Seismic Structural Health Monitoring (S2HM) provides information about the integrity of civil structures and infrastructure in the aftermath of an earthquake. However, quantifying the benefits of S2HM information is crucial to justify the investment in S2HM systems. The benefit of S2HM can be computed through the Value of Information (VoI) from Bayesian decision theory, which compares the expected costs of alternative actions with prior information (without S2HM information) and with S2HM information (before it is available). This paper aims to analyze the VoI from S2HM in civil structures and infrastructure, considering different prior information scenarios regarding seismic action. The theoretical framework of the VoI is adapted to address three prior knowledge scenarios: (i) full information about the earthquake is available (ii) the intensity measure of the seismic motion is obtained using ground motion models, and (iii) no information is available. A numerical case study of a structure in a seismic area is presented, and the effect of different prior information scenarios on the VoI is discussed. The results show that VoI is higher when the prior information is low, indicating that monitoring systems are more valuable when uncertainty about seismic actions is high.