Local Site Effects Investigation in Durres City (Albania) Using Ambient Noise, after the 26 November 2019 (M6.4) Destructive Earthquake

Site characterization of metropolitan areas, especially after an earthquake, is of paramount importance for interpretation of spatial damage distribution and taking measures that assure realistic design actions to strengthen existing constructions and create new ones. Such a case is the city of Durres, Albania, that was hit by the disastrous earthquake of 26 November 2019 (M6.4). Significant differences in structural damage were observed throughout the city, despite its uniform epicentral distance (approximately 15 km); this could be either due to varying vulnerability of the affected constructions and/or to spatial variation of strong ground motion in the city, resulting from local site effects; the latter factor was investigated in this study. This was achieved by taking single station ambient noise measurements throughout the city, at approximately 80 sites. Ambient noise measurements are favorable, as acquiring ambient noise data is an easy and effective noninvasive approach within urban environments. Measurements were processed using the widely applied Horizontal-to-Vertical Spectral Ratio (HVSR) method, following the SESAME project (2004) guidelines. Their fundamental and dominant frequencies, fo and fd, respectively, were calculated and related to the iso-depth contours of the investigated area, as well as their corresponding amplitudes, Ao, and Ad. These experimental parameters and the HVSR curves were used to group all examined sites into classes with similar properties. This clustering provided a zonation map with four categories consisting of similar shapes and amplitudes, applicable to the city of Durres. This map can be utilized as a first level zonation of local site effects for the city. In addition, dynamic properties of soil profiles in selected sites were investigated and tested using 1D synthetic ambient noise data, based on the Hisada (1994, 1995) simulation method, and compared to experimental HVSRs in proximity to the selected sites. A comparison of the proposed four categories zonation map to the observed damage of the 26 November 2019, mainshock is attempted and evaluated. The four categories zonation map with similar expected local site effects proposed in this study can be used as a first level seismic microzonation of Durres. Undoubtedly, corrections for 2D/3D effects on ground shaking must be applied to sites lying in the edges of the Durres basin

Local Site Effects Investigation in Durres City (Albania) Using Ambient Noise, after the 26 November 2019 (M6.4) Destructive Earthquake

Site characterization of metropolitan areas, especially after an earthquake, is of paramount importance for interpretation of spatial damage distribution and taking measures that assure realistic design actions to strengthen existing constructions and create new ones. Such a case is the city of Durres, Albania, that was hit by the disastrous earthquake of 26 November 2019 (M6.4). Significant differences in structural damage were observed throughout the city, despite its uniform epicentral distance (approximately 15 km); this could be either due to varying vulnerability of the affected constructions and/or to spatial variation of strong ground motion in the city, resulting from local site effects; the latter factor was investigated in this study. This was achieved by taking single station ambient noise measurements throughout the city, at approximately 80 sites. Ambient noise measurements are favorable, as acquiring ambient noise data is an easy and effective noninvasive approach within urban environments. Measurements were processed using the widely applied Horizontal-to-Vertical Spectral Ratio (HVSR) method, following the SESAME project (2004) guidelines. Their fundamental and dominant frequencies, fo and fd, respectively, were calculated and related to the iso-depth contours of the investigated area, as well as their corresponding amplitudes, Ao, and Ad. These experimental parameters and the HVSR curves were used to group all examined sites into classes with similar properties. This clustering provided a zonation map with four categories consisting of similar shapes and amplitudes, applicable to the city of Durres. This map can be utilized as a first level zonation of local site effects for the city. In addition, dynamic properties of soil profiles in selected sites were investigated and tested using 1D synthetic ambient noise data, based on the Hisada (1994, 1995) simulation method, and compared to experimental HVSRs in proximity to the selected sites. A comparison of the proposed four categories zonation map to the observed damage of the 26 November 2019, mainshock is attempted and evaluated. The four categories zonation map with similar expected local site effects proposed in this study can be used as a first level seismic microzonation of Durres. Undoubtedly, corrections for 2D/3D effects on ground shaking must be applied to sites lying in the edges of the Durres basin

Historical evolution and middle to late holocene environmental changes in lake Shkodra (Albania): New evidences from micropaleontological analysis

The 7.5 m long SK13 sediment core, drilled at Lake Shkodra (Albania) at a bottom depth of 7 m in the central southern part of the lake, was selected for multidisciplinary analysis. The sediment core age spans from 4560 cal yr BP to present. The origin and the evolution of the lake are still debated and were never investigated in detail. In historical records, until the 15th century Lake Shkodrawas nevermentioned as such, but as amarshland or as a confluence between two rivers. Our research aims to reconstruct the past biodiversity and the Middle-Late Holocene palaeoenvironmental and palaeoclimatic changes using Ostracods, Characeae, and comparing the micropaleontological data with pollens and stable isotope curves. Thirteen ostracod and five charophyte species were identified. Amongst the ostracods Candona montenigrina and Limnocythere scutariense are endemic of the lake; Candona meridionalis, Paralimnocythere georgevitschi, Metacypris cordata, Candona ex gr. bimucronata, and Cyclocypris sp. have been collected for the first time in Lake Shkodra; the last three taxa occurred only in the lower portion of the sediment core. Amongst the charophytes, Lychnothamnus barbatus and Nitella hyalina are recorded for the first time in the lake and occurs with high frequency throughout the lower portion of the core. A drastic change occurs between 1274 and 1197 cal yr BP, when 8 ostracod species out of 13 and all charophytes disappear, and the frequency of the remaining 5 species dramatically increases. The micropaleontological data suggest a decrease of the lake biodiversity since around 1200 cal yr BP linked to the transition between an ancient marshland to a lacustrine environment. This drastic event seems to be independent from any global or local climate change but linked to the complex hydrographic setting of the lake and of its only outlet, the River Bojana, discharging in the Adriatic Sea