INFLUENCE OF SEISMICITY DECLUSTERING ON GROUND MOTION PREDICTION EQUATIONS FOR CENTRAL SULAWESI SEISMIC REGION

Central Sulawesi has very complex tectonic conditions, and therefore the earthquake hazard of the region needs to be carefully examined. One of the required components to develop such examination is regional ground motion prediction equations. This study describes the development of GMPEs for Central Sulawesi based on broadband velocitymeter and strong motion accelerations recorded by instruments managed by Indonesia geophysical authority temporarily since year 2015 and 2017. The accuracy of the resulting equations is examined further by performing the seismicity declustering processes using the Reasenberg method; the declustering process is to separate mainshock events from foreshock and or aftershock events. Note that, as the site class of the instrument locations is SD, the resulting GMPEs are only for SD sites. The resulting expected geometric mean peak ground acceleration from GMPE for all shocks (dependent seismicity) is similar to that for mainshocks only (independent seismicity), except for higher magnitude earthquakes due to the limited number of data available. The expected PGA values are examined further by comparing the values with the actual PGA from earthquakes in the Sausu Fault region, including the damaging 29 May 2019 earthquake. Depending on the earthquake magnitude, the GMPEs may overestimate or underestimate the PGA values. In addition, the residual analyses are conducted to examine trends of the expected PGA values.