Structure Interpretation Using Gravity Spectral Analysis and Derivative Method in Grindulu Fault, Pacitan, East Java

Abstract

The Grindulu Fault is a one of the fault that lies alongside the Pacitan Regency, East Java. This fault is a land geological structure that is potential to be the source of earthquake disaster. The structure interpretation is carried out using gravity data by performing spectrum analysis and derivative methods to get a better understanding of the Grindulu Fault. We used gravity data from GGMplus. Spectrum analysis is performed by using Fourier transform to the bouguer anomaly. This Spectral Analysis generates a depth estimation of Grindulu Fault Zone anomaly source. Analysis of derivative methods provides information regarding the location of the fault anomaly source and information about the type of fault. Based on the result of spectral analysis, Grindulu Fault anomaly source is estimated to be at the upper limit of 160 meters and the lower limit up to 2897 meters. The Grindulu fault is interpreted to be segmented into at least 7 parts which is consisted of normal and reverse fault segmentations.

Identifikasi Sesar Grindulu Dengan Memanfaatkan Metode Gravitasi

“…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.…”

Surface Deformation Assessment due to the Grindulu Fault Activities using Sentinel 1 Data by Applying the Small Baseline Subset (SBAS)-InSAR Technique

“…Grindulu Fault passes through the Pacitan Regency and aligns with the direction of the Grindulu River. According to [1], the Grindulu Fault is most likely located between the latitude of 111.0 -111.3 East and 8.1 -8.2 South longitude, with the NE-SW orientation. The fault is divided into seven segmentations, namely GRF1, GRF2, GRF3, GRF4, GRF5, GRF6, and GRF7.…”

“…The fault is divided into seven segmentations, namely GRF1, GRF2, GRF3, GRF4, GRF5, GRF6, and GRF7. Those segmentation have different fault types: GRF 1, GRF3, GRF4, and GRF6 are reverse faults, while GRF2, GRF5, and GRF7 are normal faults [1]. Seismic activities around the Grindulu Fault have been recorded by the Meteorological, Climatological, and Geophysical Agency of Indonesia (BMKG), one of them is the 3.1Mw shallow earthquake with a depth of 10 kilometers and an epicenter of 8.170 South and 111.136 East (Fig.…”

“…Geodetic techniques such as microgravity surveys, Global Navigation Satellite System (GNSS) surveys, and InSAR, combined with geological surveys have been used to monitor deformation due to active faults [1,6,7]. GNSS or gravity methods have limitations in the data availability and distribution of observation points that are often far from the fault line.…”

Mapping Risk Level Based on Peak Ground Acceleration (PGA) and Earthquake Intensity Using Multievent Earthquake Data in Malang Regency, East Java, Indonesia

“…It is a high earthquake risk area (Bachri et al, 2021). It is caused by the tectonic activities from some faults around it, including the Grindulu fault in Pacitan and the Klangon fault in Madiun (Lestari et al, 2019;Yusvinda et al, 2021). It is also close to the megathrust subduction zone.…”