Application of epidemic type aftershock sequence (ETAS) model on earthquake data in Mentawai Islands

Abstract

Earthquakes are vibrations or shocks that occur and are felt on the surface of the earth originating from within the earth’s structure. These natural phenomena are random in both time and location, making it challenging to predict the occurrence of earthquakes. A large earthquake that occurs in a location can trigger aftershocks, so that the sequence of aftershocks is assumed to be an epidemic. The epidemic type aftershock sequence (ETAS) model is a model in the point process that considers the relationship among earthquakes. The ETAS model is expressed by a conditional intensity function which is useful for determining the probability of earthquake occurrence. The purpose of this research is to apply the ETAS model for Mentawai Islands earthquake data based on the point of the largest earthquake that occurred on September 12nd, 2007 with a magnitude of 7.7 mb. The data is obtained from the United State Geological Survey with the magnitude threshold is 4 mb and the depth threshold is 70 km. We use maximum likelihood method to estimate the ETAS model parameters. The parameter estimation results are basic seismic rate of 0.00232 earthquakes/day, productivity of aftershocks of 1.27673 aftershocks/day, efficiency of earthquakes with a certain magnitude resulting in aftershocks of 1.26408/m, decay rate of aftershock by time scale of 0.01055 day, and overall decay rate of aftershocks of 0.94119 day.