Mapping Ground Acceleration in the Purworejo Region Using the Probabilistic Seismic Hazard Analysis (PSHA) Method with Seismic Data from 1900 to 2024

Purworejo Regency is located in southern Java, directly facing the subduction zone. Its formation is alluvial, making the area vulnerable to seismic hazards. This study aims to map the Peak Ground Acceleration (PGA), Spectral Acceleration (SA), and amplification values in the southern part of Purworejo. PGA values were obtained using the Probabilistic Seismic Hazard Analysis (PSHA) method, while SA was calculated at periods T = 0.2 s and T = 1 s at a 2% exceedance probability over 50 years in both bedrock and surface layers. The data used were earthquake catalog data from the United States Geological Survey (USGS) from 1900 to 2024 with a minimum magnitude of M ≥ 5.0 and a depth of ≤ 300 km. The results show that for bedrock, the PGA value for the Purworejo region is 0.37–0.43 g, SA at T = 0.2 s is 0.79–1.0 g, and SA at T = 1 s is 0.55–0.63 g. The PGA value at the surface is 0.37–0.45 g, the SA at T = 0.2 s is 0.81–1.0 g, and the SA at T = 1 s is 0.55–0.73 g. The calculated amplification values are 1.0–1.03 for PGA and 1.0–1.09 for SA at T = 0.2 s, and 1.0–1.17 for SA at T = 1 s. Among the southern regions of Purworejo showing high PGA, SA, and amplification values are Purwodadi and Ngombol districts. These two areas have higher vulnerability to earthquake hazards compared to surrounding areas.