The sex ratio at birth (SRB), defined as the proportion of male to total live births, is a sensitive demographic indicator that can be influenced by biological, environmental, and social factors. Previous studies have reported alterations in SRB following natural disasters, particularly earthquakes, potentially due to stress-related effects on reproductive physiology and fetal survival. However, most investigations have focused on short-term monthly changes in SRB, and evidence regarding the impact of prolonged earthquake sequences on annual SRB remains limited. This study examined whether a sequence of major earthquakes affected the annual SRB in Sarpol-e Zahab County, western Iran. Sarpol-e Zahab County experienced five earthquakes with moment magnitude greater than 5 and peak ground acceleration (PGA) exceeding 200 cm/s² between November 2017 and November 2018. Earthquake information, including magnitude, location, and PGA, was obtained from the Building and Housing Research Center of Iran. Annual birth data for Sarpol-e Zahab County, Kermanshah Province, and the entire country were obtained from the Statistical Centre of Iran for the period 1390–1401 Hijri Shamsi (2011–2023). SRB was calculated as the ratio of male to total live births. Annual SRB values were compared with the overall 12-year mean using one-sample t-tests. In addition, Google Trends data were analyzed to explore public behavioral responses and information-seeking patterns following the earthquakes. A significant decline in SRB was observed in Sarpol-e Zahab County during 1398 HS (2019–2020), the year following the earthquake sequence. The SRB decreased to 0.506 compared with the 12-year mean of 0.522 (p = 0.0004), representing the lowest value recorded during the study period. In contrast, no comparable reduction was observed in either Kermanshah Province or Iran as a whole, supporting a localized effect associated with the earthquake sequence. Furthermore, the annual number of births in Sarpol-e Zahab declined markedly after the earthquakes, with post-earthquake births averaging approximately 20% fewer than those recorded during the preceding seven years. Google Trends analyses demonstrated sharp increases in searches related to “earthquake,” “Red Crescent,” and “ceiling” following the major seismic events, reflecting heightened public concern regarding safety, structural damage, and disaster assistance. These behavioral indicators suggest sustained psychological and social impacts on the affected population. The findings indicate that the prolonged earthquake sequence affecting Sarpol-e Zahab County was associated with a significant reduction in annual SRB in the subsequent year. Unlike previous studies that primarily reported monthly fluctuations, this study demonstrates that extended exposure to disaster-related stress may influence SRB at an annual scale. The concurrent decline in birth numbers and increased disaster-related online search activity further support the broader demographic and psychosocial consequences of prolonged seismic events. These results contribute to growing evidence that major natural disasters can affect reproductive outcomes and population dynamics in affected communities.