Assessment of Bedrock PGA Values based on Probabilistic Seismic Hazard Analysis in Purworejo, Indonesia

Abstract

Purworejo Regency, Central Java, is directly adjacent to the Indian Ocean in the South, where there is a subduction zone between the Indo-Australian Plate and the Eurasian Plate. The movement of these plates has the potential to cause earthquakes, so for mitigation purposes with the design of earthquake-resistant buildings, PGA analysis and Earthquake Hazard Curve are needed. Data is sourced from the 2017 Indonesian Earthquake Hazard Source Map Book using Hazard Analysis software (USGS PSHA) GMPE modified. The attenuation function or GMPE (Ground Motion Prediction Equation) used is also the same as that used to create the Indonesian Earthquake Hazard Map of earthquake source mechanisms consisting of subduction, fault, and background earthquake with a return period of five hundred, one thousand, two thousand and five hundred, five thousand, ten thousand years. The results show that for a 2500-year return period, the most contributing earthquake source in the Purworejo Regency is a subduction earthquake source, with Kaligesing Subdistrict having the highest PGA value of 0.209 g and Bruno Subdistrict owning the lowest PGA at 0.186 g. The distribution of PGA values at this return period shows that the PGA values increase as the location approaches the subduction earthquake source from North (0.15 – 0.20 g) to South (0.20 – 0.25 g). Based on the PGA value, the Purworejo Regency area could feel the occurrence of earthquake vibrations. However, it is still necessary to mitigate the occurrence of earthquakes by building earthquake-resistant buildings to minimize losses when a major earthquake occurs in the future