# Seismic Assessment and Strengthening of a Load-Bearing Masonry Structure Considering SSI Effects
## 4 Type of Analysis Performed
### Time History Analysis  
For the linear time history analysis of the structure, three strong motion time histories were selected based on the guidelines in [23], and for each time history, three accelerograms were used: two for the horizontal directions and one for the vertical direction.  
The seismic records selected were those from the Northridge earthquake (Pacific Palisades--Sunset station, Los Angeles, CA, USA, 1994, Mw = 6.7) [14], the Kahramanmaras earthquake (Turkey, 2023, Mw = 7.7) [15], and the Kocaeli earthquake (Duzce station, Turkey, 1999, Mw = 7.51) [14]. The process of selecting earthquake records for the seismic evaluation of the Archaeological Museum of Lemnos illustrates a methodical strategy that integrates historical seismic information with ground motions pertinent to the region. However, a more robust site-specific justification would enhance the analysis. The incorporation of the Northridge earthquake (1994, Mw = 6.7) offers a significant historical context as one of the most thoroughly documented seismic occurrences, providing high-quality accelerometric data that acts as a standard for comparison and guarantees the inclusion of well-analyzed ground motion characteristics. Moreover, the choice of two Turkish earthquakes--Kahramanmaras (2023, Mw = 7.7) and Kocaeli (1999, Mw = 7.51)--demonstrates the geographic closeness and seismotectonic resemblance to the Lemnos site. Both the Turkish seismic zones and the North Aegean region are affected by the intricate tectonic interactions between the Eurasian and African plates, including the westward extension of the North Anatolian Fault system into the Aegean Sea. The Kahramanmaras earthquake supplies contemporary ground motion data utilizing modern recording techniques, while the Kocaeli earthquake provides insights from a significant strike-slip event that shares similar fault mechanisms with those anticipated in the North Aegean region. Nevertheless, the authors ought to offer clearer justification concerning tectonic similarity, the appropriateness of source-to-site distance, the compatibility of original recording site conditions with the Category D soils at Lemnos, and whether the spectral characteristics remain representative after scaling to align with Eurocode 8 requirements, which would bolster the credibility of employing these records for evaluating this vital cultural heritage structure. The ground motion records were modified to match the target response spectrum specified in [23], within the period range of 0.2T to 2T for each direction, following the methodology outlined therein. Spectral matching as shown in Figure 9 was performed using the Seismomatch software (v. 2025) [43].  
According to the spectrum defined in [23], the building is classified as Importance Class III, with an importance factor of \(\gamma\)I = 1.2. A behavior factor of q = 1.5 was adopted, appropriate for masonry structures. The seismic zone is classified as Zone Z2 with a design ground acceleration of Ag = 0.24 g, and a vertical design acceleration of Av = 0.9 \(\times\) Ag. The site soil is categorized as Type D (S = 1.35), and a constant damping ratio of \(\zeta\) = 5% was assumed in the analyses.  
For each earthquake record, two separate load cases were created by reversing U1 and U2 (Load Case Data--Linear Direct Integration History) for each horizontal accelerogram. The following load cases were created:  
* Kahramanmaras1 (Kah1) and Kahramanmaras2 (Kah2),
* Northridge1 (Nor1) and Northridge2 (Nor2) and
* Kocaeli1 (Koc1) and Kocaeli2 (Koc2)