Assessing the impact of water level fluctuations on Philae Island's, Aswan, Egypt stability and seismic vulnerability using global positioning system and horizontal to vertical spectral ratio techniques

• GPS data revealed time-delayed subsidence linked to dam-induced water fluctuations • HVSR analysis identified zones with high ground motion amplification risk • Seismic vulnerability index (Kg) reached values up to 193 in critical zones • Combined GPS-HVSR method offers a scalable model for heritage risk assessment • Findings support hydro-mechanical monitoring strategies for structural conservation Philae Island, a critical cultural heritage site in Egypt, faces significant engineering challenges due to dynamic hydrological conditions from the Aswan High Dam and inherent seismic activity. This study presents an integrated engineering approach utilizing Global Positioning System (GPS) monitoring and microtremor measurements to quantify elevation changes and assess the seismic vulnerability of the island's temple structures. Our GPS analysis (2021-2023) reveals a novel time-delayed inverse correlation between water level fluctuations and island elevation, demonstrating gradual subsidence during high water periods and uplift during low water loads. This highlights complex hydro-mechanical interactions critical for structural stability. Furthermore, Horizontal to Vertical Spectral Ratio (HVSR) analysis across 16 stations identified fundamental frequencies ( F o : 0.92–1.22 Hz) and peak H/V amplitudes (A o : up to 13.5), delineating zones susceptible to ground motion amplification. The derived Seismic Vulnerability Index (Kg: 4–193) quantitatively identifies areas of elevated seismic risk. Compared to previous heritage monitoring studies, our integrated GPS-HVSR method not only captures both hydrological and seismic influences in a single framework but also reveals sub-daily deformation patterns previously undocumented, offering up to 25–30% higher temporal resolution than conventional seasonal scale surveys. These engineering insights underscore the necessity of continuous geophysical monitoring and site-specific analysis for effective risk mitigation. The findings provide a robust framework for an integrated heritage risk management strategy, combining advanced geodetic and geophysical techniques with precise leveling, satellite imagery, and 3D laser scanning, thereby ensuring the long-term structural resilience and safeguarding of the Philae Temple against from future seismic threats.