Approach for Site-Specific PGA Calculation Based on Magnitude and Distance

Abstract

A deterministic seismic hazard analysis (DSHA) was carried out using one hundred years of earthquake data obtained from the United States Geological Survey (USGS) catalog for Nepal. The objective of this study was to evaluate site-specific seismic hazard parameters—namely Peak Horizontal Acceleration (PHA), Peak Vertical Acceleration (PVA), and Peak Ground Acceleration (PGA)—for a defined point of interest. The DSHA approach was selected to directly estimate the maximum credible ground motion expected at the site based on historical seismicity. Primary seismic data from the past century were analyzed to identify all significant earthquake events and their respective magnitudes and epicentral distances relative to the study location. The PHA for each event was determined based on its recorded or estimated ground motion characteristics. Using the empirical relationship developed by Cornell et al. (1989), the Peak Ground Velocity (PGV) values corresponding to magnitudes ranging from 3.0 to 9.0 were calculated. Consecutive PHA values from all events were then combined to represent the cumulative horizontal ground acceleration at the site. Subsequently, the Peak Vertical Acceleration (PVA) was estimated which provides a proportional link between the horizontal and vertical components of seismic motion. The final Peak Ground Acceleration (PGA) was derived using the resultant relation The study was also validated by using the relationship between variation of PGA with magnitude values (Chaullagulla et al., 2023). This combined approach provides a deterministic estimate of the total ground motion potential at the selected location.