Comparison of Gardner-Knopoff, Gruenthal, and Uhrhammer Earthquake Declustering Methods for PSHA in Aceh and the surrounding areas
Juellyan (a,b), Bambang Setiawan (c*), Muttaqin (d)

a) Master Student, Department of Civil Engineering, Universitas Syiah Kuala, Banda Aceh, 23111, Indonesia
b) Awardee, Program Riset Unggulan Universitas Syiah Kuala Percepatan Doktor (PRUU-PD) Lembaga Penelitian dan Pengabdian kepada Masyarakat (LPPM), Universitas Syiah Kuala
*bambang.setiawan[at]unsyiah.ac.id
c) Program Study of Geological Engineering, Department of Earths Engineering, Universitas Syiah Kuala, Banda Aceh, 23111, Indonesia
d)Department of Civil Engineering, Universitas Syiah Kuala, Banda Aceh, 23111, Indonesia

Abstract

Earthquakes occur on the earth^s surface due to the sudden release of energy from within, which causes seismic waves. In seismology, the terms mainshock and foreshock are known. These terms describe earthquake events in two stages, the main earthquake stage and the seismic events after the main one. However, the earthquake data catalog generally does not separate the mainshock data and aftershocks. This separation is crucial for further research, i.e., modeling earthquake recurrence for Probabilistic Seismic Hazard Analysis. There are many methods to separate earthquake data based on mainshock and foreshock. This study uses three declustering methods: the Gardner-Knopoff method (1974), the Gruenthal method, and the Uhrhammer method (1986). The purpose of this study is to compare the three methods so that the results of which method show the highest a-value and b-value results for seismicity conditions in Aceh. The results obtained from this study are the Uhrhammer method (1986) with an a-value of 5.82, a b-value of 1.05, a total of 1893 main shock events, 305 clusters, and 3.3% of the total seismic moment released at that location. The Gruenthal method shows the results with an a-value of 4.53, a b-value of 0.823, a total of 776 mainshock events, 304 clusters, and releasing a seismic moment of 1.3% of the total seismic moment at that location. Gardner-Knopoff method (1974) showed results with an a-value of 5.1, a b-value of 0.929, a total of 1097 main shock events, 319 clusters, and a release of 1.08% of the total seismic moment at that location. The Uhrhammer method (1986) is suitable for seismic hazard assessment with the maximum level of risk. Meanwhile, for more conservative results, the Gruenthal method is recommended.

Keywords: Aceh, earthquake, mainshock, foreshock, declustering

Topic: Interdisciplinary Geosciences