Sains Malaysiana 54(8)(2025): 1889-1900

http://doi.org/10.17576/jsm-2025-5408-02

 

Seismotectonic Characteristics of the Cugenang Fault, Cianjur, West Java, Based on a-Value, b-Value, Seismic Moment and Satellite Gravity (Earthquake Data of 2008 - 2023)

(Ciri Seismotektonik Sesar Cugenang, Cianjur, Jawa Barat, Berdasarkan Nilai a, Nilai b, Momen Seismik dan Graviti Satelit (Data Gempa Bumi 2008 - 2023))

 

ATIN PRIHATINI¹, RINA DWI INDRIANA^2,*, AGUS SETYAWAN² & MUHAMMAD FAHMI²

 

¹Physics Undergraduate, Department of Physics, Faculty of Science and Mathematics, Diponegoro University, Semarang, Indonesia

²Department of Physics, Faculty of Science and Mathematics, Diponegoro University, Semarang, Indonesia

 

Received: 13 February 2025/Accepted: 26 May 2025

 

Abstract

The formation of fault in Cugenang, Cianjur Regency, West Java, caused an earthquake on 21 November 2022, with a magnitude of 5.6 SR, resulting in significant losses and casualties. The orientation of the Cugenang fault is N 347° E, dip 82.8°, depth 10 - 11 km, and a dextral strike-slip mechanism. This research aims to analyze the seismotectonic activity in the Cianjur area using a-value, b-value, seismic moment, and gravity field anomaly data. The processing of the b-value, a-value, and seismic moment was conducted using earthquake data from the Indonesia Meteorology and Geophysics Agency's website, which includes longitude, latitude, magnitude, and earthquake depth (1 January 2008 - 28 February 2023). Gravity field anomalies were processed using GGMplus satellite data. The results indicate that residual gravity anomaly values and seismic moments are inversely proportional to the a-value and b-value. The seismic moment values range from 12.2 to 14.7, the b-value from 0.2 to 1, the a-value from 1.1 to 2.1, and the residual gravity anomaly is -16 mGal to 26 mGal. The earthquake's epicenters were distributed north of the Cimandiri fault in the Rajamandala segment, coinciding with the location of the Cugenang fault. The average earthquake depth ranged from 10 km to 20 km, suggesting that the earthquakes occurred in young volcanic rocks. The presence of active faults and brittle volcanic rocks makes the area around Cianjur prone to earthquakes and increases the potential for additional new faults.

Keywords: Characteristics; Cugenang; fault; new; seismotectonic

 

Abstrak

Pembentukan sesar di Cugenang, Kabupaten Cianjur, Jawa Barat, menyebabkan gempa bumi pada 21 November 2022 dengan kekuatan 5.6 SR yang mengakibatkan kerugian dan kehilangan jiwa yang besar. Orientasi sesar Cugenang ialah N 347° E, kemiringan 82.80°, kedalaman 10 - 11 km dan mekanisme gelinciran dekstral. Penyelidikan ini bertujuan untuk menganalisis aktiviti seismotektonik di kawasan Cianjur menggunakan data nilai a, nilai b, momen seismik dan anomali medan graviti. Pemprosesan nilai b, nilai a dan momen seismik dijalankan menggunakan data gempa bumi daripada laman web Agensi Meteorologi dan Geofizik yang merangkumi longitud, latitud, magnitud dan kedalaman gempa bumi (1 Januari 2008 - 28 Februari 2023). Anomali medan graviti diproses menggunakan data satelit GGMplus. Keputusan penyelidikan menunjukkan bahawa anomali graviti sisa dan nilai momen seismik adalah berkadar songsang dengan nilai a dan b. Nilai momen seismik berkisar antara 12.2 hingga 14.7, nilai b dari 0.2 hingga 1, nilai a dari 1.1 hingga 2.1 dan anomali graviti sisa -16 mGal hingga 26 mGal. Pusat gempa bumi tersebar di utara bahagian Rajamandala Sesar Cimandiri, bertepatan dengan lokasi Sesar Cugenang. Purata kedalaman gempa bumi berkisar antara 10 km hingga 20 km, ini menunjukkan bahawa gempa bumi berlaku di batuan gunung berapi muda. Kehadiran sesar aktif dan batuan gunung berapi yang rapuh menjadikan kawasan sekitar Cianjur terdedah kepada gempa bumi dan meningkatkan potensi penambahan sesar baharu.

Kata kunci: Baharu; ciri; Cugenang; seismotektonik; sesar

 

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*Corresponding author; email: rinadwiindriana@lecturer.undip.ac.id