Garsela Fault and other NE-SW active faults along the southern part of Java Island

Abstract

Most earthquake studies focus mainly on offshore subduction zones that often produce high-magnitude earthquakes. However, onshore active fault earthquakes also common to cause significant devastation, due to their proximity to human activity and their relatively shallow depth. Most of active faults in Java show a west-east (W-E) trending direction. However, the devastating Opak Fault ruptured in a NE-SW trend. Recent studies indicate that some shallow seismic clusters in Java cannot be associated with any known active fault traces. These seismic activities reported occurring in southern Garut, Cipamingkis (Sukabumi), Halimun-Salak Mountain (Bogor), and Grindulu in Pacitan. These seismic clusters show similar direction to the Opak Fault that ruptured an Mw6.4 earthquake in 2006 with thousands of fatalities. Here, we describe a brief review of the NE-SW trending active fault in the southern Garut area. Earthquake is a natural phenomenon with a repetitive mechanism. Therefore, we must be aware of the future hazard that has been demonstrated by recent seismic activities in this area.

Magnetotellurics (MT) and Gravity Study of a Possible Active Fault in Southern Garut, West Java, Indonesia

“…The position of the basement undulations coincides with the magmatic intrusion in geothermal fields. It indicates that the magmatic intrusion may be part of the NE-SW trending local-high ridge which is observed as a young volcanic body lineament on the surface [29]. The lineament of intrusive bodies can be interpreted as a series of dyke intruded through the weak zone of fault plane.…”

“…The neotectonic process generates earthquakes in the subduction megathrust and onshore faults, and most of them rupture in the relatively W-E direction, such as the the Cimandiri [8,24], Lembang [25,26], and Baribis Faults [27,28] in the western part of Java island. Several other seismic activity clusters have been reported with a relative NE-SW direction in the southern part of Java Island in recent years, one of which is the Garsela Fault [29]. Little is known about the Garsela Fault, and the interpretation was mainly based on the focal mechanism analysis of the 2016 and 2017 earthquakes [2].…”

Identifikasi Sesar Grindulu Dengan Memanfaatkan Metode Gravitasi

“…Identifikasi kehadiran dan karakteristik struktur fisis bawah permukaan bisa dilakukan dengan memanfaatkan beragam metode geofisika dan teknik pengamatan serta pengukuran besaran yang relevan (Avila et al, 2016;Arisbaya et al, 2021). Salah satu metode geofisika yang dapa t secara efektif digunakan untuk identifikasi kehadiran dan karakteristik struktur fisis bawah permukaan di berbagai belahan dunia adalah metode gravitasi (Barbosa et al, 2007;Essa, 2013;Altinoğlu et al, 2015;Biswas, 2015;Justia et al, 2018;Al-Khafaji et al, 2019;Nurwidyanto et al, 2019;Ming et al, 2021).…”

“…Temuan variasi klosur tinggi dan rendah sepanjang arah timur laut-barat daya (NE-SW) menunjukan variasi jenis batuan bawah permukaan di sekitar lokasi penelitian. Secara umum, peta kontur anomali lokal (Gambar 2a) dan anomali regional (Gambar 2b) menunjukkan bahwa jalur Sesar Grindulu adalah sepanjang timur laut-barat daya (NE-SW) sesuai dengan peta geologi Lembar Pacitan (Samodra et al, 1992) dan temuan terdahulu yang relevan (Gultaf et al, 2015;Fahrudin et al, 2019;Cholifah et al, 2020;Arisbaya et al, 2021). Untuk memperkuat dugaan tersebut maka dilakukan analisis lebih lanjut dengan menggunakan teknik SVD.…”

“…Hasil teknik slicing yang ditunjukkan pada sebagai kelima plot grafik SVD pada Gambar 4 menujukkan bahwa Sesar Grindulu merupakan kombinasi antara sesar turun (normal fault) dan sesar mendatar atau sesar geser (strikeslip fault) sesuai dengan klaim penelitian terdahulu berbasis analisis paleostres tektonik batuan dari Gultaf et al (2015). Namun, penelitian terdahulu yang lain (Parera et al, 2015;Yusvinda et al, 2020) melaporkan bahwa Sesar Grindulu merupakan sesar turun sedangkan temuan terdahulu yang lain (Cholifah et al, 2020;Arisbaya et al, 2021) melaporkan sebagai sesar mendatar atau sesar geser. Perbedaan temuan antara tim peneliti satu dengan yang lain membuktikan bahwa masalah penentuan jenis sesar sebagai struktur batuan geologi bawah permukaan yang kompleks membutuhkan metode dan teknik yang terpadu untuk hasil yang lebih akurat.…”