Sains Malaysiana 50(4)(2021): 1157-1164

http://doi.org/10.17576/jsm-2021-5004-25

Analysis of Geomagnetic A_p Index on Worldwide Earthquake Occurrence using the Principal Component Analysis and Hierarchical Cluster Analysis

(Analisis Geomagnetik Indeks A_p pada Kejadian Gempa Bumi Serata Dunia menggunakan Analisis Prinsip Komponen dan Analisis Kelompok Hierarki)

NUR HIDAYAH ISMAIL¹, NAZHATULSHIMA AHMAD¹*, NUR ANISAH MOHAMED² & MOHAMMAD REDZUAN TAHAR¹

¹Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Federal Territory, Malaysia

²Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Federal Territory, Malaysia

Diserahkan: 5 Mei 2020/Diterima: 9 September 2020

ABSTRACT

Geoeffective solar events, especially the coronal mass ejection (CME) and the high-speed solar wind (HSSW) will induce geomagnetic storm upon its arrival to Earth. The solar events could trigger an earthquake occurred during the arrival. In this study, the focus is on the proxy of the geoeffective solar events, which is the geomagnetic A_p index and the data of shallow worldwide earthquakes. The main objective was to investigate the impact of geomagnetic storms on the occurrences of earthquakes from 1994 to 2017 from a statistical perspective. The geomagnetic A_p index data was obtained from the Helmholtz-Centre Postdam - GFZ German Research Centre for Geosciences and the shallow worldwide earthquake data were from the United States Geological Survey (USGS) earthquake catalogue. The Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were used to analyse the data. Two groups were obtained from the PCA biplot: Group 1 - before the event (Day-4 to Day-1) and Group 2 - after the event group (Day 0 to Day+4). A two-cluster solution was obtained from the HCA, which shows that days before and after geostorm are divided into two main clusters. The statistical results show that earthquakes activity might have different behaviour before and after the geostorm occurred. In conclusion, the results emphasize that there are differences between days before and after the geostorm occurrence, hence, the solar influence upon earthquake occurrences cannot be neglected entirely.

Keywords: A_p index; earthquake; geomagnetic storm; solar activity

ABSTRAK

Aktiviti geokesan suria yang memberi kesan kepada bumi seperti letusan jirim korona dan angin suria berkelajuan tinggi akan menyebabkan ribut geomagnetik berlaku di Bumi. Aktiviti yang kuat dan geokesan mungkin boleh mencetuskan gempa bumi semasa ketibaannya. Fokus kajian ini adalah pada proksi aktiviti suria yang sampai ke bumi iaitu indeks geomagnetik A_p dan data gempa bumi cetek dari seluruh dunia. Objektif utama kajian ini adalah untuk mengkaji dari perspektif statistik kesan ribut geomagnetik terhadap kejadian gempa bumi tahun 1994 sehingga 2017. Data indeks geomagnetik A_p dimuat turun dari Helmholtz-Centre Postdam - GFZ German Research Centre for Geosciences dan data bagi gempa bumi pula diperoleh daripada katalog gempa bumi United States Geological Survey (USGS). Analisis komponen utama (PCA) dan analisis kelompok hierarki (HCA) telah digunakan untuk menganalisis data. Dua kumpulan diperoleh daripada dwiplot PCA: Kumpulan 1 - sebelum kejadian ribut geomagnetik (Hari-4 hingga Hari-1) dan Kumpulan 2 - selepas kejadian (Hari 0 hingga Hari+4). Melalui HCA, kelompok yang telah diperoleh menunjukkan bahawa hari sebelum dan selepas ribut geomagnetik terbahagi kepada dua kelompok utama. Hasil statistik menunjukkan bahawa aktiviti gempa bumi mungkin dipengaruhi oleh ribut geomagnetik. Kesimpulannya, kertas kajian ini menegaskan bahawa terdapat perbezaan dalam bilangan gempa bumi, sebelum dan selepas kejadian ribut geomagnetik. Oleh itu, pengaruh Matahari terhadap kejadian gempa bumi tidak boleh diabaikan.

Kata kunci: Aktiviti suria; gempa bumi; indeks A_p; ribut geomagnetik

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*Pengarang untuk surat-menyurat; email: n_ahmad@um.edu.my