applied today, relies on the calculation of the Horizontal-to-Vertical Spectral Ratio (HVSR) of ambient seismic noise, typically recorded at a location by a three-component velocity sensor. According to [5], this single-station ambient noise approach was initially developed in Japan by [6], based on the work by [7] for characterizing site response under seismic loading, and was later popularized and disseminated by [8; 9]. In the early 2000s, the application and further development of the method exhibited mobility and broader use in Europe (e.g., [10; 11]) and later in Canada ([12; 13]) and South America [14]. In general, HVSR analysis is currently applied worldwide to estimate the site fundamental frequency, and in certain circumstances site amplification factors, as it is observed in weak ground motion of earthquake excitation (linear soil behavior), though this factor is still debatable among the community (among others; [1; 15]). In fact, the appropriate density of site characterization in the built environments proposed in this study is achievable by easy to perform, low cost, non-invasive geophysical methods. Such methods are based on ambient noise from both anthropogenic and natural sources. A series of investigations have been carried out over the past three decades worldwide, aimed at deriving quantitative information on site amplification through non-invasive techniques, based principally on surface wave interpretations of ambient noise measurements [2]. In urban areas affected by strong earthquakes, microzonation studies are usually performed. As a first step, ambient noise measurements are applied, and using the HVSR method. some dynamic properties of surficial geologic layers are estimated, while comparison with earthquake damage distribution is also attempted (among others [16; 17; 18; 19]). In summary, HVSR can provide useful information on surface geologic layers, such as their fundamental frequency (f\({}_{0}\)) and its corresponding amplitude (A\({}_{0}\)). If used in joint inversion with dispersion curves (DC), it can constrain the shear wave velocity profile of the site under investigation. It is a low-cost and easy to apply method, constituting a first basic step in microzonation study.