Statistical Analysis of Seismicity in West Sumatra (2015–2025) and Aftershock Decay of the 2009 Padang Earthquake Using Gutenberg–Richter and Omori–Utsu Laws

Icha Untari Meidji; Nur Afni Oktavia Nusi; Harsano Jayadi

doi:10.20414/konstan.v11i01.926

Icha Untari Meidji Universitas Negeri Gorontalo
Nur Afni Oktavia Nusi Universitas Negeri Gorontalo
Harsano Jayadi Universitas Tadulako

DOI: https://doi.org/10.20414/konstan.v11i01.926

Keywords: Padang, Earthquake, Gutenberg-Richter Law, Omori-Utsu, aftershock decay

Abstract

Previous studies on seismicity in West Sumatra have generally focused either on frequency–magnitude distribution or aftershock decay separately, with limited integration of updated earthquake catalogs and combined statistical approaches. This study examines the seismicity of West Sumatra using the Gutenberg–Richter (GR) law and the Omori–Utsu aftershock decay model for the 30 September 2009 Padang earthquake. Earthquake catalogs from the United States Geological Survey (USGS) covering the last ten years and the aftershock sequence of the 2009 event were analyzed. The GR law was applied through cumulative frequency–magnitude distributions to estimate the a- and b-values, which represent seismic activity level and magnitude distribution. The Omori–Utsu model was used to determine the decay parameter p and the initial aftershock activity constant K. The results show a strong linear frequency–magnitude relationship with a relatively high b-value, indicating dominant small- to moderate-magnitude earthquakes and high seismicity. Aftershock activity follows the Omori–Utsu decay pattern with a moderately slow decay rate. These results emphasize the influence of subduction zone dynamics and provide important implications for earthquake hazard mitigation in West Sumatra. These results provide updated seismic parameters for West Sumatra, support regional seismic hazard modeling, and contribute to refining empirical parameter estimation for the Sunda subduction setting.

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