Synthetic Accelerogram of Modal Summation Technique and Its Validation with the Pidie Jaya Earthquake Data

The PGA (Peak Ground Acceleration) estimation is the essential parameter in Seismic Hazard Assessments (SHA). PSHA (Probabilistic SHA) relies on generalized attenuation equation which contains uncertainty for estimation of PGA. A sophisticated method, NDSHA (Noe-Deterministic SHA) procedure has advantages in determination of PGA from realistic model of synthetic accelerogram from source-specific properties and cooperates with the structural model of sites. At the regional scale, calculation of PGA is based on one-dimensional modal summation technique. We validated the synthetic accelerogram with observations during the M 6.5 Pidie Jaya earthquake on December 7th, 2016. Those observational accelerograms data were recorded by two stations of three-channel accelerometers deployed by BMKG, namely KCSI and LASI. Based on recorded data of the stations, evidently, the synthetics accelerogram has been well verified at the KCSI station which is located on bedrock area and less suitable for the LASI station which is located on thick sediment region. The modal summation technique is not suitable for the area located on thick sediment layer because the amplification effect which works in two-dimensional regime cannot be handle by the one-dimensional approach. Two or three-dimensional approach should be applied to the sedimentary layer at a local scale NDSHA in order to compute the amplification effect.